Many XJ-S owners may consider this book reference material, and don't bother to look at it until they need to work on something or spend some money on the car.  Unfortunately, sometimes the money spent could have been saved if they had read about how to avoid problems in the first place! And, yes, sometimes the money saved can amount to thousands of dollars; both the Lucas and later Marelli ignition systems have faults that can cost you an engine or even the entire car in very short order.

Hey, it's up to you; it's your car, your time, and your money.  However, I highly recommend you read this book!  Jaguars are not drive-it-and-forget-it cars; they demand a certain amount of awareness on the part of the owner, and reading this book cover-to-cover will go a long way toward making the owner aware of his car --and possibly save him loads of $$$ in the future, as well as making Jaguar ownership a more pleasant experience.

If you cannot be convinced, at a minimum please read about the following topics:

WHAT'S IN A NAME?: First and foremost, it's high time to quit abusing the name "Jaguar".  It does not rhyme with "quagmire"! According to Jim Isbell: "At a recent Jag Club meeting they showed a video of the history of Jaguar from the Swallow to the present.  I was most interested to see how the owners and perpetrators of the Jaguar company pronounced it.  There were several old voice interviews and I listened very carefully every time one of them spoke.  The pronunciation I got from those interviews was: Jag-u-wer.  I think the people who invented it must know how to pronounce it."

The name of the car that this book addresses is the "XJ-S" --or, at least that was the name.  Up until 1982 the dash actually had its own part number, since the four characters on the back end of the car were four separate pieces; through the rest of the 80's, the four characters on the back of the car were a single badge, but the hyphen was still apparent.  Since the badge on the car itself has to be considered the ultimate authority, up until 1991 anyone referring to the car as an "XJS" was in error.  This was a very common error, since XJ6 and XJ12 do not have dashes in the names and it was commonly assumed that this was normal Jaguar naming convention.  Unfortunately for anyone trying to keep such things straight, even the folks at Jaguar were guilty of this error, as evidenced in several of their brochures and manuals.

According to Paul Skilleter's book "Jaguar XJS: A Collector's Guide", when the bodywork was revised for the 1991 model year the name of the car was officially changed to "XJS" to emphasize the change.

I will also mention what a "Daimler" is.  Daimler was a British automobile company that was bought out by Jaguar in 1960.  However, Gottlieb Daimler also founded a German automobile company that merged with Benz & Cie. in 1926 forming Daimler-Benz AG (later DaimlerChrysler, still later Daimler AG).  The Mercedes manufacturer registered the name Daimler in the US, so Jaguar cannot use the name in the US even though the former British company by that name belongs to them.  Daimler-Benz always called its cars Mercedes (after somebody's girlfriend many decades ago), so there are no cars known as Daimlers sold in the US.

While the British Daimlers were originally a distinct line of automobiles, eventually they became variations on Jaguars.  Regarding the cars covered by this book, the Jaguar XJ12 was also sold as the Daimler Double Six in some countries, with detail differences including a distinctive fluted grille.

S TYPE: From "Great Marques - Jaguar" by Chris Harvey:

The S type (no hyphen) and most other lines of Jaguar saloon were discontinued when the XJ6 was introduced in 1968.

In a shameless attempt to capitalize on William Lyons' glory of years past, Ford/Jaguar introduced a new S-type (with hyphen) in 1998.  David Berman says, "The S-TYPE is related to the Lincoln LS6/8.  This is known as the DEW98 platform."

So why is all this discussion in a book on the XJ-S? Because some people insist on referring to the XJ-S as an "S-type".  Makes sense; the rolling phallic symbol known as the E-type in Europe and elsewhere was marketed as the XKE or XKE in the US, so it naturally follows that Jaguar's marketing department must be similarly misguided regarding the XJ-S.  Connoisseurs of the E-type sometimes get huffy if you are so base as to refer to their cars as XKE's, so people may actually think they are using the more proper term for the XJ-S when they call it an S-type.

So, how common is this error?  Believe it or not, it spread to the marketing department at Jaguar again!  The 1981 XJ-S sales brochure said:

Jaguars have always been distinguished by a special grace of form and a rare poise in motion.  Yet even among the legendary Jaguars of the past, this new S-type stands out.  The XJ-S does what Jaguars have always done --only better.  It is quick and responsive, stable at speed, silent in motion and notably luxurious.

Despite the disinformation tactics of those goobers, it's really not proper to refer to an XJ-S as an S-type; the mid-60's car was an upscale compact saloon, and even the 1998 knockoff appears to follow along that same theme.  The XJ-S is clearly in an entirely different class.

VIN NUMBER DECODING: There are two different VIN numbering schemes for the Jaguar XJ-S.  All cars have a VIN number stamped into the sheet metal dead center in front of the hood seal, and this VIN corresponds to the scheme described below, based on input from Richard Mansell, William Noorloos, and Paul Skilleter's book.

Position 1-3 denotes manufacturer
             SAJ = Jaguar<,/P

Position 4 denotes marque
             J=Jaguar
             D=Daimler

5th is model
             N=XJ-S
             S=XJR-S
             T=Special edition

6th is class
             A=baseline
             J=Japan
             K=Japan with airbag
             L=Canada
             M=Canada with airbag
             V=USA spec with manual belts
             W=USA spec with driver airbag
             Y=USA spec with passive belts.

7th is body type
             C=Cabriolet
             D=Convertible
             E=Coupe
             F=2+2 Convertible

8th is engine type
             B=3.6 4VB
             C=3.6 4VC or 3.6 4Y
             D=3.6 4VD or 4.0 4Y
             E=3.6 4VE
             K=5.3 F
             S=6.0
             V=5.3 A
             W=5.3 B
             X=5.3 C
             Y=5.3 D
             Z=5.3 E

9th is Transmission and steering
             3=Auto RHD
             4=Auto LHD
             7=manual RHD
             8=manual LHD

10th is model or year change
             A=XJ-S original spec
             B=HE coupe
             C=AJ6 coupe and convertible
             D=V12 convertible
             E=facelift (1992-)
except for USA, Canada and Korea where from 1981 the 10th letter indicates year of build starting with B=1981.  Skip the letter I, so J=1988.

11th is emission control equipment
(up to 1987: manufacturing plant, C=Browns Lane)

12th-17th are the vehicle's unique number.

Andrew Stott says, "My car is UK spec, pre-HE, made in 1979, D-Jetronic.  The VIN is JNAEW1AC101185.  One confusing thing is that the character in the VIN that denotes the transmission and steering is a '1' and according to the books it should be a '7' as it is a manual RHD car.  In Skilleter's XJ-S Collectors Guide, he gives details of the last production XJ-S manual.  It was made in 1979 and had a VIN of JNAEW1AC1018xx; this would suggest that the '1' in the transmission character position is valid for a RHD manual car."

Now, if you have a US-spec car, there is a tag within the left edge of the windshield that carries a totally different VIN number.  This VIN corresponds to the following scheme, from the "MOTOR import car crash estimating guide" for the US:

4th Position - Model Line
             A=XJ6
             A=Vanden Plas
             C=Sovereign
             F=XJ6
             H=XJ6, Sovereign
             K=Vanden Plas
             M=Majestic
             M=XJ12
             N=XJ-S/XJSC
             P=XJR/Sport
             S=Jagsport
             T=Rouge/Classic

5th Position - Class/Restraint
             A=Passive Seat Belt (87-89)
             T=Driver Air Bag w/Passive belt
             V=Active Seat Belt
             W=Driver Air Bag (90-95)
             X=Driver & Pass Airbag
             Y=N.  American Spec (83-87)
             Y=Passive Seat Belt (89-93)

6th Position - Body Style
             1=4 door sedan
             2=2+2 Convertible
             3=2 door Cabriolet
             4=Convertible
             5=2 door coupe

7th Position - Engine Code
             0=5.3l 12 cyl, Calif.
             1=4.0l 6 cyl, Supercharged
             2=4.2l 6 cyl, Calif.
             3=4.2l 6 cyl
             3=6.0l
             5=3.6l 6 cyl low compression
             6=3.6l 6 cyl high compression
             7=4.0l 6 cyl
             8=5.3l 12 cyl
             9=4.0l 6 cyl

8th Position - Transmission & Steering
             4=Automatic (LHS)
             8=Manual (LHS)

9th Position - Check Digit

10th Position - MODEL YEAR
             D=1983
             E=1984
             F=1985
             G=1986
             H=1987
             J=1988
             K=1989
             L=1990
             M=1991
             N=1992
             P=1993
             R=1994
             S=1995

11th Position - Assembly Plant
             C=Browns Lane, England

12th-17th Position - Production Sequence Number

Alex Dorne had a US-spec car shipped to Sweden, and reports that the process included removing the VIN tag at the left side of the windshield -- possibly to avoid confusion between this VIN and the one under the hood.  He was allowed to keep the windshield tag.  Also, the VIN under the hood also appears on the aluminum panel inside the trunk, just to the right of the latch.  He postulates that this may have been stamped as part of the Swedish import procedures as well.

ACTIVE SEAT BELTS? They don't look very active.  Peter Cohen clarifies: "It means that if you are not "active" and "actively" fasten your seat belt, it ain't gonna be fastened.  As opposed to "Passive" seat belts that are motor mouse driven."

WHAT'S IN A YEAR?: Now that you have deciphered your VIN and know for sure what year your XJ-S is, do you really know what year your XJ-S is? If you live in the US, perhaps you've noticed that each model year seems to appear several months before the year itself, which certainly makes it doubtful that the car was actually built in the year it's purported to be.  Apparently, the "model year" is a term that varies from country to country, and --of course --the US has the least rational definition.  Peter Cohen says, "For those interested in trivia, here's how it works: In the US a given model year can only be manufactured to be offered for sale on a single January 1st.  That's the only rule.  This can result in the following (more or less true) example: A certain 1996 model of vehicle began manufacture in December 1994, was put on sale 2 January 1995 and continued to be sold as a 1996 model until September 1996 (although legally they could have been sold until 31 December 1996).  This is not to say that one that remained unsold on 1 January 1997 would have become a 1997.  It is the date that it is intended to be sold as a "current" model that the regulation applies to.  So, that's what happens when marketing types run amok.

"I find it particularly galling when you go to buy a used car.  You will be asked the same price for a 4 year old car as for a 5 year old car.  You don't know what you are buying unless and until you remember to check the manufacture date, and even then it probably won't help your bargaining position.

"On US spec vehicles, the certification label should say something like "This vehicle meets all US specifications...in effect for model year 19xx." IMHO, that is what year a US spec car is, regardless of the manufacture date or what's on the title.

"When you get outside of the US, "year" becomes too simplified of a question.  I don't think that non-North American spec cars come labelled with month/year of manufacture.  In England, cars are referred to by their registration letter, which changes on 1 August each year.  So a leftover model becomes next years' car by virtue or having the newer

John Littler adds, "In Oz, date of manufacture is required on the ADR compliance plate.  We have a nice simple system where a car made in '88 is an '88 model."

Unfortunately, this MY hogwash can't help but cause some inconsistencies in this book.  For example, one person's quote might describe a fix on his '88 when somewhere else it's made clear that the problem shouldn't even exist past 1987.  There is simply no way to correct such things in everyone's direct quotes, although whereever possible attempts are made to clarify which configuration a quote is intended to reflect.  In general, if this book states that something applied to a particular range of model years, please allow about one year of leeway before deciding whether or not it applies to your car.

XJ12 STYLES: For the benefit of those XJ12 owners who read this book, I am including some info on the various different cars that have all been called an XJ12.  The following is courtesy of B.J. Kroppe: "XJ12s were made in Series III body style until 1992 (yes, alongside XJ40 6-cylinder models).  XJ12s in XJ40 body style were made for one year.  Whether it was only one-half of a year or a full year, it was 1994.  XJ12s in X300 body style were made from 1995 1997, when the V12 engine was retired from production.

"Note there were no XJ40 5.3l cars produced."

Steve Lipscombe explains why the Series III XJ12 continued long after the XJ40 was introduced: "The first XJ40 was certainly designed with a narrow engine bay to prevent the British Leyland management forcing the Rover V8 unit on them.  Later, when privately owned, they redesigned the bay to take the V12.  This was before the Ford takeover and the X300."

CABRIOLET: David L. French, a US owner, describes the Cabriolet: "It has the body profile of the convertible that was made later but has a 3-piece removable hardtop.  T-tops up front and a fully removable hardtop on the rear.  Totally factory made."

Since the Cabriolet lacks the buttresses of the coupe, it stands to reason that the body isn't as stiff in that area.  Jaguar apparently addressed that problem by adding "ladders" underneath the rear suspension.  Julian Mullaney reports: "The ladder brace was fitted to Cabrios from the factory.  Quite crude looking.  You can easily spot it on a cabrio just looking from the side.  I think it connects the chassis with steel bars fore and aft of the diff.  It passes under the diff.  The ladder frame does not connect to the subframe, it is definitely a chassis stiffener."

The Cabriolet was apparently offered in 1986-87-88 model years.  David King says, "There were at least 1900 Cabriolets shipped to the US and all were V12s even though it looks as if in the rest of the world the AJ6 was the more common engine for the Cabrio.  There were a total of 5014 Cabriolets built during their production run: 5013 Jaguars and a one-off Daimler."

HESS & EISENHARDT CONVERTIBLE: The XJ-S was designed in an era that never expected to see a convertible again; they were expected to be outlawed for safety reasons.  For many years, the only way to get an XJ-S convertible was to hire one of many aftermarket customizing outfits to cut the roof off your coupe.  By the mid-80's the expected ban on convertibles had failed to materialize and convertibles were making a comeback, so Jaguar responded by contracting with Hess & Eisenhardt in Cincinnati, Ohio to make convertibles from coupes to be sold as new cars at the Jaguar dealerships.  After two years, the response had been so good that Jaguar began making its own convertibles at

Mike Cogswell elaborates: "The H&E's were built in '87 and '88 (my '88 is one of the last, possibly the last).  The H&E is easily spotted by:

1. The small oval Hess & Eisenhardt badge on each side behind the front wheel well.
2. The top folds down flat, the later factory convertible tops are pretty high when folded.
3. The H&E has four window rocker switches.  Early ones are separate, later ones in a single gang of four.
4. The factory convertible has a small, ugly hump in the sheet metal on the side right behind the doors.  This covers the tops of the rear quarter windows, which don't fully retract.

"There are many other differences, but those are some of the most obvious."

David Johnson adds, "The top also looks better than the regular convertible because it is fabric, not a plastic." This may be true for only some of the H&E tops, though.  Another owner says, "I figure they had the tops made in California by Robbins."

Supposedly the building the H&E's were made in burned down, but H&E is still in business making limousines and other things.

Of course, the nickname H&E is only too likely to cause confusion with the H.E. used to describe the V12 engine with the Michael May-designed heads.

If you are considering the purchase of a used XJ-S, there is one very important thing to do: Insist upon having a compression check performed -- by an independent mechanic, if possible.  On a V12, one or two bad cylinders can easily go unnoticed on a test drive if you aren't familiar with how the Jaguar should drive.

If any cylinders read lower than the rest by more than 10% or so, be aware that an engine overhaul will cost thousands.  You will probably decide to pass on the car unless it is really cheap and you plan on engine work anyway.

Note that it is unusually difficult to pull the spark plugs on this car, so a compression check will involve a couple hours labor on the part of your mechanic.  Money well spent.

Mike McGaw suggests that, if the car has ABS brakes, special attention be paid to their condition.  Apparently some owners, upon learning how much it will cost them to repair their ABS brakes, decide that the solution is to disconnect the warning indicators and sell the car.  This is liable to lead to a very expensive and a very dangerous situation indeed.  There is a diagnosic process described under "Accumulator Testing" on page 457 that is easily performed and will go a long way toward instilling confidence in the condition in the system.

One other noteworthy comment regards mileage.  If properly maintained, the Jaguar can easily pass 200,000 miles before any major renovation is needed.  So, the prospective Jaguar buyer would be well advised to pay a little less attention to what the odometer says and a little more attention to the completeness of the maintenance records.

As far as everything else on the car is concerned, it's pretty much the same as buying any other car.  Bodywork and repainting are always expensive, and are more so on a Jaguar.  Rust is always a call for concern.  Apparent bodges or slipshod repairs are signs of trouble.

If you're really a careful shopper, read this entire book first.  It will give you a really good idea what pitfalls to look for in a used car.

GETTING SERVICE: Keeping your Jaguar in good working order is like anything else: If you want it done right, do it yourself.  Doing as much of your own maintenance as possible is highly recommended, based on experiences shared on the online discussion lists (many of which are related in this book).  You might be thinking, "Yeah, but wouldn't I be better off hiring somebody with a lot of experience working on these cars?"  The answer: You're holding all the experience you're ever likely to need.  That's why the book was so named.

Nevertheless, there will be owners who don't want to get dirty, or don't have the time, or don't have the tools, or don't have a garage, or for whatever other reason would simply prefer to pay someone else to work on their car than do it themselves.  There's nothing wrong with such a strategy; it simply must be made clear that such a decision should not be made with the expectation that the car will get better service.  More convenient, maybe; quicker, quite possibly.  But a long history of experiences with Jaguar dealers, specialists, mechanics, and the like indicate that the XJ-S owner should expect more problems if he takes his car somewhere for service than if he maintains it himself using this book as a guide.

That said, some guidelines on finding a good mechanic: First, note that the XJ-S has been out of production for some time now, and Jaguar dealerships are not likely to be all that enthused about working on it.  Some dealers might be lucky to even have a mechanic on staff that was there when these cars were built, and all the newer mechanics will have been trained on the current models rather than the older models.  When you pull into a dealer for service, don't be surprised if the only enthusiasm displayed towards you and your car comes from a salesman anxious to talk you into trading in that old pile of junk on a brand new whatever.

With a car such as the Jaguar XJ-S, you will invariably be far better off finding an "enthusiast" --a guy who loves these cars and loves to work on them.  Even if he works in a dilapidated shack, you're likely to be much happier with his work than you would taking the car to a shiny dealership that doesn't care about your car.

Of course, enthusiasts can be hard to find.  One excellent idea would be to ask other Jaguar owners who they take their cars to.  If there is a Jaguar club in the area, ask them.  Finally, if there simply are no enthusiasts in your area, consider finding out where the nearest one is anyway; even if you don't take your car that far away for oil changes and the like, there may come a day when you need someone to call who can really help.

Striking out totally in the enthusiast search, your next best option would be to simply find a good independent mechanic.  If he's willing to tackle a Jaguar, he will probably be capable of fixing most of the problems likely to crop up; it's not that different from other cars.  If you do a little reading in this book before you go, quite likely the two of you can get started in the right direction towards getting your problems sorted.

I'd like to suggest that you simply make a copy of this book and give it to your mechanic to help him work on your car, but experience shows that this doesn't work very well.  Many mechanics seem to consider it an insult that you would suggest that he needs help from a book.  Others apparently can't read.  And almost none of them are inclined to put that kind of time into learning about Jaguars, especially since they have never seen a book like this one and are unaware anything of the sort exists.  So, perhaps you might offer a copy, or perhaps just discuss your car with him and if he asks how come you know so much you can tell him about it.  If you happen to find a mechanic who expresses an interest in the book, I'd suggest you have a keeper; if he actually reads a significant portion of it, he will be the best mechanic you're likely to find.

Meanwhile, if you will read this book, you will find yourself far better able to judge whether or not a mechanic is up to snuff on the Jaguar XJ-S.  You will become an informed consumer.

PARTS REPLACEMENT STRATEGIES: For those obsessed with keeping their cars in original condition, obviously only original parts will do.  The suggestions throughout this book are for those who simply want their cars to run and to minimize cost and grief in the process.

Experienced British car enthusiasts will agree that most of their reliability problems come from two sources: Non

Rumors abound as to why the rubber and plastic parts on British cars tend to crap out so soon.  One rumor says there is a law in Britain requiring the use of natural rubber rather than the far superior synthetic elastomers.  Whatever the cause, the Jaguar owner is well advised to replace the original Jaguar seals, hoses, belts, etc., with non-British substitutes whenever feasible.

It has been suggested that the various vinyl and rubber protectants on the market, such as STP Son Of A Gun, can be used to help many rubber components last longer.  Sandy Gibbs: "When I owned a TR8 I had many of the same problems regarding engine heat and rubber components.  I found Armor All and Son of a Gun were useless unless applied every three or four days (if you drive the car much).  What did work was brake fluid, of all things.  You have to soak the part in question pretty well then rub the fluid in.  Let the part dry before running the car.  This procedure may have to be repeated two or three days in a row but then the rubber is revitalized, after that one need only repeat the procedure every two or three months.  The key here is keeping the brake fluid off anything but the rubber part.  This process works on nearly any rubber part except, for some reason, tires."

Lucas has been called the "Father of Darkness".  Contrary to popular opinion, Lucas did not invent darkness --they merely perfected it to a fine art!  The owner is well advised to replace Lucas electrical components with alternative products when feasible.  It should be noted that many of the electrical parts on a Jag are not really Lucas; the "Jaguar" stereo is probably made in Japan, and many of the EFI components are Bosch relabelled as Lucas.

Other than electrical and non-metallic parts, Jaguar components are typically excellent, and most are reasonably priced.  Whether it is better to replace a broken item with the Jaguar original or a substitute must be decided on an individual basis.  A good general rule is: If the original failed of its own accord, it might be better to try another source.  But if the failure was secondary (due to something else failing first), the Jaguar parts may very well be the best there are; substitutions are in order only where the prices of the originals are unreasonable.

Regarding rebuilt parts, Randy Wilson says, "There are many companies out there that rebuild to a price, replacing only the "common" failure part.  Their attitude is it's cheaper to only replace the one part and let the consumer figure out which units need more work than it is to full rebuild and test every unit.  This is true with electrical, a/c, steering gear, and other things.  The real sad part is these unscrupulous clowns often drive the reputable rebuilders out of the market by the price difference.  Rebuilds are a pain.  The cheap ones are no bargain.  And just buying an expensive one is no guarantee.  It may be a thorough rebuild, or it may be a cheap one that your vendor is making a killing on."

The XJ-S Repair Operation Manual (commonly referred to as "the ROM"), is expensive (around $100) and mediocre; not only is it somewhat difficult to follow, it is also fraught with errors.  Nevertheless, it's still probably the best choice here.

From the introduction of the XJ-S until 1982, Jaguar offered a basic ROM, part no. AKM 3455, ©1975.  This edition does not cover the GM400 automatic transmission.

With the introduction of the H.E. in 1982, Jaguar issued an addendum titled Jaguar XJ-S H.E. -Supplement to the Repair Operation Manual, part no. AKM 3455/S1, ©1982, commonly known as "the H.E. Supplement".  They also issued an updated edition of the ROM, AKM 3455 Ed 3 "incorporating H.E. Supplement", ©1982.  Understandably, the H.E. Supplement included in Ed 3 is identical to the Supplement available as a separately bound volume.  Ed 3 does cover the GM400 automatic transmission, though.

In 1984 part no. AKM 3455 Ed 4 was issued; this apparently represents the last correction and update to the ROM itself, even though rather than incorporate the H.E. data into the main part of the manual it continued to feature an H.E. supplement.  From 1984 on, the ROM was updated solely by the addition of supplements; "Ed 4" comes with Supplement A only, "Ed 4/2" (©1989) comes with Supplements A & B, and "Ed 4/3" (©1995) comes with Supplements A, B, and C:

Physically, the ©1975 ROM and ©1982 Supplement came as separate softcover books with off-white covers, while in the Ed 3 and Ed 4 versions Jaguar incorporated the manual and supplements into a single binding.  John M. Smith has the Ed 4 printing, and somehow got a hardbound copy: "Pre-H.E. sections in white pages.  H.E. supplement at rear in green pages."  Steve Draper reports on his Ed 4/2: "It is a single softbound volume." Chris Carley got the Ed 4/3, "One book soft bound in Jag green.  Each supplement has black edge at the beginning page with heading so you can flick through & see it."

Supplement A in the Ed 4 books is apparently quite similar to the ©1982 separately-bound H.E. Supplement, even though the ©1982 Supplement is 63 pages while Supplement A is 74 pages.  The pages must be counted by hand since neither of these supplements have sequentially numbered pages.  This book contains many references to the ©1982 Supplement, since the author owns a copy; readers should generally presume that the references apply equally well to Supplement A.

Unfortunately, when you actually try to buy a repair manual, you not only may have trouble telling which version you're getting --you may have trouble telling if it's a ROM! For some reason, many booksellers have an aversion to actually listing the title as clearly printed on the front of the book.  Rather than offering an XJ-S Repair Operation Manual, they will call it an "Official Shop Manual", "Official Jaguar Repair Manual", or whatever other name they can dream up to confuse the customer.  In general, if the price is in the $80-$120 range, you can assume it's the XJ-S Repair Operation Manual, but it never hurts to ask to make sure before shelling out the cash.

Also note: With some bookstores, if you tell them what year car you have, you may get only what they think you need; this author has an '83, and ended up with the ©1975 edition ROM and the ©1982 Supplement.  While this may be considered acceptable, a later ROM is always better since they still contain the earlier info; the Ed 4 is clearly an improvement over the ©1975 ROM even if you own a mid-70's XJ-S simply due to the corrections incorporated.  And there is always the possibility that you may decide to upgrade some part of your car with the parts from a later car.  Just about the only reason to accept an earlier ROM is if you find a clearance price.

Note that if you have the GM400 transmission, you will want to insist upon the Ed 3 or Ed 4 edition; the ©1975 ROM covers only the Borg-Warner, and the ©1982 Supplement doesn't help.  The Ed 4 edition covers the GM400 quite thoroughly, as described by Patrick MacNamara: "My ROM AKM 3455 Ed 4 has an extensive chapter on removal, fault finding and overhaul for the GM 400.  It also contains everything on the BW except removal.  Interestingly, the table of contents lists both transmissions and all related chapters as the same for both (ie 44.00.00 is data and description for the GM, while 44.00.00 is hydraulic flow charts for the BW).  You just have to make sure you are looking at the correct chapter 44 in the text as there are two."

If you happen to get stuck with the ©1975 ROM and wish to work on your GM400 automatic transmission, your best bet would be to get a separate repair manual for the tranny.  Andrew Kalman suggests How To Work With And Modify The Turbo Hydra-matic 400 Transmission by Ron Sessions, Motorbooks International, 1987, 224 pages, 300 illustrations; ISBN 0-89738-267-8.  Kalman says: "It seems quite complete, with a historical overview, basic maintenance, operation, overhaul, modifications and speed tuning." This book is highly recommended by many; for example, Mark Johnson says, "If Kirby had compiled a book on transmissions, this would be it."  How's that for an endorsement!

Of course, you will still lack instructions on how to remove and reinstall the GM400 in an XJ-S, but you can pretty much make that up as you go along (with help from the transmission mount info starting on page 342 in this book) --or you could just buy a Haynes manual, described below.  The Sessions book plus the Haynes manual will still be cheaper

Your second repair manual option is to purchase the XJ-S Service Manuals, which come as sets of several volumes each.  If you thought the Repair Operation Manual was expensive, the series of XJ-S Service Manuals ought to be good for a major coronary: Several hundred bucks a set.  On top of that, you may end up having to buy more sets than you anticipated; while the later edition ROM's contain all the info on earlier cars, the multi-volume Service Manuals do not.  Richard Mansell: "Now that I have the manuals in my hot little hands it appears to be more complicated than I thought.  The pre-H.E. to 87-88 manuals (JJM 10 04 06) appear to be based around the pre-H.E. with extra sections to cover the differences between these and the H.E. (pretty logical so far).  The new manuals, up to 91, (JJM 10 04 06-20) come in 5 volumes rather than the earlier 4 but only appear to cover the additions since the earlier manuals for the 5.3 plus a random selection of the original information.  Oh, and it covers the 4.0 engine too.  In other words, if you have an '89 to '91 5.3 and you want to know about the new ignition, etc., you will need both sets as the later volume set refers to many sections that only exist in the earlier set; e.g. under the heading "Cylinder heads overhaul" it says:

gypsy Remove left and right hand cylinder heads, see 12.29.01.

Where is 12.29.01?  Only in the earlier set!  Since the five-volume set costs more than the earlier one, I assumed it would be a complete guide to the later cars.  Wrong!

"The only thing of great value in the five-volume set that is not in the four is the Marelli ignition.

"Each set comprise of hardback green ring bound folders with a white growler and the words Service Manual on the front.  The copyright of the first manual is 1988.  JJM 10 04 06-20 has the copyright date of 1991.

"I understand that there are add-ons, JJM 10 04 06-201 and 202 that cover models '92 to '96. 6.0L engine plus other changes."  The H. D. Rogers web site (page 712) confirms this, and reiterates that these later manuals are not standalone either -- if you have a '92-on car you will need all of these sets to cover it.

Robert Woodling says, "I have purchased both the factory four-volume set and the Repair Operation Manual.  The four-volume set in some instances provides better detail while the ROM provides a better step-by-step approach."

Before buying the multi-volume Service Manuals, you might want to consider the CD-ROM mentioned below.  In fact, you might have to; Keith Lumsdaine says, "As of December 2000, the official Jaguar Workshop Manual part number JJM 100406 20 for the 1991-on cars is no longer available, as Jaguar have now [Feb 2001] issued it with the Supplements JJM100406 201 & JJM 100406 202 in CD-ROM form."

The only XJ-S repair manual made by anyone other than Jaguar is a Haynes manual, Jaguar XJ12 & XJS.  This was manual #478 in Haynes' old numbering scheme, and is #49015 in their new numbering scheme --but it's the same book either way.  It's a lot cheaper than the Jaguar publications (under $20), cheap enough you might as well pick one up even if you plan on buying the Jaguar books anyway.  It's based on portions of the factory manuals with some photos of a teardown of a Daimler Double Six added.  This repair manual is referred to simply as "the Haynes manual" throughout this book.

Classic Motorbooks catalogs list a Haynes manual titled Jaguar 12-Cylinder 1972-85, but this is actually the same book -- Classic Motorbooks simply cannot bring themselves to list the correct title.

The Haynes manual benefits from some recall and technical bulletin info that does not appear in the Jaguar manuals.  It includes some basic procedures for the GM400 automatic, including a removal/reinstallation procedure, but no overhaul info.  It only covers up to 1985, so owners of later cars will not get any info on the ABS brakes, Marelli ignition, etc., and would therefore be better advised to get the Repair Operation Manual with suitable supplements.

Gross errors in the ROM as well as the Haynes are addressed in this book, since the author owns both books; it is suggested that owners mark all corrections in their manuals as they read about them.

REPAIR MANUALS --6-CYLINDER XJ-S'S: The Jaguar XJ-S Repair Operation Manual,, AKM 3455, does not cover the 6-cylinder engines at all, nor their respective transmissions.  Gerda Kennedy of Bookspeed (page 722) says, "There is a separate manual for the XJS 6-cylinder 3.6 and 4.0" and that Bookspeed can provide it.  The part number is AKM 9063.  Unfortunately, Walter Petermann counters: "I picked up the AKM 9063.  It only covers the 3.6.

Petermann goes on to describe the publication: "There's 9 'booklets', about 30-45 pages each.  The complete manual is AKM 9063, but each book has its own number e.g.  AKM 9063/1../2 etc.

Book 1: intro, general specs, engine tuning data, jacking, lubricants, maintenance, service tools.
Book 2: Engine
Book 3: emission control, fuel system, cooling system, manifold & exhaust
Book 4: Clutch, manual gearbox
Book 5: Propellor (?), final drive
Book 6: Steering, front suspension, rear suspension, brakes, wheels & tires
Book 7: Body
Book 8: Air conditioning
Book 9: windscreen wipers & washers, electrical, instruments

"The AKM 9063 is now discontinued."

Note that AKM 9063 does cover the 8CU electronic fuel injection system used on the early AJ6, which never appeared in any other Jaguar and therefore may be a bit difficult to get info on elsewhere.

Even if you have a later 6-cylinder car, buying AKM 9063 might still make more sense than buying a V12 ROM.  Perhaps you might choose to buy AKM 9063 along with another book --such as an XJ40 (1988-94 XJ6) manual --that covers the later engine configurations (the XJ40 and the ‘88-on 6-cyl XJ-S have the same engine and transmission).  XK's Unlimited (page 697) offers a book called the Jaguar XJ6 Workshop Manual -- Owners Edition: "Covers 1988 to 1994, 180 pages.  This is an "Owners Edition" manual, meaning it is a boiled-down version of the full factory manuals and covers the maintenance and repair projects most likely to be tackled by an owner."  The good news is that it's only about forty bucks.  A Haynes manual might also be a consideration; see below.

There apparently is a later Jaguar publication that covers the 6-cylinder XJ-S.  XK's Unlimited offers a book titled XJ-S 3.6/XJ-SC 3.6/XJ-S 4.0 Service Manual, number 11-0252D (which may be an XK's number rather than a Jaguar number).  It's priced at a little over $100, indicating it may be the equivalent of a ROM.

If you're interested in the multi-volume XJ-S Service Manuals described above, Richard Mansell indicates that they do cover the 6-cylinder engines.

If you have a 6-cylinder XJ-S, the Haynes manual #478/49015 will be no help with the engine or transmission at all.  However, you could opt to buy the Haynes #478/49015 to cover the rest of the car and Haynes manual #49011, Jaguar XJ6 1988 thru 1994: Automotive Repair Manual, ©1997 (thanks to Loudon Seth for this info) for information on the engine and transmission, as well as the later IRS with outboard brakes.  Or, you could supplement the Haynes #478/49015 with the Jaguar XJ6 Workshop Manual --Owners Edition described above.  Either combination of two books should cover most of what you need to know, with the notable exception of the 8CU EFI system used on the 1983-87 3.6 cars.

REPAIR OPERATION MANUALS --XJ12, DAIMLER DOUBLE SIX: This book is on the XJ-S, but I'll be a nice guy and list what little I know about Repair Operation Manuals for saloons as well.  John Littler reports that for Series I/II cars, Jaguar issued one manual for the XJ12 and another for the XJ6, but starting with the Series III they issued a single manual to cover both.

Regarding the S I/II manual, Littler says, "Jaguar XJ12, Daimler Double Six, Repair Operations Manual.  Publication Part No. E190/4.  Copyright 1979.  Covers Series 1 and 2 (of which the only significant difference are carbs vs. EFI and the swap to GM400 halfway through the S2 model run - not the start contrary to common belief.)"

"Series 3 Service Manual - 3 items listed on first page:

Service Manual complete, AKM 9006 Edition 2
Service Manual Book 14, AKM 9006/15 Ed. 2

"Copyright 1985.  Covers both XJ6 and XJ12 series 3; the XJ12 has both H.E. and Pre-H.E. sections although they aren't particularly differentiated.  The S3 manual I have doesn't seem to cover the late XJ12 S3's (1987-92).  It covers P and D Jetronic but there's no mention made about the later ECUs."

ADDING YOUR OWN BINDER: If you get a softbound ROM --or any other manual from Jaguar or the UK in general -- and decide to tear it apart, holepunch it, and put it in a 3-ring binder, you will find that it is a metric sized book and won't fit in a US-standard 8½" x 11" binder.  If you're in Europe that's no problem, but here in the US you may find it a bit of a challenge.  Better office supply stores sell metric "A" size binders, but you'll also need to get the proper 4-hole punch.

Another option is to drop into a Wal-Mart and buy a photo album intended for the Kodak Advanced Photo System; these albums are quite a bit larger than standard notebooks yet retain the standard 3-hole pattern.  Having a 3-hole punch with an adjustable paper stop is a plus, so you can adjust the stop to center the holes on the longer pages.  Just throw the photo sleeves out, although the section dividers are nice, you'll wanna keep them to separate the manual from the supplements and the like.  These photo albums have the added benefit that they are really nice quality; this author even found one with a dark green, gold, and black cover that looks like it could have come from Jaguar.

PRIMERS: If you are new to automotive tinkering, you should buy one of the many books on the market explaining general procedures for car repair.  While this book is written to be as clear as possible, it is not intended as a primer and no efforts are made to explain standard auto repair procedures.  For example, this book may describe in great detail how a particular electrical component has a history of shorting out at a particular spot, but it will not provide any instructions on how to use a VOM to track down a short.  Quite the contrary, the reader is expected to know how to do things like track down a short, so problems that are easily isolated and corrected may not even be mentioned.

PARTS BOOKS: Jaguar also makes parts books.  Many owners suggest these books are more helpful to the mechanic than the repair manual; they contain exploded views of just about everything which are often easier to understand than the step-by-step text in the ROM or Service Manual.  And it helps to know the part number of what you need when placing a parts order by phone, since the names of Jaguar parts are often confusing and mercurial.

Stephen Wood describes the parts book for the early XJ-S: "Jaguar Parts Manual, RTC-9109-B, for the XJ-S, 1976 to 1982, pre-H.E. cars."

This author owns the one for the next generation: "Jaguar Parts Catalogue, XJ-S H.E. and XJ-S V12", RTC9888CE, August 1987.  Note that the title might be misleading; this parts book does not cover the pre-H.E. cars.  The title probably reflects the fact that the H.E. badge on the car was replaced with a V12 badge starting with VIN 125020 even though otherwise it's still the same car with the same engine.  This book covers models from the introduction of the H.E. engine through the mid-1980's --which should be kept in mind when using it, remembering that "up to" really means "from the introduction of the H.E. up to" and "from" really means "from this point until 1987."  Richard Mansell reports on the next edition after that: "...the Jan '87 to late-'89 parts book (RTC9900CA).  IMHO1 this is laid out a lot better than the earlier parts manuals as it has a description for each item on the same page as the pretty picture.  If you have an '87 to '89 3.6 or 5.3 XJ-S this guide is well worth getting, especially to aid reassembly."  He has a point about the layout since RTC9888CE has no descriptions at all on the page with the illustration but rather has the descriptions listed in the back under the part number.

JAGUAR BOOKS ON CD: The Jaguar Daimler Heritage Trust (page 691) offers several of the repair manuals and parts catalogues described above on CD-ROM.  Compared to the paper publications, these CD's are dirt cheap: £12.77 1 IMHO is an Internet abbreviation for "in my humble opinion".

H.E. VS. NON-H.E.: The H.E. (High Efficiency) engine, with 11.5:1 compression (12.5:1 outside the US) and a swirl combustion head designed by Porsche expert Michael May, was introduced in July 1981 and indicated by the letters "H.E." on the back of the car in place of the former "V12" emblem.  In 1986, the H.E. emblem was unceremoniously dropped and a V12 emblem was used once again, but the H.E. combustion chamber design continued to be used in all Jaguar V12 engines until it ceased production.  If you have an engine laying around and need to know which it is, the trick is to look at the spark plugs.  The plugs on the pre-H.E. tilt forward or rearward and are relatively easy to replace.  The plugs on the H.E. tilt toward the centerline of the engine just enough to make them a real pain to get a socket on.

ENGINE NUMBERS: The engine number is stamped on the top rear center of the block just forward of the joint with the GM400 transmission bellhousing, but it is typically hard to find because it is covered with grime.  Paul Hackbart sends this tip: "Take your oil dipstick out and get on the passenger side of car.  You can stick it through near the oil pressure sender and scratch away until you see it.  Just make certain you clean it off afterwards."

The XK's Unlimited catalog includes a guide of engine numbers for the XK 6-cylinder and the V12.  It provides the following info on the V12: 7S1001> E-type Series III 3/1971-2/1975 7P1001> XJ12 Series I 1972-73 7P4000> XJ12 Series II 1973 (Carbs) 7P25001> XJ12 Series II 1974-79 (EFI) 7P?> XJ12 Series III 1979-8? 8S1001> XJ-S up to 1980 8S18001> XJ-S H.E. 1981-87 For more detail on XJ-S engines, Richard Mansell sends this helpful data from "The XJ-S Collectors Guide": 8S4551 Feb 76 Canister type oil filter introduced 8S5203 Oct 76 Revised EFI 8S6454 Modified fuel pump 8S7017 Apr 77 GM400 introduced 8S8632 Nov 77 Stronger manual trans selector shafts 8S10195 May 78 Modified air filter box to stop blowing off!! 8S11262 Oct 78 Ignition amplifier re-located 8S13094 Oct 78 Twin V groove water pump pulley introduced 8S16401 Nov 80 Digital P injection introduced* 8S17194 Nov 80 Sump plug relocated 8S18001 Jul 81 HE Introduced Most changes after this are listed by VIN number but the following are listed too:

The popularity of over-square engines in racing is actually somewhat artificial.  Most racing programs divide competition into classes based on engine displacement.  An over-square design provides the most power for a given displacement, since it permits higher RPM and provides room for large valves.  However, these priorities do not translate well to street use.  Over-square engines tend to be heavy for their displacement; a larger displacement engine of comparable size and weight can be constructed with a nearly square configuration.  The over-square layout also results in larger surface areas in the combustion chamber, which absorb combustion heat and reduce fuel efficiency.  And while the design provides excellent power at high RPM, it tends to lack torque at lower RPM; since people like their engines to be turning slowly when cruising on the freeway, an over-square engine can seem anemic under these operating conditions.

Ford suspended production of the V12 for 1993, and reintroduced it in 1994 as a 6.0 liter (366 c.i.).  More than merely an engine enlargement, the change made the V12 much less over-square, since the change was entirely an increase in stroke; the new engine has a 90 mm bore and a 78.5 mm stroke.  This would tend to make the engine much more suitable for street use.  It remains more over-square than most engines, and hence can provide excellent performance at high RPM, but is more tolerant of stop-and-go driving conditions and tall final drive ratios.  The Michael May-designed H.E. combustion chambers remain in use in the larger engine, while the compression ratio has been reduced to 11.0:1.  Tom Walkinshaw Racing (TWR) was offering 6.0 litre engines much earlier.  According to Richard Mansell, "TWR started making ‘sporty' XJ-S's in 1984.  One of the options then was a 6.0 litre engine." John Goodman reports that TWR also made 6.2 and 6.4 litre versions, and maybe even a 6.7.

Later on the JaguarSport XJR-S also had a 6.0.  Mansell: "When JaguarSport officially started producing the XJR-S in 1988 only a 5.3 litre engine was available.  It was not until mid-89 that the 6.0 litre was introduced as standard.  This was then discontinued in 1993 as by then the standard XJ-S now had a 6.0 litre engine."

Note, however, that the 1993-on updated engine has a lot of other features these earlier engines lacked, such as a revised bolt pattern for connecting the GM400 transmission.

WHAT'S IN A REDLINE?: Some people, probably accustomed to American pushrod V8's, feel that the 6500 RPM redline marked on the tach is really aggessive and far too high for an engine this big for everyday use.  Nothing could be farther from the truth; this is not an American pushrod V8, it's an OHC V12 with an unusually short stroke.  Roger

"The real problem taking these engines to 6000 and above is that the GM 400 torque converter distorts under centrifugal loads so that the blading can make contact creating fine metallic particles which then cause accelerated wear of the transmission.  A way around this is to use a furnace braized converter which is more rigid and able to tolerate the higher r.p.m. without distorting so much." END OF AN ERA: The final Jaguar V12 engine was built April 17, 1997.

This problem is especially serious in the case of the Jaguar XJ-S.  Several problems the car seems to have, including vapor locks, distributor seizings, and ignition amplifier failures, may be exacerbated by hot shutdowns.  The underhood temperatures may skyrocket after a hot shutdown, and Jaguar is known to have had underhood temperature problems during development of this car.

Whenever you are driving the car hard, always drive the car leisurely for a few minutes before shutting it off.  If you are forced to shut the engine off after running hard --having a mechanical problem, for example --at least open the bonnet to allow the heat to rise out of the engine compartment, providing some convective cooling.

See page 228 for tips on improving post-shutdown cooling.

KNOCKING/PINGING/PINKING/DETONATION/WHATEVER: Regardless of what you call that sound, it ain't good for an engine.  A brief description of what's going on: When an engine is running properly, the fuel/air mixture within the cylinder is ignited by the spark plug and the flame front grows continuously and spreads throughout the combustion chamber until the entire charge has been burned.  However, while this is going on, the piston is moving upwards towards the head, compressing the charge and thereby heating it.  In the most severe cases of knocking, the compression causes the charge to self-ignite before the spark plug even fires.  The result is that the entire charge ignites at once, rather than the gradual ignition of the flame front moving through the charge.  This "explosion" has been likened to hitting the piston with a hammer.  It can damage the piston, connecting rods, and the bearings in both ends of the con rods.

What usually happens is less severe, however.  The spark plug fires well before the piston reaches the top of its stroke, so the flame front has begun its travel while the compression is still in progress.  Since the burning charge is expanding, it is compressing the unburned charge into the far corners of the combustion chamber.  The combined effects of the piston rising and the flame-induced pressure causes the remaining portions of the charge to self-ignite.  The actual amount of charge exploded in this fashion can vary anywhere from a tiny portion to the entire charge, so knocking can be either severe or barely detectable.

There are many factors that contribute to knocking.  The most notorious is compression ratio; the higher the compression ratio, the more likely it is for the charge to be detonated.  Another key issue is the octane of the fuel, which is a measure of how hot it must be before it self-ignites; the higher the octane, the hotter the mixture must get before it will burn.  And ignition timing is a factor, since lighting the mixture earlier will cause more of the charge to be burned

Other factors include the intake air temperature, the fuel temperature, and cylinder wall and head temperatures.  EGR, which puts some inert gases into the mixture, makes it harder to ignite and therefore reduces the tendency to knock.  Also, there are some minor details that can complicate the issue; sharp edges in the combustion chamber can act as "glow plugs" and ignite the charge prematurely.  Carbon deposits can increase the compression ratio, as well as provide glowing embers to preignite the charge.

Knocking can be difficult to detect on the Jaguar V12.  All those little cylinders mean that each knock is small, and all that sound deadening built into the car keeps the driver from hearing much of anything in the engine compartment.  Basically, if you can hear it at all, you might need to be concerned.  On the other hand, Mike Wilson reports: "I asked the local Jaguar rep and he had the audacity to say that "All Marelli cars ping".  He said it was even in the owners manual!  So, I came home and read mine and sure enough, there it was in black and white!  It said that a small amount of pinging was normal and if it happens on flat roads under no load, to see your dealer for further assistance."

If something needs to be done about pinging, the usual reactions include changing to better octane fuel or retarding the timing.  On the later XJ-S with Marelli ignition, you can't adjust the timing by just rotating the distributor, so a jumper was provided that can be pulled to put the system onto a more retarded map when needed.  Even if we try to buy good fuel, occasionally we always seem to get a tankful of real crap, and this jumper is a handy fix to get us to the next fillup.

Joe Ziehl shares some experience: "My mechanic told me to first try a higher octane fuel because while retarding the timing may help, the preignition might be caused by something other than spark plugs, such as carbon in cylinders or on pistons.  He also recommended that I treat the gasoline and run the car hard for a few days.  This made a significant improvement in the pinging."

Jeff Elmore reports: "I had been getting some slight pinging under medium acceleration after the car had warmed up.  I had tried many things, including checking the timing, high octane gas, etc.  Then I tried the temperature at the thermostats.  It was 213°F on one side and 203°F on the other.  I just changed the thermostats and topped off the coolant (almost half a gallon low), and the pinging is gone.  The car now runs better as a result, with my guess being that a lower CWT sensor means more fuel and power."

Andrew Stott reports: "Autocar magazine had an XJ12 HE on long term test and in their 12,000 mile report (May 8 1982) they had quite a bit about the knocking noise and clouds of smoke at around 4,000rpm in 1st following a couple of weeks of gentle, town driving.  Apparently, the Jaguar engineers discovered this quite early on in the development of the May heads and ran special endurance tests to highlight any problems, none were found.

"In their 36,000 mile report (April 9 1983) Autocar actually had one of the heads removed and found nothing at all amiss, not the slightest suggestion of pinking damage, and no measurable ovality or wear in the bores.  There are pictures in the report.  They also ran performance tests and found the car to be just as it was at 12,000 miles.

"Both these reports are in the Brooklands book on the XJ6 & XJ12 Series III (1979-1985), ISBN 0 946489 98X."

The experience on the internet discussion lists indicate there is one sure-fire cure for knocking: the Italian Tune-Up.  Get the car fully warmed up, then while cruising along at about 60 mph, move the shifter into 2 and punch it.  Hold the pedal to the metal until somewhere close to redline, then let off and coast back to 60 --and repeat.  The first time or two, the car will show its displeasure by stumbling and blowing great clouds of black smoke out the rear.  After a few such accelerations, the car will react much better to being punched, even feeling as though it is anxious to do it again, and there will be no trace of smoke.  Owners consistently report there is no longer any trace of engine knock either, and the car runs better all around.

Obviously, an Italian Tune-Up wouldn't be a good idea if the engine has serious mechanical faults such as fuel supply problems, overheating problems, etc.  It also wouldn't be good to run it through a speed trap.

People think I'm makin' this stuff up about the Italian Tune-Up.  Bill de Creeft provides a quote from a British car magazine after the HE engine came out: "...if one runs the car for not less than a working week of relatively gentle driving, typically commuting with no longer journeys between, then, once properly warm, accelerates flat out, the engine goes through a period between 4500 and 5000 rpm of loud detonation accompanied by pale but noticeable exhaust smoke.  You learn, after the first rather frightening occasion, to keep your foot down regardless, to accelerate through

OCTANE: ...ain't octane.  If only things were simple.  John Littler picked the following explanation up from an internet discussion; I presume that ULP stands for UnLeaded Petrol and PULP stands for Premium: "The US does things differently to the rest of the world (I bet you've heard that before!).  In Australia the octane reported at the pump is the RON (research octane number).  There is also another octane that you never hear about called MON (motor octane number).  The MON is determined in a similar way, but under more severe conditions (so it yields a lower number).  In the US they report AKI (anti knock index) which is an average of MON and RON.

"The ratings for ULP and PULP are typically: MON RON AKI ULP 82.5 91 87 approx PULP 86 95.5 91 approx

You can see that the US 91 is actually our PULP.  This is the US mid-grade (also the main grade in Europe).  They also have a premium grade which has an AKI of 93 or a RON of about 98."

Littler adds his own editing to this snippet: "I wish it were true that the US had a mid-grade rated at 91 AKI/95 RON.  Then it would be suitable for my Jag which requires 95 RON.  Unfortunately the US mid-grade is only 89 AKI/94 RON, so I have to pay for the 93 AKI/98 RON Super-Unleaded.  If the Jag had a knock sensor I would risk trying the 94 octane stuff, but it doesn't, and the dealer has warned me to always use 98.

"BTW, prior to 1973 the US reported octane as RON like the rest of the world."

UNLEADED FUEL: XJ-S owners in the US have been using unleaded fuel for decades, but many owners in other countries are only recently facing the prospect of leaded fuel being no longer available.  Since some of their owner's handbooks specify the use of "Four Star" leaded fuel only, they are understandably concerned.

Addressing this concern, Roger Bywater of AJ6 Engineering (and formerly with Jaguar Engine Development) wrote an excellent article for Jaguar World magazine (see page 723), Vol 10 No 3, January/February 1998, page 42.  Some of the high points are summarized here.

There are two reasons for concern regarding the use of unleaded fuel: Octane and valve seat lubrication.  Valve seat lubrication is simply not an issue in the Jaguar XJ-S; every engine the car has ever been built with has an aluminum head with hardened valve seat inserts, and the part numbers for these parts are the same for US-spec models always intended to run on unleaded fuel.  If you have shoehorned in a Chevy engine old enough to have a cast iron head with no inserts and designed to require leaded fuel, well, shame on you.

Octane is another story.  The US-spec engines have lower compression ratios to run on lower octane fuel.  To be able to run the high compression engines on lower octane fuel, either the compression ratio will need to be lowered or the timing will need to be retarded.  If the engine is being rebuilt anyway, lowering the compression ratio (different pistons, thicker head gaskets, machining the combustion chamber, whatever) may be workable, but most people will prefer to simply retard the timing.  Bywater suggests that there's very little difference between a high compression engine with retarded timing and a low compression engine with advanced timing anyway.

With the Lucas ignition systems, retarding the timing is simply a matter of turning the distributor to a new setting.  Bywater says that for the 95 octane unleaded that will be available in the UK and Europe, about three degrees should do it, although as many as five may be necessary for older cars with a lot of carbon buildup.  On Marelli ignition cars, retarding the timing only requires pulling a jumper to switch the ignition ECU to a more retarded timing map.

UNLEADED FUEL --AJ6 ENGINE: If you own an early (‘83-87) AJ6-engined car with the Lucas 8CU EFI, you can retard your timing by simply turning the distributor.  However, if you have a later (‘87-on) 3.6 with the 9CU engine control system, the ignition timing is controlled electronically and not so easy to change.  According to Bywater's article, there are two options: You can remount the crankshaft position sensor using the mount from the later 4.0 AJ6 engine, or you can remove the crank pulley and reposition the toothed rotor by drilling new mounting holes.

John Littler says, "Well, for around $50US you can get a little gizmo from a number of vendors which then gives you a dial to advance or retard the stock timing by up to about 5 degrees either way (does it on the fly so it just takes 1 degree off whatever the ECU says etc).  Definitely available from Summit (MSD and Crane), also available in Oz from two other suppliers as well.  Lastly, seeing as I believe the AJ6 use Delco ECU's (is that right?), then a copy of the Kalmaker software will let you change anything you want on the EPROM."

THE DANGERS OF RUNNING LEAN: Most people tend to think of their car's fuel system as an on/off proposition: either you've got fuel, or you don't --and if you don't, it won't run, so you've gotta fix it.  There is, however, a third possibility that bites the Jaguar V12 owner only too often, and that is running lean.

Running lean is no big deal if you're driving gently; in fact, there are modern automobiles designed for "lean burn" operation, which means that at light throttle they can operate quite a ways leaner than stochiometric in order to optimize fuel economy.  But running hard --in any gasoline engine, Jaguar, lean burn, whatever --with an air/fuel ratio leaner than stochiometric is just asking for engine damage.  A Jaguar V12 that has been running lean for a year but has never seen full throttle is probably as good as new, but hold that pedal to the metal for 30 seconds and a couple of new pistons will probably be needed.

Why am I making a big deal out of this?  After all, the XJ-S has EFI, which should provide reliable fuelling at all throttle conditions.  The later models even have oxygen sensors that will correct for either lean or rich conditions on the fly.  Why worry?  Well, there's plenty to worry about.  If the fuel pump or other parts of the fuel system aren't up to par, the EFI system may provide correct fuelling under normal driving conditions, but when floored the fuel supply can't keep up -- and the engine runs lean just when it is most dangerous! And, horror of horrors, there are absolutely no warnings that you're in trouble; everything on the dash looks just great, the engine sounds just dandy, and the car has plenty of pep - right up until it starts missing on a couple of cylinders because the pistons are toast.

If you ever intend to explore the lower half of the pedal travel on the Jaguar V12 (and who doesn't?  Why else would you own the car?), it is recommended that you install air/fuel ratio indicators, which are commonly available; they are very popular with performance enthusiasts for exactly the same reason: they provide a warning before it's too late.  These indicators operate off the signal of a regular oxygen sensor.  If your car doesn't have oxygen sensors, you can purchase generic sensors (the heated type are recommended), and it's a simple matter to have bosses welded into the exhaust downpipes to install them.  If your car already has oxygen sensors, there's no need to install more; the indicators will read the signal from the existing sensors without interfering with EFI operation.

Both Jeg's (page 717) and Summit (page 720) offer LED air/fuel indicators, and they're even reasonably priced.  You'll probably want two indicators, since you have two oxygen sensors --or perhaps you can rig a switch to read one sensor and then the other with a single indicator.  The indicators usually feature three colors of LED.  If the engine is running near stochiometric mixture, LED's near the center of the display are lit, and they are usually green.  The rich and lean sides of stochiometric are usually red and yellow LED's, but some indicators have red as rich and some have red as lean; make sure you understand that it is lean that means trouble, whichever color the LED's are.

When the engine is running in closed-loop mode (warmed up, light throttle), the indicators should be reading green.  When floored, the ECU goes into open-loop mode, which means it should run richer than stochiometric.  A rich indication when floored is OK.  If the gauge ever starts to read on the lean side of stochiometric while you have your foot in it, lift your foot now and investigate problems in the fuel system before you romp on it again.

Air/fuel indicators can help you spot a lot of ills, including totally unheard-of problems not covered in this book.  You'll be able to monitor how your fuel system is working at all times and notice when something goes wrong.

The May 1996 issue of Skinned Knuckles has an article, "Oxygen Sensors & Air/Fuel Ratio" by Hugh Poling, in which the author points out the limitations of air/fuel indicators that use a conventional oxygen sensor for input.  Some A/F indicators have three LED's, indicating lean, stochiometric or rich.  Others have more than three, apparently indicating different degrees of lean or rich; according to Poling, these indicators are wired so that particular voltages from the oxygen sensor light up particular LED's.  The indicators Poling objects to are the ones that are actually marked with different Lambda values; "From the SAE Transaction pertaining to oxygen sensors, this relationship of voltage to LED markings is bogus...Since the standard oxygen sensor covers a very narrow range of only a few percent around stochiometric, this labeling is fraudulent." In other words, an LED indicator connected to a conventional oxygen sensor is quite reliable at indicating whether you are running lean or rich, but do not rely on it to tell you how lean or rich.  Note that there are instruments on the market that can provide accurate indications of mixture within the lean or rich ranges, but you'll know if you buy one --they are very expensive, and they do not use a conventional oxygen sensor for a signal.

OIL CHANGING: If you buy an oil drain pan from the local auto parts store, slide it under the Jag, and open the plug in the sump, you may be in for a messy surprise.  The Jag V12 will drain around 11 US quarts of oil, and this is more than the capacity of many conventional oil drain pans.  Either be sure to get a really big pan, or figure out how to drain the sump into two pans.

Here's an idea: Get one of those plastic oil drain tubs that features a spigot to pour the oil into bottles without a funnel.  When the tub is sitting on the floor, the spigot acts as a spillover; if too much oil is drained into the tub, it'll come out the spigot rather than spilling over an edge.  With the tub sitting under the engine, set another container under the spigot.  Your total drain capacity hence becomes the total of both tubs.

A disposable aluminum turkey broiling pan works great for that second pan.  If it doesn't fit neatly under the spigot as is, it's not difficult to mangle the edge a bit to allow it to sit right.

OIL FILTER REPLACEMENT: The oil filter on the Jaguar XJ-S mounts nearly vertically, the way they all should; the dirt stays in the filter as it's being removed.  Considering the position, you can do your engine a favor by filling the new filter with oil prior to installing it.  When you start up, you will get pressure that much sooner.  There are also reports that prefilling may help protect the element itself from rupture when the engine is started.  You will find it helpful to use a small screwdriver or some such to poke through the smaller holes in the base of the filter and push open the flap a little to provide a vent while trying to pour oil in the center hole.  And be patient; it takes a minute or two for oil poured into the center hole to soak through the element and fill the outer chamber.

It has been noticed that some filters for the XJ-S are different from others.  Some are very large, extending almost level with the bottom of the pan.  Others are of conventional size.  Some have a series of flats around the bottom edge to fit the socket-type filter wrench that goes on the end, and some don't.  Since you can't get to this filter from the side, it is recommended you get a filter wrench that can be used from the end, and make sure the filters you purchase can be removed with your wrench.  The socket-type filter wrench works well and is cheap, but requires the series of flats on the filter.  There are also coil type and strap type filter wrenches that will work on most any filter; note that the coil type cannot be used to tighten the filter.

Peter Cohen says, "I have found that if I hand tighten them as much as I can with one hand with the little bit of leverage available down there, I am able to hand remove them as well." Peyton Gill adds, "I got a box of disposable latex rubber gloves (used in the medical industry).  They provide additional grip and make hand removal and installation much easier plus keep your hand clean when the oil runs down the filter.  These things are cheap and can be bought at drugstores.  It really makes a big difference applying torque."

Cohen provides some part numbers listed for earlier XJ-S's: "Fram PH2931 is correct, and I have used them for years on my 1989 XJS.  Purolator L30255 is the new numbering scheme that replaces L3255. (They just stuck in a zero for some reason.)"

Dave Hernt reports that later spec filters fit better: "Both the PH2995 and L30381 are the filters specified for the 6.0L

OIL FILTER REPLACEMENT -- EARLY CANISTER TYPE: Until sometime in 1976, the XJ-S came with a canister filter assembly.  Not only does this make it more difficult to change, but more care must be taken to make sure everything is working properly.  Mike Morrin had a problem with a non-replaceable bypass valve that sits in the bottom of the canister: "I noticed that the bypass valve was actually about half way open!!  This is presumably not good for filtration efficiency.  On dismanting the bypass valve, it became apparent that the alloy valve body had been strained, probably by someone tightening up the filter assembly with something not seated correctly.  I was able to straighten and reassemble the valve, and it looks like it should work as good as new."

SEALING SUBSTANCES: If you would prefer that your Jaguar not leak oil, the first thing you must get through your thick skull is to ignore all guidance on sealants and gasket dressings provided in the official Jaguar publications.  Most of their callouts are obsolete, many were wrong the day they were printed, and --let's face it --Jaguar has absolutely no credibility regarding leak prevention.  To top it all off, Jaguar manuals and TSB's have a nasty habit of calling for some esoteric product that's only available in industrial quantities via special order.  Forget the Jaguar sources and follow the guidance in this book instead.

Note that "gasket dressing" and "sealant" are two different things; a gasket dressing is used to help a gasket seal properly, while a sealant is used where there is no gasket.  Nobody is strict about the use of these terms, but the wise mechanic will note how a product is intended to be used and avoid trying to use products for applications they are not suited for.

It's easy to get all wrapped up in which sealant or dressing is "the best", but all you really care about is that it doesn't leak.  There are many products that will fill that bill for any particular application.  Being readily available locally in small

If it's a gortex gasket, don't use any substances on it; assemble it dry.

If it's a paper gasket, use a gasket dressing such as Hylomar on both sides.

If the joint involves two close-fitting metal surfaces with no gasket, use a sealant such as Loctite 518.

Those guidelines will cover almost everything that needs sealing in the Jaguar XJ-S.  There are a couple of special cases, though.  The sides of the rear main bearing cap require a gap-filling sealant that can be injected; for this, copper silicone sealant works well although it's not particularly easy to squeeze into the slots (the top of the rear bearing cap should be sealed with Loctite 518).  The threads on the sandwich plate bolts with their heads inside the sump should be sealed with Permatex #2 non-hardening sealant.  The head gaskets and exhaust manifold gaskets are metal sandwiched around a fibrous core and should be assembled dry.

GASKET DRESSINGS: As noted above, Hylomar is readily available and works just fine.  Hylomar is a blue goo that never hardens.  Jaguar mistakenly specified Hylomar for use as a sealant in gasketless joints, which is a large part of why these cars leak; it eventually gets blown out of such locations.

On gaskets, Greg Fronczak of Jag Services prefers a Toyota sealant, part number 023500102.  This is a black substance.

Chad Bolles suggests a non-hardening sealer from a GM dealer, part no. 1050026.

Roger Homer suggests a Caterpillar product. "I'm not sure of its official name/number but I just go into the local Caterpillar dealer and ask for a tin of Cat Red." Bolles and Homer recommend these last two products primarily because of ease of disassembly later; the gaskets easily peel off the metal parts with no need for scraping.

SEALANTS: As noted above, Loctite 518 is readily available and works just fine.  Everything that Loctite makes with a number starting with 5 is a sealant, though, and many of them will work in the Jaguar V12.  Loctite 573 and 574 have both been used successfully between the tappet blocks and the heads.  Steve Cranswick likes Loctite 5900 Flange Sealant.  None of these are likely to be as easy to find as 518, though.

For those who can't seem to find Loctite 518, Karl Nelson says, "Permatex is now a division of Loctite, and Permatex 51813 is the same thing as Loctite 518.  Permatex 51813 is widely available at NAPA stores, and is advertised as Anaerobic Flange Sealer."

Joe Bialy adds, "The '13' in 51813 signifies the size of the package the 518 comes in.  For instance, IIRC, 51845 is a caulking gun sized package of 518."

Unfortunately, this all describes a typical PCV system --not the one in the Jag.  Rather than the flow-through scheme of a typical system, the V12 has only one opening into the crankcase.  This vent is connected to a chamber built into the LH air filter housing.  The chamber has a fairly large opening into the air filter housing itself.  The PCV valve is also connected to this chamber.  Flow-through ventilation of the crankcase is clearly not possible.  It's doubtful such a system will apply a significant vacuum to the crankcase, other than when the LH air filter is plugged up.  The only objective it will achieve is pollution control; vapors cannot escape the crankcase without going either into the air intake or into the inlet manifold.

LEAK CONTROL VIA PCV: In the July 1999 issue of Jaguar Driver magazine, Crispin Hales relates a story about a V12 E-type that had been converted from the original Zenith-Stromberg carburetors to SU's by a previous owner.  The car leaked oil badly, and one by one all the leaks were corrected except for the rear main seal.  After procrastinating for

It's unknown what the PCV system on the SIII E-type looks like, but it wouldn't appear that the system on the XJ-S would help reduce leaks this well.  Of course, you should fix the leaks! But perhaps it'd be nice to achieve the leak reduction benefits of a typical PCV system on this V12.

It would be easy enough to make this system work like a typical PCV system: remove the PCV valve from the chamber on the LH air filter housing and plug that hole, leaving the crankcase vent connected to the air filter housing via the chamber.  Install the PCV valve into the crankcase itself.  That way, the PCV valve will draw air from the LH air filter housing into the crankcase through the metal mesh, through the crankcase, and through the PCV valve into the intake manifold.

Of course, there's no hole to connect the PCV valve to! You'll have to make one.  As far away from the existing vent as possible is good, but not essential.  You want to avoid any place where there's a lot of oil splatter that the PCV might suck up, but most engines put it right in the valve cover so installing it in the RH cam cover should work just as well.  If you're good, you can drill a hole in the cam cover that's the same size as the hole in the chamber where the PCV valve was originally installed so you can install the same valve in the same grommet.

Other options would be to find a way to connect it to the plug for the timing chain tensioner or to a half moon seal.  Either way would avoid cutting on expensive metal parts.

Remember that you're not bound by the original PCV valve.  A check through the selection of PCV valves and grommets in an auto parts store may generate some ideas.  Some PCV valves have a 90° fitting on them, which might be helpful.

If you manage to install the PCV valve somewhere in the right rear area of the engine, note that you should be able to take the tube connecting both intake manifolds to the PCV valve off and turn it around backwards and reinstall it, providing a ready connection to the right rear.  Of course, you can just connect up some hoses to the same fittings and route them anywhere.  Connecting to both manifolds is probably good, since you want to have the same effect on mixture on both banks.

Obviously, it is of considerable importance that the owner take care to maintain the integrity of the crankcase containment; an opening into the crankcase will not only cause an oil leak at that location, but it will also allow air to enter and reduce the effective vacuum in the crankcase and thereby cause oil leaks elsewhere.  A classic location for such a leak on the Jaguar V12 is the timing chain tensioner cover (see page 47), but any opening into the crankcase will do it.  Make sure your dipstick is seated properly, make sure your oil fill cap has a good gasket under it, etc., etc.

PCV FOR WORN ENGINES: In the course of maintaining a slight vacuum in the crankcase, the PCV system must deal with whatever leaks exist to allow air into the crankcase as well as blowby from the piston rings.  With a very worn engine, the piston ring blowby may overpower the PCV system even if all the crankcase openings are properly plugged.  The EPA doesn't really care as long as the air intake to the crankcase comes from the air filter housing; when the vapors overpower the PCV, the excess comes out into the air filter housing and gets pulled into the engine anyway.  It just makes the inside of the air filter housing grungy.  The systems the EPA don't like are the ones with a vented oil filler, where the excess vapors get blown all over the engine compartment and out the bottom of the car.

Of course, you might not care for the oil leaks that result when the PCV system is overpowered.  It has been suggested that, even though an engine rebuild at this time is prudent, the addition of a second PCV system may help keep the oil leakage to a minimum until you can schedule enough time for an overhaul.  Back in the days of carburetors, adding a second PCV system would have been troublesome because you would have to figure out how to get enough fuel into the engine at idle when all that intake air was bypassing the carburetor venturis.  However, with EFI you really don't have anything to worry about; just install it and the EFI system will meter the fuel accordingly.  You may have to adjust the idle speed screw a bit.  Note that the piston/ring wear rates on the Jaguar V12 are so low that if you are considering this band-aid fix on an engine with less than 200,000 miles, you are advised to look for damage or leaks elsewhere first.

PCV VALVE: The genuine Jaguar PCV valve is part number C 44231, and the valve itself is stamped E7 AC 3848.  This thing costs about $40.  That's extortionate.

Kelly Spongberg says, "I replaced ours with a generic jobber one made for older Ford V8 engines.  It is exactly the same size, and seems to work fine."

A quick review of the selection of PCV valves at a local auto parts store revealed that it may be difficult to find a PCV valve that won't fit the Jaguar V12.  There are a couple that appear nearly identical, such as the Fram FV202.  There are a bunch more that are the same shape except they have a hose barb on the outlet end --but since that end gets jammed into the grommet in the chamber on the LH air filter housing, you won't see it and it'll work fine.  There are yet a few dozen other PCV valves that appear the same as these except that they have an "F connector" on them that allows the connection of two hoses; you can just pull the F connector off and install it in the Jag.  There are even "generic" PCV valves that come with a selection of F connectors; throw all the connectors away and use the PCV valve as is.

Of course, there may be a good reason why there are dozens of PCV valves available that all appear interchangeable: they may have different innards, like different springs or port sizes so they flow differently at different operating conditions.  Dave Osborne bought a valve that was visually nearly identical to the Jag valve for $3.  However, when installed the idle was 100 RPM lower than before.  Apparently the Jag valve has a stronger spring in it that holds the valve a bit open at idle, while the Ford valve has a weaker spring and is totally closed off at idle.

Big deal? Perhaps not.  You can simply readjust the idle.  And, considering the way the PCV system works on this car, it's questionable if the PCV valve does anything of value anyway.

MISFIRE: With 12 cylinders, some people might not even detect a misfire.  An easy way to check --as well as to tell which bank is acting up --is to fold a dollar bill in half and hold it over an exhaust pipe outlet and listen to the flapping that results; a misfire is usually obvious.  Steven Draper adds, "According to the most recent Jaguar Repair Information Periodical, the official procedure is to use a one hundred dollar bill and send it to the dealer for evaluation.  Unfortunately, the bill cannot be returned."

COMPRESSION CHECK: First, a brief description of how to properly perform a compression check on any car: The battery and starter must be in good condition.  All of the spark plugs should be removed.  Power to the ignition system should be disconnected, since an electronic ignition system may be damaged trying to fire with the spark plugs disconnected.  And the throttle should be held at least part way open, usually by jamming something in the linkage.  On a car with EFI, it would also be helpful to disconnect the power to the EFI system or fuel pump to prevent fuel flow.  With a compression gauge fitted to one spark plug hole, the engine should be turned on the starter through several compression strokes, until the reading stabilizes at a peak value.

On the XJ-S, it would be most helpful to have the type of compression gauge that screws into the spark plug hole and has a lengthy hose.  Trying to hold the press-in-place type on this engine is not easy.  Also, since the A/C compressor usually has to be removed to get at the front plugs, you will probably have to run the test with a dangling drive belt; try to position it so there is no tension on it, and the crank pulley can turn within it without driving it.

On the US-spec pre-H.E. engine, the readings typically will be about 130-150 psi.  The US-spec 5.3 liter H.E. engine has 11.5:1 compression, and will read about 200-220 psi.  Note that readings will be lower at high elevations.  Keep in mind, however, that the absolute values are not as important as the relationship between them.  There are dozens of factors that could affect the absolute values (including the calibration of your gauge), so if your readings are

If one cylinder reads low, it is customary to add a couple tablespoons of motor oil into that spark plug hole and test it again.  In theory, the oil will temporarily seal bad piston rings but won't seal a burned valve, so this test may indicate the level of disassembly needed.  Of course, the oil probably won't seal a burned piston or a hole in a cylinder liner, so the results are best taken with a grain of salt.  Either way, the head has to come off.

LEAKDOWN TEST: The leakdown test is gaining in popularity among mechanics, who feel that it gives a better indication of the actual quality of the sealing of the compression chamber than the compression check.  To perform a leakdown test, compressed air at a known pressure (usually 100 psig) is fed through a device with an orifice in it and into a cylinder via the spark plug hole.  The pressure downstream of the orifice is measured, and the leakdown rate is calculated as the percent which the pressure dropped across the orifice.  If the leakage out of the cylinder is very low, the pressure after the orifice will be very close to the pressure before the orifice, and the percent of pressure lost will be low.  If the compression chamber has big gaping openings in it, the main restriction in the flow will be the orifice itself, and the pressure after the orifice will be closer to ambient -- and therefore the percentage lost will be much higher.

When performing this test, it will be necessary to lock the crank still.  The air pressure in the cylinder will try to turn the crank to BDC, but at BDC one of the valves is likely to be cracked open, making your leakdown readings meaningless.  Try to lock the crank somewhere between halfway up on the compression stroke and halfway down on the power stroke.

Note that, when doing such a test on the Jaguar V12, it'd be a good idea to take the oil filler cap off the left cam cover.  We wouldn't want a well-sealed crankcase (hah!) to cause unwarranted favorable readings.  Also, just in case there's a leak in a head gasket, the radiator cap should be removed to prevent pressure buildup in the cooling system.

Kyle Chatman points out that if the leakdown test finds excessive leakage in a cylinder, it might be possible to determine whether the leakage is from the rings, the exhaust valve, or the intake valve by listening closely at the oil filler cap, the air intakes, or the exhaust pipe outlets.  And a bad head gasket might cause bubbles in the coolant (especially if it's the center cap that was removed) or other motion in the coolant level.

It's entirely possible that the leakdown test is highly regarded simply because it gives results in percent.  It should be pointed out, however, that the percent has no real basis and is entirely dependent upon the size of the orifice in the test device --and Randy Wilson says "and there is no such thing as a standard orifice size." In order to be able to compare the results of one leakdown test against another, it would be necessary to confirm that the orifices used were the same size and had exactly the same flow characteristics and that the same air pressure was used for the tests.

Wilson adds: "Next question is: How much air leakage is acceptable? This all depends on how big the cylinder is.  The bigger the bore, the more ring area there is to leak by.  Typically, the valves are bigger, too.  Here we could really use a percent of leakage vs. base volume, but our tester is effectively measuring finite volume of flow."

There are other concerns involving leakdown tests.  For one thing, since the engine does not turn during the test, it really only gives an indication of the leakage at one piston position.  While this is usually adequate, it may fail to identify certain types of problems such as localized damage on a cylinder wall.  Perhaps the careful mechanic could slowly turn the engine over by hand while doing the leakdown test, and watch the gauge for variance in the readings.

The leakdown test does have the advantage, however, that if a mechanic is using the same leakdown tester at the same pressure all the time, he can get a real good idea of just what condition cars are in.  While compression readings will always vary from car to car, the percentage readings from his trusty leakdown tester should give very consistent indications on cars in similar condition regardless of compression ratio or other variables.

HEAD GASKET CHECK: Michael Neal suggests two methods of checking the integrity of the head gaskets.  First, remove the rubber hood that connects the PCV system to the engine just forward of the oil filler cap, and look inside it.  Milky deposits are an indication that water is getting into the oil, usually a sign of trouble.

For a more definite check, Neal recommends removing the spark plugs, pressurizing the cooling system to 15 psi, and leaving it overnight.  Then have someone turn the starter while watching the spark plug holes.  Mist (or worse, a solid stream of water) coming out of a plug hole means it's time for engine work.

Of course, pressurizing the cooling system usually calls for a special tool.  It basically is an adapter radiator cap and a hand pressure pump; Stant is the common manufacturer and it runs $60 to $70.  In a pinch you could tee into the small hose on the center fill pipe and apply pressure.

TAPPET NOISE: Roger Bywater of AJ6 Engineering and formerly with Jaguar engine development, says, "In fact a recognised source of tappet noise on the V12 is excessive side clearance of the tappet in the aluminium carrier allowing it to ‘rattle about'.  Remember the XK used cast iron tappet sleeves and they expand and contract at the same rate as the tappet so the clearance remained more or less constant.  This does not happen on the V12 and the minimum diametral clearance is set by the need for a top size (high limit of tolerance band) tappet to not jam in a bottom size carrier bore at minus 40 degrees in a Canadian Winter.  The other extreme of a bottom size tappet in a top size bore could well be quite sloppy when fully warm and the way the cam moves it around can be very critical.  Cam profile, tappet clearance, side movement, rotation and rock-over at peak lift, as well as valve seating geometry, all come into what is actually quite a complex phenomenon.  For the record the range of diametral tappet clearances involved run from about 0.0005" to about 0.002" at room temperature.  I wonder how many engine builders have even thought about measuring such things?"

OIL PRESSURE: An oil-fed sleeve bearing, such as used in the main and connecting rod bearings of automobile engines, is an excellent device -- much more so than most people understand.  When the parts are rotating, the parts ride up on a film of oil, much like skimboarders skim easily across very shallow water and seem to coast forever.  When operating properly, the metal parts do not touch each other, and there is essentially zero wear.  The friction is entirely within the film of oil.

This system doesn't work at a standstill, however, the same way the skimboarder will sink to the bottom when he stops moving.  The entire reason engine bearings have a soft, replaceable surface is because they must ride on this surface for a very brief time at startup, before oil is pumped to the bearings and before the bearings establish a film to ride on.  The hard steel surface of the crankshaft should slide on the soft bearing with very little wear on either, but startups still account for the vast majority of normal bearing wear.

The shearing action of the oil tends to heat it somewhat; there is very little heat generated from shear, however, and many cars get by without oil coolers.  The main cause of heating of the oil is by contact with hot parts, notably the bottom surface of the pistons.

The pistons are likewise supposed to skim up and down the cylinders on a similar film of oil.  It doesn't work nearly as well, though, since the piston stops at each end of its travel for an instant, and because there is a less positive flow of oil to this area.

This system also does not work very well for the contact between the camshaft and the followers.  This is because the contact area is a very thin line rather than a broad area.  If one of the two parts were as soft as the crankshaft bearings are, the force at the contact point would quickly tear it up.  In the Jaguar V12, these parts are immersed in oil during operation.  This ensures they are adequately lubricated, even during startup since the oil stays there, but it also generates more heat churning the oil.

There are two primary bearing failure modes in any engine that result from lubrication problems.  The first and most easily understood is excessive wear and damage due to lack of lubrication.  The second is bearing overheating due to insufficient cooling oil flow.  These two are very different; in the latter case, the bearing may have enough lubrication to prevent wear, but gets hot enough to melt the soft bearing material because the same oil is staying in there and getting hotter and hotter, rather than cool oil flowing through.

All engines tend to display a drop in oil pressure at idle; the pump moves less oil when the engine is turning slower, but the openings through which the oil flows are the same size no matter what the engine speed.  The Jaguar V12 is no

There is no magic value for oil pressure.  The only real need for any pressure at all is to get oil to all points in the engine, and this would only require a couple psi.  Oil pressure is monitored simply to insure there is oil flow, which is essential.

If your car has always had low pressure at idle when hot, and it gradually over the years gets a little lower, don't worry about it.  If it suddenly has much lower pressure than it used to, you may have a damaged bearing that is allowing oil to flow through too fast; the cause should be investigated.  If your car suddenly has no oil pressure at all, stop immediately, do not drive it one more minute until the problem is located and corrected.  Many motorists fail to understand the importance of this, so I will emphasize: If the red light on the dash comes on indicating that you have no oil pressure, it is not good enough to "take the next exit."  You should pull over immediately, possibly even shutting the engine off while still moving.  A towing fee, and even an illegal parking ticket, is a minor expense compared to an engine replacement, which is the inevitable result of driving with no oil pressure.

Do not add oil thickeners to your oil.  While these may increase the indicated oil pressure at idle when hot, they do no real good and can do considerable harm.  In particular, when cold the oil may be so thick that very little flows and most of the output of the oil pump is wastegated through the pressure relief valve.  While there is good pressure, there is little flow to the bearings, and they may fail due to lack of cooling flow before the engine and the oil warm up.  This is also a good reason not to run the engine too hard until it is fully warmed up.

OIL PRESSURE SENDER: The oil pressure sender on the pre-'92 XJ-S is notorious for leaking; see page 47.  It's also fairly well known for electrical maladies.  Tom Mackie says, "My oil pressure sender is getting flaky.  I connected an ohmmeter and found that rather than nice varying resistance readings, it sometimes goes open.  Which makes me wonder how accurate this particular unit has been all along."

If the connector on top is loose, Mike Morrin provides some insight: "The connector moving around is due to some little plastic pegs broken inside, and will cause the sender to read low.  You can uncrimp the top and get inside to glue it down."  Since uncrimping is difficult, others suggest cutting right through the circumference of the can to get the top off, fixing the innards, and putting the top back on with aluminum tape or JB Weld or some other mechanical means.

Ed Sowell provides electrical data to aid diagnosics: "Here are the measurements from my sender and gauge, for what it's worth:

Oil pressure sender (markings: PTR 1001/10/EC 700kn/m2, 29-7 Part #46272):

Engine off: 350 ohms

Cold engine idle: 80 ohms (I believe the oil pressure is about 60-70 psig under these conditions)

Oil pressure gauge:

290+ ohms = 0 psig

55 ohms = 50 psig

10 ohms = 100 psig

short to ground = off top of scale."

I'd like to be able to tell you what commonly available sending unit can be used for a substitute, but I can't; nobody's worked one out yet.  The pre-'92 Jaguar V12 uses a 0-100 psi oil pressure gauge while Jaguar 6-cylinder cars use a 0-80 psi gauge, so senders from other Jags won't work.  Before trying a sender from any other car, make sure it has the 0100 psi range.  Electrical oil pressure gauges with 0-100 psi ranges are very common as aftermarket items, though, so perhaps the sender from one of those will work.  Summit (page 720) and Jeg's (page 717) offer many such gauges, or you can probably find a fair selection in a local auto parts store or speed shop.  Unfortunately, the senders are often included with the gauge itself rather than sold separately, but you still might get off cheaper than buying the Jag part even throwing the gauge away.

There are two issues that must be addressed to get an aftermarket sender to work.  The first is physically installing it.

The second concern is finding a sender with the correct pressure vs. ohmage response.  Unfortunately, neither Summit nor Jeg's provide such data; if you can't find such specs or talk a local shop into letting you check one out with a tire pump and a VOM, you may just have to take the risk and buy one to see what their electrical characteristics are.

For now, your best option may be to shop around the mail order places for the OEM part, since prices on this item seem to vary widely and it sometimes can be found for a quite reasonable cost.

If you have the ‘92-on with round gauges, you are in worse trouble.  Read about steady oil pressure below.

REPLACING THE OIL PRESSURE SENDER: Julian Mullaney says, "Use a crow's foot and several thin extensions.  It is a superb test of dexterity and patience, but I did it.  To install the new one, I attached it to a coat hanger and started the thread that way."

Stefan Schulz says, "Have you tried a plumber's tool called a basin wrench?  GBP5 at the nearest DIY store."

Craig Sawyers says, "What I did was undo the banjo bolt that links the camshaft oil feeds to the back of the alloy pedestal that holds the oil pressure sender.  Then I undid the two 7/16" af bolts that hold the pedestal down and took the pedestal plus oil pressure sender out as a unit.  Changed the sender, and reversed (as they say) the removal procedure.  Made it all very easy, when originally it looked damned near impossible.  The Jag ROM and Haynes were less than useless."

REALLY STEADY OIL PRESSURE: Bill Letter reports: "Today the kitty went in for a number of "adjustments", the most important of which was to determine why my oil pressure gauge always reads 58 psi at idle (hot or cold).  On my last visit to the same dealer for the same problem, I was told that the gauge was working fine and according to Jaguar Spec.  Today I was shown a TSB that explained that Jaguar changed the oil pressure senders on the XJ12 Sedan and XJS V12 (in 1996) to a new type which is actually not a sender at all.  It seems (according to the dealer) that numerous customer complaints of their oil pressure gauge reading too low (less than 25 psi) when hot at idle caused Jaguar to discontinue manufacturing the oil sender and instead replace it with an oil switch which acts like an idiot light (when there is more than 7 psi pressure it will always read 'ON' or in my case 58 psi, when there is less than 7 psi oil pressure it will read 'OFF' or zero psi).  So it was explained to me that the updated oil switch was installed in my car last year.

"It is Jaguar TSB Number 15-13 dated 06/95 and covers all cars with V-12 engines and some AJ16 engines on the XJS (MY '95 on).  They removed the senders and installed a simple switch because of customer complaints that the needle would read lower oil pressure when hot at idle!"

You may have difficulty trying to undo this "upgrade" since the real sender is officially NLA.  Gregory Wells of Coventry West, Inc. explains in detail: "The sender issue is confined to '88-on XJ40 cars and '92-on XJ-S with 4.0L, 5.3L, and 6.0L engines (VIN 179737 onwards).  Jaguar has superceded all sender numbers (viz.  DBC4418, DBC5513, DAC7879, DAC11141, LMD5640AB) to JLM20791, which looks like the old C42200 (now superceded to LHD5642AA) switch for the oil pressure light on the Series III cars.  Included in the bag with the sender is a small harness which seems to only have a resistor in it.  If one orders any of the above five part numbers from Jaguar, a JLM20791 will be supplied.  I've checked the '88-92 XJ40 fiche, the '93-94 XJ40 fiche, the '87-91 XJ-S fiche, and the '92-on XJ-S fiche and they all show gauge sender part numbers that eventually supercede to the on/off sender p/n."  However, if you're persistent, you may be able to find a dealer or supplier that has some of the real senders in old stock.

Note that none of this seems to apply to the pre-'92 XJ-S.

ENGINE OVERHAULS: If you take your XJ-S to a disreputable dealer with major engine problems, they may tell you that a fine machine like this cannot be rebuilt, and try to charge you $10,000 to put in a new engine.  Of course, one of the features that make this a fine engine is that it can be rebuilt.  It is not a disposable engine; all wear items can be replaced.  Even the cylinder liners can be easily replaced, so there is no need for boring and honing or for oversize pistons.  Of course, if you've overheated the engine and warped the block, or you've had a major engine fire, you will definitely need a new motor.

If the engine has to be rebuilt but you aren't up to the task yourself, you may find it challenging to find a mechanic you feel is competent to do the job.  Fortunately, if you live in the US, there may be an alternative to taking your chances with the local grease monkeys or a Jaguar dealer: Crow Engineering, 1-800-537-4146.  This is a very interesting business run by a British guy named Stewart Plant who apparently spends a few months each year in the US.  By appointment, he and an assistant will drive to your house and rebuild your engine in your garage.  He arrives in a panel van with all the tools and parts needed and will typically finish the task in a week or so.  He and his assistant sleep in the van; the only accommodation they ask from you is to use your shower.  Their services are not cheap, but they're undoubtedly cheaper than paying a dealer for a new engine --and you're more likely to be told why your engine was damaged and how to avoid it happening again.

Rebuilding by the home mechanic is not out of the question.  It's imposing at first; the engine compartment is crammed quite full.  But with this book, a repair manual of some sort, a good set of tools, and time and patience it can be done - and the money saved will probably be enough to pay for that good set of tools!  The biggest disadvantage of going this route is usually the time involved; typically, a mechanic will disassemble the engine, figure out what parts he needs, order the parts, and then wait, and wait, and wait for the parts to show up --only to find out that a few of them are incorrect and must be returned and reordered.  And, of course, on reassembly he will figure out what he forgot to order.  As a result, even though only a week or two of actual labor may be involved, the car may be scattered all over the place for a couple of months or more.

If you decide to tackle such a teardown, note that the V12 weighs something like 700 pounds as it is pulled from the car.  You don't want to be working with flimsy hoists or engine stands; obtain the heavy-duty stuff, perhaps even items intended for trucks.

ENGINE ASSEMBLY LUBE: When an engine is first started after assembly is when much of the wear occurs --in the several seconds it takes before oil pressure and flow to the bearings is established.  To counter this problem, there is a product called "Penrite Camshaft & Engine Assembly Lube".  This is made specifically for use on all plain bearings (mains, big ends, etc.) as well as on cams, when assembling a rebuilt engine.  It claims to withstand loadings "greater than 200000 p.s.i.", which is almost 100 tons per sq. inch.  It is an Australian product, but equivalents may be available in other countries.

Another idea is to simply fill the freshly-rebuilt engine with oil through the galleys instead of the filler cap, thereby lubing all the bearings before it ever turns over.  All you need is a pressure vessel capable of holding at least 3 or 4 quarts with a tire valve at the top and a hose out the bottom with a selection of fittings that will thread onto the oil filter fitting.  After reassembly, you thread the thing onto the oil filter fitting, put new oil in the tank, close it up, and apply compressed air to the tire valve.  The pressure will blow the oil into the galleys and on into the bearings.  After enough oil has been blown in to establish steady oil flow through the system, the feed is cut off before the tank empties and blows air into the

Andrew Holley describes what he did with a motorcycle engine: "What I did was get hold of an old fire extinguisher, the water/stored pressure type.  Has about a 15 litre capacity; the handle has a tyre valve built into it with pressure gauge as well.  After draining and cleaning, filled it with oil and attached the hose via a suitable fitting to one of the oil cooler lines.  With about 60 psi of air in the tank, it forced the oil through all the passageways.  Simple and effective."

Tom Amlie: "Prelubing a rebuilt engine is sometimes difficult, but in this case it was easy.  There is a pipe plug on the little pedestal that holds the oil pressure sender and the idiot light switch.  As best I could tell, it was 1/8 NPT.  Got a cheap ($13) plastic garden sprayer and cut the hose to match 1/8 pipe.  Put 8 quarts through it.  Worked great."

You might want to use a good assembly lube and pre-oil the engine before startup.  Blowing oil into the galleys will do wonders for reducing wear in bearings and cam followers during that first startup, but you won't get any oil on the cylinder walls until the crankshaft is spinning.  So having a good assembly lube on the cylinder walls is a good idea.

MANIFOLD CROSSOVER PIPE HOSES: On the author's '83, the intake manifold crossover pipe is connected to the manifolds with a short, straight piece of 1" hose at each side.  However, sometime before '89, the assembly was changed so that pieces of hose with 45º bends are required.  A cursory look at the two assemblies leads one to believe that the parts themselves are in fact unchanged, and the later cars were merely assembled with elbow hoses to relocate the crossover pipe higher across the back of the engine.  This might actually be helpful in making condensation drain out of the crossover pipe back into the manifolds rather than into the vacuum line to the ECU, which really messes things up.

If you have the earlier straight hoses and need to replace them, it's obviously pretty easy to find pieces of 1" hose.  As for the later parts, Jeff Elmore says, "The dealer quoted me $22 apiece for these three inch long, 7/8-1" diam hoses with a 45 degree bend in it.  Bennett Auto Supply had a Goodyear coolant bypass hose that fit perfectly for $2.62 apiece.  Part number #gyy 63064."

Whatever you fit, note that the vacuum inside these parts is considerable, and long unsupported sections of rubber hose will be sucked flat.  With the earlier design with straight hoses, it appears to be sufficient to merely be sure to insert the hoses far enough onto the fittings that there is only a short area of hose that doesn't have fittings within it.  If you must have longer sections, you may need to insert a piece of wire coiled like a spring to hold the hose round, or perhaps just a short section of tubing.

RUNNING WITHOUT AIR FILTER HOUSINGS: Frank Perrick points out that if the engine is to be started without the air filter housings bolted on, the bolts themselves must be screwed in.  The bolts that hold the air filter back plate onto the butterfly housings actually go all the way through the housings and are threaded into the intake manifold.  If these bolts are left out, the holes provide a major butterfly bypass and the engine will overrev.

CAM COVER WORK: If you need to get down to the cam covers or beyond, Victor Naumann sends this awesome tip: Remove the PCV crossover manifold, fuel rail and injectors, air injection manifolds, both fuel pressure regulators, the ignition amplifier, the intake manifold crossover pipe, both butterfly housings, and both intake manifolds as one piece.  Be sure to disconnect the butterfly return springs before lifting.

CAM COVERS OFF?: If you remove the cam covers for any reason that is not intended to involve further disassembly of the engine, it cannot be reiterated too many times that every bolt, nut, tool, or whatever that is in this vicinity should have a string tied to it with the other end tied to your finger.  If a metal part falls down into the timing cover while you're fiddling around, see the section on timing cover removal on page 93.  Peter Smith suggests "I shove a big rag

The repair manuals provide complete instructions for timing chain disengagement and camshaft removal, except they neglect to remind you that you might want to measure the valve clearances before disconnecting the timing chain and removing the cams.  The assembly must be together to make the measurements, so measuring before disassembly will save you having to slap it back together to measure it later.  Of course, if you plan on reseating valves and the like, the measurements won't do you any good anyway.

You might be able to replace the timing chain without removing anything beyond the RH cam cover.  See page 95.

CAM COVER DECORATION: Some of us think those Jaguar decals on the cam covers are not in keeping with the general class of this automobile.  One suggestion is to remove the decals and attach some brass insignias with screws - making sure not to cause a leak.  Might even find just the right key fob to use.

A suggestion from Steve Averill: "If you want to find something a little better looking that the Jaguar decal on the valve cover, why not either get it photo etched or alodyned? That'd be more apropos than sticking on something that'd probably wind up looking "tacked on" & you could pick any pattern that appeals to you."

If you have them off anyway and have a milling machine at your disposal, you might consider skimming the top of the ribs, leaving the black paint in the grooves between the ribs.  It'll really make it look snazzy.

CAM COVER GASKET/HALF MOON SEAL: This joint is one of the most notorious sources of oil leakage on the Jaguar V12, although it's possible some of that blame is misdirected; between the tappet block leaking (see page 70) and the banjo fittings leaking (see page 44), sometimes it's hard to be sure just how much of the oil is actually coming from the cam cover gasket or the half moon seal.

Many owners are surprised that the cam cover gasket is a thin piece of cardboard (or, later, a thin Gortex sandwich), expecting to see a thick layer of cork or some such.  The thick layer of cork is typical on engines with stamped steel valve covers, but the cam covers on the Jaguar V12 are a quality aluminum casting with precision machined mating surfaces.  A thin gasket should seal just fine.  Of course, the original cardboard gasket won't, but it's not because it isn't thick enough; it's because it's a cheap cardboard gasket.

Most of the newfangled gaskets introduced by Ford are only moderately expensive, but the Gortex sandwich cam cover gaskets are obscenely expensive.  Apparently as a result, some of the mail order places continue to stock the old paper versions.  There is irony in that, since Ford updated nearly all the gaskets wholesale whether they were notorious for leaking or not but the ones that probably needed the update the most were the cam cover gaskets.

Also involved in this joint is the half moon seal, a semicircular rubber plug used at the back end of the tappet block to fill an opening made while machining the cam bearing journals.  This plug is set in the opening, the cam cover gasket is set on top of it, and the cam cover is installed to hold them both in place.

There is an inherent problem with this combination of gasket and half moon seal.  In this author's opinion as an engineer, a reliable sealing of the cam cover is not possible when assembling as Jaguar intended --even using the later gortex gaskets.  A gasket -- any gasket -- will only seal properly when securely compressed between two hard surfaces.  Above the half moon seal the cam cover gasket is not compressed; the rubber plug does not provide a hard surface for the cam cover to press the gasket against.  Instead, the rubber plug merely deforms a little, leaving the gasket locally uncompressed.  It's no surprise that leaks are common.  The most common leak path may actually be between the gasket and the cam cover above the half moon seal, rather than around the half moon seal itself.

To effect a reliable seal, we will be departing from Jaguar's instructions for installing the cam covers.  I will suggest three different methods.  The first --and cheapest and simplest and quickest --method is to use the OEM rubber half moon seal but omit the cam cover gasket entirely.  Seal the entire kit 'n kaboodle with Loctite 518, including all the way around the rubber half moon seal, and bolt the cover on.  The rubber half moon seal will therefore be sealing against metal both top and bottom, and should work fine.  Likewise, Loctite 518 should provide a reliable seal in the joint

The other two methods involve providing a rigid surface for the cam cover gasket to be compressed against, and then use the Gortex cam cover gaskets.  Paper cam cover gaskets are not recommended, period.

John Napoli says, "I figured it was better to fill them than to play games with those silly seals.  Anyway, I filled the half moons up with Marine Tex.  I clamped wood on both sides, faced with wax paper, and positioned so that the goo stood proud of the mounting face.  After it set, I filed it down flush.  Seems to have worked.  I buy Marine Tex at marine supply stores."  If you have the cam covers off anyway, you might want to go ahead and pull the camshafts and the tappet blocks so you can do this job on the bench.  Marine Tex dries hard, hard enough to serve as a base for compressing the cam cover gasket properly.  JB Weld might be an acceptable substitute, available in most auto supply houses.  Napoli points out that the only reason you would ever need this opening again is for boring out the cam bearing journals to an oversize, and if this is necessary then it won't be difficult to use the boring machine to remove all the Marine Tex.  After completion of the reboring, you'll probably want to install some more Marine Tex!

Edwin Hyatt did this job: "Used two old credit cards and a couple of miniature C clamps on the outside and inside of the U and piled the JB on.  Filed flat the next day."

Bob Gallivan: "After you mix up the JB Weld use a hair drier to heat it up until it flows easily then fill the halfmoon spot, may even want to heat the tappet block in that area to help any air to escape."

The mold-in-place idea will probably only work with the tappet blocks out of the car.  When they are on the engine, they are held at an angle, so you'll have trouble getting the JB Weld to stay in the recess while it sets up.  Of course, you could jack up one side of the car 30 degrees and fill one side at a time!

John Ashcroft went a slightly different route: "Got some body filler and filled an egg cup to the top, pressed the old seals in to just under surface; when filler was hard, removed h/moons, perfect female mould.  Mixed up some JB weld, heated with heat gun and poured into mould.  Removed from mould after 24hrs. and they are perfect, even have the little groove for some Ultra Copper RTV, just have to dress the top so it is flush with tappet block.  Checked the fit with prussian blue, had to file just a fraction of what was left of the ridges."

The third method is a more difficult and expensive but esthetically pleasing route.  This author designed some aluminum plugs to replace the rubber half moon seals, and Ron Morse was kind enough to fab up a set for testing the idea.  Figure 3 shows an updated design.

There are no tolerances shown on the drawing, so a description of which dimensions are critical is called for.  The 1.0625" diameter fits very snugly in the opening, and the opening itself is rather precisely machined as a cam bearing journal diameter.  It might be acceptable to make this diameter a hair smaller, but it cannot be any larger or it won't fit in the hole.

The 0.531" height dimension is critical, since it locates the platform for the cam cover gasket to be compressed against.  This dimension should be held even if the 1.0625" dimension varies.

The .430" width is necessary to fit around the boss on the tappet block.  This dimension can be made larger, but if made smaller it can make the part difficult to install.  Since the width of the boss was not held to tight tolerances by Jaguar, if possible you should measure it before having this plug made and widen that .430" dimension even more if necessary.

Apply a coating of Loctite 518 or 573 or 574 to the curved mating surfaces before installing the plug.  Don't apply sealant to the flat top surface; the gasket will seal against this surface, and Gortex gaskets should be installed dry.

Or, you could consider installing the plugs with JB Weld or Marine Tex.  Getting them out later might prove to be a challenge, but they shouldn't ever need to come out.

If you don't want to make these aluminum plugs, Ron Kelnhofer (page 718) has some for sale.

Using aluminum half moon plugs and Gortex gaskets should keep the cam covers sealed until the sun burns out.  Of course, if you have to remove the covers later for valve adjustment, you'll need new Gortex gaskets --and those suckers are pricey.

It is not recommended that you attempt to use the aluminum half moon seals with no cam cover gaskets.  The height of the flat surface of the aluminum half moon seal would need to be very precise indeed to seal properly with no gasket.

It has been suggested that it may be simplest to just heliarc weld the openings in the tappet block shut and machine the gasket surface.  There is no way I would recommend this, though; the distortion likely to result from such welding would surely compromise the seal between the tappet block and the head as well as play havoc with the alignment and concentricity of the cam bearing journals and tappet holes.

CAM COVER BOLTS: Once we've addressed the shortcomings of the half moon seal, we still have other problems to deal with.  Neal says, "New bolts are also necessary.  Unfortunately these parts are only carried by the dealer."

Before ordering bolts, determine whether your engine requires SAE bolts or metric bolts.  Judging from the 1988 Jaguar Parts Catalogue, the change from SAE to metric took place with engine number 8S24175.  The part number for the new metric cam cover bolts is FS-106251/J.

The replacement of the bolts may not be as much due to the excellence of the new bolts as to the lousiness of the old bolts.  The original bolts -- both SAE and metric --have a "triangulated" thread that presumably helps it to drive into the aluminum housing, but probably is also very effective at boogering the aluminum threads up.  Martyn Sandbrook says, "I recognise these as "taptite" screws.  We used to use these in the telecoms industry way back in the seventies.  They are like selftappers but they "form" a thread rather than cut one and are supposed to be better.  You don't see them these days.  I thought they were junk when I first came across them.  Seems strange to be using them in a leak-critical area as they only grip on the outer lobes once the thread has been formed and won't take much tightening torque."

If you'd rather not pay Jaguar prices here and seek other sources for bolts, note that 7/16" hex heads will not do, you can't get a wrench or socket on it; either 3/8" (or smaller) hex head, socket head (allen wrench drive) or Torx drive bolts will be necessary.  And you might want to look at the access before you select bolt head styles, since you may want to retorque them a while after replacement.  Of course, buying el cheapo grade-zilch bolts (like most slotted head screws) is not a good idea; not only will they rust pretty badly, they may not hold enough tension to keep the cam cover gasket from leaking.

An alternative bolt that would work on SAE threaded engines was found at a Home Depot in their "specialty fasteners" rack.  It is called a "serrated flange bolt"; it has a 3/8" hex with a washer face and a row of serrations around the bottom of that washer face.  The biggest problem will be finding enough of them to do the job; often such racks in hardware stores only contain a half dozen or so.

Another alternative SAE bolt: This author bought a box of 1-1/4" "alloy steel" 1/4"-20 "socket head cap screws" from a local industrial fastener supplier --less than $20 for a box of 100.  These fasteners are jet black.  Strength is not a problem, alloy steel cap screws are stronger than Grade 8.

The original SAE bolts were 1" long, so replacing them with 1-1/4" bolts provides enough length for some washers under the heads (and perhaps for thicker gaskets, if you find something non-OEM).  There's no problem with bolts being too long, since the end just comes out the back side of the flange on the tappet block.  Using the longer screws also makes use of all the threads available in the tappet block, including the ones at the bottom end that haven't been worn by the lousy OEM screws.

If you need M6 socket head or flange bolts, finding them locally may be more troublesome --at least here in the US.  Craig Sawyers says, "Well, here in the UK, the challenge is to find non-metric SS screws!"  Again, going with slightly longer screws than the OEM 25mm items -- perhaps 30mm -- might be a good idea.

Dave Oxenreider says, "I found a whole slew of 18-8 stainless steel socket head cap screws in both metric and English in the McMaster-Carr catalog.  Averaging about $25 per box of 100." Joe Bialy opted for non-stainless (no good reason for stainless here, actually): "Part #91290A332 for $7.34".  See page 711.

Another source would be Barnhill Bolt; see page 710.

If you have a local Grainger outlet (page 711), the Grainger catalog doesn't seem to list any suitable M6 socket head screws but they carry "button head socket screws" which use a smaller Allen wrench but will work.  The box of 100 screws 30mm long is stock number 3L184 and costs less than $20.

On the other hand, if your cam covers need M6 screws, it might not need screws with unusual heads.  The typical generic locally-available M6 screw has a 10mm hex head.  It appears that a 10mm socket will actually fit in the recess, making the search for socket heads or flange bolts unnecessary.

An idea that might work with either 7/16" or 10mm hex head screws: If you can find some sleeves with a length of perhaps 10mm, 1/2", or 15mm, you could use them together with screws that are proportionately longer (40mm, 1-3/4", or 45mm) which would raise the location of the hex head enough to enable you to get a socket on it with less trouble.  A cursory inspection of this author's engine indicates you certainly wouldn't want to go any longer than 15mm --you'd start interfering with the bottom of the intake manifold.  There is a spot at each end of each manifold where a bolt hole boss is provided (holds fuel pressure regulator at the front, other stuff at rear) and it might actually help to grind away a

If you can avoid interference, having the heads up higher might actually make it possible to retorque these bolts without pulling the manifolds off!  It wouldn't be easy by any stretch, but it might be possible.

With the socket head cap screws, the author used split ring lock washers and flat washers.  As noted on page 27, flat washers are always recommended when a bolt head or nut sits on aluminum. (Note: TSB 12-35 specifically prohibits the use of washers under the special Jaguar bolts in this location.  Put that down as a fundamental disagreement between their engineers and this engineer --and note that this engineer's cam cover bolts haven't come loose and the gaskets don't leak, claims which several other owners report cannot be made about the official Jaguar assembly procedure.)  This author found some very suitable flat washers on a bubble card in a Wal-Mart: They are size 12, also known as 3/16".  If you ask for 1/4" flat washers, you get washers that fit so loosely on the screw that it looks like a socket head might pull through the hole!  Also, the OD of the standard 1/4" washers are bigger than the flat area on the cam covers, so you'd have to cut them down to get them in.  Conversely, these #12 washers fit perfectly on a 1/4" bolt and are the correct OD for the cam cover flats.  Make sure you find cheap #12 washers; better quality ones might have closer tolerances and not fit a 1/4" bolt.

Should you use lock washers?  This author thinks so; after all, they can't hurt.  Craig Sawyers replaced his cam cover gaskets with new paper gaskets, and they shortly began to leak; when he went back in there, he found the bolts loose.  Why?  Well, maybe it's because the paper gaskets compress and relax the tension on the bolts, and therefore switching to the Gortex sandwich gasket is the fix; or it may be because these bolts are simply too short to stay tight without lock washers (see page 27) or some other retention scheme.  The situation is rife with opinions, but note that it's really hard to retorque these fasteners without removing the intake manifolds.  This is not a place to save money or weight; if it might help avoid problems, do it.

You can buy enough flat washers and lock washers to do this job for less than two bucks total.

Another type washer that will work on the cam covers is the 1/4" spiral groove washer used in a couple other places on the V12 -- if you can find a supply of them.  These washers serve as both a flat washer and lock washer in one.  Also, the 6mm wavy spring washers mentioned on page 27 as a substitute for the spiral groove washers will work nicely.

There is one other benefit to going with longer screws with spacers.  Longer screws have more "stretch" when tightened to a particular torque, and therefore hold tension better and are less likely to vibrate loose.  It might still be a good idea to include lock washers, but providing yet another scheme to help keep tension on those cam cover gaskets can't hurt.  The spacers might omit the need for flat washers, depending on the wall thickness of the spacers and therefore how well they distribute load onto the aluminum face.

As always, be sure to use anti-seize compound on the threads when assembling.

TSB 12-35 specifies that the cam cover bolts be torqued to 9.5-11.5 N-m (7-8.5 ft-lb).  They didn't mention whether this was for the later metric bolts or the earlier SAE bolts, but hopefully it won't make much difference.  It's also probably a good spec whether you're using their special bolts or some of the generic substitutes described above.  It's not really a place where torque is critical, however; just tightening until they feel tight should be good enough.

TIMING CHAIN TENSIONER: To replace the tensioner requires removal of the timing cover which would put this section under "Engine Work --Front".  However, the problems occur when retracting the tensioner, which is usually done when removing the cams or the heads -- so it's here in the "Engine Work -- Top" section.

There are few design features of the Jaguar V12 as poorly conceived as the material the arch of the timing chain tensioner is made of.  If you manage, on your first try, to retract the tensioner and reengage it successfully without breaking this arch, you should consider yourself lucky.  The arch apparently works well when new but gets brittle with age or heat, and an old one can be broken very easily.  Michael Neal, who works on Jaguars every day, says "I've become so paranoid of old tensioners, my failure rate has been very high as of late.  I'm not too surprised though, most of the cars have been approaching ten years old.  I've been as careful as possible, knowing exactly what I was doing, and

The problems may have to do with the V12's proclivity towards overheating.  Craig Sawyers says, "The V12 chain tensioner is, according to the technical article that was published when the V12 was launched in the early '70s, made from molydisulphide-loaded nylon.  Just looking up the spec for something else, I found that Nylatron GS is just such a material.  All the characteristics that are listed makes this a sensible choice for the tensioner blade, apart from a continuous working temperature of 100°C maximum, with maximum non-continuous temp of 145°C.

"I'll wager that embrittlement of the blade is due to a combination of the oil environment and overheating.  I have only the evidence of one piece of information: My engine had never overheated, and the blade, although grooved where the chain had worn it, was still flexible after 160,000 miles."

Other engines have arched timing chain tensioners in which the arch itself is made of spring steel.  It would seem a simple matter to design a replacement arch for the Jaguar V12 tensioner made of spring steel, thereby eliminating the fracture problems permanently; if noise or wear is a concern, the spring steel arch could be faced with Teflon or some such.  However, despite more than two decades of trouble with this piece of crap, apparently neither Jaguar nor any aftermarket companies have opted to offer an improved part.

CRANKSHAFT DAMPER/PULLEY REMOVAL: First note that, contrary to the repair manuals, it is not necessary to remove the crank pulley to get the water pump off.

Also note that what looks like a bolt head in the center of the crank pulley is actually a hex fixture for turning the engine by hand.  Two smaller bolts must be removed to remove this hex, and the real pulley retaining bolt is underneath.  Then one more note: Since you already have the belts loose or off, you can remove two more small bolts and remove the pulley from the crank damper entirely.  This provides much better access to the big crank damper bolt so you can use a box end wrench or some such.

What size wrench fits that bolt head?  Craig Sawyers: "That damned thread is a 7/8 inch BSF.  The AF measurement is 1.300 inches for that thread.  I got a 7/8 BSF, 3/4 Whitworth socket to do the job."  See page 26 for more info on Whitworth/BSF, including ideas on finding tools.  If you can find a 33mm socket, it'll fit perfectly.  Unfortunately, even numbers are the standard in larger sizes, so it's pretty hard to find anything closer than 32mm or 34mm.  Hard, but not impossible; Jan Wikström says, "I have a cheap Taiwanese socket set from the flea market; it has every mm size from 12 to 35.  There are far more sockets than the ISO standard sizes, but the odd ones can come in handy."

Bob Christie says you can get 33mm sockets from MSC.

Apparently 33mm is a common size for truck lug nuts, so that's another avenue of pursuit.

You might want to avoid the smaller drive sizes here.  Robert Warnicke says, "I broke two 1/2" drives before I finally removed the bolt with a pipe wrench."

If nothing else works, you can use a file or grinder on the hex to make a 1-1/4" or 32mm socket fit.  You can just use a big adjustable wrench (or Warnicke's favorite, the pipe wrench) to get it loose, but you will still need to find a socket that fits to carefully torque it during reassembly --which is of considerable importance, as described in the discussion of key failures below.

To loosen and retighten the bolt, it is necessary to hold the crank still.  You can remove the starter to jam the flywheel, but that is definitely the hard way.  An easier way would be to use the access hole on the left side of the engine, the one with a rubber plug and intended to provide access to the torque convertor mounting bolts.  Michael Neal provides an even simpler access: Just remove the cover from the bottom of the torque convertor housing.

Of course, on my car I can just put it in 5th gear with the emergency brake on!

Matthias Fouquet-Lapar suggests: "Once you have removed the upper part of the pulley (the one which drives 3 belts), you can easily use its 2 screws to attach a home-made bar on the damper."  This is perhaps the best method of all, since pulling this lever and the torque wrench together works really well when trying to carefully torque that bolt up on installation.

Besides holding the crank still, there's also the problem of getting the bolt loose.  One idea that solves both problems would be to use an impact wrench --the way an impact wrench works, the inertia of the crank is all that's necessary to hold it still.  But there's not enough room in the car to use an impact wrench, so that will require either pulling the radiator or the engine.

Shane Mantoszko says "use a good long-handled socket/torsion wrench, put it on the front crank nut, brace it on a strong part of the engine bay, disconnect the coil, and then turn your ignition key for a few quick bursts, and viola, the crank nut will be loose..."

Dale Knaus says, "I used what we call a "slug wrench".  It is a box end wrench made extra heavy with a striking pad on the other end.  It is made to hit with a hammer to tighten and remove nuts.  I borrowed the tool from the industrial plant where I work; they are probably available from industrial tool supply companies."

Regardless of how well these methods may work getting the bolt loose, remember that you'll still need to deal with

CRANKSHAFT PULLEY -SHEARED WOODRUFF KEY: Paul Konitshek, Michael Neal and several others report that the woodruff keys that align the crankshaft damper/pulley are a known problem area.  The keys may become worn or totally sheared, allowing the pulley to reposition itself around the crank.

The immediate effect of this slippage depends on which ignition system you have.  If you have a pre-1989 car with Lucas ignition, you might not even notice unless things get really bad and start chewing up parts.  Neal reports: "It almost never gets to the point where the pulley comes loose." If it merely slips, it usually won't become apparent until you try to set the ignition timing; the timing marks are now completely wrong, so you'll get really confused.  If you have the later Marelli ignition system, the damper slipping will immediately screw up the ignition timing since the sensors are on that damper.

Note that there are two keys used.  There is a "split cone" that is similar to those used on industrial pulleys.  The pulley fits onto the outside tapered surface of the cone and is aligned with one key.  The cone slides over the crank and is aligned with another key.  When the bolt securing the pulley is tightened to specification, the split cone compresses securely onto the crank like a collet in a chuck.

Roger Bywater, who was in charge of belt drives for the V12 at Jaguar at one time, explains: "The purpose of the keyway is purely for location and accurate alignment during assembly.  In almost all assemblies of this type the key is not intended to transmit any torque, indeed it is not strong enough, the friction of the tightened joint is meant to do that.  There must always be some clearance around the key so if the joint comes loose torsional vibes will always fret and destroy the keyway.  Many later engines do not have keyways anywhere, relying only on friction.  The Jaguar V8 camshafts are typical with the timing sprockets just placed on the end, timing marks all lined up, and nipped up very tight with a central bolt - that's it.  If they come loose the sprocket can just spin round - only it never happens.

"The answer is to make sure the friction inside and outside the cone cannot fail so the bolt needs to be tight to the point of yield to keep the whole assembly under tension.  Possibly the bolt tightening figure is marginal at the lower tolerance quoted of 125 ft-lbs so maybe the top figure of 150 ft-lbs should be the rule.  In fact the AJ6 manual quotes 203 Newton Metres (with no tolerance) which equates to 150 ft-lbs for the same size bolt which seems to support this view."  Note that the threads need to be "lightly lubricated" for the torque readings to be anywhere near correct; this author recommends anti-seize compound, which will also help get it apart next time.

If the torque is supposed to be transmitted via friction between crank and cone and between cone and damper, obviously it'd be a good idea not to put any anti-seize compound on those mating surfaces.  In fact, you might want to be careful there's no oil on them -- although hopefully it'd get squeezed out while torquing.

So, if the torque is supposed to be transmitted via friction, how come the Jaguar V12 has a history of key failures here?  Neal: "It seems only to happen if water has gotten into the nosecone on the crank.  The area is always very rusty when the front pulley is removed.  The woodruff key is either broken or eroded away from the rust." Of course, this area is exposed to the elements, there's no keeping water out of it; whether or not these parts rust probably depends on whether the crank seal is keeping them well oiled.  Perhaps they all rust, and Neal only notices the ones that have sheared keys are rusty because those are the ones he has to work on.

The failure history could be because the engineers at Jaguar screwed up, either underestimating how much torque this joint would need to transmit or overestimating how much torque the joint could handle.  However, it's entirely possible that most or all of these failures came from somebody not torquing that damper bolt down adequately.  Even presuming they were torqued correctly at the factory (!), mechanics are always fiddling around in this area --such as when replacing a leaky crank seal.  Perhaps some of the mechanics are not being as meticulous as they should be in applying full torque during reassembly.  Take a lesson: make very sure you torque that bolt properly!  Just zipping it on with an impact wrench is unacceptable.

Neal: "In some cases the slot in the crank is widened a bit but a new key usually secures it substantially."  If the crank

CRANKSHAFT PULLEY -GETTING THE KEY OUT: Sometimes the keys won't come out, notably the key on the crank itself.  Suggestions include using a pair of angle cutters to grab it and walk it upwards, and using a suitable chisel to cut under the key to pry it out.  The suitable chisel needs to be a hair narrower than the key, and can be made from old lathe bits or "cut nails".  Cut nails are made from flat stock, giving them a sort of trapezoidal shape, and are really hard for pounding into masonry.  Greg Guillaume: "Here's what I did: Get a 1" chisel, lay it on the crank, perpendicular to the crank, up against the key.  Then whack away with a hammer on the opposite side of the chisel.  The shape of the chisel is just right so it bites into the key, the 1" width hangs over the end of the crank, and you get a lot of room to swing the hammer.  Of course, the chisel is a little beat up, but it worked great."

CRANKSHAFT PULLEY -SPLIT CONE PROBLEMS: Dan Jensen says, "The split cone was broken in three places.  Rather than pay $$ for a replacement, I just stuck it back into the damper/pulley with Hylomar sealant and gently replaced it.  It centered properly and has worked great for 35K miles."

CRANKSHAFT PULLEY -RUBBER DAMPER PROBLEMS: Chris Yewdall owns a '91 convertible, and started having noise when operating the roof. "When lowering the roof with the engine running, a squealing noise is heard from under the hood until the roof is fully lowered.  After a few more months/miles the squeal happens most times you start the car for a few minutes until the revs build up as you drive away.  Eventually, the voltage on the battery charge guage on the dashboard drops to 12V (about 1/4 of the way up the guage) and the battery goes flat.  Occasionally, the alternator will charge normally or just below normal, particularly on a freeway journey."

Sounds sorta like a loose belt problem, but it wasn't.  After wasting too much money on things like an alternator rebuild, the problem turned out to be the crank damper itself.  When he got the failed part back from the mechanic, he reported on it: "On inspection, it is the bond between the inner pulley (which keys onto the crankshaft) and the rubber damper which has failed since the inner pulley rotates freely on the inner surface of the damper.  The rubber has hardened to the point where it has cracked in lines between the inner and outer pulley.  It feels more like bakelite or plastic and has no flex at all.  Believe me, it's not hard to spin the outer by hand."  The other three belts are driven by rigidly-mounted pulleys but the alternator belt is driven directly from the outer ring of the crank damper, so this rubber breaking loose causes drive problems for the alternator.  A heavy alternator load, such as operating a convertible top, aggravates the problem.

If you're having trouble confirming if your damper has sheared, put a mark on the center portion and a mark in line with it on the outer portion.  Run the car for a while, then shut it off and check the marks.  If they are no longer aligned, you need a new damper.

Interestingly, this type failure was apparently unknown on the earlier cars with Lucas alternators driven by V-belts.  Those cars also had Lucas ignition systems, and the timing marks for setting the ignition timing were on the outside edge of the crank damper.  As a result, such a slippage between the inner and outer portions of the damper would have made correct timing impossible.  Most of the cars with the later Bosch 115-amp alternators and ribbed belts (see page 574) also have Marelli ignition, and the timing is not adjustable --but is established by a pickup at the front damper.  This pickup senses trigger points attached to the inside portion of the damper, so they are unaffected by slipping of the outer ring and the engine runs normally.

It's easy to blame these damper failures on the higher loads imposed by the 115-amp alternator or even on some change in build quality between the V-belt dampers and the multi-groove dampers, but there is one more possible cause for

FRONT OIL SEAL REPLACEMENT: Peter Cohen points out that the Jaguar repair manual's procedure for replacing the front oil seal involves removing the radiator --which, in turn, supposedly requires depressurizing the A/C freon circuit.  Boy, I hope you read this first!  Depressurizing the freon circuit is totally unnecessary to get the radiator out (see page 197), and if you don't mind working in tight quarters, taking the radiator out is unnecessary to change the front oil seal.  Matthias Fouquet-Lapar says, "I've done this in my garage without pulling the radiator.  Once all the belt- driven hardware is removed, there is enough space.  I did not even take out the fan shroud."  Brian Sherwood says, "I replaced mine without pulling the radiator --not very convenient, but possible.  The most difficult parts were: 1. removing the old seal (finally had to prick a small hole in it, and screwed in a sheet metal screw to pull on), and 2. getting the pulley bolts thru the lock plate, pulley, and into the crank damper -- can't see these at all, have to do by feel."

Tom Amlie had trouble getting the new seal installed in tight quarters. "If I kept trying to do it like the books said, I would still be at it.  Book says to tap the new seal in.  Not possible.  Go to Home Depot or similar and get a PVC drain pipe fitting (reducer) to fit the seal.  Carve on it until it works.  Then use that huge bolt that holds the pulley/damper to push it in.  Works like a charm."

When you buy the front seal from Jaguar, you get the seal and the spacer sleeve it rides on in one box; this may be a recent development, apparently a new part number has been issued.  Matthias Fouquet-Lapar says, "The new part at least includes the spacer.  The part number is JLM 10613."  However, if you buy a generic seal somewhere else (or maybe older stock from Jaguar), you'll probably get just the seal.  You can look at the condition of your sleeve and see if you think this will cause a problem.  Peter Smith says, "If the spacer appears worn it can simply be reversed on refitting because the seal does not ride at the half way point.  The new seal will then ride on an unworn part of the spacer."  Whatever, you will want to take the sleeve out, because the proper order of assembly is to install the seal and then install the sleeve.

You might also consider putting some sealant between the crank and the spacer prior to installation to prevent oil from travelling between the crank and the sleeve and leaking out the splits in the split cone under the pulley.  There are no reports of leaks along this path, but if it did leak people would think it was the front seal, so who knows? Maybe it's a common leak!

Cohen adds, "When I did my front seal 7 years ago, the collar that came with the seal had to be tapped into place, even though the old one slid right off.  The dealer assured me that that's normal, they loosen up with time.  This is not true.  I had to drive the collar off after 7 years and 70,000 miles.  It's a good thing the timing cover was off, because I don't know if I could have gotten a grip on it from the front."  Who knows, maybe Jaguar figured out how the oil was leaking out so new seals come with a coating on the inside of the sleeve to seal it.

Also of note, illustrations in the repair manual indicate that the sleeve has a keyway, but according to Alex Dorne they lie; "The sleeve is not keyed."

V-BELTS: Most V-belts are available in either solid or notched varieties.  There is no appreciable difference in strength, since the strength of all V-belts comes from a layer of cord unaffected by notches.  The cord is in the outside edge, making that part stiff to force the softer, inner portion of the belt into the groove in the pulley.

The notches in the inner surface help the V-belt flex, and are beneficial when the belt must turn around a small pulley.  It is therefore recommended that a notched V-belt always be used for the alternator belt on the XJ-S.

The notches in a belt can cause noise.  For this reason, most V-belts use an unevenly-spaced series of notches rather than

POWER STEERING PUMP INSTALLATION: Jim Isbell points out that the bolt holding the belt tensioner to the power steering pump should be installed from the rear to the front. "The bolt, if put in from the back with the nut end toward the radiator can be removed with the pulley in place.  If put in backwards it cannot be removed with the pulley in place."

FAN BELT IDLER PULLEY INSTALLATION: Jim Isbell says: "The bolt that connects the adjuster screw to the idler pulley must be put in from the back with the nut toward the radiator.  If this is put in backwards the adjustment range of the idler is greatly reduced."

TIMING COVER REMOVAL: If you want to remove the timing cover to replace the front oil seal, don't waste your time; the front oil seal presses in from the outside, and Jaguar even provided some prying slots for removing the old one.  See the info on seal replacement on page 92.

If you do need to remove the timing cover, Section 12.65.01 of the ROM lists 13 steps, the first two of which are as follows:

1. Remove engine and gearbox assembly from the car.
2. Remove cylinder heads from the engine.
Fortunately, there is an alternate method.  To remove the timing cover with the engine still in the car and the heads in place, proceed as follows:

1. Remove the belts, fan and its mounting bracket, A/C compressor front bracket, and all the other ancillary stuff in the way.
2. Remove the front crank pulley -- see page 89.
3. There are three studs threaded into the timing cover that protrude upward through the front edge of each head.  Remove the nuts and washers, then grab the studs with a pair of Vice-Grip pliers and unscrew them.  Note: Some of the studs are trapped and cannot be removed; once these are unscrewed, merely retain them (with duct tape) in a raised position while the cover is being removed.  Once the cover is off, they can be removed.
4. Remove the retaining bolts holding the timing cover to the block.
5. The timing cover is essentially pinched between the heads and the sandwich plate.  Michael Neal, who is a Jaguar mechanic and uses this method regularly, says "I loosen as many of the sandwich plate bolts near the front as possible.  I believe it works out to about 4 or 5 back, going between the subframe and the motor.  I then use a Snap-On medium sized ladyfoot prybar and go in the hole where the oil cooler adapter bolts onto the sandwich plate.  I pry against the bottom of the tube that the adapter goes into and the inside of the sandwich plate.  This pulls down the right front corner of the sandwich plate and allows some space for the timing cover to move.  The prybar over-centers and locates itself while holding the plate down.  It is very important not to pull down too far.  The bolt holes are very prone to cracking and the break will spread out toward the center of the sandwich plate."  See page 97 if you wish to remove the sandwich plate entirely.
6. REASSEMBLY: Since your studs were all boogered up by the Vice-Grips, buy new studs with the same threads but longer.  Saw or grind them off until they are 1/4" longer then the originals.  Then, grind flats on this 1/4" to ease the reinstallation and any future disassembly.  Be sure to clean up the threads so the nuts go on easily.  Remember to slide the trapped studs in place before installing the

TIMING CHAIN DAMPENERS: These are the steel plates mounted alongside the chain along several of the straight sections between sprockets.  The Haynes manual, Chapter 1, Section 42, Step 5, suggests using quick-drying paint to mark their locations before removal.  Craig Sawyers says, "Nice idea, but no dice.  Have a look at the bare block and you will see that the dampers fit onto raised bosses.  There is no accessible metal to either paint or scribe a line on to show the original position of the dampers."

If you move them, the use of an elaborate (and undoubtedly expensive) special tool JD.38 is required to properly position them.  Advice: Don't move them!

You already moved them?  Sorry, at present I can offer no help.  I am including this section to describe what they are and how they work.

A roller chain is a fairly decent and reliable drive mechanism at low speed.  However, 6500 RPM is another story; at higher speeds, chains can whip, flutter, buzz, and otherwise dance around their path around the sprockets.  At certain resonances, a chain whipping back and forth can cause very high tension stresses, resulting in damage to the chain, sprockets, camshaft bearings and tensioner.

These plates are designed to prevent this.  If the chain is moving smoothly and along a straight line like it should, it shouldn't even touch the plates.  But if it starts to whip, it hits a plate --which absorbs the energy of the whip, and allows the chain to return to a calm motion.

Based on this theory, it would be logical to assume we could just bolt the plates on so that they are immediately adjacent to the chain without touching it.  There are a couple problems with this plan.  First, if you follow the official Jaguar assembly order, the plates must be installed and the timing cover bolted up before the heads are installed, so having the chain in place --meaning the tappet blocks, camshafts, and camshaft drive sprockets in position --is not possible.  Of course, you could always trial fit the heads, tappet blocks, camshafts, sprockets, and timing chain in order to set the plate positions, then tear it all apart again.

The second problem is that I'm really not providing enough information for proper positioning.  I'm only providing the theory; presumably, during development of this engine, the optimum positions of these plates were precisely determined, and they may be far more critical than simply "close to the chain without touching it."  Improper positioning of these damper plates could be catastrophic, causing a broken timing chain which in turn causes pistons to impact valves in open position.  You see, the real purpose of this section is not to save you effort; it's to discourage you from assuming the position of these plates is unimportant, skipping important steps, and causing yourself a great deal of heartache down the road.

TIMING CHAIN REPLACEMENT: The timing chain in the Jaguar V12 is a conventional double-row roller chain.  Typically, the wear on chains of this type is much more significant than on the sprockets, and usually the chain can be replaced without replacing the sprockets.  This is in sharp contrast to the "silent" timing chains used in many American V-8's, where it is customary to replace the timing chain and sprockets as a set.

Another characteristic of typical roller chains is that wear on the sprockets increases with the use of worn chains; if the chain is renewed regularly, the sprockets can last almost indefinitely.  The Jaguar timing chain is so cheap that it is recommended that it be replaced whenever the engine is disassembled far enough to do so.  The sprockets are so expensive that you will want to do whatever it takes to keep from having to replace them.

In general, the sprockets don't need replacing unless an inspection shows signs of serious wear --one side of each tooth looks different than the other side.

Per Jan Wikström, "According to a Reynolds chain handbook that I mislaid some time back in the seventies, so my memory may be slightly off here, the way to determine whether a sprocket warrants replacement is to hang the new chain over the sprocket and apply a strong pull (that's an Imperial strong pull, not a US strong pull!) in the normal drive direction.  If more than three links ride up noticeably on the teeth, the sprocket is too worn."

Once you've decided to replace the chain, the next question is whether to pay Jaguar prices or simply drop into an industrial supply store and buy generic chain.  You don't want cheap chain, that's for sure --but most industrial supply stores actually carry really good chain, probably as good or better than the chain sold through Jaguar.  Many of these stores will also happily explain to you why you want a good chain rather than a cheap one and perhaps even show you examples of each.

When ordering a chain from some parts houses, the chain they offer is a length of generic industrial chain and a master link to put the ends together.  This leads many owners to question whether they want to do this or pay for the Jaguar part which is a loop without a master.  Those aren't the only choices, actually; if you think a master link is a problem, that same industrial supply store will offer to make the loop for you.  They have the special tool on hand to properly roll the end of a pin over to make the chain into an uninterrupted loop.  And this will still save you perhaps 2/3 of the cost of the Jaguar part.  Remember, Jaguar isn't fabricating custom chain for this application; the chain they sell was purchased from an industrial supplier and made into loops.

Some argue that having a master link is a real problem, as though they are weak or some such.  They are not weak; they are typically stronger than the other links.  They do, however, have some history in motorcycle applications of failing catastrophically.  This isn't because they're weak but rather because they can be taken apart; whatever clip or cotter pin is used to hold them together can come out and cause the master link to fall out.  This is especially a concern on a motorcycle where running over some brush might knock the clip loose on a master link.  There's also the concern that some motorcycle mechanics are meatheads who can't figure out how to get the clip on the master link securely.

Of course, there is little chance of foreign interference in a master link inside the Jaguar V12 block.  If you are offered a chain with master link, simply look over the retention scheme.  If it looks like something you could get together and trust that it won't fall apart at 6500 rpm, go with it; don't worry that it's somehow not as strong as the other links.  If it looks like something that might come apart, consider having the chain permanently made into a loop at the shop rather

Some master links are held together with a clip that slides over one pin and snaps onto the other.  There's no known history of these coming loose, but the fact that they involve a groove around the end of both pins suggests a possible improvement: you can simply discard the single clip and install two tiny E-ring clips instead, one on each pin.  There's little chance that an E-ring clip would come off in use, and both of them would have to come off before the chain breaks.  They are prone to getting dropped during installation, though, so be sure to tie a thread to each one before installing.

Of course, you need to find the correct size chain.  Tony Bryant says, "One possible gotcha is the old Brit vs US standard thing.  It appears there are two standards for 3/8" duplex chain: BS288/ISO606/DIN8187 and ANSIB29.1/ISO606a.  The differences are subtle but probably serious.  From the Reynolds chain book, the differences are (BS vs ANSI):

Roller width (i.e. between the inside plates) 5.72mm vs 4.68mm

Roller dia 6.35mm vs 5.08mm

Plate height 8.26mm vs 8.66mm

Plate outer width 1.04mm vs 1.3mm

Pin dia 3.28mm vs 3.59mm

Pin length 23.8mm vs 25.65mm

Breaking force 18500N vs 20000N

"So make sure you get the right chain, or I'm guessing very bad things™ will happen."

It's possible to replace the chain by removing only the right side cam cover and without bothering the timing cover at all, but this requires the use of a master link --if contemplating, make sure the chain you purchase isn't already formed into a loop.  Retract the tensioner, then break the old chain on the top of the cam sprocket (grind the end off two pins and slide a link out) and connect the new chain to the end of the old one with the master link.  Have someone turn the crankshaft slowly while you feed the new chain in and the old chain out, being sure to keep the cam sprocket engaged at all times.  When the master link comes around again, disconnect the old chain and connect the new chain back to itself.

It is highly recommended that the latch on the timing chain tensioner be rocked after, or preferably during, this timing chain replacement on the chance that the new chain is significantly shorter than the old worn one was and therefore the tensioner needs to back up a bit to allow it to sit properly.

OIL PUMP CLEARANCES: If you happen to have the Haynes manual, the clearances specified for the oil pump don't seem to make sense.  So, I will include the values from the ©1975 ROM here:

Driven gear to housing: < 0.005" (0,127mm)

Drive gear to crescent: < 0.006" (0,152mm)

End float - both gears: < 0.005" (0,127mm)

Note that, according to the ROM, all measurements are taken with the pump removed from the engine.  Since the crankshaft is therefore not holding the drive gear in position, it is free to move as far away from the crescent as the tightness of the gear teeth will permit.  It appears a rare case that it will meet the 0.006" limit; 0.040" is more likely!  Despite the clarity of their measurement procedure, it is probable that the specified values represent clearances in place, with the crank holding the drive gear in its correct location.

Mike Morrin: "I cannot believe the figures in the Jaguar manual.  The endfloat on the gears in my pump was over 0.020".  At the time I was rather alarmed, as the engine had by all accounts only done 55,000 miles.  I carefully inspected the old parts for wear, and found that the factory machining marks were still visible on the gears, and the wear on the pump housing was negligible.  This pump must have left the factory with clearances way beyond the published limits.  So I put the old pump back and crossed my fingers.  The oil pressure seems OK (when measured with an

Of course, if endfloat is the only problem, some of us have been known to skim a little metal off the mating surface of the housing to bring it back down.  With a little care, it's even possible to perform this fix on aluminum housings by laying a piece of sandpaper on a plate of glass and sliding the housing back and forth on it.

OIL PUMP REPLACEMENT: According to Thomas E. Alberts, the 1992 upgrade of the V12 included a new design oil pump --and that the old design oil pumps are no longer available. "The original part number is C38453 or C40177.  That part was officially superseded by EBC3163 which is the pump for 1992 on.  EBC3163 is supposed to fit the older engines but some pieces are required to adapt it.  This pump is at least twice as expensive as the earlier version, and the adapter (they call it a pump collar) is $45 plus some additional bolts are required."

Note: If you only need to replace piston rings and/or liners, you might not need to do bottom end work on the Jag V12.  See the ideas on page 79.

OIL PAN REMOVAL: The crankcase bottom is actually two pieces, a pan and a sandwich plate.  The pan, which exists only at the rear of the engine, comes off easily enough.  However, any hope that this will get you anywhere is quickly shattered.  The crankcase is fully baffled (necessary to prevent foaming, reduce heat buildup and power loss, and insure proper oil flow to the pickup in a high RPM engine), and there is one baffle the length of the engine that cannot be removed without removing the sandwich plate.

Contrary to the manual, the sandwich plate can be removed without pulling either the front suspension assembly or the engine out of the car.  It's a real pain, though, so you might still consider one of those options.  To remove the sandwich plate:

1. Unbolt the steering rack without disconnecting hoses, steering column or tie rods.  Lower the rack a few inches and let it hang there.
2. Remove the fan to allow the engine to be raised without hitting the shroud.
3. Remove the nuts from the two main engine mounts, and use a hoist to lift the front of the engine as far as possible.
With all this done, the sandwich plate will just barely come out rearward.  Putting it back in, with new gasket in place, will also be a lot of laughs.

While you're in there, replace all the O-rings you can find, such as those in each end of each oil tube.  If they leak they just leak into the crankcase, but each leak reduces oil flow to the engine.  Use Viton O-rings, so you won't have to go back in there anytime soon.

OIL PAN/SANDWICH PLATE BOLTS: Technical Service Bulletin 12-35, which introduced the upgraded gaskets used throughout the engine, also specified new bolts for holding the sandwich plate and the oil sump to the engine.  The explanations given applied to both the sump and the cam covers, so it is probable that the same sort of generic bolt & washer substitution described at length for installing the cam covers starting on page 60 could also be applied here - although these bolts are a size larger, so the specific parts mentioned won't do.

See also the notes on TSB 12-53 on page 48 regarding sealing the threads on the sandwich plate bolts with heads inside the oil sump.

TSB 12-35 specifies a torque of 21-27 N-m (15.5-20 ft-lb) on the sandwich plate bolts and oil sump bolts.  No mention

MAIN BEARING REPLACEMENT: If you find yourself needing to replace the main bearings without removing the crankshaft, the job can be accomplished the same way as most cars: Roll the upper bearing shell around and out.  If it's difficult, insert a cutoff head from a nail into one of the oil passages of the crank and turn the crank to roll the bearing around.  However, when installing the new bearings, remember that the Jaguar block is aluminum.  It is recommended that the outer leading edge of the bearing shells be smoothed slightly with a file to prevent them digging into the aluminum when installing.

REAR OIL SEAL: If you think your rear oil seal is leaking, you might want to check again.  The rope seal used up to VIN 160010 has proven to be very reliable indeed; an informal survey of owners on the internet indicated that the rear oil seal was often blamed for leaks, but the leaks were always later found to come from other sources.  The upper mating surface of the rear bearing cap is one possible source, as Jaguar didn't see fit to seal it at all --see Figure 7 below.  The sides of that cap were sealed with "hockey sticks" on early cars, but later assembly instructions call for injecting silicone instead; apparently the hockey sticks would dry up and harden and start leaking.  Besides these possibilities right near the rear seal, there's also the half moon seals (page 60), oil pressure sender (page 47), tappet block banjo bolts (page 44), and a host of other items that may be leaking above or around the rear of the engine and dripping down to look like a rear oil seal leak.

If your rear oil seal is leaking, please see the note on the PCV system on page 51.

REAR OIL SEAL --UP TO VIN 160010: Up through engine number 8S.66782, the rear oil seal was a "rope seal", a chunk of waxy rope crammed into a groove surrounding the crank journal.  This is sometimes called the "two-piece seal" since there's one piece of rope crammed into the journal on the block to form the upper half and another piece of rope crammed into the bearing cap to form the lower half.

At first it seems apparent that the upper half of the rear oil seal cannot be replaced without removing the crank.  However, Dick Russ reports that there is a tool called "Sneaky-Pete", P/N 2700 by the Lisle Company in Clarinda, IA, that will enable the seal to be replaced without removing the crank.  The tool costs only $6 or so and is available at Pep Boys, AutoZone, etc.  It consists of a length of music wire and some tiny grippers that can be used to bite into one end of the new seal and pull it into place around the crank.

ENGINE ENLARGEMENT: There are two ways to get more power out of an engine: tune it to obtain more horsepower per liter, and enlargement to provide more liters.  Of the two, enlargement has some definite advantages: if the horsepower per liter is not changed significantly, the durability may not suffer; the "manners" of the engine, important in street applications, may remain as stock or even improve; fuel economy may remain nearly unchanged; and the use of higher octane fuel or octane boosters may not be necessary.

Indications are that the Jaguar V12 has a lot of room for expansion.  A 5.3 liter (90mm bore x 70mm stroke) for two decades, it was enlarged by Jaguar in the early 90's to 6.0 liter (90mm bore x 78mm stroke).  AJ6 Engineering (see page 713) once offered engines bored and stroked in sizes up to 7.1 liter and 405 BHP.

The room for expanding the bore seems to be limited to around 98mm.  The stroke, however, can go a long way, and since it is so over-square to begin with, getting too under-square is not a problem.  Bill White (see page 721) has prepared a Jaguar V12 for use in a 3/4-scale replica of a Spitfire fighter plane.  He expanded the bore and stroke to 96mm x 95mm --almost an inch of additional stroke --for a displacement of 8.4 liters! This was done without significant modification to the block, and the stock H.E. heads were used.  At 3000 rpm, this engine produces 500 ft-lb of torque in naturally-aspirated form, and 820 ft-lb when supercharged as it is in the aircraft.

According to White, that isn't the limit by any means.  He reports that an outfit in the UK called Forward Engineering

Changes to the engine displacement require modifying or replacing the EFI.  The stock EFI is hard to modify; it has a fixed (trimmable, but fixed) map for intake manifold vacuum and RPM versus fuel.  If the displacement is altered, this relationship changes.  One solution is an aftermarket EFI system that is completely programmable and re-programmable (see page 310).  Most choose to ditch the EFI at this point for carburetors, introducing the problems outlined on page 310.  And the emissions inspector will not smile at them.

LOTSA VALVES: There have been experiments to adapt the 4-valve DOHC head from the Jaguar AJ6 engine to the V12.  The cylinder spacing and bolt patterns are the same --according to Roger Bywater, not because the AJ6 was derived from the V12, but rather because there was a plan to put the V12's H.E. head on some versions of the AJ6.  If the DOHC heads are just bolted onto the V12, on one side the intake ports will be on the outside and the exhaust ports will be toward the center --not good.  So, one of the AJ6 heads must be turned around backwards --and some complicated fabrication work is required to get such things as the cam sprockets rearranged.  Bill White (page 721) has worked with this idea, among others.

Steve Averill reports that the Autumn 1988 issue of Jaguar Quarterly has an article on "a 60 valve DOHC V12 that was under development by Warrior Automotive Research.  They expected to achieve 100 bhp/litre in low tune with a 5.8l engine.  The head had 3 inlet & 2 exhaust valves per cylinder."  No word on what's happened since, but Warrior's phone number was given as 061-928 3284 in Cheshire if anyone wants to try a call.

BOOST: There has been at least one experiment in Australia in turbocharging the XJ-S, but the results were apparently not good.  Officially the problems were blamed on the inability to assemble a drivetrain that would handle the 1000+ hp for more than a few seconds.

Chris Sleeman (also in Australia) reports on a 1998 endeavor: "When I picked up my Daimler Double Six yesterday from my local Jaguar specialist, he showed me an XJ-S he is working on.  It is a '76 model, with a 6.8 Litre Twin Turbo V12.  The motor was built by them, and the customer is apparently going to enter it into the Targa Tasmania in April.  The motor is being dynoed next week, but they say it puts out around 700hp.  It is running 0.8 bar of boost at the moment, and will be using Motec injection."

Somewhere out there, Bradley Smith is driving around his XJ-S with twin belt-driven Whipple superchargers.

NITROUS: Martin R. Fooks has a nitrous system in his XJ-S: "The Nitrous system was supplied by Trevor Langfield (page 719) and is a customized "High Power Nitrous" system.  Because of the size of the hit to the engine (150BHP) they installed a progressive controller, which fits neatly in my car where the trip computer used to be.  This enables me to control the way the extra power is delivered to the engine, such as starting power, ending power, time delay and time from starting level to ending level.

"I am very happy with the Nitrous installation, which really seems to be very smooth on the V12.  Trevor's people have the computer equipment to work out power and 0-60MPH times and that is where the figures came from.  As a side note, it ran 5.3 seconds 0-60 with a standard TH400 and only 75BHP jets in the NOS system instead of the 150 jets.

"Nitrous got a very bad press in the past, caused mostly by people adding too much power to their engines, or by not richening the fuel mixture when the NOS was injected.  The casualties in my case have been the torque converter and the rear IRS mounts, which were all bar 1 ripped off."  (See page 402 regarding rear suspension mount weakness.)

"The engine is stock except for the exhaust and intake, and I have had no problems at all with it (unlike the torque converter).

"Their main concerns with adding 150BHP were not with the engine as they believe it to be a very strong and reliable item.  The standard transmission and torque converter were their main objection to the increase which as it turns out was well founded."

"The amount of power provided in total by the NOS system can be changed by installing new jets at an English price of 7 pounds per pair, so if 150BHP proves too much to handle, you can always fit a smaller pair taking very little time and expense.  200BHP is the maximum obtainable by my kit.  My suppliers stated to me that as a rule they do not fit systems with more than 50% of the original engine power (which is why I'm only using 150 Jets instead of 200).  Obviously this is not the case if you bullet-proof your engine."

CAMSHAFT REPLACEMENT: Most performance enthusiasts will agree that replacing the camshaft (or camshafts; the Jag V12 has two, some cars have four) is the most effective way to change the performance of an engine.  The entire personality of a car can be radically altered by merely changing the camshafts.

Chad Bolles reports that Isky makes high performance camshafts for the Jaguar V12.

Rob Beere Racing Services (see page 714) also offers hot cams, as well as tappet shims in extreme thicknesses that may be necessary for such installations.

Note that any camshaft alterations should be accompanied by an EFI system modification; there will be increased airflow at wide open throttle, but since the feedback circuit is disabled under those conditions the fuel supply will remain at the original fixed map with no trim.  The engine will therefore run lean at full throttle, a situation that begs for burned pistons and valves.

There has been some confusion regarding the difference between pre-H.E. and H.E. cams, since published valve timing data on the two engines seemed to differ.  However, Bywater points out that they actually use the same part number camshafts. "When the V12 was launched the valve timing was quoted in Walter Hassan's SAE paper 720163 as being 17,59/59,17.  When the H.E. version was launched in 1981 the supplement to the manual quoted cam timing as 13,55/55,13.  In fact, the same cam profile had been in use since the early 1970s and continued through into the 1990s under part numbers C42176/7, therefore all EFI V12s were produced with these cams.  Now it is not widely known that for some time the V12 was mildly plagued with excessive tappet noise and in the course of dealing with the problem the quietening ramps on the cams were altered at least once around 1972-3.  I was personally involved in an investigation into the causes of a spate of tappet noise around 1978 and am not aware of any cam change ever being made to the V12 in production for any other reason than to reduce valve gear noise.

"Measurement of true cam timing is not a straightforward matter and it has been accepted practice to measure from the point where the quietening ramp ceases and the lift curve proper commences.  For those who are not familiar with the term, a quietening ramp is an area at the flank of the cam where the rate of lift is small, at around 0.0005" per cam degree, and to be fully effective must extend rather higher than the widest clearance likely to be encountered.  The idea is that any reasonable running clearance found in use it will always be taken up at a predetermined velocity which should not give rise to noise.  If the ramp geometry is changed, as we know happened on the V12, then the timing as measured at the top of the ramp could also vary and this accounts for the small difference of timing quoted at different times in its life."

Mike Cogswell elaborates: "Duration itself can be misleading, since almost nobody measures duration from the instant the valve leaves the seat until the instant it returns.  Instead, duration is commonly measured at some point where there is noticable flow, albeit typically a very low fit.  This is important, since different cam grinders measure duration at different lift, hence one man's long duration might be less than another's short duration.  Caveat emptor, as always."

Bywater again: "It is perhaps of interest to note that over the years Jaguar used virtually identical valve timing on all their mainstream engines.  Consider the following:

Clearly having found something that worked there was great reluctance to change from it, although the smaller displacement engines often had softer timing to beef-up the low speed torque as the following examples show:

SS 1.5 litre 10,50/50,10

XK 240 saloon 10,50/50,10 (5/16" lift)

Note also that hot cams might not have the expected effect.  AJ6 Engineering (page 713) once offered a milder cam than stock, and the result was higher mid-range torque and a nearly one full second quicker 0-to-60 time.  Bywater explains: "...we introduced some short duration cams for the V12 back in about 1984.  They certainly boosted mid-range performance, especially appreciated with the 3 speed BW and GM transmissions, but suffered a marketing problem because they gave slightly less peak power so we eventually discontinued them.  We sense that attitudes are changing and many drivers are realising that a performance gain around 40-70 m.p.h. is far more valuable than adding to a rarely seen top speed so we may well offer a modernised version of such a camshaft again in the near future."

TORQUE LINK: When the engine/transmission turns the driveshaft, the reaction is a twisting force trying to tilt the engine/transmission assembly on its mounts.  There are only three mounts, two soft rubber mounts under the engine and the complicated spring assembly under the tranny.  The tranny mount really does little to counter this force; the torque is entirely taken by the two motor mounts.

Since the mounts are soft, the torque can move the engine around quite a bit.  If the car is not stock and producing more torque than originally intended, the left-side mount may actually be damaged since it is put in tension under extreme conditions.

A racing trick is to add a fourth connection between the engine and the chassis.  By adding a link, torque can be taken up before the engine moves very far or stresses the mounts too much.  Newer FWD cars are usually designed with such a link, but front-engine/rear-wheel-drive cars typically rely on rubber in tension.

Under torque, the engine twists, which means the top moves to the right, the left side moves up, etc.  A link can be added anywhere that restricts this movement, but it is usually preferable to put it either on the left side of the engine connecting downward to the chassis, or from somewhere near the top of the engine connecting to the left side of the compartment.  Either of these locations puts the new link in tension (preferable for such parts) and helps keep the motor mounts in compression (protecting the rubber).

Backyard mechanics have been known to accomplish this fix by bolting a length of chain between the left-side exhaust manifold and the chassis.  Under normal conditions, the chain is slack and does nothing but rattle.  When the engine tries to lift, the chain pulls tight and stops the motion.  This method does work, but it is hardly a suitable fix for an XJ-S; the chain makes too much noise, and the sudden jolt when the chain gets tight is not conducive to an impressive ride.

To do a professional job, a better idea is to install a link made from threaded rod with some rubber bushings (available at any auto parts store), washers, nuts, and some fabricated brackets to provide holes for the bushings to fit into.  Rubber bushings are essential, since a rigid connection would transmit vibration directly to the chassis.  If necessary, shield the rubber parts from radiant heat from the exhaust system.

Alternatively, the ingenious mechanic may find a way to make a link from one of those FWD cars fit.

It should also be noted that the motor mounts on the XJ-S are not actually between the engine and the chassis, but between the engine and the front suspension subframe.  This provides two layers of isolation between engine vibrations and the chassis: the motor mounts and the subframe mounts.  Hence, adding a torque link from the engine directly to the chassis would defeat some of this isolation and perhaps expose the occupants to increased noise and vibration.  If possible, it would be preferable to connect the torque link to the subframe as well.  Or, use really soft bushings on it.

AIR FILTER REPLACEMENT: K&N Engineering, Inc., makes permanent air filters consisting of special fabric sandwiched between aluminum mesh and treated with oil.  They have much less flow restriction than stock paper filters while providing improved filtration.  Tests on race engines show only a slight drop in power compared to no filters at all!  Since these filters are permanent and cleanable, they can even save money in the long run.

The K&N part number is 33-2011 for any V12 XJ-S.  Note that stock air filters changed when the ABS brakes were added; since the housing shifted forward, the blank-off area over the throat had to move rearward.  The K&N filters have no blank-off area, so the same part number fits either application.

Note that the 33-2011 filters will also fit most XJ12's, but not the last couple of years.  The XJ40-and X300-based XJ12's (1993-on) went to a remote filter housing similar to that used on the 6-cylinder XJ40 and X300, except that they have two of them -- one on each side of the car.  If your car has air filter housings that are mounted right on the butterfly housings and uses filters that are 16.5" x 5.75", you need the 33-2011.  If your filters are 8.37" square, you need 332003.  The K&N catalog also lists a 33-2579 as fitting some V12's, but this is apparently an error.

IMPORTANT: The K&N's look like they can go in either way outward and either end forward, but you must install them with the flat side towards the butterfly.  In other words, install the filter into the cover so it sits flush with the bulk of the element within the cover, and then install the cover onto the engine.  Installing the other way, with the bulk of the filter nearer the butterfly, can cause the butterfly to get fouled with the filter element.  This would be seriously bad, possibly causing the throttle to jam wide open.  The concern is exacerbated with AJ6 Engineering's enlarged butterflies, but there's no reason not to be careful with the OEM butterflies.

Needless to say, if you've been running these filters the wrong way around, you should clean them before reinstalling them correctly.  Otherwise you'll be putting the dirty side of the filter facing the butterfly.

Installed correctly, the K&N's don't seem to cause a problem with the OEM butterflies because they are pretty stiff.  If you want to be safe, it is a simple matter to fab a device to positively keep the filter element and the butterfly apart.  This author used stainless steel wire 1/10" (2.5mm) thick from an old radio antenna.  Just fashion a loop in the wire to fit over one of the four bolts that hold the air filter housing to the butterfly housing, then a gentle arch over to the diagonally opposite bolt.  Make sure the butterfly moves freely underneath the arch before buttoning up the assembly.  If the air filter element decides to distort, the arch will keep it out of the butterfly.

The correct end of the K&N filter forward is not as critical, but you might as well get it right.  The flat edge is a bit longer on one end than on the other, and the longer edge goes towards the front of the car.

Roger Bywater of AJ6 Engineering says, "...we gave up using K&N filters some time ago because they fall to bits around the edges where the air box clamps up.  We raised the matter with K&N Europe, for whom we do consultancy work on occasions, but they claim not to be aware of the problem..."  AJ6 Engineering now offers their own design permanent washable foam air filters.

Glen E. MacDonald notes, "Roger Bywater gave up using K&N filters because "they fall to bits around the edges where the airbox clamps up".  True enough.  However, I was determined not to trash an otherwise perfectly acceptable (and expensive to replace) pair of filters.  The fix I found was to take four suitable lengths of windshield washer hose, split lengthwise.  These are then slid over the edges of the filter, after cleaning off whats left of the 'bits' Bywater refers to.  I made this alteration over 3 years ago and haven't had any problem since."

Of course, K&N filters come with a "million mile warranty", so another option would be to gripe to K&N about the problem.

For some of us, performance is not the issue with air filters; the wear rate of an engine can be closely related to the filtration of the air intake, and any risk of inferior filtration would not be worthwhile.  K&N claims that a NASCAR stock car fitted with its filters will outperform a car with no filters over a 500-mile event, since the deterioration of the engine due to contaminated air over 500 miles will exceed the power loss due to the intake restriction of a K&N filter.  K&N claims excellent filtration --although there have been some contradictory reports from other sources.  K&N filters

Either K&N or the stock paper filter is probably acceptable from a filtration standpoint.  However, speaking as an engineer, I must express doubts about the filtration efficiency of most of the foam filters I have seen (I haven't seen the AJ6 Engineering foam filters).  A foam filter works on a similar theory as the K&N, the foam providing a media for the air to pass through that is coated with sticky oil.  However, the passages between the cotton fibers on a K&N filter are very tiny indeed, it's hard to imagine how a speck of dust could get through without sticking, but some foam filters you can see through.  And even some of those you can't see through appear to have passages that are quite large.  And I've also seen foam deteriorate, with crumbs of foam breaking off and going into the inlet.  And even if the chunks of foam don't harm the engine, note that each chunk leaving leaves an opening for more dirt to pass through the filter unimpeded.

OPENING UP THE AIR INTAKES: Each of the air cleaner housings has a long tapered tube with a relatively small opening for the air intake.  The purpose of the small intake opening is to accelerate the air to near Mach 1 at wide open throttle.  This prevents intake sound from coming forward through the intake.  In other words, it makes the car quiet.

Unfortunately, the air is now moving fast, and there's an air filter up ahead.  If the air is allowed to simply run into the filter, the energy associated with the speed will be wasted, and the result is a loss of pressure.  Therefore, Jaguar provides the tapered tube to gradually and efficiently slow the air down, recovering most of the energy and pressure.  Jaguar designed this tapered tube as long as they could fit under the hood.

Also unfortunately, once the air reaches Mach 1, the passage is "choked" and all the sucking the engine can manage will not increase the amount of air flowing through it.  The opening therefore forms an absolute control on the maximum amount of air going into the engine -- and therefore the HP generated.

If you cut off this intake tube and form a large opening for the air intake into the air cleaner housing, you will eliminate this restriction.  If you interfere with the mounting of the temperature sensor in the left side intake tube, relocate it into the housing itself (drill a hole and use a nut on the inside); it can sense the air temperature anywhere in there.  Because the EFI system detects manifold vacuum, the system will automatically compensate for the increased airflow; no tuning modifications are required.  There is no effect on emissions, so there should be no complaints from inspectors.

At part throttle (most of the time with an engine this powerful), the butterfly acts as an air-accelerating restriction, and no sound gets out anyway.  The car will sound like it did before.  However, when you open it up, you will be greeted with a sonorous growl from under the hood.  This is a very sexy sound, but some Jag owners may not like it.

The performance improvement goes along with the noise.  In any situation where there is still no sound, there is no change in performance either.  When the engine growls, there is more airflow than there was before.

This mod will have no effect on fuel economy, except when you hear the growl; at that point, increased fuel use accompanies the increased airflow and increased power.

You can give this mod a trial run without much effort.  Unscrew the air temperature sensor, then reconnect the wire to it and tape it down anywhere convenient.  Then, remove both air filter covers and tie the air filters in place with some wire.  This setup will provide the same performance (and a little more noise) than the intake tube removal described above.

OPENING UP THE AIR INTAKES -VERSION 2: AJ6 Engineering (page 713) has gone through several variations on air filter housing intakes attempting to provide an optimum balance between unrestricted flow and noise.  What they now offer with their induction upgrade kits are replacement covers that appear largely unchanged from OEM except that there is an additional intake opening on the bottom with a hose leading to another little bellmouth intake mounted in the vicinity of the front anti-sway bar.  Perhaps AJ6 Engineering will sell these covers separately, or perhaps one could just adopt the idea and fab similar additional intakes.

OPENING UP THE AIR INTAKES - VERSION 3: FasterJags (page716) offers a replacement air intake system called the Growler.  It replaces the entire air filter housing assembly with a pipe that curves forward and has a cylindrical K&N filter mounted on the front end.

COLD AIR INTAKE: Any engineer will tell you that an internal combustion engine will run more efficiently (more power and better fuel economy) on cooler intake air.  Most automobiles nowadays (including some Jaguars) have hoses directing cool outside air into the air cleaners rather than the hot air of the engine compartment.  The XJ-S is a notable exception; perhaps they felt that the hoses would make their engine compartment less attractive.

While opening up the intakes on the air filter housings as described above, a flange can be provided for an intake hose.  The author's installation used 3" exhaust pipe, but 2½" pipe would work nearly as well (still four times the area of the stock inlet) and would probably be easier to install.  Intake hoses in many sizes can be found at most parts stores, and some have built-in clamps.  Remember to provide flexibility in the system, since the engine moves around on its mounts.

All of that was easy.  The hard part is routing the intake hoses somewhere.  One possibility on the XJ-S is the back end of the headlight compartments.  By making a hole and providing a flange for the hose (2½" or 3" pipe again), cool air can be routed from existing openings just inside the grille through the space behind the headlights and into the intakes.  An opening must be made in an unseen panel within the headlight compartment to permit air flow.  The modification will also require relocating the headlight relays.  Be sure to clean up the intake path as well as possible when you're finished, and check your air filters for debris after driving a while.

On cars with ABS brakes, the air cleaner assemblies are essentially unchanged except that they are moved forward to avoid the brake system.  The same basic mod works; the intake hose just needs to be a bit shorter.

The good news here is that this mod will reduce the noise from the Version 1 mod.  The intake hoses, as well as the sheer length of the intake path, will help dampen the growl.

Since the EFI temperature sensor will detect the cooler intake air temperature, once again no tuning mods are needed.  The cooler air provides improvements at all operating conditions, and will improve fuel economy.  There is even less tendency to overheat.  The only effect on emissions is a reduction in nitrogen oxide emissions.

Peyton Gill reports, "I used a Dremel to cut the horn out of the air filter cover and then rounded the "not so perfect hole" with a grinding stone mounted in a drill press.  I did not use the exhaust pipe Kirby mentioned, I went to Home Depot and got 2 inch gray PVC couplings.  The ones I got came from the electrical dept.  The couplings I used have threads on one side and open for a PVC pipe on the other.  The conduit works good because you can get a "nut" that fits the threaded side.  This nut I'm talking about is more like a threaded ring, it is very common in the electrical conduit world.  The rounded hole you leave when you cut the horn out is close to the same size as the threaded side of the coupling and the nut inside the air filter holds the coupling tightly in place.  The hole I cut was not perfect so I sealed any openings with black RTV (silicon).  I did have to relocate the ballast resistor pack on the right hand side and managed not to have to relocate the relays on the left hand side.

"I used a hole saw (maybe 2 1/4 inch) or whatever size slightly larger than the conduit coupling threads to cut holes in the panels behind the headlights.  Since the hole was only slightly larger than the threads so they screw fairly tightly in plus a little more RTV to be sure they hold.  I got a flexible hose from Pep Boys (they have hoses made for air filter intakes).  I took my conduit coupling with me and found a hose that fit snugly over the pipe side.  The hoses have clamps that snap into place and one of the hoses fit my conduit perfectly.

"All that was fairly easy; the good part comes when you attack the "hidden panel" described in Kirby's book.  This panel is between the headlight opening in the front and where the hole was cut in the engine compartment.  You can see it easily enough when the headlight assembly is removed.  Seeing the panel is one thing, cutting a hole in it's another.  There is not much room to work or cut.  I got a 12 inch extension for my drill and put the hole saw on this and cut a couple 2 inch holes in the panel.

"The air temp sensor also has to be relocated.  I drilled a hole in the air filter cover and placed the sensor in the direct air

OIL COOLING: The standard oil cooler on an XJ-S is a "relief" unit, meaning it only cools the oil that doesn't go through the engine.  However, as pointed out by Bob Tilley, the XJ-S sold in Germany is fitted with a "full flow" oil cooler system, and the parts are available through Jaguar.  We can make assumptions about why the German cars would be different than other cars, possibly involving those Autobahns.

John Goodman adds, "It's worth pointing out to others who own later model V12's who may not be aware that all V12 HE engines after engine no. 8S44317 had full flow oil cooling, can't remember the year this was introduced."

Both oil systems, as well as almost any other in automotive use, work like this: Oil is drawn from a pickup in the sump into the oil pump.  The oil pump is a positive displacement pump, meaning it will move a particular amount of oil for each rotation, regardless of how much pressure it has to apply to move it; if something gets plugged up or the oil is

In the basic relief oil cooling system in the Jaguar V12, only the oil that is relieved by the pressure relief valve is piped to the oil cooler in front of the radiator, and from there back to the intake of the oil pump.  In the full flow system used in German cars, the oil destined to go to the galleys is piped to the oil cooler at the front of the radiator and then back to the filter head assembly to continue through the filter and into the galleys.

Physically, the distinction is like this: in the relief system, oil feeds out of the outlet elbow at the bottom front of the filter head to the right side of the cooler.  From the left side of the cooler, it goes to a fitting on the bottom front of the sandwich plate on the crankcase.  It doesn't simply return into the sump here, but instead goes directly into the inlet elbow on the bottom of the oil pump.  Hence, the oil pump actually draws suction from two places: the sump pickup and the return from the cooler.

The front of the full flow filter head has a pair of fittings that don't exist on the early style relief filter head and are sealed off on later style relief filter heads -- the change probably due to the desire to use the same casting for both relief and full flow filter heads.  In the full flow system, oil to the cooler starts at one of these fittings on the filter head itself instead of the outlet elbow; the outlet elbow still exists, but the port on the front is sealed off.  The oil feed is piped to the right side of the cooler.  From the left side of the cooler, it goes back to the other fitting on the filter head.  The oil pump therefore has only one intake, from the pickup in the sump, and the bottom of the sandwich plate either has no hole or has a blank-off cover on it.

The relief system has an inherent shortcoming in that it tends to vary the amount of cooling incorrectly.  When the oil is cold, it is also thick, and the pressure relief valve has to relieve a great deal of it in order to limit the pressure.  As a result, flow through the cooler is high --precisely when not needed.  On the other hand, when the oil is hot and thin, very little or none at all is relieved, and hence flow through the cooler is minimal -- precisely when it is most needed.

The full flow system always flows the oil through the cooler before it goes through the engine, so there is always cooling.  And, the coolest oil in the system is the oil fed to the galleys, so it can be expected to reduce the incidence of burned bearings.

The relief system has another trait that causes consternation.  In order for a relief valve to work properly, it really needs to relieve to a place of zero pressure --such as directly into the sump.  Because this system relieves through the oil cooler, there may be a significant amount of pressure on the back side of the relief valve --the backpressure caused by the flow of thick, cool oil through the tiny passages in the cooler.  The pressure of the oil the engine sees -- and therefore the gauge sees --is the relief pressure of the valve plus the backpressure of the oil cooler.  The backpressure of the oil cooler will vary greatly with oil temperature; when cool and thick, the pump will be trying to push a great deal of oil through it, but when hot and thin it may see little or no flow at all.  The combination of the viscosity changes and the flow changes make for extreme backpressure differences.  As a result, the oil pressure registering on the gauge will vary quite a bit more between cold and hot than on most cars.  This doesn't seem to cause any harm, but it does cause owners to get overly concerned.

If you wish to retrofit the full flow cooling system to a car that came with the relief cooling system, you will need the following parts.  The corresponding part numbers for the relief system are also shown: Part Relief p/n FF p/n Oil Suction Pipe Oil Suction Elbow Oil Suction Elbow Gasket Relief Assembly Relief Outlet Elbow Oil Cooler C35512 C33869 C31063 C42796 or EAC7755 C38802 C43923 EAC6424 EAC6422 C31063 EAC6398 EAC6789 CBC2692

Plus a few bolts, nuts, O-rings, etc., all of which can be purchased locally.  If you're the industrious type, you can probably improvise all those clamps and brackets too.

You might also be able to avoid buying the relief outlet elbow; you can reuse the old one if you can plug the opening in it.  You will have the part that screws into it, oil feed pipe EAC1380, laying around doing nothing if you want to cut the fitting off and make a plug out of it.

The 1987 Parts Catalogue shows the same sandwich plate used for both systems; a square blank-off plate EAC6420 and gasket EAC6421 are used to cover the unused hole under the oil pump elbow on cars with full flow cooling.  In all probability, later on when all cars were fitted with full flow oil cooling, the sandwich plate was altered to omit the hole.  But anyone doing the retrofit is probably going to prefer simply bolting on the blank-off plate to replacing the entire sandwich plate.  And they could easily make a blank-off plate and gasket rather than buy them.

To replace all these parts would require pulling the sump off the engine to replace the oil suction pipe and the oil suction elbow.  However, in theory anyway, these replacements may not be necessary, and the retrofit might be accomplished without pulling the sump.  The difference in the oil suction elbow is that the one for the relief system has the second inlet on it, and this inlet is readily accessible via the opening in the bottom of the sandwich plate.  If this second inlet is securely plugged, it will serve the purpose of the EAC6422 part.  This can be done by making a suitable part that plugs both the second inlet on the oil suction elbow and the opening in the sandwich plate, or by using a separate plug - perhaps like the rubber expansion-type freeze plugs --on the suction elbow, along with a simple blank-off on the sandwich plate.  In fact, the original sump inlet adapter C37882 can be used if you find a way to plug it.  Going this route would not only reduce disassembly requirements, but it also eliminates the need for purchasing a new oil suction pipe, oil suction elbow, and oil suction elbow gasket --as well as bottom end gaskets you'll have to replace when you open it up.

Note that the difference in the oil suction pipe --which is, in fact, the pickup --is unknown.  But there is no reason to believe the one designed for the relief system won't work properly for the full flow system.  Perhaps the design was changed slightly to fit the revised oil suction elbow.

OIL PRESSURE RELIEF HOSE: While fiddling with the sandwich plate off, Karl Huff was told by a Jaguar shop that "while I'm in there I should replace the oil filter pressure relief hose (?) with a new one from the 6 litre engine."  This is probably referring to the question mark shaped line.

OIL FILTRATION MODS: Much of the following was pilfered from an article by Nigel Calder in the March/April 1994 issue of Ocean Navigator magazine.  It was primarily about auxiliary engines for sailboats, but the issues discussed here apply to any piston engine.

Oil contamination is divided into two categories: chemical and physical contamination.

Chemical contamination degrades the oil, causing a loss of lubricating properties, and also may introduce substances that attack engine parts.  Heat and age can cause oil to oxidize and thicken, encouraging the formation of sludges and varnish.  Water can be introduced even in a tight engine by condensation within the crankcase, and causes emulsification.  If there happens to be any sulfur in the fuel, some can find its way past the rings and combine with water to form sulfuric acid which promptly attacks engine parts.  Unburned fuel coming past the rings also dilutes the oil, lowering its viscosity.

Chemical contamination is combated by additives in the oil.  Eventually, however, the additives are consumed and fail to counteract the contaminants.  At this point, the oil needs to be changed.

Physical contamination refers to metal particles and dirt in the oil.  The metal particles come from wear between moving parts.  The dirt comes through the intakes, and a portion makes it past the rings.  The problem is obvious in that such particles will increase the wear on bearings and the like.

It is tempting to take comfort that the oil filter is preventing the particles from getting into the workings of the engine.  Unfortunately, it is not as effective as one could hope.  The typical paper-element oil filter will catch particles down to about 30 or 40 microns, but damage is caused by particles down to about 2.5 microns.  These smaller particles build up in the oil and pass right through the filter, cycling through the engine again and again.

The full-flow filter cannot be made with a tighter mesh because the restriction to oil flow would be too great.  In addition, if the filter gets clogged, either the element breaks open (dumping all the dirt into the engine), or the flow is inhibited.  Usually a relief valve is provided to allow oil to bypass a clogged filter, allowing crud of all sizes to circulate through the engine.

There are two excellent ways to combat physical contamination.  The first is by installing a bypass filter.  A small percentage of the pressurized oil from the outlet of the full-flow filter is diverted into a separate filter with a tight mesh element to stop particles down to 2.5 microns, and from there right back into the sump.  An orifice is provided to prevent an excessive amount of oil from taking this route, which might starve the engine.  If the filter gets plugged, no problem -- the flow stops, and 100% of the oil goes through the galley as before.  But as long as a small amount is going through the bypass filter, within only a few minutes all of the engine oil is cycled through it and the amount of suspended particles is greatly reduced.

The other method is essentially the same, except that the bypass filter is replaced by a centrifuge that causes the particles to collect on the inside of a spinning cylinder.  These are typically only available for larger engines.

These solutions are even better than changing oil at short intervals.  Even with frequent oil changes, particles appear in the oil immediately and continue to build up.  The bypass filter, however, continuously keeps such particles from causing engine wear.

Note that a bypass filter does not address chemical contamination.  Such an installation would be effective at reducing engine wear, but the oil needs to be changed at the same intervals to prevent the additives from failing.

An outfit called TF Purifiner (page 719) offers a package that includes a bypass filter system along with a small heater that boils off water, fuel, and coolant to minimize the chemical contamination so the additives last longer.

Surfing the WWW, Mike Claus found that other products are available from Baker Precision Bearing (page 714), Fram and Amsoil.  "Fram offers an automotive by-pass filter in its product line that features a pleated-paper element and easy "spin-on" replacement similar to original-equipment-type units.  Ask for the Fram "PB50" with mounting hardware.

"Amsoil's bypass unit is connected to the oil pressure sending unit and returns oil to the pan, thus requiring some mechanical ability or the services of your mechanic for the initial installation.  The company states that its bypass unit, which employs a user replaceable, pressed-fiber element, refilters all the oil in an engine every five minutes, and keeps it analytically sparkling clean for the (recommended maximum) element life of 25,000 miles! It even extracts and contains any water that has (inevitably) condensed into the oil...which if allowed to remain in circulation will often result in the formation of corrosive acids."

Of course, one might immediately ask: if a bypass filter is such a good idea, why didn't such a quality automobile as a Jaguar come with one from the factory? Well, you have to consider the options the way the manufacturer does.  The lack of a bypass filter will not cause engine failure before some extended mileage, especially if the owner has been paying the dealer for oil changes on a regular basis --and even if the engine does fail due to dirty oil, the manufacturer is not likely to incur any liability.  The additional cost, multiplying the cost per car times the thousands of cars sold, is significant.  And the additional risk of failure --one of the oil lines to a bypass filter blowing open or some such --may be more than the company wants to accept.  Just having to tell prospective buyers that there are two oil filters that need regular changing may be seen as a marketing disaster, especially in this era of drive-it-and-forget-it cars.

You, as the owner of the car, may think differently.  You have a significant investment in your car, the risk of a blown high-pressure oil hose is no big deal to you (messy, but not particularly expensive), and you are the guy who will have to pay for a new engine when this one wears out.  Basically, if you are the type to own a Jaguar for the life of the car, a bypass oil filtration system would be a wise investment.  Of course, if you plan on selling the car soon, or plan to crash it rather than wear it out, it'd be a waste of money.

PRE-OILING BEFORE STARTUP: A lot of the wear on any engine occurs at startup, when the engine must run for a few seconds before oil pressure is established.  Russ Lehman sends this tip: "I've got a "Pre-Luber" on my van because it only gets driven about once a week or so, and the pre-lube brings the oil system up to pressure by pumping oil through the engine before starting.  These pumps are fairly common on marine engines for the same reasons.

"The pump is fed from a line attached to the oil pan and pumps into a tap where the oil pressure sender is attached.  The pump allows oil to pass through the normal routes for normal engine operation, while not allowing oil to pass backwards through the pump (I think it's a piston pump).  The motor is switched through the ignition key in the aux position (controlled by MOSFETS), and will stop when the engine ignition is switched on."

There are other systems, including a simple pressure reservoir that holds pressurized oil after shutdown.  During startup, a valve is opened, pressurizing the system before the starter is engaged.

Note that such systems may be of limited benefit.  While the bearings in the bottom end of the engine may experience much less wear, it is not usually worn bottom-end bearings that require an engine rebuild.  More often, it's worn pistons/rings/cylinders that eventually convince an owner it's time for an overhaul, and a preoiler does little or nothing to reduce piston/ring/cylinder wear.

ADDING EMISSIONS CONTROLS: Huh?  Well, Germany now has a taxation system that penalizes cars without emissions controls so severely that many German XJ-S owners are seeking to retrofit.  For many years the German version had no catalytic convertors or oxygen sensors even though they were provided in the US.

According to Jeffrey Gram, the following outfits (all in Germany) will install emission controls in cars that were not originally equipped with them:

IF ALL ELSE FAILS: Most Jaguar owners feel that if you want a Chevy, you should buy a Chevy.  But there are those who think otherwise, and for them there are several outfits that offer kits for replacing the Jaguar V12 with a Chevy V 8.  John's Cars (page 717) offers two kits for the XJ-S, one for a small block Chevy and one for a big block.  Another outfit to check with is Jaguars That Run (page 717).  The 90° V-8 is an excellent engine layout; it has even firing order, and its primary and secondary imbalances are 100%

Sir William Lyons, founder of Jaguar, apparently didn't like V-8's.  When Jaguar bought out Daimler in 1960, Daimler had two V-8 engines in production, and Lyons scrapped one of these immediately and the other a few years later.  When it became apparent that the venerable Jaguar XK inline 6 would no longer cut the mustard, Lyons responded with the V12.

If you must shoehorn a cast iron V-8 into your Jaguar, do yourself a favor and purchase some cast aluminum valve covers.  They will absorb a lot of the noise of the valve train.  A cast aluminum timing chain cover will also help reduce racket.  Replacing the timing chain with something with less slop, like a set of gears, will make the engine run smoother.

Of course, a better idea yet would be to opt for the newer cast aluminum Y-block Chevy V-8's.  Not only are these engines far superior mechanically to the cast iron models (despite retaining the pushrod valve train), they also come with modern EFI and ignition systems and improved automatic transmissions.

SPARK PLUG REPLACEMENT: Note that this task is much easier on the pre-H.E. because the spark plugs are vertical.  On the H.E., the plugs are tilted inboard just enough to make the job truly miserable.  Most of the tips below were developed to deal with the H.E.

First problem is getting the plug wires off --and back on later.  Jan Wikström, who owns a pre-H.E.: "I've made up a pair of "pusher" tongs out of a bent piece of 4mm high-tensile fence wire.  Same idea as the common barbecue tool, but the jaws originated as a short piece of 9mm copper pipe split lengthwise and brazed to the wire.  This gets a good grip on the cable just above the rubber cap on the terminal.  This tool needs to be bent to a slight angle above the jaws."  The same idea might work on the H.E., but expect to have to vary the details to make it work well.

Another idea is to use a length of 1/4" steel tubing and some bicycle brake cable to make a "snake grabber".

If you have access to a wet/dry vacuum cleaner, use the hose with no attachments to clean around the plugs before removing them.  Just poke the hose over the end of the plug.  Compressed air can also be used.  John Bertsche adds: "I came up with a cool tool for cleaning out the crud around (and in) the spark plug holes.  A turkey baster --pull off the bulb, duct-tape the other part to your shop-vac hose, and you've got a high-intensity, pinpoint (well, almost) vacuum nozzle that'll fit right into the spark plug hole.  Works great!  You can use it to scrape dirt and crud out of almost any nook and cranny, and it won't scratch the aluminum."  Note that you can purchase a set of small vacuum attachments at Wal-Mart intended for cleaning things like computer keyboards, and those attachments would also work well here.

Using normal tools, it generally requires removing the cruise control actuator and unbolting the A/C compressor on the H.E. to replace the 1A and 1B plugs.  Matthias Fouquet-Lapar says, "Jaguar offers a tool, it's in the rear-section of the XJ-S parts manual.  It fits perfectly and you don't need to remove the A/C compressor."  Steve Holst says, "I ended up using the official Jaguar spark plug removing tool that came with the tool kit to replace the plugs.  It worked wonderfully and I didn't need to move the A/C compressor one bit.  I ended up unbolting the cruise bellows only.  I'm very glad I gave it a try."  This plug wrench (CAC5368) comes in the XJ-S tool kit, but it's amazing how often used cars don't have a tool kit.  If you need to buy the plug wrench, shop carefully; they supposedly can be had for under $20, but Jaguar dealers have been known to ask much more than that.

Ah, but things are never that simple.  Peyton Gill says, "The tool's socket well was too shallow for the NGK plugs I installed."  Graeme Mawson concurs: "My car is an '85 V12 with NGK plugs; the tool provided does not fit over the plug, i.e. the stem of the plug is too long for the barrel of the tool!  Perhaps there are two different tools!"

After much discussion about differences between types of spark plugs, it turns out that Mawson is correct --there are two different tools.  The earlier tool, CAC5368 --used up until at least Peyton Gill's '86 --will not fit a spark plug.  However, sometime later Jaguar revised the tool so it would fit a spark plug.  The two wrenches appear to be identical in construction, but the later version, CBC4096, has a hole in the top of the socket that goes all the way through; when a spark plug is in place, you can peer in between the pivot joints and see the top of the electrode.  Brian Schreurs says, "It does not come with the T-handle so one would have to buy a piece of rod and cut to fit."  The T-handle is C36612/2, a part number for a straight piece of steel rod.

Apparently, the spark plug tool part number was superceded again by CCC4813.  It's not known what that difference is.

It may be possible to modify the earlier tool by simply drilling a hole through it.  You'd hope that it's not --you'd hope the tool is made of harder steel than that --but in fact it appears pretty soft and cheap and may be drillable.  John Bertsche says, "The factory tool I had in the trunk fit on them fine...just wasn't up to the stupendous amounts of torque required to crack them loose."  David Littlefield says, "The factory tool is very cheaply made, frankly.  Mine has a big sticker on it with a British flag and says "Thanks for buying British!"  I kept ending the phrase in my mind with "in spite of the fact that you are spending half your weekend trying to change impossibly located spark plugs with the incredibly cheap, POS tool we supplied you.""

There are T-wrenches sold for 5/8" spark plugs, and a good one might actually do the job.  Unfortunately, all this author has found are cheap ones --even poorer quality than the Jag OEM tool --and the swivel invariably breaks as soon as torque is applied with the swivel in any position other than straight, which makes them worthless for this task.  Mawson says, "I have bought several box type tools to undo the plugs but as indicated above they always break or 'round off' long before all 12 plugs have been removed.  Furthermore on the V12 without removing the likes of fuel lines, A/C compressor, cruise control, distributor or throttle mechanism, when the tool does break (with stupendous amounts of torque applied) it is more than likely that other things get broken as well (usually fingers or knuckles)."

Littlefield says, "Another suggestion for an under-the-compressor tool might be to cut down an old spark plug socket that has the flats on it, and maybe even enlarge the ratchet hole so it can fit further down the plug."  Using this idea, Larry Barnes made a tool that actually works: "I took a regular spark plug socket and:

There is one more possibility in spark plug tools.  J Harper points out that Eastwood Tools (page 704) offers a telescoping spark plug socket.  This thing collapses into a little hockey puck which you position over the plug, and then telescopes into a socket shape around the plug.  Cute.

Even with a workable tool, you might want to move the compressor anyway.  Fouquet-Lapar, despite having the plug tool, says, "I still remove the compressor and the throttle pedestal, mainly to clean things up at the same time."  Littlefield left the compressor in place and says, "after this experience, I think I know what surgeons go through during an operation.  Working through a narrow hole with long instruments, trying hard not to break something vital.  I was even using forceps to hold tubes and wires back to get to the areas I needed to go!"  Craig Sawyers says, "I have that Jag tool.  However, I have always found it impossible to use under the aircon compressor.  The problem is that the

If you decide to remove the throttle pedestal, John Napoli says, "Rather than removing the coil, throttle switch, etc. separately, consider removing the whole ball of wax as one.  Simply remove the four bolts holding the throttle stand to the engine valley, and it all comes out as one."

You may run into problems getting those four bolts out as well.  It's not too difficult to remove in the midst of an upper-engine teardown when you're taking everything out of the way anyway, but for the spark plug job you'd like to remove just the pedestal without removing things like the oil pressure sender.  The problem is the two bolts at the rear side of the pedestal; they are easy to see, but not so easy to get a wrench on.  First tip: obtain a 7/16" swivel socket --or a 10mm swivel socket if the later engines have metric bolts here.

The first time you have the pedestal off, saw off the lugs on the right side that were apparently originally intended to hold a coil.  That will make access a little easier next time.

Napoli decided to make some access holes in the pedestal: "On my car, I modified the throttle stand further to lighten it, improve airflow in the area, and make it easier yet to get in and out.  I drilled a series of large holes all over.  Cleaning it all up and polishing a bit makes it look nice, improves gas mileage, reduces emissions, and decreases quarter mile times."

Peter Cohen says, "The last time mine was out, I slotted the holes for the two rear bolts so that I could start the threads and then mount the pedestal."

As long as you're going to the effort of taking the plugs out, it wouldn't be a bad idea to go ahead and perform a compression check.  It's a good way to keep a watchful eye on engine condition.

Before installing the new plugs, it is recommended the time be taken to carefully inspect the threads.  Competition is fierce among the plug manufacturers and they generally cannot afford to spend a lot of time and effort making perfect threads every time.  One small burr on a steel spark plug can wreak havoc on the threads in the aluminum head.

Be sure to use anti-seize compound on the threads.  Do not use normal grease, as this may hamper proper grounding of the plug, and it also may get hot and form a crust that makes it even harder to remove the plugs.  And do not use a graphite-based lubricant, as graphite may react with the aluminum and weaken it.

When installing spark plugs, it is helpful to use a piece of 3/8" hose to get them started.  Press the hose firmly over the top of the plug and use the hose to feed them into place and thread them in finger tight.  Then the hose can be pulled off and a socket used for final tightening.

There are warnings not to tighten the plugs past 8 ft-lb. of torque. 8 ft-lb. is not enough to turn the plugs loosely in the threads unless they have been recently cleaned and chased, but the point is well taken.  It is an aluminum head, and tightening "three grunts" is both unnecessary and costly.  Just tighten until you feel them seat, make sure they're snug, and quit.

SPARK PLUGS: A quick survey of a group of Jaguar experts clearly indicates that NGK is the plug to use.  The study may have been unscientific and the reasons may have varied, but the consensus was clear and overwhelming.

The H.E. engine uses taper seal plugs; the pre-H.E. engine uses washer-seal plugs.  For the H.E., NGK used to make at least two plugs, TR5 and BPR6EFS.  Both were resistor type, but the TR5 was a "V-Power" plug with a little notch cut in the center electrode.  Jim Moore says, "They go by numbers now; an NGK 2238 is recommended by NGK for my '85 XJ-S, turns out it has TR5 written on other end of box and on the plug."

There are many gimmicks used to sell spark plugs.  One common feature that may be of some benefit: It is easier for a

Supposedly, it's actually more important that the sharp edges be on one electrode than the other.  With old-fashioned ignition systems, the center electrode was always the anode and the ground was always the cathode --and the sharp edges really need to be on the cathode, which means they're on the wrong electrode with the V-power plugs.  Apparently NGK fixed that; Richard Mansell quotes from a Jaguar publication on the changes for the 1992 model year:

"A new design sparkplug, BR7EF, incorporating a V groove earth electrode, is fitted to improve efficiency and provide better firing consistency."

Note that very little else changed about the Jaguar V12 for the 1992 model year; one can safely conclude that the upgraded spark plugs would work well in older H.E. engines.

NGK certainly isn't the first company to offer multiple sharp edges on the ground electrode.  ND plugs have had a grooved ground electrode for years.  A highly-advertised plug called the Splitfire charges several times as much as regular plugs for providing a couple of extra edges for the spark to jump to.

If you happen to have a distributorless ignition with double-ended coils (only offered on Jaguar V12's in the mid-90's, and only in the saloon) then half the plugs have their polarity reversed, and the sharp edges need to be on the center electrode again!  You can't win.

Another idea in spark plugs that gained popularity in the 90's is platinum electrodes.  Platinum is an obscenely expensive metal -- makes gold look cheap --but it doesn't take much of it to make a spark plug electrode, just the tiniest dot at the gap.  And that dot makes the plug last several times as long, which is the reason some modern cars can claim 100K miles before the first tune-up.  Note that while platinum-tipped plugs may cost considerably more than standard plugs, they do not offer any improvement in performance at all; their entire benefit is in durability.

Following the crowd, NGK has introduced new plugs for the V12, similar to their earlier offerings but with platinum in the tips.  As a result, it is increasingly difficult to find non-platinum NGK plugs.  David Buchner doesn't like platinums because he feels you should get in there and check things more often than every 100K miles, but even with such an attitude one might be forced to use platinum plugs and just regap and reinstall them!  Might wanna be careful about filing the gap, though; platinum isn't all that hard, a few passes with a file and the little dot might be gone!

Bosch Platinums were among the first platinum-tipped plugs to make a name for themselves --and it was a bad name.  Randy Wilson says "I've found that Bosch standard plugs do not perform quite as well as Champions or NGK, but are better than most common American plugs.  I have, however, never had any success with their platinum plugs.  If the engine is running well, they don't seem to make any improvement, and if the engine is not well, they foul easily and are not cleanable."  But don't let the bad reputation sour you on either platinum or Bosch plugs; Bosch has since introduced the "Platinum +4" plug, which has four ground electrodes (more edges!) but also seems to have corrected the problems the earlier Platinums had.

There is no appreciable disadvantage to using resistor plugs.  The resistance limits the current flow, which in turn reduces spark plug wear and radio interference.  Prior to the actual spark, there is no current flow so the resistance has no effect on the voltage available at the electrodes.

SPARK PLUG GAPS: The proper gap for the H.E. engine is 0.025" --you can confirm this by checking the decal on the underside of the hood.  Most plugs come out of the box with a 0.032"-0.035" gap.  The gaps must be checked prior to installation.  Oversize gaps can cause poor performance at high RPM, but worse they can contribute to rotor failure and resulting catalytic convertor meltdown in cars equipped with Marelli ignition -- see page 161.

Reports are that some dealers are installing spark plugs with 0.035" gap.  If your dealer is doing this, the least you should do is never darken his doors again.  Better yet, file a complaint with the EPA, since spark plug gaps are an "emission critical" specification (that's why it's on the decal under the hood) and it is illegal for them to be violating it.  If you happen to suffer a catalytic convertor meltdown as a result, please sue the dealer and help put him out of business.

STRIPPED SPARK PLUG HOLES: Since you have read this book, used anti-seize compound on the spark plug threads, and didn't overtighten, you will never strip spark plug threads.  However, the PO3 or the idiot you've been taking the car to for service may not be so careful and leave you with plugs that simply won't come out without bringing the threads with them.  Aaargh!

The official Jaguar fix involves recessing, drilling and tapping the holes for larger threads, installing an insert, and installing a small pin to prevent the insert from unscrewing.  Note that the inserts will be different for H.E. and pre-H.E. engines, since the pre-H.E. used washer seal plugs while the H.E. uses taper seal plugs.  Generic inserts may work fine, but regardless of insert used the head surface should be recessed prior to installation to ensure that the tip of the plug will be positioned at the same level as before.  If the surface is not recessed, the plug will seat in a slightly retracted position and result in a lower compression ratio on that cylinder as well as possible effects on the swirl pattern in the H.E.  Mike Morrin reports success using helicoils to repair the H.E. plug threads --something one wouldn't expect would work, since it would appear to require drilling out the hole far enough to destroy the taper seat. "If drilled carefully, about 30% of the taper seat is lost.  I think the remaining seat is still enough for a good seal."

SPARK PLUG INDEXING: Does "anal-retentive" have a hyphen? If you answered yes, you may be interested in knowing that "indexing" spark plugs may improve performance in the H.E. engine.  In the H.E. combustion chamber, the compression stroke squeezes the fuel/air mixture out of the area over the inlet valve and into the area over the exhaust valve, causing a swirl.  This fuel/air mixture is swirling when the spark occurs.  If the ground electrode on the spark plug happens to be positioned with its back side into the swirl, then the spark is partially hidden from the fuel/air flow, possibly hindering proper ignition.

To avoid this, mark the side of each spark plug with an indelible magic marker to indicate where the ground electrode is.  The position you want to avoid is with the back side of the ground electrode aimed toward the nearest end of the head; in other words, you don't want the electrode on the spark plugs in the front three cylinders on the forward side and you don't want the electrodes on the spark plugs on the back three cylinders on the aft side.  If any end up in these positions when installed, then exchange that plug with another.

Please do not use a lead pencil to mark the plugs.  Graphite conducts electricity, and will cause "tracking" down the side of the ceramic and short out the spark plug.  Your engine will run much worse than before you indexed the plugs.

SPARK PLUG WIRES: If your ignition wires need replacing, there's really no reason to buy the Lucas originals; several companies offer aftermarket sets to fit the Jaguar V12.  Or you can purchase two 6-cyl or 8-cyl ignition wire sets from any auto parts store and combine them into a set for the V12.  Here are some tips:

You can get anything from a roll of wire and a package of connectors all the way to completed, ready-to-install sets; I used a "semi-tailored" set --one end of each wire comes with the spark plug connector attached, but you cut the other end to length and attach the distributor cap connector yourself.  The wires on the V12 are shorter than most, and this permits the right length so you don't have lots of excess wire laying around.

Another feature to look for is the angle of the spark plug connector.  Some are straight, some are 90 degree, a few are 45 degree.  What the V12 needs is a slight bend; the ideal kit has connectors that are straight to begin with but can be bent to whatever angle is needed.  This allows providing different bends at different cylinders --working on these plugs, you need all the help you can get!

There is also the issue of bends at the distributor cap end of the wires.  Some wires have straight connectors so they come straight upward out of the cap, while others have 90º bends here so the wires come off the sides of the cap.  Either will work on the XJ-S, both are a pain to install and route.

3 "PO" is a car collector's term for "Previous Owner".  It is often used with a derogatory connotation.  Sometimes the abbreviation "DPO" is used.

There is also the choice between 7mm and 8mm wires.  Ideally, one would choose 8mm wires, since the Jaguar ignition system is really hot and it's all but impossible to route the wires away from other things.  Magnecor (see below) offers a 10mm set!

Most aftermarket kits seem to be bright colors.  Deal with it.

Jim Belkoff writes, "I found that Pep Boys can special order a custom set of 8mm silicone wires that are made in the US by Borg-Warner.  I paid the $45 in advance and picked them up a day later.  They are of high quality and include three wires with 90-degree plug boots (for the number one wires at the compressor and another location -your choice, I guess).  The kit even came with a tube of dielectric grease.

"For those of you who don't like the bright aftermarket colors, take heart -this set has tasteful light grey wires, black plug boots and dark grey distributor boots.

"The length was very close on most, and exactly spot on with some of them.  Even the ones that were a shade long weren't so huge that they flopped every which way.  I have had problems with aftermarket wires in the past (mostly semi-custom 7mm sets) and these are the closest in length and the highest quality I have used so far."

John Smith of Brisbane, Australia says, "I noticed that most parts shops have made up spark plug wires in a variety of lengths.  I bought a set, nice blue colour, that had 90 degree connectors for the distributor and straight connectors for the plug ends - the same as the original wires.

"I measured the various original wire lengths and these are: 1A 38cms (15 inches) 1B 43cms (17 inches) 2A 25 (10) 2B 35 (14) 3A 28 (11) 3B 17 (7) 4A 30 (12) 4B 25 (10) 5A 40 (16) 5B 38 (15) 6A 38 (15) 6B 46 (18) Coil 19 (8) These wires were 8mm and fitted perfectly."

Greg Benjock bought an 8mm Belden Wire set from NAPA and was not very happy with it. "The custom ordered kit came with wrong terminations (all were 180deg).  All 13 terminations on the distributor cap in fact must be 90 deg type.  And terminations and boots for plugs 1A, 6A, 1B, and 6B are best fitted with 90 degree units.  It looked very much like an inexperienced person put the job together."  Of course, maybe the cap connectors are a matter of opinion; this author's are all straight connectors and work just fine!

All that said, it should be noted that the original Lucas wires are usually not very expensive; the only valid reasons for using aftermarket wires are availability, a need for a dash of color, and a healthy contempt for all things Lucas.

SPARK PLUG WIRE THEORY: When the 12V power to the coil is cut off, the magnetic flux causes a spike in the voltage at the high tension lead.  When that voltage rises sufficiently to jump the gaps in that circuit (one between the rotor and cap in the distributor, another at the plug), current begins to flow.

Once a spark begins, the air is ionized at both gaps.  This drastically lowers the electrical resistance of the gaps themselves.  With 50,000 volts or so to work with, the current flow can rise dramatically.  If allowed to rise unrestrained, this has several detrimental effects.  First, the high current flow drains the energy stored in the coil quickly, so the spark doesn't last as long.  Second, the high current flow tends to erode the spark plug electrodes faster than necessary.  And third, the high current flow causes a considerable amount of radio interference due to EMI radiating away from the plug leads.  Besides all these negatives, there are absolutely no positives.  High current flow is not beneficial to the ignition process, only the voltage needed to start the spark is necessary.  Advertisements talk about getting "energy" to the plug gaps (energy is voltage x current x time), but that's usually a sign of a company trying to peddle snake oil; the only place in an ignition system to be concerned about energy is in building up the field within the coil (the energy the Lucas "Constant Energy Ignition" and the GM "High Energy Ignition" are referring to).

It's easy to limit the current flow once the spark occurs, though: Put a resistor in the circuit.  A resistor won't affect the onset of spark at all, because before the spark occurs there is no current and therefore the resistance is of no consequence.  But once the spark begins and current begins flowing, the resistor comes into play and limits the current flow.

There are several places to put resistors in this circuit.  Using "resistor" type spark plugs is common.  Also common is the use of spark plug wires with a carbon-impregnated core, which offers some amount of resistance per inch of lead.  Perhaps not so common, it is possible to purchase resistors that fit into the wire between the coil and the distributor.

Plug wires are all different lengths within the same car, so use of common plug wires will result in a different amount of resistance between one plug and another.  This doesn't matter, as long as there is some resistance.

Some people think spark plug wires with copper conductors are a good idea.  Clearly they fail to notice that such wires are generally the cheapest available --yet do not come on any cars as original equipment.  If used with non-resistor plugs, there will be no resistance in the circuit at all, and the plugs will be eroded quickly --if the coil doesn't burn up first.  Copper core plug wires should be avoided for all applications, except perhaps fitting a new lead to your timing light; the copper is easy to solder.

A more recent development is the spiral core plug wire.  The core of these wires has a very fine stainless steel wire coiled into what looks like a long, skinny spring.  Stainless steel isn't an excellent conductor as metals go, but it nevertheless would provide an essentially zero-resistance current path if it were straight; the current limiting factor here is evidently the coiling.  Magnecor (page 707) offers such wires but is mum about the theories on which they work, claiming that too many competitors want their information.  Judging from their descriptions, they appear they work like this: The spiral core behaves as a long inductance coil.  Before the spark occurs, there is no current flow, so the inductance is of no concern --same as the resistance in the standard setup.  Once the spark begins, the high inductance of the leads prevents the current flow from rising instantly but permits it to rise gradually instead --and the ignition coil runs out of energy before the current flow can rise to a dangerous level.

Magnecor claims several benefits to this design.  One claim is that they will outlast the standard wires, because stainless steel is more durable than the carbon-impregnated silicone core.  Another benefit is that these wires are more flexible, and several XJ-S owners have reported this is true and a blessing in the top of the V12.  Perhaps the flexibility is a large part of their longevity as well, since neither stainless steel or carbon-impregnated silicone should deteriorate before the insulation layers do on either type wire, but bending the carbon-impregnated silicone wire too tightly will damage it for sure.

Magnecor also claims reduced radio and electronics interference.  This is important because modern cars with EFI can get all screwed up if the spark plug wires emit enough EMI to cause spurious signals in pickup leads.  The spiral core wires have the theoretical benefit that the magnetic field generated is aligned with the lead rather than radiating away from it in all directions.  Franck Guilloteau says, "On their claims; the idle stumble that I had was reduced noticeably, but my stereo has developed an annoying noise....so much for RFI shielding!!"  Perhaps a good idea would be to use spiral-core wires in conjunction with resistor plugs, just to be sure.

CAP AND ROTOR RENOVATION: Most of us just buy new parts periodically, but Danny Rearden says, "High tension ignition components such as distributor caps and rotors are generally only faulty if they are cracked, or have carbon tracks on the surface.  Even both of these conditions are usually repairable if you are prepared to invest a few hours.  My dad specialized in repairing obsolete vintage and racing ignition systems and magnetos where parts were completely unobtainable.

"Clean the part, first with solvent cleaner, then with strong hot detergent solution and dry thoroughly.  Inspect very carefully, with a magnifying glass if your vision is not 20/20, looking for any surface marks which were not intended to be there.

"If there is no visible sign of high voltage tracking, go to polishing.  Otherwise use a hobby knife and scrape the surface until you get to totally clean material, even if this means making a hole in the component.

"Grooves and holes can filled with epoxy filler.  We always used Epiglass Low Density Filler, designed for boat repairs.

"Polish out any marks (both in the original part and any repair), using abrasive paste, such as perspex polish or cutting compound.  These surface marks, if not removed, will be future failure points.

"If the part has a dull, porous look to the surface, a light spray of a suitable clear paint may be in order, but don't overdo it.  If the repairs were to a visible part, then coloured paint can be used.

"In the 25 years my dad was doing these repairs, I can only recall 1 or 2 items failing again, out of several hundred, and these were subject to 'owner abuse'.

"The important things are: • remove any trace of previous tracking • polish or fill any holes, cracks or scratches which could accumulate dust and moisture • stop moisture getting into the ignition in the future"

KEEPING THE IGNITION SYSTEM COOL: Possibly the worst area for heat problems is within the "V" on top of the engine.  Early XJ-S's had so much trouble with cooking the ignition amp that Jaguar created a relocation kit to move it out of this area.  Cracked distributor caps have been a problem.  Seized centrifugal advance mechanisms are a problem.  The wiring harnesses within the V always seem brittle.  All of these are symptoms of excessive heat.

Maintaining a good airflow through the engine compartment does wonders for minimizing such heat-related problems on components.  However, airflow to the V is largely blocked --not by the A/C compressor so much as by the plate supporting the front of the compressor.  See page 505 for notes on correct installation of this plate.

One simple way to improve things would be to cut a big hole in this plate.  Be careful to leave enough metal to properly support the compressor, but this will still allow a substantial opening.  Since this area is directly behind the main fan, the hole should allow some airflow under the compressor and throughout the V area.

IGNITION SYSTEM TYPES: There have been four distinct types of ignition system fitted to the XJ-S.  The first two were Lucas systems, so you can't simply refer to the "Lucas ignition system" without causing confusion.

Up to 1982, the XJ-S was fitted with the same Lucas OPUS system that was used in the Series III E-Type.  This system uses a plastic disk with 12 ferrite inserts within the distributor to trigger the ignition.  From 1982 to mid-1989, the Lucas Constant Energy Ignition system (Lucas CEI for short) was used; this system uses a 12-pointed iron star wheel inside the distributor.  These two systems can be distiguished by the amplifier; the OPUS amp is a finned aluminum block that may be located between the banks, on top of the radiator top support, or any of several other places; the Constant Energy amp is a black, flat rectangular item bolted to the top of the left side intake manifold.

It must be clarified that the most obvious distinction within the Lucas distributors has nothing to do with ignition types.  Up until 1980, the XJ-S had a Bosch D-Jetronic EFI system that required a trigger board within the distributor and a rotor with a magnet in the counterweight.  From 1980 on, the Digital P EFI system was used, and it merely picked up the ignition pulses --no trigger board required.  So, the same four screw holes in the distributor housing were used to mount a clear plastic anti-flash shield, and a new rotor with no magnet was used.  A different cap was introduced to go with the new rotor.  The OPUS ignition system, with the plastic wheel, continued in use for two more years.

The XJR-S was fitted with a Zytek ignition system.

In mid-1989, the Lucas Constant Energy Ignition system in non-XJR-S cars was replaced with the Marelli, which is an all-electronic system --there are no mechanical or vacuum advance mechanisms, the timing is handled by an electronic control unit based on crank sensors.  The Marelli system still uses a distributor, but it only serves to allow two coils to fire twelve cylinders; it does not include any timing or triggering functions.  This distributor is very distinctive in that the cap has connections for two separate ignition coils, one at the center and one off-center, and has no vacuum advance

IGNITION SYSTEM REPLACEMENT: Replacing an ignition system isn't automatically an improvement; exactly what an ignition system replacement accomplishes depends on what you are replacing and the sophistication of the system you're installing.  The pros and cons of ignition system replacement are therefore covered within the discussions of each type of ignition system found on the Jaguar V12.

IGNITION SYSTEM DESIGN: An ignition coil requires a certain amount of time to build up enough energy to produce a spark.  The faster an engine is turning, the less time there is between sparks, so the output of an ignition coil starts to drop off.  It is also apparent that the more cylinders there are, the less time there is between sparks, and the output of the ignition coil drops off even faster.

Another lesson in physics is that the higher the compression, the more resistance there is for electricity to jump a spark gap, so higher voltage is required.

The Jaguar V12 H.E. has 12 cylinders, turns at 6500 RPM, and has 11.5:1 compression, making it one of the biggest challenges for an ignition system in production automobiles.  To cope with this, Jaguar has incorporated some sophisticated ignition technology.  Also, Jaguar uses a spark plug gap of only .025" to make it easier for the electricity to jump the gap.

ROTOR REPLACEMENT: Replacing the cap is straightforward enough, but getting the rotor off is likely to be somewhat difficult since it tends to jam.  All you can do is twist, rock, and pull, and hope you get lucky and don't break it.  Or just have a spare on hand.  On the Digital P cars, there's not enough room between the rotor and the anti-flash shield to get a good grip on it, so Ned Wesley says, "if you need to remove the rotor, the method I use is as follows: make two loops of string or wire about equal in length to the rotor.  Place one loop over the front of the rotor and the other over the back.  Bring the loops together so that pressure is applied equally to both sides of the rotor.  Give the loops a slight tug and the rotor will come off."

If the rotor carrier shaft seems to want to come upward with the rotor, the rotor carrier shaft retainer is broken.  You need to try to hold the rotor carrier shaft down while pulling on the rotor by inserting a screwdriver through an opening in the anti-flash shield or some such.  This is a good idea anyway to avoid breaking the rotor carrier shaft retainer.  Once the retainer lets loose, pulling upward on the rotor carrier shaft will stretch the centrifugal advance springs far below, and you will be in for a distributor recalibration.

IGNITION TIMING: The proper advance setting is indicated on a decal in the engine compartment.  If it differs from the book, believe the decal.  The Haynes manual on page 329 seems to indicate that a N America 1981-on Digital P car should be timed at 25 to 27° BTDC at 3000, which doesn't seem to have any basis in reality; the underhood decals always indicate 18° BTDC at 3000.

The next thing to confirm is that the woodruff keys that align the front pulley with the crankshaft are in good condition.  They are a known problem, and clearly if the pulley is allowed to reposition itself on the crank, use of the timing marks will be a disaster.  The woodruff key problem is discussed further on page 90.

Before you get under the car with the engine at 3000 RPM, you might want to note what the timing mark actually looks

On the Jaguar V12, the timing indicator itself is adjustable.  If there is any chance it has been tampered with (the oil pan and sandwich plate have been removed), then the position of the indicator must be calibrated before checking the timing.

The official method for setting this indicator is to do it when the right side (A bank) head is off.  A dial position indicator can be set up to determine when the 1A or 6A piston is at TDC.  If a position indicator that will fit through a spark plug hole is available, this same method can be used with the head in place by removing the spark plug from either cylinder 1A or 6A.  Once TDC is determined, loosen the two sandwich plate bolts that hold the timing indicator plate in place, and slide the plate on its slotted holes until 0° lines up with the mark on the pulley.

If you happen to have the 1A head off and are going through this setting procedure, Craig Sawyers has an idea to make the setting more accurate --or, conversely, to make it accurate enough using non-precision measuring tools: "The manual says to set piston 1A at TDC by using a dial guage, but even this is highly inaccurate.  If the dial guage has an accuracy of 1 thou, this corresponds to a setting accuracy of 2 degrees for a 70mm stroke engine.  If, with a screwdriver, you can guesstimate to say 0.5mm, the angle error will be nearly 10 degrees, all of which makes the slotted holes on the guage plate a bit of a joke.

"What I did when rebuilding my engine was this.  When piston 1A is at TDC firing stroke, piston 6A is at TDC exhaust, and pistons 2A through 5A are half way.  I forget which stroke they are on, but two of them are on their way up, and two are on their way down.  So I set the crank up so that all four of these pistons were exactly the same distance down from the top of the cylinder liners.  If this can be measured to 1 thou, the crank angle error will be 0.04 degrees.  The trick is to carry out the measurement at the point of maximum sensitivity (half way down a stroke) rather than the point of zero sensitivity (top of a stroke).

"I'm not sure how you could achieve this with the engine in and the heads on, but if you could fashion some feeler and probe the piston positions in 1A to 5A with an accuracy of 0.5 mm, you could set the position of the gauge to an accuracy of 0.8 degrees, which is more than adequate."

There is an alternate method to set the timing indicator that doesn't require the position indicator or removing the head.  All that is required is a device that will obstruct the motion of the piston near the top of its stroke.  Such a device can be made from an old spark plug by breaking the ceramic out of it and installing a bolt through the middle.  Ideally, the length of the bolt into the combustion chamber should be just enough for the piston to hit it only a few degrees from TDC.  If you make this device strong enough, it might also come in handy for removing the crankshaft pulley someday - see page 89 -- although for that purpose it would be better if it hit the piston farther away from TDC.

Turn the engine a ways past TDC, and then screw this obstructing device into the spark plug hole of either 1A or 6A cylinder.  Then turn the engine backwards until the piston hits the device and you can't go any farther.  Note the reading from the timing marks.  Then turn the engine forward through one complete revolution until the piston hits the device again, and note the reading of the timing marks.  The two readings should be exactly the same amount before and after TDC.  If they are different, loosen the sandwich plate bolts holding the indicator plate and move it an amount corresponding to one half the difference between the two readings.

Bob Egerton provides another method of finding the true TDC: "Get an old plug and beat out the ceramic centre.  Then braze in a length of copper or other fairly small bore tube (you could probably use a really good-fitting bit of polythene tube if you cannot get access to brazing kit) long enough to see from where you are when turning the engine over by hand with your extra long wrench.  Apply a small amount of soap or detergent solution to the end of the tube and slowly turn the motor forwards.  When the bubble is largest you are at TDC."  Note again that it may be easier to use the 6A plug hole than the 1A.  And, obviously, there are many possible variations on this idea, including threading a fitting into the spark plug base and the use of a balloon instead of soap.  Note that this method won't work if you're at the top of the exhaust stroke instead of the compression stroke, so if you seem to be having trouble you might want to give the crank one complete revolution and try again.

The ignition timing on the V12 is checked with the engine held at 3000 RPM.  Although a pain, this method insures the

When checking the ignition timing on the V12, the vacuum line to the distributor vacuum advance must be disconnected and plugged.  The vacuum advance capsule is at the bottom rear of the distributor, making it quite difficult to get to this line (the larger hoses connecting to the distributor cap itself are for the distributor ventilation system, and do not affect timing).  Do yourself a favor and cut the vacuum line somewhere convenient and reconnect it with a small piece of tubing.  From then on, all you have to do is disconnect it at the break and plug it when checking the timing.

Since the battery is in the trunk, connecting the power leads of the timing light requires ingenuity.  Of course, you could just use your jumper cables as an extension cord to connect your timing light to the battery, but perhaps that isn't necessary.  The ground lead can be connected anywhere on the car.  The positive lead must go to 12V, which exists at any solid brown wire.  There are two terminals on the firewall adjacent to the valve covers, and a terminal on the back of the alternator --all difficult to get at.  Peter Smith: "I connect my timing light to the 12V power source at the headlights fuse box."

David Littlefield says, "Another solution for your timing light problem was just "illuminated" on the MG list, since both MGA's and MGB's have inaccessible batteries.  One fellow attaches his timing light to his 10 amp battery charger.  Says he had done it for years with no ill affect.  Perhaps a better solution than dragging jumper cables and C clamps around."

Since disconnecting the plug wire from cylinder 1A is difficult, disconnect the wire from the distributor cap instead; make a small jumper from an old ignition wire to use to connect the timing light.  Or, just buy an inductive timing light.  If it's more convenient, you can also check the timing using the signal from cylinder 6A.

Since you must crawl under the front of the car while an assistant holds the engine at 3000 RPM to read the timing, it is suggested you put an extra long ignition lead on your timing light so you can route it around the fender rather than feeding it through the engine compartment.  Interference with moving parts at 3000 RPM would be memorable.  Cheap ignition wire with metal conductor works well for making a long timing light ignition lead, and is available by the foot.  Steve Chatman came up with another idea: "When checking the timing on the XJ12, I discovered that I was either going to extend the wire that clamps the plug wire or feed the light through the engine compartment.  I didn't really like those alternatives and instead simply ran the timing light over and down the outside right front wing.  From there, I could shine the light under the car, using my left hand.  With my right hand, I held a mirror to reflect the light vertically.  Worked fine and seemed very safe.  Of course, you should correct for the increased distance traveled by the light, but you knew that.  I was in a poorly lighted garage at night.  Better lighting could make this approach difficult or impossible to use."

Michel Carpentier provides another way of dealing with the inconvenient location of the timing marks: "Make a pointer out of sheet metal, which you fit under one of the water pump nuts (pointing from above towards the crank pulley).

Now position the crank so it is in firing position at 3000 RPM and put a dab of white paint opposite your pointer.  From now on you can check your timing from above."

Timing is adjusted using a long screwdriver to turn a small eccentric cam on the side of the distributor underneath the cruise control actuator.  There is a locknut on the adjuster, and this is a place where a crowfoot wrench will come in very handy.

The Jaguar V12 design eliminates most wear items that would normally cause ignition timing to vary, such as ignition points or sloppy camshaft drive systems.  The only remaining reason for the timing to change would be wear in the timing chain itself, and the Jaguar timing chain normally wears so slowly as to be insignificant.  If the timing in your car is way off, it is highly recommended you determine why rather than simply readjust it.  For example: If your centrifugal advance unit seizes in the idle position, then when the car is revved to 3000 RPM the timing will be retarded by 15° or more.  If you merely adjust the timing rather than correcting the problem, then the timing will be 15° too far advanced at idle!

If your eccentric cam timing adjustment won't go far enough, the distributor base must be repositioned.  Remove the distributor cap and insert a long allen wrench to loosen the three mounting bolts at the very bottom of the unit.  Rotate the entire distributor housing in the direction needed, then retighten.  Please remember that this much adjustment should never be necessary, and causes should be investigated.

HOLDING A HIGH RPM: Michael Minglin sends a tip: "Every time I went to check the timing, alternator, etc. the book says to set the rpm to such and such.  Reaching down to that auxilary air valve when the engine is hot is not my idea of fun.  What I did was to weld a nut on top of a short bolt.  Threading a longer bolt into this nut gave me a "T" with a long top and short leg.  The short bolt goes into the RHD throttle cable bracket (not used for anything on my '84 XJ-S), Then I use the long bolt to adjust the bell crank to the rpm I want.  To make it even easier, I forced a short piece of vacuum hose onto the long bolt, at the head.  This makes it easy to adjust the bolt with your fingers."  This plan will work on either LHD or RHD cars, simply using whichever cable bracket is unused.

CENTRIFUGAL AND VACUUM ADVANCE DATA: When checking distributor advance versus tables, make sure you are looking at the H.E. or pre-H.E. tables, as appropriate.  The H.E. system develops less advance in the centrifugal mechanism and more advance in the vacuum mechanism than the pre-H.E..

Page 05-1 of the ©1975 ROM and page 05-1 of the ©1982 Supplement list data for the centrifugal advance mechanisms for the pre-H.E. engine.  Both of these charts --as well as the centrifugal advance data on page 112 in the Haynes manual --begin with a listing that says "No advance below 900", which would seem to indicate that the entire chart is talking about the amount the advance changes from idle or static settings.  However, Roger Bywater points out that this is not the case; the other entries in these charts are actual crank degree readings based on the proper 10° BTDC baseline timing at 500 RPM.  For example, the chart in section 86.35.29/4 says that the distributor should advance 6.0-8.0 degrees at 1000 RPM; since these are distributor figures, that corresponds to 12.0-16.0 degrees at 2000 RPM at the crank, and when added to the 10 degrees of baseline advance we get the 22-26 degrees of advance listed in the charts.  The charts would have been clearer if they had simply said "10° below 900" instead of that "No advance below 900" stuff.

Regarding the charts for pre-H.E. advance, Mike Morrin says, "I suspect the service manual only has data for one of the distributor variants fitted (probably C44663).  The parts book shows that there were 5 different models of distributor fitted to pre-HE XJ-Ss, and I think that the only difference was the advance curves.

C.43735 Australia (this is the one with the peculiar vacuum retard system).
C.44663 California to car 2W54183
C.43735 California from car 2W54184
C.44663 CDN/USA to engine 8S5461 (ie the 4460th engine what year??)
All other countries to engine 8S5202
C.46173 CDN/USA from engine 8S5462
All other countries from engine 8S5203
DAC1609 California from engine 8S11161 and Australia from 8S11800
DAC1380 All other countries from 8S11262

"Note that my parts book does not cover the [pre-H.E.] Digital-P cars, so there are probably 2 more I have not counted.

"On reflection, I am surprised that there is not a clearly different distributor model (advance curve) for 8:1 and 9:1 compression engines.  As far as I can see, the distributor seems to change according to degree of emission control, not compression.  For example: Australia (9:1) and California (8:1) get the DAC1609, all other countries presumably including the UK (9:1) and the rest of the USA (8:1) get the DAC1380."

For our information, Morrin also provides part numbers for the distributors on the Series III E-Type: C33148 up to engine 7S4663 (emission control) or 7S4879 (no emission control) C37443 from above.

TIMING THE PRE-H.E.: The procedure is described in the ROM, section 86.35.29/7.  Basically, you disconnect the vacuum advance, lower the idle to make sure you're off the bottom of the centrifugal advance curve, and set the timing at 10º BTDC.  Much easier than the H.E. procedure!

Unfortunately, there's probably a very good reason the H.E. went to setting the timing at 3000 RPM instead of at idle.  Roger Bywater speaks of distributor build quality problems: "Back in the early 1980's we encountered V12 distributors which could over advance beyond spec by as much as 10 degrees at 6000 revs!"  What this means is that with the timing set correctly at idle, it may still be way off at highway speeds.  You're not likely to burn pistons at idle; it is far more important that the timing is correct at highway speeds.  The H.E. procedure minimizes the implications of the problem: Even if the distributor isn't quite within tolerances, the timing will be correct at 3000 and will merely be off at idle instead.  Much safer.

So, why don't we adapt the H.E. timing procedure to the pre-H.E.?  That way, those cars will enjoy proper timing at highway speeds as well.  Bywater: "What you are saying is absolutely correct and setting the timing at low speed before any advance takes effect is just about the worst way of doing it, but to be honest I've never really thought much about it before.  In all normal operating conditions the advance could in theory be 4 degrees out yet still be within spec.  Allowing for wear and tear, not to mention questionable original build quality, the error could easily be more than that."

All we need to do is figure out what the timing should be at 3000 (or some other point in the middle of the curve somewhere) and set it there.  The fact is, we could provide a spec for timing at 2000 or 4000; it wouldn't make much difference.  As long as it's set somewhere along the curve rather than at idle where you're not even on the curve, the advance will be much closer to correct where it's important than it would have been with the timing set at idle.  Bywater suggests that it'd be best to check the timing right at the peak torque, since this is where it will be most critical due to maximum cylinder pressures.  Ideally, the timing should be checked at several places to make sure none exceed an acceptable advance, but let's not get carried away.

To generate mid-curve timing specs, we can combine the idle timing specs with the distributor advance mechanism specs.  The specs in the ROM for checking the distributor advance mechanism provide a 4º tolerance range.  A 4º tolerance band may be good enough for checking to see if the distributor is working but it's not good enough for setting the timing; we need to know what point within these tolerances is the optimum timing point.  We could assume that the tolerance is ±2º and specify timing based on the midpoint, but Bywater suggests this might not be right. "With regard to the tolerance spread it is worth remembering that all engines must be safe with the worst possible condition which implies that the most advanced point is the one to work from rather than mid-range.  I am not sure how tangible the benefits would be but if it makes it possible to run safely with 2 or 3 degrees more advance then the overall performance, response and economy should be improved.  I am sure it is worth trying but maybe a period of trial is called for with a few willing volunteers who can report back before advocating it on a wider scale."

Bywater went on to provide timing specs for all pre-H.E.  V12's: Carburetted V12's 35° BTDC @ 4000 RPM
D Jetronic: 33° BTDC @ 4000 RPM
10:1 CR pre-H.E.  Digital P 24° BTDC @ 3000 RPM
Are these correct?  You just can't get a better authority than Roger Bywater; he was the guy leaning over a screaming V12 in an engine testing room at Jaguar dialing the advance up and down by hand to develop these advance specs.  But anyone can make a mistake.  So, after you set the timing using these guidelines the first time, check the timing at idle.  If it's only different by a couple of degrees --notably if it's more advanced by a couple of degrees --the spec was correct, get in the car and drive.  If it's off by ten degrees, check to see if your advance mechanisms are working properly.  If they're OK and the timing is really that far off, perhaps it'd be wise to rethink this whole idea before putting your foot in it.

Yes, the numbers for the pre-H.E.'s sound like a lot more advance than the H.E.; that's the nature of the beasts --the

Of course, one problem is that the scale on the timing plate doesn't go far enough.  So, set the crank at 20° BTDC and paint a new mark on the damper at 0°.  Then you can use this new mark to set the timing at the spec minus 20°.

UNDERSTANDING THE VACUUM ADVANCE SYSTEM: Between August 1998 and June 1999, Kelsey Publishing (page 723) published six issues of a magazine called XJS Bulletin.  Issues 1, 2, 3, 4, and 6 contain a series of articles called "Advancing by Vacuum" by Roger Bywater of AJ6 Engineering (page 713) that are arguably the best explanations of the vacuum advance systems used on the Jaguar V12 available.  For those interested in obtaining back issues, here is a brief synopsis of what each issue's article covered: Issue 1: General concepts of vacuum advance systems
Issue 2: 1976-80 V12 vacuum advance systems, including California and Australia
Issue 3: 1980-81 vacuum advance systems (pre-H.E.  Digital P cars), Emission A and B
Issue 4: Advance concerns related to the H.E. engine
Issue 6: H.E. vacuum advance systems, Emission A and B
After June 1999, XJS Bulletin was discontinued as a separate publication and a distinct section of Jaguar World magazine was provided instead, with pretty pictures of cars but little in the way of useful technical information.

VACUUM ROUTING DIAGRAMS --WHICH IS WHICH? Good question.  The following is an attempt to clarify the applications of diagrams that appear in several documents; here's hoping I don't make any errors here, since that would really compound the confusion!

In the ©1975 ROM, there are no vacuum routing diagrams.  For the vast majority of cars of the time, the routing for the vacuum advance was simple: Straight from the throttle edge tap on top of the right side butterfly housing to the distributor.  The air pump, where fitted, was apparently uncontrolled --on all the time.  In California and Australia, the system was more complicated, but not covered in the ROM.

The ©1982 Supplement has two descriptions, one labelled "Emission B" and the other labelled "Emission A & C".  These both apply to the H.E. only, but the Emission A & C version only applies through 1982; for 1983, a vacuum regulator was added to the system.

The H.E. supplement in the back of the ©1984 Ed 4 includes a desccription of a system labelled "Emission A & C Federal, Canadian & Japanese Specification 1983 on" which includes the vacuum regulator omitted in the ©1982 Supplement.

The Haynes manual (©1986) actually contains a fair assortment of vacuum routing diagrams, enough to put the ©1975 ROM and ©1982 Supplement to shame.  Of course, they're not labelled clearly enough, so here goes: Figures 13.29 and 13.30 apply to the 1980-81 pre-H.E. engine with Digital P injection.  Figure 13.31 applies to the pre-1983 North American H.E.  Figure 13.32 applies to the 1983-on North American H.E.  Figure 13.33 applies to the Emission B (non-North American) H.E.  Figure 13.33 is labelled that it applies to the Australian models, but it's not the same system that Bywater's XJS Bulletin # 2 article shows for the 1976-78 Australian cars; presumably it's for the later H.E. models.

Of course, there are several different vacuum schemes used in the XJ-S over the years and around the world, and even some vacuum retard schemes.  Many of these do hold vacuum; if the vacuum advance plumbing doesn't include a vacuum regulator, there's no need to put an orifice in the diaphragm.

Roger Bywater says, "Of course the high temperature situation also gives the vacuum capsule a hard time and they usually need replacing every couple of years or so but a lot of so-called mechanics seem to miss that one."

Note that a vacuum advance module that isn't leaking may still need replacement.  Val Danilov says, "My diaphragm was fried rock hard, I broke it trying to test the rod movement (CRRRACK!), so I think it wasn't leaking."

The earlier vacuum advance modules came with an adjustment screw on the top.  This screw permits adjustment of the limit of travel of the module --but was supposedly set at the factory to the correct travel.  This is not intended as a user-adjustable feature; the only reason to be messing with it is a suspicion that someone else has already messed with it.  Later replacement modules don't even have the screw.

VACUUM ADVANCE MODULE REPAIR: The following procedure for rebuilding a vacuum advance module is credited to John Napoli and Val Danilov.

Before removing the vacuum advance module from the engine, you might want to take note of the best position for the vacuum line connection when it is reassembled.  And after removing the vacuum advance module but prior to taking it apart, it is suggested that you first carefully measure the distance which the actuator rod extends out of the unit.  Also, push the rod back into the unit (fully retracted position) and measure that as well.

Raw material is a generic replacement vacuum advance from a Chevy V8 --dirt cheap at any auto parts store.  Take the Chevy unit apart by prying open the case; Napoli suggests it may be easier to open the case by grinding the case all around its periphery to weaken the metal, but be careful not to get it too hot and damage the diaphragm.  What you want to get ahold of is the diaphragm/rod assembly.

Open up the stock Jag vacuum advance by prying around the crimped-on case.  In this case, you'd like to reuse everything except the diaphragm/flat link assembly, so try to do as little damage as possible to the casing; if you'll read ahead to understand how you'll be reassembling it, you may decide to simply cut or grind the lip off the edge to avoid mangling the dome itself.  Even though the diaphragm/flat link won't be reused, keep it on hand for taking measurements.

Cut the rod from the Chevy diaphragm/rod assembly to the same length as the Jag original, then set it down on an anvil or something and pound a flat spot at the end with a hammer.  No problem -- it's a Chevy part, remember?

Reassemble the vacuum advance unit using the new diaphragm/shaft assembly and all the old Jag parts.  If the casing wasn't damaged when disassembled, you may be able to simply clamp the unit togeher and gently bend/hammer the dome shut.  This works but the cannister will become work-hardened so you will never be able to do this repair this way again.

If the edges were too mangled (or you cut them off), drill the body and dome for eight fasteners; Napoli suggests 3/4" long 3-48 fillister head screws and nuts, but notes that the exact sizes aren't critical.  Sandwich the body, diaphragm (poke a hole through for the screws with a needle), spring, and dome, and bolt it all together, being careful that the flattened section of the rod is aligned properly.  This method has the distinct advantage that it permits repeated repairs later --important, since the heat in the valley of the V12 will eventually bake the Chevy diaphragm as assuredly as it did the original.

Check that the unit responds to vacuum and pulls the shaft in.

Measure carefully the extended length of the rod, mark, and drill a hole in the flattened area the same size as the hole on

Reinstall on the distributor.  Be sure to check the timing; the timing procedure requires that the vacuum be disconnected, but the module still has an effect -- you might not have gotten that extended length as perfect as you thought you did.

Note that the original diaphragm may have had a tiny orifice built into it to provide a deliberate leak.  This will usually be evident as a tiny hole through the metal disks on either side of the rubber diaphragm itself.  The vacuum advance plumbing includes a vacuum regulator and such regulators don't work reliably when there is no flow, so the orifice is in there to provide a little flow.  It appears that this orifice may not be necessary, since some genuine Jaguar replacement vacuum advance modules reportedly don't have it.  If having an orifice proves to be necessary, it can be added anywhere in that branch of the vacuum advance plumbing; you might wanna make the hole in the dome rather than in the diaphragm itself.  It might make more hiss, but you can seal it later if you decide to with a small piece of aluminum tape. Or you may be able to fit a separate device with an orifice with a tee connection into the vacuum line.  You could, for example, take a piece of brass tubing, drill a tiny hole in the side, and connect it in the line to the vacuum advance module.

If, for some reason, you are unable to reuse other parts of the original Jaguar vacuum advance unit, you may be able to use the corresponding parts from the Chevy unit.  Note, however, that doing so may result in differences in the advance curve and/or limits.  Use of a different spring will change the advance rate.  Use of a different dome with a different depth, and therefore a different place where the spring seats, will also affect the advance rate.  And use of a different dome may also affect the retracted length, allowing the diaphragm to travel too far or preventing it from travelling far enough.

If the Chevy dome happens to include a limit adjusting screw, you may be able to adjust the full-retract position after assembly to make sure it is the same as the original was.  If there is no adjusting screw, you might actually be able to add one, being careful to seal it when done to avoid vacuum leaks.  If the Chevy dome is shorter and compresses the spring too much, you may want to add a spacer ring between the diaphragm and the dome to space the dome back.  If the Chevy dome is taller and compresses the spring less, you might want to insert something within the dome for the spring to sit on.

Napoli adds, "I have seen in this month's Jeg's catalog (see page 717) that Accel manufactures a replacement Chevy vacuum advance that is adjustable.  The ad copy states that the unit is adjustable for total advance and rate.  It comes with instructions.  The unit looks just like the generic replacement I used, so the same repair approach should work." This fancy aftermarket Chevy part is still cheaper than the stock Jaguar vacuum advance module by a long shot.

If you tore things apart and then read the suggestions to take measurements first, Napoli sends some reference measurements from a junk unit he had laying around: "For reference, the measurements were taken with 1/16" of the adjusting screw exposed.  That is, from the face of the adjusting nut to the top of the unmolested screw is 1/16".  Also, this is a stock '88 V12 advance (non-Marelli) from my donor engine and the unit does not operate (won't build vacuum).  With the unit relaxed, the length from the end of the housing to the center of the hole in the actuating rod is exactly 2 inches.  Full compression of the rod reduces the length by 5/16" (i.e., 5/16" maximum travel)."

VACUUM REGULATOR AND DUMP VALVE: A vacuum advance mechanism applies more advance as vacuum increases, which means there will be minimal advance at full throttle (to avoid knocking) and lots of advance at light throttle (where knocking isn't a problem, to provide optimum fuel efficiency).  This also means a lot of advance at idle, but this can be problematic.  The manifold vacuum at idle may vary as the RPM rises or falls a bit, and this will move the vacuum advance in a direction so as to accentuate those fluctuations.  The result can be an unstable idle, sometimes even stalling.

The time-honored fix for this is to use a "throttle edge tapping" for the vacuum source.  The vacuum line to the vacuum advance, rather than simply connecting to a port on the manifold, is connected to a port located near an outward-opening edge of the throttle butterfly.  Whenever the throttle is open, the edge of the butterfly itself is on the air filter

If you'd like your Jaguar V12 to operate this way, it's very simple.  Just throw away all the vacuum advance control devices and connect a single hose from one of the ports on top of the right hand butterfly housing directly to the vacuum advance module.  This will work fine, although the total lack of vacuum advance at idle will make it use more fuel and generate more waste heat when idling.  This shouldn't be a problem; the cooling system should be able to handle the additional heat, and the fuel economy reduction is small --especially if you don't sit around idling much.  It may affect emissions tests, but ironically it may help them; in general, retarding timing seems to make it easier to pass emissions tests.  Note that most of the 1976-80 V12 models (except California and Australia) apparently did operate their vacuum advance exactly this way, and some later models did as well except that they added controls to shut off vacuum when the engine was cold to help it heat up quicker.

With later models, Jaguar used a better idea here.  Rather than providing no vacuum advance at idle, they used a vacuum regulator to provide some vacuum advance at idle.  Because the regulator provides a fixed amount of vacuum regardless of how the manifold vacuum is fluctuating, the instability problem is avoided.  In such schemes, one hose to the regulator comes from the manifold itself to provide a vacuum source, while another hose connects to the throttle edge tapping to provide a "reference" to regulate to.  When the engine is at idle, the manifold vacuum is high but the signal from the butterfly housing shows no vacuum, and the regulator throttles the vacuum to the advance capsule down to a fixed amount above that reference.  When the engine is at part throttle, both the manifold vacuum and the signal from the butterfly housing show high vacuum, so the regulator does nothing; the advance capsule gets full manifold vacuum.  At wide open throttle, both the manifold and the throttle edge tapping see very little vacuum, so the advance capsule doesn't get much either.

This is a really good system, providing a goodly amount of advance at closed throttle so the engine idles efficiently.  It also results in less of a step coming off of idle; rather than the vacuum advance going from no advance to full advance all of a sudden, it merely goes from partial advance to full advance.  The effect is smoother throttle response.

There is one problem, however: A vacuum regulator is a throttling device, and therefore cannot provide a great deal of flow suddenly when needed.  The specific case of concern here is when the throttle is suddenly floored.  In a car with simple hoses connecting to the vacuum advance capsule, the sudden lack of manifold vacuum would result in a similar lack of vacuum advance just as quickly, and the engine could proceed at full throttle with the timing properly positioned for that condition.  But with this regulator in the line, a sudden opening of the throttle will require a second or two for the vacuum to bleed off the advance capsule through the regulator.  For that second or two, the engine will be running at full throttle with too much advance, and the engine will be knocking something fierce.

The solution is another device, the dump valve.  This is a vacuum-operated valve that merely opens the line to the vacuum advance capsule to atmosphere when there is no vacuum in the manifold.

There is one other minor detail, and that is the fact that a regulator generally works better with a little flow through it; it may have difficulty regulating vacuum in a deadheaded line.  So, the vacuum advance capsule may have a tiny internal bleed orifice, small enough that the vacuum system can still apply a vacuum but preventing it from holding a vacuum.

A little guidance on plumbing: The North American models use a vacuum regulator EAC5157, and it has three hose connections.  One connection is labelled "DIST", and this line is connected to the vacuum advance capsule; a tee in this line should lead to the dump valve EAC4069 and connect to the fitting farthest from the flat side.  Another connection is labelled "CARB"; this should be connected to the throttle edge tapping, which is a port on the top of the right side butterfly housing.  The third connection is labelled "DELAY", and this one should be connected to the intake manifold; it typically is connected through a whole series of valves and controls that provide less vacuum when the engine is cold.  Basically, the regulator and the dump valve are the only things in the vacuum advance control system that are operating when the engine is warmed up; everything else in the plumbing has to do with cold starting.

Note that other markets use a different vacuum regulator, but the idea is the same.

The connection on the dump valve nearest the flat side should be connected to the intake manifold; in some cars it appears to be connected to the bottom of the right side butterfly housing, but this fitting is a ways behind the butterfly and will see manifold vacuum in all but nearly wide open throttle, and at wide open throttle it should see nearly atmospheric pressure either way.

The various emission control diagrams available invariably show the controls for the air pump on the same diagram, primarily because some of those vacuum control devices used for cold starting also affect air pump operation.  Don't get confused; other than the fact that both systems are vacuum-controlled, they really have little to do with each other.  The descriptions above only apply to the vacuum advance system.

VACUUM REGULATOR CHECKING: Stephen Tyler says his vacuum regulator was bad; "At the top of the unit is a metal disc & in that disc is a small hole.  If you apply a vacuum to the input side of the unit, you cannot obtain a vacuum out if the tell tale hole is sucking in air.  The hole is for an indication if the internal diaphram is damaged.  I removed the metal top & found that the diaphram had a hole in it.  There are probably many units like this, considering the age of these cars."  This has grave implications for the fuel economy of a lot of cars out there.

15-MINUTE TIMER: The 15-minute timer is a feature of the "B Emission" H.E. cars, which means UK/Europe spec, 82-88 or so.  If the coolant temperature is below 38°C when the car is started, the timer is engaged.  This disables the vacuum advance at idle and runs the part-throttle vacuum advance through a delay valve for 15 minutes.  If the coolant temperature is above 45°C when the engine is started, the coolant temp switch is open and the timer is not engaged.  38°-45°C is the "dead band" of this switch --whether it's closed or open depends on whether the engine was cooling down or warming up when it entered this band.

15-MINUTE TIMER --LOCATION: Everybody wants to know what this thing looks like and where it is.  Craig Sawyers reports: "It is a black box with ventilation slots, 2"x1.5"x1.5".  It has a single fixing hole at one end, and an edge connector at the other.

"Location in UK cars is: . XJ12 --under the driver's side (rhs) underscuttle, up high.  It is more or less behind the speedo, and a fight to find and remove. . XJ-S -- under the passenger side (lhs) underscuttle, much lower and easy to get to."

Steve S says, "the US 45 sec one would be located to the right of the passenger side small fuse box under the scuttle.  Nothing is fitted in this space in the UK spec.  The UK 15 min job is to the left of the passenger side small fuse box but located on a different plate to the small fuse box set closer to the firewall (bulkhead); US spec cars have something to do with the seat belts located where the 15 min timer goes."

15-MINUTE TIMER --REPAIR: The timer itself is reportedly unreliable.  Tony Bryant: "My '85 NZ Spec (= RHD Euro) had this 15-minute timer in the LH side of the LH footwell.  Cheap and nasty piece of trash.  It's a pertronix unit, based on a CD4020 cmos 14bit counter, and a CD4069(?) hex inverter with one of the inputs floating(!).  Floating input pins on CMOS are just begging for a blown up chip.  I replaced it with the 74HC equivalent, and tied the unused input to ground - before I ditched the whole system."

15-MINUTE TIMER --DITCHING: The 15-minute timer apparently causes really bad fuel economy during those 15 minutes, especially aggravating for owners whose driving patterns happen to have them within those 15 minutes most of the time they are driving.  Craig Sawyers says, "Admittedly, the V12 is thirsty, but a certain amount of that is to do with

If you're sick of using so much fuel, disconnect the timer!  The car will run just fine with full vacuum advance when cold, it just won't warm up as quickly.  Since the timer energizes the 3-way solenoid valve, the 2-way solenoid valve, and the supplemental air valve (see page 304) and de-energizes them when the 15 minutes are up, you can merely disconnect the wires from the timer or the coolant temp switch and the car will never lack vacuum advance again.  The easiest way to disable it is to just pull one of the wires on the thermal switch on the rear end of the right side coolant manifold.  This is obviously easy enough you can try it and see if you like it.

Once you decide to make this change permanent, you can make things neater by removing all of those valves and plumbing up the vacuum advance system with the same routing that effectively existed after the 15 minutes had expired.  You can also trashcan the timer itself if you want, and replace the coolant sensor with a plug.

The 2-way solenoid valve and the 3-way solenoid valve are involved in killing the vacuum advance at idle during cold starts, but the purpose of the supplemental air valve is to boost the idle RPM to compensate for the lack of vacuum advance.  Disabling the cold start solenoid valves theoretically eliminates the need for this idle boost (the Auxiliary Air Valve is intended to provide idle boost for cold starting), but if you find the car idling too slowly when cold you might consider leaving the supplemental air valve connected and disconnecting the solenoid valves only.  In this regard, this system may serve as a patch for a weak or deteriorating AAV (see page 265).

Also note that, on later cars, the same supplemental air valve was used to boost the idle when the A/C compressor was engaged.  This is a really nice feature, and one might consider keeping the supplemental air valve in place for that purpose.  If your car is an earlier model lacking this A/C idle boost, you might want to wire it up!  See page 304.

15-MINUTE TIMER -- MODIFICATION: The only problem with ditching the 15-minute timer is how long the engine takes to warm up.  The vacuum advance makes the engine run efficiently, so it doesn't generate as much waste heat.  Killing the vacuum makes the engine inefficient so it generates a lot of waste heat and warms up quickly.  Richard Mansell says, "I disconnected mine recently and found that it seemed to take a lot longer to warm up.  It is now reconnected.  I may disconnect it again for the summer (if we actually get one this year)."  Awwww, little Ricky's gotta have his heat!

Craig Sawyers suggests a compromise: "If you unplug the timer and link together the grey and pink/white wires, this connects the 45°C switch directly to the valves.  So the valves will operate until the engine reaches 45°C and then switch off.  I did this with my brother in law's XJS when his module blew."  This is a really neat fix, since it means the car will get to 45°C in a hurry and then get good fuel economy from then on.

Of course, 45°C isn't all that hot, so the heater will still not be working as well as some might like.  So, there are other possible fixes.  The most obvious would be to replace the coolant temp switch with something with a higher cut-out temp, like 70°C.  It must be stressed that the switch really needs to cut out before the thermostat temp is reached; otherwise, there's a chance that the idle vacuum advance will remain disabled indefinitely!

Another idea would be to leave the timer in place but shorten that 15 minutes to something more reasonable.  Sawyers describes how to modify the OEM timer: "The counter is a 14-bit binary counter.  The most significant bit is used to trigger the valves.  So you can select a delay of 7.5 minutes by reconnecting diode D1 internally to pin 2 instead of pin 3 on the MC14020 timer chip.  Or if you connect to pin 1, you get 3.75 minutes.

Daniel Lethiais elaborates: "You will find inside this unit a small electronic plate with integrated circuits.  Near the HEF4020B is the diode D1.  If you want a delay around 4 minute you just have to cut the connexion beetween pin3 to D1 (with a cutter, knife...) and connect pin 1 to diode D1.  It is very easy to do.

"Yesterday I have tried a connexion between Diode D1 and pin 15.  I have checked my unit outside the car with a separate power supply and an oscilloscope.  The timer is now around 2,5 mn."

Sawyers: "You can get intermediate times by changing the oscillator frequency.  This is set by the values of either C3, or R6/R7.  The timing is in inverse proportion to the parallel combination of R6 and R7, and to C3.  So halving the value of either will double the time, etc.  For instance, changing R6 from 820k to 470k (leaving other components unchanged) will reduce the time from 15 minutes to 9 minutes."

Of course, you could just try to find a replacement timer instead of getting into the schematics.

When considering shortening or eliminating the vacuum advance disable, one must consider its original intention.  Unfortunately, there's no telling what that was.  It looks like an emissions feature and in fact is part of the scheme called "B Emissions", but the UK and Europe supposedly had no emissions requirements at all when these cars were built.  It could be argued that its purpose is to get the engine warm quickly to minimize wear, but one would have to remember why a cold engine has high wear: there's too much fuel running through it.  Since this system clearly increases the amount of fuel running through it, it's questionable whether it does any good in that regard.  All in all, the entire purpose of this system may be to make the heater work as quickly as possible.  That's an expensive heater, especially since this thing provides 15 minutes of lousy fuel economy even in warm weather.

VACUUM ADVANCE MODULE -- PRE-H.E.: Mike O'Neill noticed that the vacuum advance module from an MGB will fit the pre-H.E. distributor.  However, John Nuttall found that the MGB advance unit --as well as some units for Triumphs --look similar and will fit, but provide differing amounts of advance at different vacuum levels.  So, if your engine is largely stock and you want to keep it that way, you probably should seek a Jaguar advance unit.  On the other hand, if your engine is not stock and you need to provide nonstandard amounts of vacuum advance, this provides some places to look.  Also, these units might provide materials for rebuilding your old vacuum advance module in much the same way Napoli used a Chevy part in the procedure described above.

VACUUM RETARD: According to the article "Advancing by Vacuum" by Roger Bywater in XJS Bulletin Issue #1, a vacuum retard module is typically connected to a throttle edge tapping on the inward-opening side of the butterfly.  Hence, vacuum is applied at idle, but as the throttle is opened the edge of the butterfly passes over the port so it sees ambient air pressure.  The system therefore provides a few degrees of retard at idle, but does nothing at other throttle positions.  This helps make the engine idle better, since some engines have trouble igniting the charge at high vacuum; according to Bywater, the carburetted V12's fit into this category.  By waiting until the piston is closer to TDC, the charge is more concentrated and compressed when the spark occurs.  Obviously, such a retard scheme would help emissions at idle by ensuring good ignition.

Ian Macfarlane, regarding his 1985 XJ-S: "In Australia the distributor has a retard connection on the vacuum module which is supposed to operate for about 15 min. after starting via a solenoid valve.  But the wire leading to the solenoid valve had been cut (as had the wire to the supplemental air valve).  Thus, even though the distributor timing was correct with the vacuum tubes disconnected, the engine ran at about 6 deg retarded under normal conditions.

"Although this would not exactly apply to other emission systems it is another option for those with an overheating problem - if the vacuum system was not working properly it is feasible that overheating could occur due to retardation."

Having the vacuum retard system activated when it shouldn't be is a valid concern, but this author isn't convinced that cutting the wire to the solenoid valve will do it.  According to the schematics of this system, the solenoid valve controlling the vacuum to the retard side of the vacuum capsule is a "normally closed" type, meaning that cutting the wires should render it always closed -- no vacuum retard.

Mark Jackson, who owns an '87 Australian model, says, "I have been told (and have the proof on the car) that the local dealers got so fed up with people complaining about poor performance on start-up, that they just bypassed the electronic valve mounted under the RHS manifold by routing the vacuum pipes past it."

Folks, this is probably the single most important item in this book.  Centrifugal advance seizure may be the cause behind most of the problems the Jaguar V12 has --overheating, dropped valve seats, etc. --and the reason behind most owner dissatisfaction, low resale value, Chevy engine swaps, you name it.  Is there any way I can convince you, the XJ-S owner, to take action now?  If it'll make you feel better, give me a call, I'll tell you in person: Overhaul the distributor NOW.

Sad to say, reports are that this failure mode --notorious as it is --is not widely known among Jaguar dealers and mechanics.  Despite the frequency of charging customers $10K for a new engine, it has never occurred to many of these shops that the engine failures were preventable.  Some people have reported that their Jaguar dealer overhauled or replaced several unrelated components before finally figuring out that the centrifugal advance was seized.  Others never figured it out.  Perhaps their fancy diagnostic computers don't blink "centrifugal advance seized".  Perhaps they just like collecting those fees for new engines.  Whatever, keep in mind that just because you have had your car "checked out" by the dealer doesn't mean you don't have the problem.  It's not even a certainty that the advance is OK if you specifically asked them to check it; some of these mechanics don't even know how to check it.  For those who have mechanical abilities, it is highly recommended that you check your centrifugal advance yourself, or better yet simply go ahead and overhaul it.  If you aren't the type to get your hands dirty, it probably would be money well spent to have an independent shop confirm the first shop's conclusions.

The usual indications of a seized advance mechanism are an XJ-S that lacks power at higher RPM and a nasty tendency to overheat.  In some cases, when the throttle is backed off suddenly there is a brief power surge before decelerating.  If your car doesn't have the performance at higher RPM that it should, check the advance mechanism immediately; a distributor seizure is easily fixed, but warped blocks, dropped valve seats and burned pistons are much more expensive and are the inevitable outcome of continued operation.

To confirm for yourself that your advance unit is seized, remove the distributor cap.  Attempt to turn the rotor counterclockwise.  If operating properly, you can easily turn it about 11° (H.E.) or about 13° (pre-H.E.) against a spring.  Note that this thing should feel really loose and rattly, and when you twist it and let go it should snap back with a metallic clink; if at all sticky or gummy-feeling when turned, time to overhaul.  The forces that move this thing are balanced against each other, so a very slight difference is supposed to make it move; while the springs may seem mighty strong when you're fiddling with them, even a slight amount of drag or stickiness is enough to keep it from moving as it should.  It may be movable by hand but not as far as it should or not as freely as it should.  Unfortunately, in a book such as this it is difficult to convey adequately how to tell that an advance is gummy until a person has felt a properly-operating advance for themselves.  This might be an excellent topic for a monthly Jaguar club meeting --to have someone who knows what the advance should feel like check every V12 that shows up.  Of course, if totally seized, the problem is obvious; you cannot move it at all except for backlash in the drivetrain.

Another method of checking for a seized distributor is to compare the timing (with the vacuum line to the distributor disconnected and plugged) at 2000 RPM with the timing at idle (under 900 RPM).  The two readings should differ by at least 12° (H.E.) or at least 22° (non-H.E.).  If they are the same or very close, the centrifugal advance is seized.  If the advance at 2000 RPM is more than a couple of degrees different when you come up to that RPM from idle than it is if you come down to that RPM from 4000, then the advance is sticky; overhaul it.

OK, SO IT'S SEIZED --NOW WHAT? To prevent/correct a seized centrifugal advance mechanism, it's necessary to overhaul the distributor, clean out all of the original lubricant, clean up the parts, and reassemble with a reliable lubricant.  Roger Bywater says, "Most of them probably run for years without the cap being lifted so by the time anyone does get round to it the spindle is likely to be running dry and getting built up with debris.  Adding lube at that stage may well loosen the debris and aggravate the situation so really it needs complete stripping to ensure that it will not jam at some future time."  Bywater, having worked for Jaguar, can be expected to blame the seizures on poor maintenance --and perhaps he's correct.  I personally suspect the original lubricant used at assembly was lousy, based on what the stuff looked like when I got my distributor apart!  It really doesn't matter what the cause; either way, the distributor has to come apart.

Of course, you don't have time for overhauling.  You will probably want to try the easy fix: Remove the distributor cap and rotor, and put some penetrating oil down the center and see if you can work it loose.  If you are successful, it is recommended that you check its operation regularly --or better yet, just go ahead and overhaul it when you get the chance.  The results of operation with a seized centrifugal advance are simply too costly to ignore.

This is one place where getting a new part will probably not help.  There is little wear in the distributor, and an overhauled and properly lubricated used part can be expected to last the life of the car.  But a new distributor may have the same problem as the original distributor did.  It is recommended that even a brand new in-the-box distributor be overhauled prior to installation (to get that lousy lubricant outta there).

The good news: The reported incidence of centrifugal advances seizing after they have been overhauled is nil.  This may be because the original grease is the problem, and once it's removed the problem goes away.  It may simply be because once the overhaul has been done the owner understands what's going on and lubricates it regularly.  Whatever, once the distributor has been overhauled, there is apparently no reason to expect to ever have to do it again.

DISTRIBUTOR REMOVAL: If the centrifugal advance is seized, or if you wish to prevent seizure in the future, the distributor should be removed and disassembled.  It's not difficult, but it will help to read the following sections thoroughly before tackling the job.

Note: If you prefer, it is possible to rebuild the centrifugal advance mechanism with the distributor in place.  It's easier to take it out and do it on the bench rather than leaning over the fender, though.

Before removal, care must be taken to ensure the distributor can be reinstalled with the gears meshed correctly so the rotor faces the same direction as before.  If the crankshaft is not to be disturbed, this is very simple: Note the position of the rotor prior to removal, so you can be sure it is in the same position when reinstalled.  It's a gear mesh and one tooth off would be obvious, so just note the position well enough you can make sure you are on the same tooth when reassembled.

Note: If you have the older Lucas OPUS ignition system, you are advised to position the engine at TDC on cylinder 1A, which is where the timing marks on the crank pulley line up and the rotor is pointing at the front left headlight.  If the rotor is pointing at the right side door, you need to turn the engine around one full turn.  The reason that this is important is that the OPUS has a wheel within the distributor that has three slotted holes that line up with the distributor mounting bolts in this position.  Even if you can get it off without moving to TDC on 1A (by busting up the plastic wheel, for example) you're still gonna be in a pickle putting the rebuilt distributor back on without tearing it back apart or turning the crank while the distributor is out.

If you turn the crankshaft while the distributor is out, you face additional problems.  The distributor turns once every

To get the setting right, cylinder 1A must be on the compression stroke when the distributor is installed pointing to 1A on the cap.  If you know in advance you may be turning the engine, it is easy enough to avoid problems.  While the distributor cap is off and the rotor is pointing at 1A and the crankshaft is at 10° BTDC, remove the oil filler cap.  Reach beyond the front edge of the chain and mark the camshaft gear itself (the camshaft gear turns at the same rate as the distributor).  You can use a dab of paint, or stake it, or whatever will give you a clear indication.

You might also want to mark the position of the base of the distributor, since it mounts on slotted holes.  Ideally, the base should be mounted so the correct timing is near the center of the range of the eccentric adjuster, but to begin with it will be easier to put it back where it came from.  Peter Smith: "I find that using typist's white out to paint across components can be helpful.  It can be applied over slightly greasy surfaces and if precise alignment is necessary I can draw on it with a biro."

You can insert an allen wrench through the openings in the distributor and undo three screws and remove the distributor as a unit.  However, for the purposes of doing the marking mentioned above, it may be preferable to proceed with the disassembly described below with the distributor still on the engine until you've removed enough parts to be able to mark the bottom of the housing on the inside.

DISTRIBUTOR DISASSEMBLY: Remove the rotor arm; see page 126.

Remove the EFI trigger board or anti-flash shield (whichever).  The biggest problem with removing the anti-flash shield will be dropping the tiny screws and washers, but the trigger board causes more trouble.  It is mounted with four tiny plastic screws, and Jan Wikström reports that the screws get stuck to the metal; "On my own experience of three distributors, you can expect to get two out intact.  If you're very careful."  He also reports that he has used metal screws in a pinch with no apparent problems.  When installing the plastic screws, maybe it would be a good idea to use anti-seize compound, even though it looks silly on tiny plastic screws.

Richard Dowling dealt with the trigger board screws differently: "I retapped the holes to M4 (about 2 times stronger) and fitted bigger nylon screws."

Next, remove whatever is used to trigger the ignition; on 1982-89 cars, you need to remove a C-clip, then slide off a wavy washer, then pry out a U-shaped pin.  Finally, you need to slide off the iron star-shaped inductor rotor, being careful not to damage it or deform the points.  Even more importantly, don't just pull upward on a sticky star rotor, because you may stretch the springs in the centrifugal advance mechanism underneath.  Here's a method that seems to work: Lift gently on the star rotor a little bit and insert the claw of a claw hammer under the star rotor.  Rest the head of the hammer on the edge of the distributor housing, but do not pry.  While holding the star rotor in its slightly elevated position with the claw hammer, tap downward on the center of the rotor carrier shaft with a plastic-surfaced hammer.  Once the end of the rotor carrier shaft is flush with the surface of the star rotor, if it still won't simply slide off you can position a small socket with an OD slightly smaller than the rotor carrier shaft on top and continue tapping.

On the pre-1982 cars, a plastic disk with 12 ferrite inserts was used; according to Jan Wikström, "Its hub is about an inch long (estimated; I've never seen an intact one) and all beneath the disk.  It's a tight fit on the spindle and in its keyway.  And the disk, which is all you have to apply force to, is about 3/16 in thick near the hub.  On an old car like mine, the only way to get the disk out would be by breaking it up."

Fortunately, John Nuttall found a better way: "I discovered a technique for removing the circular plastic timing rotor which, according to Jan W in your book, often breaks under extraction.  The idea is to undo the three screws which hold the movable part of the distributor body to the base.  This can be done with the rotor in place.  These screws have springs on them to allow the body to rotate when the vernier is turned.  It is then possible to push upwards on the rotor with the body with the force being applied uniformly very close to the central shaft of the rotor -much better than pulling at the edge."

Unfortunately, Wikström counters: "It's better than fingers, although it still bears on the thin part of the disk outside the

Whichever distributor you have, you must remove the three screws with springs and lift off the movable portion of the base to gain access to the centrifugal mechanism below.  You could leave the pickup assembly in place, but on the 198289 it's in the way for getting to one of the screws with springs; since it's only two Pozidriv screws to remove the pickup assembly, that's the easy solution.  Of course, it's a good idea to inspect the vacuum advance mechanism as well as the pickup module while you're there.

Note how the centrifugal weights and springs are installed.  Being careful not to stretch them, disconnect the springs from the pivot posts for the centrifugal weights; Carlos Artal says, "Use a piece of strong, thin string (such as fishing line, etc. --I used dental floss) to take away the springs without damaging them or overextending them.  It works for mounting them too.  Just get one extreme, and pull slightly outwards and up."  You don't have to disconnect the springs from the posts on the rotor carrier base plate if you don't want to; you can just let them dangle.  Yes, the two springs are different, but it doesn't matter which one goes on which weight.

Remove the felt from the top of the rotor carrier (if there is any) and observe the retainer underneath.  This is a possible cause of trouble.  The early cars had a screw there, but on later cars there's a nylon clip instead.  The nylon clip is usually brittle and cracked, sometimes allowing the rotor carrier to rise on the distributor shaft and possibly causing interference damage down in the advance mechanism.  If you don't have a screw, the procedure for removing the rotor carrier is to yank, which usually results in breaking the nylon clip.

Normally the rotor carrier shaft should slide off the distributor shaft at this point, but if it is seized some Liquid Wrench or other measures may be called for.  Please try not to bend the distributor shaft --it is remarkably thin within the rotor carrier.  And don't grab the rotor carrier shaft with pliers or vice grips --the metal isn't that hard, you'll booger up the surface, and then it will be difficult to get the plastic wheel or star wheel back on.  Once apart, clean all the crud off the bearing surfaces.  Decide for yourself whether Bywater or I am right, whether it seized due to lack of lubrication (dry) or a lousy lubricant (gummed or varnished).

LUCAS "OPUS" MARK 2 IGNITION --DESCRIPTION: This is a brief description of how the pre-1982 ignition system works, based on the more detailed description in SAE paper 720163 on the development of the engine.

The pickup within the distributor consists of an E-shaped transformer with one input coil and two output coils.  The input coil is on the center leg of the E and is fed a 600KHz input signal from the amplifier.  The two output coils are on the outer legs of the E and are wired in series so that their outputs cancel --provided the two sides of the transformer are equal.

When one of the ferrite inserts built into the plastic rotor in the distributor aligns itself with one side of this transformer, it magnetically completes the circle on one side of the E.  Since the output coil on this side is now more closely coupled with the input coil than the other output coil, its output is greater --and the two no longer cancel each other.  A transistor in the amp is toggled by the resultant output signal, triggering a spark.

TROUBLESHOOTING: Jan Wikström sends this procedure for testing the OPUS ignition system: 1. Pull the lead from coil to distributor out of the distributor and jam it under a fuel pipe so there's a gap of about 1 mm (.04in) between the brass and the nearest engine part.
2. Crank the engine.  Do you get fat, blue sparks in the gap? Then the ignition is OK and you need to troubleshoot the injection system.  If not, continue:
3. Pull the spade connector off the coil terminal marked (+).  Turn the ignition on, then test the power with a spare light bulb between the connector and engine bare metal (this is better than a voltmeter, because it will reveal a poor contact with insufficient current carrying capacity).  Is the lamp bright?  Then continue; if there's no voltage, check the ignition switch and all its wiring including the ballast resistor.
4. Touch the connector quickly several times to the terminal.  Do you get a spark now?  Then the pickup coil in the distributor or its wiring, or (less likely) the amplifier, may be faulty.  If there's no spark, turn the ignition off and continue:
5. Get a test lead with alligator clips.  Clip one end to bare metal on the engine, pull the tubular connector off the (-) terminal of the coil and clip the other end to that terminal.
6. Repeat test 4.  If you get a spark now, the amplifier or its wiring is faulty.  If you get no spark, the coil is dead."

Jaguar makes a kit to relocate this amplifier to the plate across the top of the radiator so it stays cooler.  The kit includes a new amplifier and a new pickup for inside the distributor, and costs over $300.

It is possible Jaguar includes the amplifier and pickup simply because the only time their mechanics get a call to relocate the unit is after the original unit has fried.  On the other hand, perhaps the reason the unit was originally located in such a sorry place was because the wiring needed to be as short as possible, and the replacement amp and pickup have updated circuitry necessary for the longer wires.  According to Jan Wikström, the plugs and wires used on the replacement kit are different than the original, indicating you're supposed to replace the amp and pickup together.  However, he simply spliced wires and used his old pickup, and it worked fine.  He notes, however, that the wire color codes changed; it is necessary to open the amp and verify where the wires go to ensure they are connected correctly.

Clearly, crosstalk between the 600 KHz input signal and the output wire back to the amp would be detrimental to operation, and such crosstalk could be easily caused by the wires merely being located too close to each other for too great a distance.  Also, the output wire picking up any other signals --such as interference from the ignition wires - would be ungood.

Reportedly, some owners have relocated their original amps by simply lengthening the wires, and have been successful.  Others have not been successful.  At least one owner reports that the official Jaguar relocation kit caused the wires to pick up so much interference from the spark plug wires that the car wouldn't run, and he couldn't get the system to work until he shortened the wires back to the length of the original.

Russell recommends that ribbon wire with five or more conductors be used to relocate the amp.  By using every other conductor, the unused conductors in between provide adequate spacing between the active conductors to prevent crosstalk and interference.

Russell also recommends relocating the amp to the firewall rather than the top of the radiator.  In his car, the amp was affected by water and crud thrown up from cars in front of him.  Fortunately, he was able to repair it by resoldering some connections inside.

Perhaps another solution is to leave the amp in the valley and attempt to keep it cool there.  Fashioning a heat shield from sheet aluminum for underneath it will help.  Also, see the suggestion on page 125 about cutting a hole in the A/C compressor mounting plate.

British Auto/USA (see page 692) claims to have "reinvented" this amp using modern electronics.  The amp they offer, part number JLM368/R, looks exactly like the original and is supposedly durable enough that it may be located within the V; apparently some concours judges will subtract points if the amp isn't in its original location.

Of course, if you don't care about concours points, the best relocation idea is to relocate that OPUS system to a dumpster and replace it with an aftermarket ignition system.  See page 150.

If you have a 1982-89 car with a black plastic amplifier mounted on top of the left intake manifold, you have the Lucas CEI ignition rather than the Lucas OPUS.  There is no need to worry about relocating the amp.

IGNITION AMPLIFIER --REPAIR: Referring to the OPUS finned aluminum ignition amp, Jan Wikström says: "As for the amplifier itself, there is precious little pottery involved.  I opened up the suspect one (four small hex-head screws underneath) and found that while there's a silicon blob at the cable entry and a silicon slurp for a seal around the lid, the inside is empty and there is complete access to PC board and power transistor.  No need to $pend up on a new one if it goes belly up; this unit is eminently repairable."

Phil Stuart says, "There are four transistors in the early Lucas Opus ignition amplifier, one is a big one in a TO-3 casing for amplifying and 3 smaller ones for switching.  I burnt up the smaller switching transistor.  It's fixed and running now; the transistor we finally put in was a ECG128, NPN type.  Cost $2.95 CND.  The original one was Germanium NPN;

PICKUP WIRING: Wikström warns: "One problem I've had on both cars is an intermittent break in one of the three ignition trigger wires coming out the front of the distributor, right in the moulded grommet.  This seems inherent to the design, as the big, heavy three-pin connector flops around on loose wires and should cause metal fatigue as the wire bends back and forth.  I have replaced the wires (solder joints inside the distributor) and applied spade connectors instead of the three-pin job."

COIL LOCATION: If you can't find it, you're in trouble.  If you have the Haynes manual, the caption on the photograph labelled 10.2 on page 118 says it's "at the rear of the throttle pedestal" but it lies, it's at the front.

BALLAST RESISTOR PACK: The ballast resistor pack is shown as item 164 on the Jaguar wiring schematics.  On earlier schematics, it is illustrated as a simple rectangular box with six wires connected to it, but on later schematics they show three resistors inside.  It would probably have been better if they hadn't done that, because the simplistic 3-resistor illustration is incorrect and misleading.

Section 86.35.29/3 of the ©1975 ROM is titled "Ballast resistor check", and provides a simplistic continuity test.  It provides a more detailed illustration of the ballast resistor pack --also incorrect.  Section 86.35.29/4, "Coil voltage check", Step #4 includes values for the resistors in the ballast resistor pack, but they're numbered "Resistor 1" through "Resistor 3" and "Connection 4" and "Connection 5" with no clue whatsoever what connections they're talking about.  In section 86.35.29/10, in the latter half of Step #4, inexplicably buried in the midst of a coil/amplifier check procedure, the resistance values are repeated and the illustration is provided again --this time with Connection 4 and 5 labelled, but you're still left to guess at the resistor numbers.  The Haynes manual doesn't have any illustrations of the ballast resistor pack innards, just photos of the outside.  Is it any wonder that this book has grown to over 730 pages?  Anyhow, the easiest thing to do is to simply provide a new illustration, so please refer to the figure here instead of any of the illustrations in the manuals.

It should also be noted that some of the diagrams in the Haynes book have differing color codes on the wires; for example, Fig. 4.1 shows a UW wire where the XJ-S has a W/U, and a WU wire where the XJ-S has a W/SU.

Mike Morrin explains the tach connection: The power from the center left terminal through the 7.6-9.2O resistor to the upper right terminal on the ballast pack diagram (which connects to the W/U wire) "...is the drive current for the output switching transistor.  So, the tachometer gets its drive direct from the amplifier, not from the coil circuit."

"According to the parts books I have here, there was an early version, used 1971-72 which apparently did not have the tachometer connection, and the later version, which was used 1972-80." Morrin provides part numbers:
E-type C35883 until engine 7S7559
E-type C37759 from engine 7S7560

Figure 10 -OPUS Ballast Resistor Pack
XJ-S C37759 all
"C37759 is apparently Lucas 47229."
There is some discrepancy about the resistor serving the tach.  The XJ-S ROM reports it as 100O, but the SIII E-Type
TACHO SW START
AMPLIFIER
100 OHM
7.6-9.2 OHM
0.72-0.80 OHM
0.9-1.0 OHM

"Connection 5 -Tachometer terminal and straight through internal connection (incorporated in later units marked 47227)."

That 47227 part is apparently a typo in the E-Type manual; it should say 47229, which is what is actually marked on the ballast packs.

"On reflection, I think the early unit probably had the straight through connection and the later unit the 100 ohm resistor. There does not appear to be any change in the vehicle wiring coinciding with the change in ballast."

Note that 86.35.33 describes how to remove the resistor pack.  Evidently rocket science, don't tackle this job unless you are a very experienced mechanic.  At least Jaguar didn't put any serious errors in this procedure.

If your ballast resistor pack has failed, it shouldn't be terribly difficult to put together a collection of generic resistors to replace it.  After some discussion about a ballast resistor pack in which that 7.6-9.2O resistor had blown, Gary Johnson suggested "Radio Shack (Tandy).  They sell a 10 or 20 watt 8 ohm non-inductive resistor that sounds perfect for this application."  For the main resistor serving the coil, there are a wide variety of ballast resistors available at any parts store since just about all cars used them up until the 80's; it should be easy to find one that will work.

TACHOMETER PROBLEMS: Both John Holmes and Jan Wikström had tachometers that didn't work, and both arrived at the same corrective action: they disconnected the tach signal wire from the ballast pack and connected it to the -terminal on the coil, where it's connected on every other car ever made.  Holmes: "I just know how this is wired in other cars and did the simplest circuit possible to see if the tach worked.  When it did, why change it again?"

LUCAS OPUS IGNITION SYSTEM UPGRADE: As mentioned above, British Auto/USA (see page 692) offers a replacement amplifier for the OPUS ignition system that supposedly is more reliable than the original.  Supposedly.  Steve S reports, "I had of those BA updated amps bought from SNG in UK fitted to my V12 E.  The original OPUS amp did 20 years and 90k miles in the V and was still working when I took it out after hearing that it was unreliable.  I thought I was going to "decrease chance of a breakdown".  The SNG updated unit lasted about 3 years and 7K miles before failing in the classic opus failure mode -dies suddenly when hot.  Fortunately because this was a USA inspired device it came with a lifetime guarantee (as against a UK guarantee of guaranteed until it breaks)."

LUCAS OPUS IGNITION SYSTEM REPLACEMENT: If you have any trouble with the original Lucas OPUS ignition system, it is recommended that you simply replace the entire system with a modern aftermarket ignition system.  There are several available, and most of them can be purchased in entirety for less than replacing any defective part of the OPUS system.  And the owners who have opted for such upgrades have universally reported better performance from their cars.  Note: this recommendation does not carry over to cars with the Lucas CEI ignition; that is an excellent system and there is rarely any cause to ditch it.

Lucas designed the plastic wheel within the OPUS distributor with three slotted holes that enable the mechanic to insert an Allen wrench, loosen the three screws at the very bottom, and remove the distributor as a unit.  If you install some sort of aftermarket system, you might want to consider whether or not you will be able to get that Allen wrench past or through whatever is used to trigger the pickup.  Of course, it might not be your highest priority; you could always simply disassemble the distributor in place far enough to remove the wheel to gain access to the screws.

None of the common aftermarket systems will replace the EFI trigger board.  The EFI is a separate system that just happens to have its trigger board inside the distributor.  After you've removed all the OPUS junk and installed an optical wheel and pickup or whatever, you will need to put that trigger board right back in.  If your trigger board is toast and you've priced a new one, that is definitely bad news.  However, Jaguar's upgrade trigger board --which uses Hall effect transistors instead of the reed switches used in the original --seems to be reliable, so usually you only need to buy it

LUCAS OPUS IGNITION SYSTEM REPLACEMENT --ALLISON/CRANE XR700: Allison was acquired by Crane.  By whichever name, their XR700 is a popular replacement for the OPUS.  Derek Hibbs reports: "My ign amp died as a result of convected heat last year.  A reliable replacement unit was not available so the workshop installed a Crane Cams unit.  The unit itself is located on the RHS air cleaner and it came with replacement pieces for the distributor because it uses an optical pickup."

Andrew Holley says, "I removed the Lucas (Prince of Darkness) system and fitted the Crane XR700-0300 system, took all of about 2 hrs.  The car starts first time every time, and seems to run a bit more crisply.  It has improved fuel consumption slightly, but the major benifit is that it now starts instantly, no matter the conditions."

Steve Douglass says, "After fighting problems (mostly heat related) with the original OPUS system on my car, I replaced it with a Crane Fireball system that I got from Terry's for $124.00.  The kit came with everything I needed to do the job along with good instructions.  The system has an optical pickup that goes in the distributor and an amplifier that mounts on the firewall.  Pretty much like what it replaces.  I was able to install the thing in about 2 hrs and the car fired right up."

Paul Clarkson had a hell of a time with pickup mounting brackets inside the distributor and ended up having to fab and modify stuff, but he's apparently the only one; everyone else claims the system is a simple bolt-in.  Emin Morali replied: "Try to assemble the optical pick-up unit without using any bracket.  You use only two screws and it will fit perfectly in the place of original pick-up unit."

There is some confusion about which coil to use with the XR700.  Clarkson reported, "I invested in a Crane Cams XR700 amp and PS91 coil.  Here is a reply I received from the tech. dept. at Crane Cams in reply to my query about lengthening the pick-up leads (so I could locate it in a cool place):

"The XR700 is to be used with our PS20 or PS40 coil with the supplied ballast resistor that comes with them.  The PS91 coil has such a low resistance that two ballast resistors are needed to keep the XR700 from overheating.  This also kills off some of the spark power to the point of being worse than it would be if the proper coils were used.  If you wish to keep the killer coil you will need to use the XR3000 amp that is designed to use the higher output coil.  Please fix this before proceeding.  You hook it up just as you see in the instructions and everything should be fine.  You can also add to the length of the wires on the amp if they are of the same gauge and type of wire.  Hope this helps.  Tech support, Steve 4208..."

Again, Emin Morali responds: "When I fit Crane XR700, the car was hesitating to exceed 5000-5200 rpm with misfire at the engine.  So I changed the PS20 with PS91 keeping the same OEM ballast resistor pack of my car, but adding a serial resistor of 1.4 ohm to protect XR700.  No result, the same problem continued.  This time I throw the 1.4 ohm resistor away and used PS91 with OEM resistor pack.  My problem finished.  However the possibility of damaging the amplifier pushed me to replace PS91 with a Bosch blue coil (also low primary resistance) by adding a serial resistor and no problem at all."

Clarkson says the XR700/PS91 setup was recommended by (now defunct) GT Jaguar.  Paul Squire: "Quoting their website: "Gran Turismo worked very closely with Crane on these systems.  The tech questions they receive about their systems for Jaguars are referred to us because they know we have more knowledge in this area than even they do.""

Terry's Jaguar (page 696) offers the Crane system, or you can also get it directly from Crane.

The Crane system comes with a disk with suitable slotted holes for access to the screws in the bottom of the distributor.

LUCAS OPUS IGNITION SYSTEM REPLACEMENT --ALLISON/CRANE XR3000: Emin Morali says, "I had called a Crane dealer in Florida to ask him if I can use XR3000 with PS91.  After he discussed the subject with a Crane tech., he told me that it won't work.  I did not understand the reason why, however I had seen before in Crane web site

LUCAS CEI IGNITION --DESCRIPTION: The triggering mechanism for the Lucas CEI ignition system consists of a "star wheel", a wheel with 12 points on it, mounted on the distributor shaft with a "pickup" adjacent to it.  There is a magnet and a coil in the pickup.  A magnetic field is established in which the flux passes from one pole of the magnet through the coil, through the star wheel, and back to the opposite pole of the magnet.  When a point on the star wheel aligns with the core of the coil, this magnetic flux has a nearly continuous path of iron and is therefore at its strongest. When the point is far away from the core of the coil, the magnetic flux is at its weakest because there is so much air space in its path.

Since a voltage is generated in a coil with a changing magnetic flux through its core, a voltage is generated in the pickup by the increasing strength of the magnetic flux as a point on the star wheel approaches the tip of the core.  A voltage is likewise generated by the decreasing strength of the magnetic flux as a point on the star wheel moves away from the tip of the core -- but this voltage will be opposite in polarity from the first one.  The pickup will therefore produce a voltage that suddenly reverses polarity as a point on the star wheel passes the tip of the core.  The electronics within the amplifier module sense this voltage reversal to break the ground connection to the coil, triggering a spark.

But that's not all this system does.  It waits a varying amount of time before reestablishing the ground connection to begin charging the coil for the next spark, getting the charging started ASAP at high RPM but waiting a bit longer to get started under idle conditions so as to minimize coil heating.  It also monitors the current flow to the coil to make sure that it does not exceed a set limit, which might happen at low RPM when there is more than adequate time to build up a charge in the coil.  If the current rises too much, the amp begins to cut back on the voltage applied, holding the current constant and preventing the coil from overheating.

Prior to systems with such features, coils had to be designed to handle high-current conditions at low RPM and had ballast resistors to limit the current.  With the current control features, coils can be designed more compact and without the oil inside that was needed to keep them cool.  They could also be designed with very low impedance in the primary coil without worrying about current overload problems, allowing much faster charging on 12 volts.  Unfortunately, such coils weren't available when the Lucas CEI was introduced, so two conventional coils were wired together to accomplish the task.  Later, after suitable coils became commonplace, Jaguar would replace the dual-coil setup with a single modern coil whenever a coil needed service.

During most operation, the ignition amp is merely switching the current on and off and is dissipating very little heat.  However, at low RPM when it's having to cut back the voltage to limit the current in the coil, it's having to dissipate that extra power.  It gets hot under such conditions.  The amplifier is bolted to the aluminum intake manifold to try to dissipate some of this heat to the manifold and to the cool air passing within.

Roger Bywater: "The 12.5:1 compression of the H.E. was too much for OPUS to fire and in any case it was getting to be a bit primitive by that time as it had no means of current control other than via the ballast resistor."

TROUBLESHOOTING: Randy Wilson sends this procedure: "With the engine cranking, check for:
Power to the ballast source
Power to the coil + post
Ground switching on coil - post (if so, you should have spark)
Ground to amplifier case
"If everything passes except the ground switching on the coil, then it's in the amplifier or its wiring.  "A scope put on the pickup leads should give a modified sine wave pattern typical of magnetic induction sensor.  At crank speed, I think it's around 1.5V peak-to-peak.  No scope pattern is a bad pickup."

"I've never personally seen the pickup go bad, but have run into cracked wires in the pickup harness.  Quite often jiggling the harness will cause the problem to "correct" itself; sometimes for many years.  Everything working fine after doing the scope check is bad pickup wires."

If your car runs well when cold but gets uppity when hot and you suspect the ignition amp, you might try pouring some water on it to cool it off.  If the car runs well again, you have definitely narrowed the search for a cause down to something in that little black box!

IGNITION AMPLIFIER --REPAIR: The Lucas Constant Energy ignition amplifier is a black plastic box mounted on top of the left intake manifold.  This unit is clearly labeled "Lucas" and "Made in UK".  The mail-order catalogs call for a part number DAB106, and want serious $$$ for it.

If you unbolt this unit from the intake manifold, turn it over, remove four tiny screws and remove the cover, you will see four components inside.  The predominant component is a GM High Energy Ignition (HEI) module.  This unit is so common that you can find it on a bubble card hanging from a hook in any department store with an automotive section --for around $20.  Usually this amplifier can be repaired by simply replacing the GM HEI module for considerably less than the cost of replacing the whole unit.

Simple?  Maybe not.  Dave Johnson says, "The amp on my '84 died on me several years ago.  I replaced the module with the equivalent GM module and it lasted 3 months.  I replaced the zener and the capacitor with equivalents.  I again replaced the module.  This one lasted 1 month.  I gave them one more chance (lifetime warranty) and it's worked for 4 years now.  The moral of the story?  I believe the modules available from discounters are marginal and you have to keep trying to get a good one.  Since I didn't even consider buying a new amp from the dealer I can't rate their failure rate but a GM mechanic friend of mine kept after me that the modules I was getting were junk.  He was right and I now have a working one.  No more intermittent problems.  Try another one."

Tom Drakos concurs: "After buying 3 different control modules all made by Wells, DR100, I got 3 different types of results, all of which were terrible, to the point of undrivable.  I knew the original was made by GM, so I searched the internet looking for a similar application.  I ended up with a control module made by AC Delco, part # D1906, even has the GM stamp on top like the original.  Price was a little more, $41.00 from Discount Auto, but well worth it.  The car runs like new, smooth as silk at all engine speeds and idle.

"My advice to anyone experiencing a problem with a control module would be not to use WELLS D100...these things are crap!!"

Terry Pegler apparently disagrees about the part number.  "The replacement modules that I am using are AC Delco # 10482820 from the GM Dealer.  It is made in singapore..."  Doug Dwyer adds that there were earlier part numbers for the module, starting with 1875990 in early years, but the 10482820 replaced them.

Just because you spend the big bucks on the Delco doesn't guarantee you'll get a good unit.  Owners have reported bad ones of those, too.  Just keep trying.

Shafi Keisler claims that the standard GM HEI module is rated for 6 amps but the one in the Jaguar V12 is a special unit rated at 8 amps.  Nobody has been able to confirm that claim, though.  The standard HEI works great, once you get a good one.

Reportedly some modules come with a packet of heat sink compound.  Tom Bennett says, "I just bought a GM module from AC Delco, came with a pack of silicone heat transfer goo.  I am familiar with the usual white heat sink paste; this stuff is very different, it's labeled silicone grease and contains 90% polysiloxane 10% silica."  Hmmm.  Might not be heat transfer goo; might just be goo.  Dunno why they'd provide a packet of goo, though.

Heat sink compound might not be a bad idea; applying it between the module and the ign amp housing might help the module run cooler.  Even if the module you get doesn't come with the stuff, you can get it at electronics shops.  The best way to apply heat sink compound is with a single bead, so that when you bring the parts together you squeeze the compound so it spreads out.  This way you avoid air pockets in it.

John Robison says, "Advance Auto has an electronic gizmo they can plug the GM unit into.  It simulates loading at both

Joe Bialy adds: "There are 5 connections on the GM HEI module.  The fifth terminal is the ground for the module which is actually one of the mounting holes on the module itself.  All of the coil current passes through this connection.  If the ground terminal on the module itself is not secure, ignition problems will occur."  Peter Havas adds, "The HEI's on GM engines sit atop the distributor cap, and the replacements must have a second ground wire or they burn up.  I don't know why, but having had many GM trucks which suffered spontaneous HEI failure, it was revealed by the local GM garage that you must run a straight ground as well as the little flat strip to the HEI to keep it from burning up.  This applies only to replacement units, and I have no idea why.  It works though."  There don't seem to be similar problems in the Jaguar V12 application --perhaps since the module is securely bolted to the aluminum intake manifold rather than to the distributor cap -- but it couldn't hurt to make sure the ground is solid while you're in there replacing a module.

Becky Amason says, "Anyone having repeat failures of your ignition modules should check the wires from the stator in the distributor for damaged insulation.  This is a known problem with GM HEI ignitions.  The wires flex as the vacuum advance moves back and forth, eventually breaking the insulation and shorting out the ignition module."

The other components inside the amp housing are a 1 microfarad condenser, a couple of resistors buried in a white rubber blob, and a zener diode mounted in the top of the case so the upper surface is actually visible from outside.  The condenser may actually be a common source of trouble; there are at least two reports of it shorting out when warm, so the engine runs OK when cold but has trouble when warm.  Since the condenser is connected to 12V, it shorting out causes it to get even hotter.  Pouring cold water over the amp fixes the problem for a few seconds.

The condenser is apparently only a noise reducer, being connected to the +12V side of the coil.  As such, just about any condenser would probably work.  If you're looking for a replacement condenser, you might consider the one intended for use with the GM HEI ignition system.  Auto parts stores sell a part labelled a "capacitor", but it's more than that.  This part is a little harness that has a 2-terminal connector on one end that plugs onto the HEI module, a 3-terminal connector at the other end that plugs into the GM distributor, and a capacitor attached to the 2-terminal connector.  One such part is made by Standard, part number RC-4.  Joe Bialy says, "More than likely, the cap in the connector will work as well as the Lucas cap if it is wired identically.  Noise suppression caps are not the most critical components in a system.  Typically, -20/+80% tolerance items.  I'd even bet an old "points" type would work just as well too."  Peyton Gill says, "I replaced the condenser (capacitor) in the ignition amp about a year back.  I used a condenser from a Chevy inline six distributor.  As memory serves, it required removal of the mounting bracket which was soldered to the condenser body.  It is a little longer but the diameter was about the same."

About the resistors, Walter Petermann says, "The white piece of rubber has 2 resistors in it.  One is 10k, the other 6.8k.  They are connected together at one end to terminal C of the GM module.  This same terminal goes to the coil minus and the large diode.  The other end of the resistors go to tach and fuel ECU (white/gray wires)".  The 10K resistor connects to the tach and the 6.8K connects to the EFI ECU.  On the ignition amp, both wires are the same color but the tach wire has a male terminal and the ECU wire has a female terminal; the wires they connect to are clearly distinguishable, since the ECU lead is a shielded cable and the tach wire is a plain W/S/U wire.  Craig Sawyers points out that the 6.8K resistor is actually shown on the fuel injection system wiring diagrams.  You can easily test the resistors without even unbolting the amp from the manifold; just disconnect the W/B wire from the ignition coil and the leads to the ECU and tach and measure from the W/B wire to each.  If the resistor feeding the tach fails the only symptom would be a nonfunctional tach, but a failure of the resistor feeding the ECU will stop the car with conviction.

The trick to testing the zener diode is in recognizing that it only exists to protect the amp against overvoltage, which normally occurs only when the system is operated with a spark plug wire disconnected.  Under normal conditions, it does nothing.  So, to find out if it is causing trouble, merely disconnect it.  If nothing changes, the diode is probably not the problem.  If the problems go away, you can consider finding a replacement zener diode or simply leave it disconnected; if you choose the latter option, you might want to be careful not to operate the ignition with any spark plug wires disconnected from then on.

FIDDLING WITH THE GM HEI IGNITION MODULE: This author found a warning inside a Lucas CEI ignition amp that read: CONTAINS BERYLLIA DO NOT OPEN Judging from the fact that this label was attached to the surface of the GM HEI module itself, the beryllia referred to is probably inside that module; there is nothing else within the Lucas ignition amplifier that appears to be this type of substance.

Beryllia is the oxide of Beryllium, and is used in a type of ceramic used to mount or encase electronic parts.  This ceramic conducts heat very well, helping keep the part cool, while being an electrical insulator --an unusual combination.  Unfortunately, beryllium is really as dangerous as indicated.  If you are inside the box repairing your amp, just remove and replace components.  Don't go sawing open the GM module, the dust created can kill you.

Mike Morrin adds, "There is actually very little of it used in anything built in the last 20 years except high power transmitters and some specialised power modules.  I am not sure about the GM ignition module, but if there is any, it is likely to be a pad under the power device about 2mm square and .5mm thick.  Beryllium Oxide is very expensive, so the semiconductor manufacturers avoid it where possible, the safety aspects not withstanding."

MORE TECHNICAL INFO ON THE GM HEI: Motorola once offered a publication MC3334/D which provided "analog IC device data" on a chip they made, MC3334 (and a couple of variations) which was described as a "High Energy Ignition Circuit" and was apparently used within the GM HEI module.  This document was very informative, not only on the circuit itself but on the entire ignition system it's used in.  Unfortunately, such info is apparently NLA; perhaps Motorola no longer makes that chip, leaving it to the aftermarket businesses.

ELECTRONIC IGNITION PICKUP: The electronic pickup used in the Lucas CEI distributor involves a magnet that is mounted with two screws.  Be careful tightening these screws; the ceramic magnet is much more brittle than metal items, and can easily crack.  If already cracked (notably around one of the screw holes), do not be concerned, it will not affect operation.  However, be sure not to leave any chips in there that could come loose and move around within the distributor.  It is better to discard small bits of the magnet that have broken away.

The pickup itself is apparently quite reliable, but there are a couple of indications that it may develop intermittent problems.  Don Lawson of Northeastern Classics had a customer with a car that would run fine and then suddenly quit, and after a considerable amount of frustration they finally simply replaced the distributor in entirety --and never had the problem again.  The original distributor was sent to this author for analysis, but nothing could be found wrong with it.  The pickup was monitored while immersed in water being brought to a boil, and it showed no problems.  It's possible the problem was elsewhere in the V and it was accidentally corrected while changing distributors.

Martin Walker had similar problems.  "Mine would run fine if I kept moving, but let it idle for 30 minutes, or run it in slow traffic for a long time in hot weather and it would suddenly die.  It would then not start for about 2 hours, and would then fire up OK and run well again.  This cost me much time, money and aggravation, as it eventually did this some distance from home.  The AA trailered it to the nearest Jag main dealer, who spent lots of my money in man-hours trying -and failing -to find the problem.  I paid to have it trailered back to my garage, and replaced the ignition amp before turning to the pickup.  I took it out and mounted it on a soldering iron -and at a consistent temperature (80-odd degrees, I recall) it would simply go open-circuit."

Keith Morris concurs: "I believe that the epoxy in the pickup heats up and breaks a close tolerance gap.  I have experienced this problem on an MGB and a Jaguar.  A simple replacement of the part solved the problem."

If you have decided that the pickup is a problem, don't replace the entire distributor; the pickup itself is available at most auto parts stores, made by several different aftermarket brands.  It's not cheap --over a hundred bucks --but it's cheaper than a new distributor.

Considering how many different cars use the same GM HEI ignition amp, it may be possible to find a cheap pickup that fits some other car and make it fit the Jag distributor.  The ones that fit Chevy V8's of the same era look totally different, but there are other pickups in the catalogs that do look fairly similar.

PICKUP GAP ADJUSTMENT: David Littlefield says, "The Haynes manual calls for readjusting the gap between the magnetic pickup and the iron star wheel with a plastic or non-ferrous feeler gauge.  Believe it or not, these are readily available.  I found some at Pep Boys hanging on a card beside other feeler gauges, I think they were made of brass."  Note: brass corrodes easily, and polishing removes a little metal so your feeler gauges would get progressively less accurate.  It is recommended that you spray a little WD-40 or something similar on each blade before tossing it back in the tool box, or take some other measures to prevent corrosion.

"Also, the Haynes manual says to turn the crank until one of the points on the star is next to the pickup so you can check the gap.  Unnecessary!!  Just remove the U-shaped thingy holding the star wheel in place and it will turn on the rotor carrier so you can get a point of the star in the proper position."

CONNECTORS: Mark Whitnell reports, "For the last several months the only way I could get it started was to use starting fluid.  I checked out the spark since that was an area recommended by Kirby.  The spark was very small and I suspect that the small spark could not ignite the gas but could ignite the ether (lower vapor pressure).

"I checked the distributor pick-up coil for the proper resistance according to Haynes (2.2K to 4.8K).  I checked at the connector attaching to the ig amp first...very high megohms.  Then I pulled the connector apart at the distributor.  Checked the continuity of the wiring to the ig amp...checked ok.  Then measured the resistance at the connector to the distributor...high resistance.  Looking at the two prong connector...visually it looked fine.  I went ahead an cut off the connector and measured resistance of the two wires to the distributor pick-up.  Measured resistance... 3000 ohms within the range described in Haynes.  Replaced the connector.  Voilà, starting problem solved.. good spark, etc."

COILS: The Lucas CEI system uses two conventional ignition coils wired in parallel.  The high-tension lead of the secondary coil is sealed off, and only the lead from the main coil is connected to the distributor.  Between firings, energy is built up in both coils.  When the 12V supply is broken ("the points open" in the lingo of the pre-electronic age), the energy stored in the secondary coil cannot escape through the high tension lead because it is sealed off, so the energy comes back through the 12V leads instead.  The primary coil then not only has to release the energy it has stored itself, but also the energy coming back from the secondary coil.  These two energies add to produce a powerful output at the high tension lead on the primary coil.

The secondary coil, located in front of the radiator, is not a spare or a backup; it is designed into the system for producing a good spark.  If the secondary coil goes bad or gets disconnected, the performance will suffer; typically, the engine will top out at around 4500 RPM and won't go any faster.  The secondary coil is not special, however, and can be replaced with a conventional coil provided the high tension connection is covered so that it cannot arc to ground.

Since mid-1989, XJ-S's have gone to a Marelli ignition system that also uses two coils.  However, the Marelli coils are not wired together; each one fires only six cylinders.

According to Alan Jenks, "Jaguar now recommends replacing both coils with a single "solid" (not oil filled) coil (#DAC 6093) that fits in place of the main coil.  The aux coil and wiring is removed." Roger Bywater says, "The best coil to use on Lucas HE V12s is DAC 6093 (Ducelier coil - 0.62 ohms primary); only one needed and works well in place of earlier twin coil set up.  If you can find another coil with primary winding resistance of 0.5 -0.6 ohms maybe it is worth a try.  If the resistance is any more than that it will not be able to build up enough coil energy to fire a spark at the higher end of the rev range when the coil "on time" is very short (about 1.4 milliseconds at 6000 revs).  It might also struggle around the peak torque point.  Although the V12 constant energy ignition module is fairly tolerant (it runs OK with the blanked second coil removed -albeit with a loss of spark energy) I have encountered some that behave very oddly if the coil is not the correct load match.  The DAC 6093 might be a bit expensive but it does the job..."

He adds that the original parallel coil arrangement was "conceived when coils of sufficiently low resistance were not available."  That's no longer true; it's not too difficult to find coils with a 0.6 ohm primary impedance today.

MARELLI IGNITION: In this age of electronic wizardry, many modern cars have done away with the mechanical centrifugal and vacuum advance mechanisms and do the whole job with microprocessors.  In some cars, the distributor is done away with altogether, and separate ignition coils are used instead.

Since Jaguar incorporated the Marelli ignition system in 1989, this is essentially the type of system used.  There is no centrifugal or vacuum advance mechanism; the timing is all done electronically.  However, rather than using lots of separate coils, the distributor was kept, using two coils and directing the spark mechanically.  This distributor is clearly lacking many of the internal parts of the earlier models, since it no longer handles the timing functions.  The rotor is actually two rotors in one, and the cap is two six-cylinder caps in one, so each coil is operated as though it is running a six-cylinder engine.  The computer that handles the timing is located near the passenger's feet, and has a vacuum line to it.

The V12 can be accurately described as two six-cylinder engines; each bank has the same firing order and the same natural balance as an inline six-cylinder engine (note: conversely, a V8 is not two four-cylinder inline engines).  Hence, the V12 actually runs smoothly on six cylinders, and drivers who have not read this section may make the fatal mistake of trying to press on to the next exit or the next gas station.  According to LaRue Boyce, symptoms to look for include: "Loss of power, more gas smell but no noise, just the no power feeling.  Oh, the loss of vacuum also causes the transmission not to want to shift.  You will know when it happens, there is no power, just enough to get you to 45mph on flat ground."  Julian Mullaney says, "When my car started running on 6 it was very noticeable.  I thought that the tranny was slipping at first because I had to give it so much throttle to get it moving."  Note that, with the typical failure mode described below, this happens all at once; there is no intermittent operation where it runs well most of the time and drops to low power on occasion.  Once a bank shuts off, it's gone for good.

Running a non-cat V12 with no spark on one bank fills the inop side of the exhaust system with fuel -- a disaster looking for a place to happen.  Since the XJ-S exhaust system loops up and over the rear suspension, it should be able to hold several gallons of fuel before it starts pouring out the tailpipe!  Since there is no spark in that bank at all, the owner might just get away with it --but he'd better hope his ignition system doesn't mysteriously start working again!  The same goes for a cat-equipped car that had an ignition failure when started from cold; the cats won't work when cold, so the fuel in the exhaust system on that side may never be ignited.

If the car is equipped with catalytic convertors and they were at operating temperature when the ignition failure occurred, the cats will burn the fuel as it arrives, and things will getting considerably hotter in a big hurry.  What's worse, if the car continues to be driven, more throttle will be applied to get any speed out of it, so even more fuel and air will be dumped into these cats.  The inevitable result will be a cat meltdown within seconds.  What's worse, often the cherry red-hot catalytic convertors will ignite something, perhaps by melting through the fuel hoses that are above and not too far away.  The car is immolated so fast you'll barely have time to pull over and get out.

You don't want to be driving on six cylinders, not even for a minute.

If you were dozing when you read those last few paragraphs, pinch yourself, clear your head, and go back and read them again.

DISTRIBUTOR ROTOR PROBLEM: Unfortunately, a one-bank ignition failure turns out to be a common occurrence on Marelli-equipped V12 Jags.  Although anything that kills one side of the Marelli ignition system can cause the car to run on six cylinders and threaten a cat fire, there is one possible cause that clearly outweighs all others in terms of frequency of occurrence.  Randy Wilson: "The most common failure, the one that kills the A bank, is the center post of the rotor burns through, allowing a ground path from the rotor contact straight to the distributor shaft."  This characteristically results in a fire or meltdown in the right side cats only, since it is always the A bank ignition system

John Goodman reports that the XJR-S uses a Zytek ignition/fuel injection system --see pages 307 and 721.  "Basically it is a modified Lucas distributor; even the rotor arm is standard.  However the vacuum and mechanical advance mechanisms have been removed (ECU-controlled vacuum sensor and programmed advance).

"It has a magnetic "Hall effect" engine speed sensor and a similar timing sensor.  The 'Hall' effect thing has an inner and outer wheel.  The inner one has one notch and is the timing signal/ speed sensor, similar to the Marelli crank sensor, the outer star like wheel has twelve notches/spikes to control injectors.

"It appears that to set the timing exactly you really need the dealer to plug in the "JaguarSport magic laptop".  In the set up screen there is a function .  This is where you set the distributor to the 10 degrees BDC at idle for the ECU to get its base line input.  After exiting the screen the ignition timing reverts to the control of the ECU.

"So, under the ECU control, at idle you should be seeing 3.5 degrees and at 3000 rpm it should be around 18 degrees if the timing is right.  It is a damn inconvenience not being able to check or set the ignition timing without the software."

The Zytek system continued to use the altered Lucas distributor even when the baseline XJ-S was fitted with the Marelli ignition.

The Jaguar V12 was fitted with a distributorless ignition system for a short time just before it was discontinued, but didn't make it into the XJ-S; Roger Bywater of AJ6 Engineering (page 713) says, "It was on the 300 range saloon and we have a dealer technical guide telling all about it.  There were two amplifier modules driving two coil modules each containing 3 double ended coils for a bank of 6 cylinders.  All driven by a Nippondenso Engine Management system."

Rick Wilder, who owns a '95 XJ12, says, "I had the impression that the distributorless ignition was only added in the 1996 MY.  That erroneous impression was reinforced by alldata.com, which shows the Marelli ignition on my MY.  I just took the valley cover off to see what's up and found the 2 coil packs, each with 6 spark plug wires attached, and no distributor."

The Jaguar V12, of course, is different.  It has two thermostat housings, one at the front of each bank.  The XJ-S radiator is a side-flow radiator divided into a top third and a bottom two-thirds; the end tank on the left end of the radiator either has an internal baffle one third of the way down, or actually consists of two separate end tanks.  The coolant coming from the left bank, via the left side thermostat, enters at the top left and flows left-to-right through the top third of the core.  Then the coolant from the right bank comes in, mixing with this already-cooled fluid.  The mixture then flows right-to-left through the bottom two thirds of the core and on to the pump.  Each thermostat also controls a bypass directly back to the pump inlet via a "cross pipe"; as the thermostats open to allow coolant to the radiator, these bypasses are closed off by a disk on the bottom of each thermostat.

It is unknown why Jaguar contrived a dual-thermostat system, but it was probably just to reduce plumbing --not having to get the fluid from both banks back to a single thermostat housing.

Because the mixed fluid goes through the pump and to both banks, both banks are always seeing the same incoming coolant temperature.  When the thermostats are closed and the fluid is bypassing into the cross pipe, both banks will also see the same flow rate, and therefore will warm up at the same rate.  When the thermostats are fully open and the bypasses are closed, however, the left (B) bank will always see a lower flow rate than the right (A) bank, and therefore will run warmer.  This is due to the radiator design; the fluid from the left thermostat outlet has to pass through the upper third of the radiator core to get to the exact same place the fluid from the right thermostat outlet goes to directly.  As a result, the backpressure at the left radiator inlet will always be higher than the backpressure at the right radiator inlet.  Since the flow to both banks is from the same pump and it is not a positive displacement pump but a centrifugal, most of the flow will naturally take the easier route through the A bank.

The action of the thermostats may accentuate the differential flow at operating temperatures.  When the thermostats are only partially open, the bypass leads directly back to the pump inlet while the route through the radiator has a higher backpressure.  As the higher backpressure begins to slow the flow in the left bank, the coolant arriving at the left thermostat begins to get warmer.  As a result, it closes off the bypass some more, further reducing the flow in the left bank!  Some have advocated installing a colder thermostat in the left side to compensate for the warmer running bank, but this would seem to be the exact wrong thing to do; it could arguably be better to put a warmer thermostat in the left side so the bypass stays open and flow is maintained through the bank.  Flow will be reduced in the radiator, though, possibly causing the entire engine to run hotter.

As long as the cooling system is clean and operating properly, the differential cooling flow between banks doesn't seem to cause any problem.  However, there are three implications the XJ-S owner should be aware of:

1) The coolant temperature sensor for the EFI system is on the left thermostat housing.  Since this side is running warmer than the right and the EFI system will be adjusting the fuel mixture for the entire engine accordingly, the right bank is likely to be running a little leaner that the left.  Of course, on cars with Digital P EFI and oxygen sensors, the system will automatically correct the mixture on individual banks --as long as you're in closed-loop mode.  When you put your foot in it, you go into open-loop mode --and when your foot is in it is precisely when you don't want to be running lean!  You can only hope that the open-loop scheduling includes enough enrichment to overcome the effects of the temperature differential between banks.  Again, as long as the system is clean and operating properly, there doesn't seem to be a problem.

2) The coolant temperature sensor for the gauge on the dash is on the right thermostat housing.  This means that the left bank can have zero flow and be overheating severely, and the driver would have no indication from the dash as long as the right side still had good flow.

3) While the system works fine when clean and operating properly, the double-pass radiator scheme seems designed to accentuate any problems that develop.  While the coolant flow is always lower through the left bank, the radiator getting obstructed internally seems to increase the difference in flow --possibly because the flow from that bank has to go through twice as many passes of the obstructed radiator, or perhaps just because the thermostats are closing off the bypass fully.  Whatever, the incidence of dropped valve seats or other overheating damage is much higher for the left bank.

Roger Bywater has a different theory about why the left bank seems to drop more valve seats: "If the V12 overheats for any reason B bank is likely to suffer more than A bank and I believe this is because A bank is fed from the low side of the water pump whilst B bank is fed from the top.  Therefore any condition which might promote cavitation at the pump will have a more damaging effect on B bank."  There are even those who suggest that the left bank suffers more than the right because the big belt-driven fan is blowing air over the right bank, although this is a minor factor at best.  Rather than trying to decide which theory is correct, note that all these theories might have some validity!  The B bank is definitely the one at risk.

Bywater relates "...an observation from when I first started doing Japanese Heat Damage Tests, which involved an extremely arduous simulated incline run.  The test was carried out on a chassis dynamometer in a temperature controlled environment with airflow coupled to road speed.  The punishing part was a simulated gradient lasting (going from memory) 20 minutes at high load and moderate speed in which the airflow through the radiator is barely adequate to cool the engine.

"Before we added supplementary fans to live with the test most cars would overheat badly towards the end and I remember that a V12 dropped a few valve seats on one occasion.  The dropped seats were in the left hand head.  This was a test fleet car in sound condition so all those theories like radiator or heater blocking are not relevant.  I do not accept that airflow around the engine is a significant factor.

"I think just about any car would have overheated in the circumstances.  A pair of electric fans mounted in front of the radiator kept the problem under control (I cannot be sure if that was done on the V12 but it certainly was on the 4.2) so maybe that should be suggested to anyone whose driving pattern gets into similar territory.  Personally I was dubious about the fans making much difference but the engineer in charge of cooling systems assured me it would work and he was right.  The setup was used in production on XJ6s for the Japanese market only (it is shown on the parts slide) but I don't think the V12s ever had it."

RECOMMENDATIONS: Despite the proven shortcomings of the cooling system design, many experienced XJ-S owners insist you can avoid trouble by scrupulously maintaining your cooling system.  This author does not agree.  If you put any stock in what I say, you will make four changes to your cooling system immediately:

1) Install coolant filters in the upper radiator hoses.  I recommend the Tefba's, although the Ganos also work fine.  See page 190.  Note that you might also want to install a convenient coolant drain to aid in servicing these filters.

3) Install a "flushing tee" in the highest point in the heater hose, and use it whenever you're changing coolant.  See page 180.

4) Install foam weatherstripping in every nook and cranny where air might get around the radiator rather than going through it.  See page 226.

Those are all easy.  They'll only cost you a few bucks and won't take more than a couple of hours.  In addition to those four items, there are two things that should be done when the opportunity presents itself:

1) If the radiator ever must come out for any reason, convert the system to single-pass.  If that radiator is going back in, have the radiator shop modify it first.  If a new radiator is going in, make sure it's a single-pass radiator.  See page 198.

2) If you ever have any trouble with that belt-driven fan, chuck the whole thing and install an electric fan in its place.  See page 219.

HOW HOT IS TOO HOT? Just about the first question everyone asks is just how high the needle can get before it's time to start worrying.  Unfortunately, all too often owners ask people who should know, including supposedly certified Jaguar mechanics, about their gauges reading halfway between N and H, and are told, "That's OK, they read there all the time, don't worry about it."  These people are liars, and you can tell ‘em Kirby Palm said so.  Many, if not most, of the maintenance headaches occurring on Jaguar V12's can be traced to overheating -- not just one-time overheating, but long, persistent, chronic overheating, the type that can only happen when the owner is ignoring the gauge --usually because someone told him it was OK.  If anyone tells you your temp readings are OK, ask him if he will guarantee that and agree to pay for engine repairs when the valve seats drop.

Trying to get a handle on just what constitutes a reason to panic on the XJ-S temperature gauge has long been difficult, since reports from owners seemed inconsistent or contradictory.  The gauge being an example of British electrics has only added to the uncertainty.  However, by noting many such reports on the internet discussion list and following several of them while the owners checked things and made corrections, this author has been able to derive the following guidelines.  Note that these descriptions apply to the vertical or "barrel" coolant temperature gauge found in the pre-'91 XJ-S; those with later cars with round gauges will most certainly see similar behavior in general, but I can only offer a few reports on where the needle sits when the car is running properly -- see below.

Some vertical gauges reportedly have temperature scales in degrees, while others have merely a C at the bottom, an N dead center of the scale, and an H at the top.  This description will refer to the C-N-H scale but both type gauges are apparently identical except for the paint.

There are basically four situations that the vertical gauge will indicate:

1) If your car has a properly-operating cooling system fitted with 190°F (88°C) thermostats, the needle will always be sitting on the N when the car is warmed up.  Perhaps just a hair to the high side of the centerline of the scale, but always within the width of the letter itself, never above it.

2) If your car has a properly-operating cooling system fitted with 180°F (82°C) thermostats, the needle will always be sitting about 1/4" below the N when warmed up.

3) If your needle seems to wander around a lot, you have air in your cooling system.  See the section on filling and bleeding on page 179.

4) If your needle is above the N, your car is overheating.  If your needle is halfway between the N and the H, your car is severely overheating.  And don't worry about the needle being on the H; it will never get that far.

Note that these guidelines apply to the XJ-S as configured from the factory --with the gauge sender located in the right

Believe it or not, it appears that the vertical gauge is actually quite reliable.  In many (but not all!) of the reported cases of the needle being above the N due to problems with the gauge or sender, it was plainly obvious that there were gauge problems --often with all four gauges, and sometimes pegging them against the upper end of the gauge seconds after cold start.  More subtle faults in the electrics, such as corroded connections, always seem to cause the needle to read low (often all four gauges at once --see page 591) or to not read at all, staying at the C end.  A high temp reading that appears even remotely plausible is usually a cause for concern.

A lot of owners describe the situation when talking about their temp readings, such as how hard they've been driving down the freeway or how hot it is outside today.  Unfortunately, such qualifiers are usually an indicator of trouble. Engine coolant temperature is controlled by the thermostats, and should not vary beyond their control range regardless of conditions.  And their control range (from fully closed to fully open) is pretty tight indeed; it has been described as "three needle widths" of travel on the gauge.  Since the cooling system should always have some margin (excess cooling capacity) so the thermostats can control the coolant temp, the indication should always be within this control range.  If the gauge ever indicates more than a couple of needle widths above the regular operating temperature with whatever thermostats are installed --including reading on the N with 180°F thermostats --it means that the thermostats are no longer in control, they are wide open, and it's absolutely everything the cooling system can do to hold the temperature indicated.  Obviously, if things get just a hair worse --the outdoor temperature rises a couple of degrees, one more tube inside your radiator gets plugged up, you sit in traffic a few more minutes, whatever --the temp is going to rise some more.  Overheating damage is imminent, you need to be taking corrective action now.

The only way "corrective action" would include replacing thermostats is if the thermostats are bad.  Merely switching to colder thermostats is not corrective action; if the cooling system can't hold 190°F, it won't be able to hold 180°F either. Replacing 190°F thermostats with colder thermostats won't fix anything unless the 190°F thermostats were defective.

HOW HOT IS TOO HOT? -LATER XJ-S ROUND GAUGE: James Teston says, "I have a '92 with the round temperature gauge. (Not the barrel gauge)!  It looks like this: C\N/H ^ | And this is where the needle stays (Between the N and the right hash mark)."

Steve Gallant says, "My 93 XJR-s with 6.0L engine runs the same regarding temperature --middle of the N to just slightly to the right.  It has been this way since I purchased the car with 5k miles on it."

Howard Gladman concurs: "My 95-6.0L exhibits same reading.  Once the the needle reaches about a needle width to the right of N the Aux fan switches on and the needle stabilizes. 56,000 on the clock and running strong."

It's a pretty safe bet that all three of the above cars are running 190°F thermostats.  If you're running colder thermostats, expect readings farther left than these -- and if you don't see them, fix your cooling system.

COOLANT TEMPERATURE SENSOR RELOCATION: As mentioned in the description of the cooling system above, the coolant temperature sensor for the EFI system is on the left thermostat housing while the coolant temperature sender for the gauge is on the right thermostat housing --and both are on the wrong side.  It would be better if the EFI coolant temperature sensor was on the right side and the gauge sender was on the left side, for two different reasons.  As a result, an owner could rationally decide to move the EFI sensor from left to right, or the gauge sender from right to left, or to move both, essentially exchanging the two.  All moves are covered here; make your own choice.

It'd be really nice if both sensors were the same thread so you could just swap them.  Unfortunately, the gauge sender is

To move the gauge sender to the left thermostat housing, you're gonna have to drill and tap a 5/8"-18 hole.  This will require two tools you probably don't have: a 9/16" drill bit, and a 5/8"-18 tap.  9/16" drill bits are not too difficult to find, but note that they are only available to fit 1/2" or larger drills!  They make 1/2" drill bits with reduced shanks all the way down to 1/4", but the idea of a drill bit any larger than 1/2" reduced to 3/8" shank seems to have completely eluded the market.  A 14mm drill bit might also work, but they aren't available to fit a 3/8" drill either.

One possibility is obviously to rent a 1/2" drill.  Another idea: you can carefully grind six flats on the bottom 1/2" of the shank of the bit.  Then you can chuck up a socket driver in your 1/4" or 3/8" drill, snap a socket onto the socket driver, and insert the hex on the bottom end of the drill bit into the socket.  It might be a little wobbly, but if you drill the hole as large as possible with conventional drill bits beforehand (1/2"), this hokey arrangement should do an acceptable job of enlarging the hole.

This author bought a 9/16" bit with a 1/2" shank and three long flats to help it fit securely in a chuck.  By grinding three short flats in between the existing flats, a 12mm socket fit quite well --and doesn't hurt the bit one iota, since the original flats are intact and would still fit properly in a 1/2" drill.

Another option, of course, would be to replace the OEM gauge sender with a generic sender with similar electrical characteristics but threads that fit the existing EFI sensor port on the left thermostat housing.  Good luck.  If you wish to try this, note the OEM sender registers 412O at 40ºC.

You can install the gauge sender anywhere in the left thermostat housing that will see coolant flow from the heads.  It should not go in either the bypass passage or the passage to the radiator, since either may be closed off at one time or another.  On a pre-8S44060 engine, the obvious place to put it is on a flat that was clearly intended for such a boss but never drilled, right on top and near the rear end of the housing.  From engine 8S44060 on, there's already a hole here with a sensor in it, so this location isn't an option.

There's another flat surface apparently intended for a boss just rearward of the EFI sensor, but this port location connects to the bypass passage.  Also, the boss is too small for drilling and tapping a 5/8" hole.

Another option, of course, is to just drill out the EFI coolant temperature sensor boss and retap it for the gauge sender.  That leads to the next problem: you now need somewhere to put the EFI coolant temperature sensor.  And over on the right side is ideal.

There are at least two existing ports on the right side; the one where the gauge sender goes, and the one where the thermotime switch goes.  On the author's '83, there is no thermotime switch; there is a plug in the hole.  Doesn't help, unfortunately; both holes are too large for the EFI coolant temperature sensor.  So, you have two options: either drill and tap one of the existing holes out to a significantly larger size, install a plug, and drill and tap the plug to fit the EFI sensor; or just install a suitable plug in the old gauge sender hole and drill and tap an entirely new hole in the coolant manifold for the EFI sensor.  There are a couple of locations that will serve.  Note that the EFI sensor could just as easily go on the rear coolant manifolds.

For a plug for the old gauge sender port, I'd suggest: another sender.  In fact, just leave the original sender there and buy a new sender DAC2583 for the left side.  The senders are less than ten bucks each.

In fact, as long as you have two gauge senders, just install another wire and a switch somewhere so you can switch from one to the other to monitor both sides of the engine with the same gauge.  If you go this route, you might want to replace an original C40106 sender with another DAC2583 just to make sure any difference in indicated temp is due to a real difference in temperature rather than a difference in sender.

If you have just read through this section and have decided to make this mod, note that unless you can figure out how to use taps and drills down in some fairly tight places, you will need to remove the thermostat housings to do the drilling and tapping.  Probably the easiest way to do that will be to remove the air filter housings and then unbolt the entire manifold assembly --thermostat housing, coolant connecting pipe, and rear coolant manifold --and move the entire assembly rearward far enough to disengage the hose connecting the thermostat housing to the crossover pipe.  So, while you're preparing for this job, go ahead and buy a total of eight coolant manifold gaskets EBC 9634, two air filter housing gaskets EBC 9635, and both thermostat cover gaskets EBC 8330 and EBC 8331.  You may also want to get

BLOWING COOLANT: In general, if you are blowing coolant, your car is running too hot.  If you have a pre-H.E., pressure relief at the radiator cap on the header tank on the left wheel well will blow coolant or steam out the little tube into the wheel well.  Note that, if you fill the system right up to the cap, it will blow a little coolant the first time you run simply due to expansion.  You should be able to tell when it's actually overheating, since it will blow much more energetically.

If you have an H.E., pressure relief at the radiator cap on the header tank on the left wheel well will cause coolant or steam to blow into the plastic "atmospheric catchment tank" within the compartment behind the left front wheel.  This tank, in turn, overflows via a tiny tube out the bottom of the car at the very rear of the left front wheel well.  If the tank is empty or nearly empty, you may not be able to tell that the cap is relieving pressure; steam may condense within the plastic tank, and nothing visible comes out the tube.  If the overflow tank is totally full -- which it can get to if the owner continues to top up the system on a regular basis --any pressure relief can push liquid out of this tube, even if it's steam that's coming out of the header tank.  And, again, if the system is topped up, it may push a little liquid out the first time it's run without overheating.

Finally, as noted on page 186, the overflow tube coming out of the atmospheric catchment tank is a classic example of poor design, so more than likely any flow out of this tank will be all over the inside of that compartment and come leaking out of nooks and crannies, such as out the joint between the rocker panel and the fender.

OVERHEATING DAMAGE: In any aluminum-block engine, severe overheating can result in a warped block or warped heads, which in turn normally call for an engine replacement.  In the Jaguar V12, a more common symptom of an overheated engine is a dropped valve seat.  Since the heads are aluminum, the valve seats are sintered iron rings that are pressed into the aluminum.  Since iron and aluminum have different coefficients of thermal expansion, overheating will cause a loose fit and the seat can just fall out.  After that, it holds the valve part way open and bangs around in there.  Amazingly, reports of broken valves are rare; more often the owner who continues driving despite the annoying ticking under the hood allows the valve to beat the seat to pieces, which in turn bang up the piston, the other valve, and the head.

Do not continue to drive when the car is overheating.  If no other options are available, drive it short distances at a time, shutting it off and allowing it to cool before starting again.  And don't continue to drive if it sounds like a Chevy with bad lifters, either -- you've already dropped a seat, but you might as well quit before you do even more damage.

If at all possible, don't shut off the engine when the car is overheating; many have reported that's when the valve seats drop --when the engine is stopped.  Instead, find a water hose and leave the engine running as you hose down the radiator through the front grille.  Once the temp gauge comes down, then shut it down --and call a tow truck, do not start it again until you have addressed its overheating problems.

OVERHEATING --H.E. vs. PRE-H.E.: Roger Bywater indicates that the pre-H.E. cars had some tendency to overheat: "With regard to the marginal cooling at sustained high speeds the H.E. had a slight advantage in that the higher compression ratio raised the thermal efficiency and reduced the heat losses to the coolant.  It was also noticeably over-fuelled at high revs which must have helped further and the problem, slight though it was, seemed to be solved.  Distributor build quality was also better by this time."

2) The radiator must be clear, no blockage or sludge; unfortunately, this is difficult to check conclusively on the XJ-S without removing it from the car and removing the end tanks.  Crud in the radiator will cause overheating under all conditions, but usually more at speed than at idle.  Experience indicates that any radiator maintained following the owner's handbook guidelines for more than ten years is likely to be plugged.

3) Suspend the thermostats in a pan of water on the stove and bring them to a boil.  Do not let them contact the bottom of the pan.  If the thermostats are not visibly wide open by the time the water boils, replace them.  Their usual failure mode is to open only slightly.

4) Retarded timing will cause overheating under all operating conditions.  See the sections on ignition timing beginning on page 126.

a) A seized centrifugal advance mechanism may be seized at any position from idle to max advance.  Usually, it will be correct at one particular RPM, retarded everywhere above that RPM, and overadvanced everywhere below.  Conditions with retarded timing will cause overheating.  Conditions with overadvanced timing can also cause overheating but usually not as severe; the more obvious problem is knocking.  See page 137.

b) A blown vacuum advance module will cause timing to be retarded at low throttle while correct at full throttle, so the car will overheat more when driving gently.:
5) There may be debris obstructing airflow through the radiator, such as dirt and leaves --either plugging the fins themselves or within the space between the A/C condenser and the radiator.  See page 202.:
6) A bad fan clutch causes overheating only in stop-and-go traffic or other conditions where motion of the car doesn't provide enough air flow.  See page 215.:
7) The fan shroud needs to be properly installed and sealed up against the back side of the radiator.  See page 226.:
8) The fan shroud flaps should be intact and free to flap as intended.  If they are missing, overheating when stopped and idling is likely.:
9) There needs to be foam surrounding the radiator to prevent air from bypassing it.  See page 226.:
10) Front spoiler -- it must be there, and it must be properly mounted.  See page 227.:
11) Automatic transmission problems can be putting too much extra heat into the radiator.  See page 324.:
While all of the above items point to common faults, it must be said that far and away the most common cause of overheating on XJ-S's that are ten years old or more is a plugged radiator.  If you are having cooling problems, address the easy items first, but you might as well go ahead and plan to remove the radiator and have it rodded, recored, or replaced.

FILLING THE COOLANT SYSTEM: The ROM and the Haynes both provide a detailed coolant fill procedure and give dire warnings about engine damage caused by hot spots if the procedure is not followed.  Allow me to add: they ain't kidding.  Reportedly, one indication that the system has not been properly filled and bled is that the coolant level light comes on every now and then while driving.  Another is a temp gauge that seems to wander around.

Of course, you could just take your car to the Jag dealer and let the experts change the coolant so you don't have to

Steve Gallant: "Same for me here.  My car was serviced by a very reputable main dealer as part of a pre-purchase service.  After receiving the car, I noticed the low coolant light came on on my first drive.  I performed the factory procedure for filling/bleeding, and the light was extinguished.  I must have added close to a quart of coolant.  So even dealers don't take the necessary time to perform this operation 100% successfully."

Wally Magathan: "My car was also serviced by a reputable dealer, but I didn't know it was routine for them to ignore the bleed procedure until now.  I've now bled the system, put in almost a gallon, and hate to think what's been going on in the engine in the month since they "fixed" my radiator hose."

Jim Isbell provides a great tip on filling the coolant system: "Getting the water into the system has always been a problem on the XJS because of the two fill points.  I always tried to do it on level ground before and spent many minutes shaking the car to get all the air out of the system.  Today, just by accident, I was parked in the driveway with the nose of the car elevated and I didn't feel like moving it.  So I pulled the cap on the header tank and filled the car (about two quarts) then I pulled the cap on the crossover pipe and added another quart.  The air bubbled out quickly and the car was completely full in no time.  I recapped both vents and it's finished.  From now on I will park the car with the nose uphill when I fill the radiator."

The engine is deliberately designed for the coolant to flow upward with no air pockets, but when parked on level ground it just barely flows upward.  Tilting the nose up should make the air clear out a lot better.  Offhand, it's probable that you can't have the nose too far up until the air bleed port on the top left of the radiator is higher than the fill opening on the crossover pipe.

Be sure to bleed the air out of the heater circuit while filling the cooling system.  See below.

AIR BLEED VALVE: At the top left corner of the radiator is a small fitting used to allow air out while filling.  Mike Morrin says, "The first few XJ-S (1975 model year) left the factory with a threaded plug."  Then they switched to a little winged valve for most pre-H.E. cars -- but for H.E.'s, they went back to the plug.  Morrin: "The owner's handbook and manual give instructions for both types of fitting."  Both items were the same thread, 1/8" BSPP --so if you're here in the US, don't lose that plug!  If you'd prefer the convenience of the valve, C45587, it will fit where the plug fits; the valve sits a little higher and therefore closer to the hood, but this doesn't seem to be a problem.

AIR BLEED AT THE HEATER VALVE: There is none, but there should be.  Since the line comes out of the right side coolant manifold, goes upward until it gets to the heater valve and then downward until it connects to the bottom left corner of the radiator, it forms a big bubble when filling the coolant system.  Therefore, you need to disconnect a hose at the heater valve to let the air out when filling.  A disconnected hose creates two openings, one on the end of the hose and the other on the end of the fitting it was attached to.  As you fill, coolant will start to pour out of one of the openings first; put a thumb over that opening and continue to fill until coolant starts to pour out of the other opening, then reconnect the hose.

Of course, it'd be more convenient if there were actually a bleed port.  Douglas Dahl says, "2 clamps and a $0.99 5/8" connector at any auto parts store.  It is the same as the T's used in the flushing kits out there and comes with a screw top."  These black plastic "flushing tees" are commonly available in 1/2", 5/8", and 3/4" size, and you'll need the 5/8" for this job.  The straight section of the tee has hose barbs of the specified size while the connection off the side is a male garden hose fitting, and it comes with a blank-off cap with a rubber washer inside.  It really could not be any simpler to install or use.  If your local auto parts store doesn't sell these flushing tees individually, it may sell the flushing kits which contain three tees --one of each size --plus one cap and a few other items, all for less than five bucks so it still won't break you.  Note: you might want to check the passages inside the tee for plastic mold flashing before installing.

Please note that installation and use of an air bleed in the heater circuit does not mean you don't need to follow the

When filling the cooling system, it is suggested that you run the car for a few minutes with the climate control system off.  With it off, the heater valve will remain open, so the cooling system will have a chance to push the air pockets out of the heater circuit.  With the system on, it may just close that heater valve as soon as the engine is started unless it's cold enough inside the car for the system to call for heat.

ANTIFREEZE: Don't operate the Jag or any car without antifreeze in the cooling system.  The name "antifreeze" is an unfortunate misnomer, and pure water is a totally unacceptable coolant --even in Hawaii.  Antifreeze not only prevents freezing, it also retards corrosion and crud buildup, helps prevent boilover, and serves as a water pump seal conditioner. Running pure water will result in early water pump seal failure.  Also, replace the antifreeze annually, because the inhibitors in it wear out and it becomes corrosive.

Scott Fisher sends the following wisdom: "In the context of the automotive cooling system ethylene glycol is not an anti-corrosive agent; it is in fact corrosive.  To offset this fact, manufacturers add anti-corrosives (inhibitors) to the glycol.  These preparations, while in good condition, perform well in both minimizing corrosion and preventing freezing of the coolant.  However, over the life of the coolant the anti-corrosion properties of the inhibitors are depleted.

"Water aids corrosion in three main ways: 1) bringing free oxygen in close contact with the metals so that corrosion (oxidation) can occur.  2) Water is conductive.  Once water has been flowing in your cooling system for some time, its conductivity will rise as it picks up metal ions.  The water may serve to promote electrical activity which may erode metals by galvanic action.  3) Some of the metal ions in the water may also react directly with the metal surfaces.

"Apart from supporting the above three processes, ethylene glycol has the added unfortunate property that it oxidizes through several stages to oxalic acid.  The products of ethylene glycol oxidation by oxygen and subsequent reactions include: aldehydes, carboxylic acid, nitric acid, glycolic acid, glyoxylic acid, oxalic acid, formaldehyde and formic acid.  Most of the series of oxidation products to and including oxalic acid are directly corrosive to metals.  Added to this, oxalic acid is highly toxic.

"To combat the above acids and other corrosion activity, antioxidants and alkaline formulations are added to the glycol mix.  These include many compounds which are used in cooling systems where antifreeze properties are not required and include primary, secondary and tertiary amines; organic and inorganic phosphates, silicates cresols and other phenolic substances; a wide variety of sulfur compounds; soaps; alkali metal salts; and borates.

"These inhibitors slow down the corrosion process caused by the glycol and the water.  They may coat the metal surfaces and prevent corrosion by passivation.  Passivation is the process where the a protective film forms on the metal which prevents further contact with the solution.  Unfortunately, in all coolant preparations (with or without glycol) the inhibitor system (during engine operation) is being continuously depleted in the performance of these actions.  For this reason, proper cooling system maintenance is critical.

"One aspect of cooling system maintenance that we can all easily follow is to minimize "aeration" of your coolant.  Aerating accelerates the uptake of free oxygen from the atmosphere.  As free oxygen is one of the essential ingredients for corrosion, the importance of minimizing it's uptake is clear.  To this end you should make sure all your hoses are in good condition and clamped tightly.  "Closed systems", where an expansion tank and recovery system closed to the atmosphere is used, also help in this regard.

"If you overheat (boil) glycol-based coolants they must be replaced immediately as this accelerates the oxidization process of the glycol to acids."

LONG LIFE COOLANT: Peter Cohen says, "I noticed that the manual called out "phosphate free" coolant.  The statement I am referring to is on Page 26-03 of Volume 2 of the XJS Service Manual (JJM 10 04 06) under the heading "ANTIFREEZE".  The V12 HE motor is essentially unchanged since long before the existence of non-phosphate coolant.  Ergo, the Jaguar V12 has been doing fine on normal coolant for all these years, so why ask for non-phosphate

"After much searching, the only non-phosphate stuff I could find at the time was Prestone 460 Long Life coolant.  The Prestone 460 has the distinct disadvantage of being brown, so now coolant leaks are the same color as oil leaks (and the same color as rusty old coolant).  I have since found Texaco Havoline Long Life, which is orange."

Jim Belkoff answers, "Beyond the phosphate-free issue and the long-life issue, Texaco DEX-COOL (and I assume the Prestone equivalent) contains no silicates.  From what I understand, silicates are abrasive and gradually eat away at water pump seals.  Texaco and GM have done tests to prove this new coolant results in fewer water pump replacements.

"The reason the new coolant lasts so long is the carboxylate inhibitor system that's added to the base ethylene glycol.  I would suggest taking a look at Texaco's website (www.texaco.com).

How important is phosphate-free coolant?  Apparently we should ask the folks at Saturn.  Cohen: "In their first year of production, Saturn recalled and destroyed all of the first cars they sold because "they were shipped with the wrong coolant, which could destroy the engine block".  Given that they could simply have issued new motors, this was an impressive waste of money."

Peter Cohen says, "DEX-COOL apparently eats silicone sealants.  If you are replacing your water pump, do not use silicone sealant on the gasket.  Either use no additional sealant, or use Permatex."

LONG LIFE COOLANT --MAYBE NOT: That orange long life coolant sure sounds good, but eventually enough negative reports appeared to convince many owners to stick with the traditional green stuff.  In fact, enough negative reports appeared to convince many auto mechanics to avoid the orange stuff like the plague.  Gary Penovich says, "Chevrolets and other late model GM cars have been affected by brown sludge.  It seems that extreme driving conditions and/or low coolant situations lead to a gelatin-like thickening of the stuff."

Wally Plumley, on the Porsche 928 discussion list, discussed coolants with Texaco reps and learned that long life coolants are not suitable for "open" cooling systems in which air is present in the cooling system.  In other words, it's not suitable for systems that don't have a coolant overflow tank --such as the pre-H.E. XJ-S.  It's also not suitable for systems that leak.  "Silicates in conventional coolants will "plate out" or coat metal surfaces inside the cooling system.  If the cooling system gets low on coolant, the plated silicates will give some corrosion protection to the metal that is then exposed to hot, moisture-saturated air.  DEX-COOL has no silicates, so if the coolant level gets low, the metal exposed to hot, moisture-saturated air has no corrosion protection, and will corrode relatively quickly."  Of course, this wouldn't matter to anyone whose car never got low on coolant.

Bernard Embden argues that DEX-COOL is not only inappropriate for systems that don't have an overflow tank, but for system with unpressurized overflow tanks --which would include all Jaguar XJ-S's.  "On my 88 Grand Prix with its non-pressurized expansion tank, (tank does not have a "pressurized radiator cap") a nasty sludge built up around the expansion tank filler cap with DEX-COOL installed.  The crap was hard and not easily removed.  Based on my experience, it appears that DEX-COOL reacts with the atmosphere to form this sludge.  GM agrees that low coolant resulting in radiator contamination is the death bell of DEX-COOL.  A "low coolant" condition creates an "air pocket" within the radiator that allows a deposit accumulation unique to DEX-COOL.  Once this deposit attaches itself to the radiator cap, the cap loses its sealing ability and a vicious cycle of low coolant/more deposits starts.

"Without a pressurized radiator cap, the cooling system has a large and variable "air pocket" in the non-pressurized expansion tank.  This allows DEX-COOL deposits to start to build up immediately in the expansion tank and is ultimately drawn to the radiator cap.  Once on the radiator cap sealing surface it prevents proper sealing.  From this point on your radiator is on borrowed time."

RETROFITTING OLDER CARS WITH LONG LIFE COOLANT: Jim Crider says, "A few years ago, someone thought a long-life coolant (original plan: life of vehicle) would be a Good Thing.  This leads to Organic Acid Technology coolant (OAT), which is marketed as "DEX-COOL" by GM and has been factory-fill in their products (except C4 Corvette --not sure about C5 Corvette) since 1995.  It's the orange or orangy-red stuff.  Someone along the

"Many European automakers use a hybrid of OAT --HOAT (Hybrid Organic Additive Technology --clever, huh?), which is the OAT package with a small amount of silicates added to increase the cavitation resistance and make it less aggressive against those seals and gaskets.  This is often pale yellow in color.  This stuff seems to offer pretty much the best of both worlds --it's not quite as long-lived as straight OAT, but it is much better behaved in operation than OAT, much like conventional coolant.

"Note that these three different additive packages are not really cross-compatible.  No, they won't eat the insides of your radiator if you mix a little of one in with another in a pinch, but you'll be better to get the system flushed out and a fresh mix of 50/50 whatever your car needs put back into it.

"If I owned a car that came with OAT or HOAT from the factory, I'd likely stay with it.  The anti-corrosion additives, in particular, leave residues on the walls of the various coolant passages (that's how they work -- the residues coat the base metal and prevent corrosion), and it's tricky to convert an engine that's been run with one style of package to use another package and get the full benefit.

"Switching from conventional to OAT, for instance, requires a mild acid flush of the cooling system after removal of the conventional coolant and before pouring in the OAT if the long-life corrosion benefit of the OAT coolant is to be realized.  Just pouring the OAT in after draining the conventional won't gain the full measure of added coolant life the OAT marketers (notably Texaco) like to use as selling points."

Somewhere in the midst of all this, the labelling on the containers of DEX-COOL quietly changed, making far more modest claims for durability and combatibility.

Quoting from the Popular Mechanics web site: "Now let's look at "retrofit" and "drain and fill" and explain what you can and can't do safely, and a bit of why.  If a vehicle has a copper-and-brass radiator, forget a retrofit, says General Motors, because the organic acid (orange) antifreeze may not provide adequate protection for the lead solder in that radiator.  The Chrysler orange hybrid combination of silicates and organic acids is meant to provide special protection for the water pump.  Sorry, you can buy it only at a Chrysler-brand dealer.

"Prestone believes you can retrofit to its organic acid orange almost any vehicle with an aluminum radiator and cooling system that has been well-maintained and is in good condition, if you do it right.  However, the antifreeze maker recognizes the possibility of a problem with Dodge truck 5.9-liter V8 water pumps, for which green or yellow/gold U.S. antifreeze is recommended–if you don't get Chrysler's specific orange."

A 1998 magazine article quoting Applied Chemical Specialities Co. (a competitor of Havoline) put the retrofit issue more strongly: "DEX-COOL is an excellent antifreeze to be used in brand new cars in which traditional phosphate/silicate antifreeze has never been used.  However, if any traditional antifreeze has ever been used in your car's cooling system, it is strongly advised to avoid using DEX-COOL.  This is because, short of a dangerous strong acid cleaning or complete replacement of ll parts within the cooling system, it is physically impossible to remove all residuals of phosphates and silicates - even with repeated flushing.  If DEX-COOL is used in such a system, deposit formation will be almost instantaneous and will seriously affect your car's cooling system efficiency and performance.  Because most corrosion occurs under such deposits, it will also affect the long-term corrosion prevention in such a system as well."

In a more Jaguar-specific vein, Al Askevold reports some problems with DEX-COOL: "Besides the bad report about DEX-COOL from the radiator shop who did my recore, I could not remove my rad caps without damaging the rubber seals, and my Tefba filters -I had to remove them and clamp them in a vice to remove the tops.  I tried several different kinds of lubricant on the parts with no effect.  I finally flushed the DEX-COOL, I am now using a different brand, so far no problems."

WATER: The antifreeze needs to be mixed approximately 50/50 with water, but if you care about your cooling system you might want to be careful about what water you use.  The garden hose may be convenient, but it's not necessarily healthy for the car.  The biggest problem to be concerned with is dissolved solids, that stuff that's left in a pot after you boil water away.  Since boiling is often going on alongside the hottest parts of the engine (cylinder liners, head), this same stuff is left there.  As a scale on the metal surfaces, it can insulate them from the coolant and make the cooling system less effective.  When the scale flakes off in chunks, it can find its way into the radiator and plug up some of the tiny tubes.  Finally, the scale is somewhat abrasive, and therefore is not particularly good for the seal in the water pump.

This problem might be considered minor.  There are only about two gallons of water introduced to the system at each coolant change, and that amount of water only has a finite amount of dissolved solids in it.  This appears to be the attitude the auto manufacturers take, since there are no radiator hose filters in a car from the factory (see page 190).  However, if you change your coolant often or use really crummy water, you might be contributing to the plugging of your radiator.  If your car loses coolant and you add water daily from a garden hose, you might as well go ahead and pull your radiator and have it rodded out.

To minimize problems with dissolved solids, you should use distilled water, deionized water (also known as demineralized water), or water that's been purified using a reverse osmosis process.  All three types are generally available at the local grocery store for perhaps 75 cents a gallon; at some places, you can take your own jug and get it even cheaper from a dispensing machine.  Deionized water is sometimes called "purified water", and is usually labelled that it "serves distilled water uses".

Grocery stores also sell various types of drinking water, including spring water.  These may not be any better than the tap water, since they may contain lots of dissolved solids -- they just contain dissolved solids that taste good.

Other processes advertised include ozonated water, which is a process to kill germs, and carbon filtered water, which is a process to remove volatile compounds that affect the flavor.  Neither process has any significant benefit for cooling system use.  The first time the engine is warmed up to operating temperature, the germs will be dead and the volatile compounds will have boiled away and been removed from the system by the air purge system.

There are arguments about using rain water or condensate from an A/C system.  The argument is that they are both "distilled"; however, the other side of the argument is that they apparently pick up quite a load of dissolved solids somewhere along the way, either from pollutants in the air or from dust or whatever.  Look at the container that collects the water and judge for yourself if it's OK for the inside of your cooling system to have similar stuff in it.

Peter Smith reports from "...a series of brochures from Tectaloy.  It says "the preferred water is demineralised.  Do not use spring or bore water."  The brochure illustrated that the corrosion effects on welded aluminium were serious, and that as little as 1 volt earthing through the cooling system could chew out an aluminium radiator in weeks (probably do the cylinder head a power of no good as well).  It also notes that true distilled water is getting harder to obtain due to the cost of production and the energy required in the distillation process.  Also "if you believe rain water is the answer just reflect for a second on the damage it does to gutters and tanks, and they're usually galvanised against corrosion.  Spring water is totally unsuitable as it is full of minerals and salts".  Summary was that distilled, demineralised or reverse osmosis water were the most suitable."

One thing you should definitely not use is "softened" water from one of those water softeners that is recharged with salt.  Dave Lokensgard says, "Never use softened water in a cooling system containing aluminum.  Water softeners are ion-exchange units, not de-ionizing units.  The main bad actor coming from the water in aluminum corrosion is the chloride ion, and water softeners work by replacing all anions in the water (negatively-charged ions, like phosphate, sulfate, and so on) with chloride, and all positively-charged ions with sodium ion.  This is why they are recharged with salt (sodium chloride).  So softened water is the worst thing you can use in a cooling system."

Jason Korke: "The coolant I bought was designed to be mixed with water.  It was made by Castrol which in Australia is I believe fairly well regarded.  It wasn't cheap!  The bottle said, "Mix with demineralized or soft water.""  It is unknown why Castrol's directions would say such a thing; perhaps they meant naturally soft water (water with few minerals) as opposed to softened water (water in which the minerals have been exchanged for salt).

If you work in a science lab, an electric power plant, or some other type of industrial facility that uses clean water, you may actually be able to get ahold of some really pure water --something chemically much closer to unadulterated H2O than the distilled, deionized, or RO stuff you can buy locally.  Believe it or not, this may not be good.  Pure water is a solvent; it would actually be quite effective at corroding your aluminum, iron, and brass parts if it weren't for the protective additives in the antifreeze.  So, although the total lack of dissolved solids is nice, perhaps it'd be better if you added some dissolved solids before using; drop a few chunks of scrap aluminum and copper into the jug and let it sit a while before using it in your cooling system.

If you want to learn more about water, there is a "WaterNet" forum on the Internet.

RADIATOR CAPS: The XJ-S H.E. has two radiator caps, but only the one on the header tank (left side of the engine compartment) is actually meant to operate as a conventional radiator cap; namely, to control the pressure in the system.  The one on the cross pipe (at the top right of the engine) is really just a place to add coolant, using a standard radiator cap because they're available.  If one or both of the caps go bad, they may be replaced with standard coolant-recovery radiator caps.

The early XJ-S H.E. originally came with two different caps that were chained in place to make absolutely sure you didn't mix them up.  However, as Alex Dorne points out (and Jaguar eventually figured out), there is no opening out of the chamber between the lower seat and the upper seal in the fitting on the cross pipe.  As a result, it doesn't really matter what pressure rating the cap is you install there; the upper seal will totally seal that opening, no pressure relief is possible.  The cap on the header tank will always establish the pressure limit within the cooling system.  So, Jaguar now offers two identical caps as a replacement so it doesn't matter if you mix them up.

Nowadays all radiator caps are coolant-recovery type, but I will point out the difference anyway.  In non-recovery systems, any coolant that was relieved by the radiator cap merely blew overboard, and when the system cooled back down air would be drawn back in.  Radiator caps made for non-recovery systems usually had a brass diaphragm under the top cover that primarily served as a spring to keep the cap from rattling; it didn't matter if it didn't seal, since coolant was just going overboard and air was being sucked in anyway.

In a recovery system, coolant released is collected in a reservoir and sucked back into the system on cooldown.  While the configuration of the radiator opening hasn't changed, it now becomes more important that the top cover of the cap actually seal.  When the engine is cooling down and drawing coolant back in, any leaks at this joint will cause it to draw air instead.  So, modern coolant-recovery caps have a rubber seal in place of the brass diaphragm.  Since this type cap works just fine on non-recovery systems, it is doubtful if anyone actually makes the older style anymore.

COOLANT RECOVERY SYSTEM: Hey, all cars have them nowadays, it's not rocket science.  Each time an engine heats up, the expansion and pressure buildup blows air, gasses, and coolant past the radiator cap and into a recovery tank, where the air and gasses bubble to the top.  When the engine cools down, the contraction draws coolant back from the bottom of the recovery tank.  However, on the XJ-S the coolant return line from the pressure cap to the "atmospheric catchment tank" behind the left front wheel is unusually long.  Since the expansion/contraction of an engine only moves a little water at a time, it requires several thermal cycles to purge the air out of the hose (unless you overheat and blow steam).  Each time you open the pressure cap, you allow the water to drain into the atmospheric tank and the line to fill with air.  If you keep opening the pressure cap to check the level, it will never get a chance to work properly.

Even the tiniest leak in the coolant circuit will screw up a coolant recovery system.  You may not be concerned about a very slight loss of coolant, but you should be.  The engine takes several hours to cool down, so the rate at which coolant is drawn back from the recovery tank is glacial indeed.  With even a tiny leak in the system, this suction will draw in air from outdoors instead.  Once you have pockets of air in the system, the next event in your life will be an engine rebuild.  Steve Haley says, "I found that even being a cup and a half low on coolant makes a big difference in the location of my gauge needle."

ATMOSPHERIC CATCHMENT TANK: On the H.E., the atmospheric catchment tank is a plastic container located directly behind the left front wheel, within the bodywork.  "Atmospheric" means that it's not pressurized; it's basically an open container to pour coolant into.  To get to it, remove the left front wheel and remove the sheet metal panel at the rear of the wheel well.

The vent on the atmospheric catchment tank is somewhat unusual.  On most cars, the coolant recovery container is within the engine compartment, and when it overflows (like, when your car is overheating big time), the fluid coming out the vent just dribbles out onto the ground.  In the XJ-S, however, such leakage would result in antifreeze throughout the bodywork --unacceptable.  So, the container has a vent line that is routed out the bottom of the car.  For this vent to work as intended, the container must be airtight.  The design is really lousy, however, and it is likely to leak throughout the bodywork when overheating anyway.

To prevent such localized flooding, try this idea: install a pan underneath the atmospheric catchment tank to catch any coolant that spills out of it, and provide a drain from this pan out the bottom of the car.

According to Mike Morrin, the pre-H.E. doesn't have an atmospheric catchment tank; relief from the radiator cap on the header tank just drains into the wheel well.  He suggests that an overflow tank might be a useful retrofit.  Considering the problems with the OEM tank noted above, it might be wiser to simply purchase a generic "coolant recovery system" such as those offered by J. C. Whitney.  Note, however, that such generic tanks may be designed to overflow all over the place rather than out a tube; either mount them somewhere that this isn't a problem, or provide a tray to catch the overflow and route it out the bottom of the car.  Tank volume may also be a concern, so if given a choice get the largest container you can find.

ATMOSPHERIC CATCHMENT TANK FILLING: Ideally, you'd like to have a minimum of a couple of inches of coolant in the bottom of the atmospheric catchment tank.  However, you'll notice there's no convenient way to put any coolant in it!  Apparently, Jaguar expects you to just add coolant at the header tank, and eventually some of it will get into the catchment tank eventually.  Or maybe you're supposed to disconnect the hose from under the cap on the header tank, put a funnel in the end and hold it high and fill it that way.

Steve Haley had a better idea.  "I added a fill hose which I ran back out through the same hole as the others."  This would give you a filler location in the left rear corner of the engine compartment.  Note that the point where this hose enters the atmospheric catchment tank should be airtight, so if it overflows the excess coolant will come out the vent line behind the LF wheel rather than pouring all over everything.

Even with such a nifty filler scheme, you still don't have any good way to tell what the level is.  If you arrange your filler hose to end about two inches above the bottom of the tank, you can find out by blowing into it.  If you hear bubbling, the level is at or above the end of the hose, and you don't need to add coolant.  If the blowing just whooshes into the tank freely, you need to add coolant.  If you think you might have too much coolant in it, you might even connect a siphon and drain the excess through this hose; when it gets down to the two-inch level, it will suck air and automatically quit siphoning.

COOLANT RECOVERY HOSE: The line from under the radiator cap on the header tank to the atmospheric catchment tank is anything but simple --or reliable.  In the engine compartment, where you can see it with the hood open, it is a sturdy thick-walled 5/16" hose.  When it gets into the compartment behind the LF wheel well, where you can't easily inspect it, it connects to an adapter that steps the size up to 3/8", which then connects to a length of thin-walled rubber tubing (which actually appears smaller than the 5/16" hose).  This 3/8" hose then bends downward 90º and into the atmospheric catchment tank.

One common problem is that the thin-walled tubing may get kinked making that 90º bend --sometimes because somebody has fiddled with the hose in the engine compartment and pushed more of it into the hidden compartment, tightening up the bend.  Michael Aiken says, "My coolant recovery hose was kinked as it enters the atmospheric bottle.  This made the recovery system totally inoperable and could lead to more severe damage anywhere in the cooling system, as this is the only way pressure is vented as the coolant expands.

"It can easily be tested by disconnecting the hose at the top of the neck of the expansion tank and blowing in the hose.  It should offer little resistance to air flow and you should hear a gurgling sound behind the LF wheel.  I applied 30 lbs of pressure and no flow.  It was really kinked.  It could also possibly be broken which is not as severe but could lead to slow coolant loss.  The hose is a soft rubber and makes two 90º turns in 5 inches.  The second turn (the one that kinked) has a radius of less than an inch.  I cut the hose off just above the bottle cap, installed a 90º 3/8" heater elbow (plastic) and a non-crimping heater hose back to the original connector.  Cost less than $4.

"If I were reading this I would take the 2 minutes and check it out.  Unlike most cars this recovery system is completely out of sight and problems are likely to go undetected.  This hose is really flimsy (unlike the hose from the tank neck into the wheel well which seems very strong) and just fell apart as I took it off."

Another problem is the little adapter, which is steel and therefore subject to corrosion.  Craig Sawyers reports, "Mine was rusted solid inside, and so totally inoperative."  Steve Haley says, "The short metallic slightly conical connector was completely plugged with corrosion.  The hose into the tank crumbled in my hands...and the metal brackets were rusted and in pieces."

Yet another concern: The end of the rubber hose inside the atmospheric catchment tank obviously needs to be open, both to allow coolant out and to suck coolant back in.  In some cases, the hose blows coolant just fine, but when sucking the tip of the hose gets sucked onto the bottom of the tank (or even onto the side, if someone is really unlucky).  It then can't pull in any more fluid even though surrounded by fluid, so the system pulls in some air from somewhere else instead -- or starts sucking radiator hoses flat, which is also trouble.

The fix is easy: pull the hose out of the atmospheric catchment tank, and redesign the tip of the hose so it can't possibly get sucked onto a surface.  One idea is to punch a 1/4" hole through the hose crossways about a half inch from the tip.  This will prevent the hose from sucking up the bottom 1/2" of the fluid in the atmospheric catchment tank, but typically you'd rather not suck up the dregs anyway.

When fooling with the coolant recovery hose, remember that the hole where it enters the top of the atmospheric catchment tank is supposed to be airtight so that fluid won't overflow out that point if the tank gets full.

AIR PURGE SYSTEM: When coolant is added to a cooling system, there is always some air diffused in the liquid.  Over time, this air will come out of solution and rise to the top of the liquid, forming air pockets.  To avoid creating hot spots (since the air won't cool the metal adjacent to it as well as the liquid would), the idea is to design the system so the air will collect in a spot where it won't do any harm so the owner can deal with it at his leisure.

In old pickup trucks, the top of the radiator was the highest point in the cooling system.  As a result, any air in the system would tend to collect right under the cap; all the owner had to do was top it up on occasion and the rest of the circuit would remain air-free.  Unfortunately, when Jaguar designed the XJ-S, the hoodline of a 1950 Ford pickup was not considered acceptable; not only would the top of the radiator have to be so low that it would not be the highest point in the system, but it wouldn't have a cap on it either.  Hence, more elaborate measures were necessary to continuously purge air out of the system.

These measures changed with the introduction of a second radiator cap on the bypass pipe with the introduction of the H.E.  Mike Morrin says, "The Pre-H.E. XJ-S has only the cap on the header tank.  The level of the cap is marginally below the radiator vent valve (with the car on level ground)."  There was a small tube from the top right corner of the radiator over into the top of the header tank on the left wheel well.  The bottom of the header tank was connected into the return line from the heater line, which is essentially the suction side of the pump.  The pump operation would therefore draw a flow from the top of the radiator into the header tank.  Within the header tank, the air would tend to rise out and collect under the radiator cap while liquid coolant went out the bottom back into the circuit.  The owner simply tops up the system every now and then to keep air out. With the H.E., it was decided to add a second fill cap on the bypass pipe.  This formed another high spot where air would collect.  So, the air purge tubing from the top of the radiator to the header tank was modified to include a hose connection for a line from a tap just under this second cap.  Unfortunately, this complicated matters; the bypass pipe is connected to the suction side of the pump, so it's at low pressure.  So, the coolant and air is likely to flow into the fill

Correction: The ©1982 Supplement, page 26-1, Fig. 2 showing the cooling system schematically shows the ejector (item 18) incorrectly; the line from the radiator and the line from the left side thermostat housing are interchanged.  Simply look at the tubing on your car to see the correct scheme.  The same schematic with the same error is included in the Haynes manual, page 334, Fig. 13.6.

The XJ12 with carburetors has a second radiator cap on the bypass pipe, but lacks the ejector-based air purge scheme.  Its air purge scheme operates similarly to the pre-H.E. except that it's connected to the coolant passages in the induction housings rather than to the top of the radiator.

On the H.E., in addition to the ejector scheme, a "water valve" EAC4168 was installed in the air purge connection to the bypass pipe.  This is basically a check valve that allows air to flow out towards the header tank but won't allow coolant to flow from the top of the radiator into the bypass pipe.  This water valve is built into the fitting on the bypass pipe itself.  This requires a 3/8" fitting at that end, and since the air purge tubing is 1/4", Jaguar uses a special hose that's 1/4" on one end and 3/8" on the other.  Of course, if you want to replace the hose, you can use a piece of 1/4" hose, a piece of 3/8" hose, and an adapter.  Tony Bryant says, "I've brazed a 3/8" fitting onto the bleed pipe to be able to use "standard" 3/8" heater hose here."

Folks, this horrible recommendation is probably the single biggest reason Jaguar didn't make it on its own and had to sell out to Ford.  Many Jaguar mechanics owe their livelihood to this terrible advice, since a high percentage of their work is traced to this stuff plugging up the bottom half of the radiator and contributing to Jaguar's reputation for overheating problems.  Please, do not use any leak-sealing substance within the V12 cooling system.  If the system leaks, fix it.

To make sure no Barrs Leaks gets in there, you're gonna have to keep the car's cooling system away from Jag dealers.  Craig Sawyers reports: "Here's a horrible thing.  I bought Jag antifreeze, determined I wasn't going to run the risk of damaging my glitzy re-built V12 with the wrong stuff.  Anyway, my dealer casually tossed in a Jaguar box marked "2xJLM 636".  "What is this?" say I.  "Oh -corrosion inhibitor".  That sounds good I think, particularly given the recent thread on water types for radiator use, and electrolytic corrosion.  Well, guess what is in the box?  Two nicely packed bottles of (unmarked) Barrs Leaks.  AAARGH!  Will they never learn!  Needless to say, they are still in the box, and will never even have sight of my rebuilt rad."

If the car is more than a few years old and having overheating problems, it's not a bad idea to just take the radiator to a shop and have it rodded to restore its effectiveness --especially if you're not the original owner and the previous owner may have been using leak sealers.  John Napoli reminds you to clean out "the engine block, heater core and don't forget to remove and flush the expansion tank --these are commonly forgotten repositories of Barrs Leaks."

OTHER THINGS PLUGGING YOUR RADIATOR: Another major source of particles for plugging the tubes in the radiator is rust scale, which primarily comes from four items in the XJ-S cooling system: the header tank, the cross pipe, and a coolant connecting pipe on top of each head.  Replacing some or all of these items with non-steel substitutes would reduce or eliminate this source of crud.  See pages 204, 208, and 211.

GURGLE SOUNDS: Paul Burke says, "I had a gurgle which was coming from around the heater matrix.  It started fairly quietly and only became audible when the car was stopped.  I thought it was probably the air-conditioning system ha.  The sound became loader over time and more apparent under acceleration.  The noise turned out to be virtually (well maybe not all, but more than normal) the full pump output going through the right hand bank of the engine, out the back, through the heater matrix, along the hose that runs along the left hand side of the engine, into the small "T" into the bottom hose and back to the pump thereby effectively bypassing the left hand side of the engine and the radiator.

FIXING A PLUGGED RADIATOR: Once you come to the realization that your radiator is plugged, there are generally five things you can opt to do about it.  The first is to go down to the store and buy some product intended for "flushing" cooling systems and use it according to the directions.  A quick survey of owners on the internet indicated that this never does any good.  Paul Bachman says, "I was told by a good source (must have been good 'cause I can't remember who it was) that since the advent of aluminum engines and aluminum radiators there are no longer any radiator flushing products that do anything useful at all.  It seems the chemicals that used to do a fairly good job of cleaning out a brass/copper radiator cause serious corrosion to aluminum.  Soo... rather than face complaints (lawsuits?) from people who don't read directions, all such useful products just quietly disappeared from the shelves about 15 years ago.  I believe he went on to state that the antifreeze additives that were capable of keeping a brass/copper radiator free from blockage were deleted at about the same time.... thus the reason why most of our radiators are blocked or becoming blocked.  From my experience (from before 15 years ago), I have to say that this theory seems to have merit."

Unfortunately, the next four options all involve removing the radiator.  Deal with it.

The second option is to have the radiator "boiled".  This involves dunking the radiator in some kind of vat full of chemicals and cooking it for a while.  Again, a survey of owners indicates that this only rarely works with the XJ-S radiator, possibly because of the types of junk that typically plug it.  Considering how much effort it was to get it out and put it back in, you might want to rethink this option.

The third option is to have the radiator "rodded".  In this case, the radiator shop removes the covers on each end of the radiator and rams a rod through each tube from end to end, cleaning all the accumulated deposits out.  He then solders the covers back on and pressure checks the assembly.  This usually does the trick, although there have been a few reports when it didn't; it may depend on how skilled your local radiator shop is.  Jim Isbell says, "Some shops don't know that to properly clean it both tanks have to be removed.  If they only do one and you don't see any improvement it just might be because it wasn't cleaned properly."

Keep in mind that rodding does not render your radiator as good as new; the passages are unplugged but not all deposits can be cleaned away, and some parts may be stressed or weakened during the procedure.  Sometimes the shop will even report that the radiator is toast and cannot be rodded, and suggest option number four.

The fourth option is to have the radiator "recored", which means they take the end covers off and solder them onto a new center section entirely.  Apparently all brass radiators are made of comparable configuration cores, so the shop will be able to find a suitable core.  You need to ensure the new core is at least as good --and possibly better --than the original was.  Any upgrade generally involves the number of "rows" the core has.  There is also a difference in fin spacing, but if given a choice you should probably opt for the bigger fin spacing; the amount of cooling capacity is a secondary concern compared to the likelihood of the fins getting plugged with debris, and it's difficult enough to hose out the radiator on this car.

The fifth option, of course, is to have the radiator replaced.  You can opt for an OEM radiator --but in this author's opinion, you'd be nuts to do so.  As long as you're buying a radiator anyway, take the opportunity to convert to a single-pass arrangement as described on page 199.

If you're doing any of this work on your radiator, you should be installing coolant filters to make sure that it doesn't get plugged again --probably within seconds of starting, as all the crud sitting in your block is promptly flushed into your freshly-cleaned radiator.  Also consider the other items on the checklist on page 198.

COOLANT FILTERS: Everybody who has taken their XJ-S radiator to a shop and had it rodded out has been told that it was really plugged up.  The Jaguar recommendation to use Barrs Leaks in this system is often blamed, but there are apparently other contributors as well.  Rust scale coming off the inside of the header tank and cross pipe is a source of crud.  Some mechanics use too much silicone sealant so it leaves a bead around the joint, and later on this bead peels off and starts looking for a passage to plug.  And those who replace their coolant often but mix it with hard tap water are introducing a whole new supply of minerals with each change; when the engine heats up, all these minerals deposit on

Why don't they make a "last chance" filter to install in the upper radiator hose to catch all this junk before it can get into the radiator and plug things up?  There are no small passages in the engine, the chunks could just flow right through the block, but catching them before the radiator should greatly extend the time between roddings.

They do.  In fact, it's a fairly popular idea among car enthusiasts, so there are several different model coolant filters available.  Peter Smith identified one excellent brand: "The manufacturer is
Tefba
122/124 Silverdale road
Silverdale NSW Australia 2752
Phone: 02 4774 2022
Fax: 02 4774 2777

"It consists of a black nylon moulded body which resembles a jam jar approx. 2 inches (50mm) diameter by 2 inches high.  It has a screw lid and the inlet and outlet pipes come in at base level such that the side elevation resembles an inverted "T".  When you unscrew the lid you look down inside and see a stainless steel filter screen placed across the flow path of the coolant.  The filter screen is bent to form a delta shape or arrow head pointing in the direction of the flow.  This provides a filter element size effective of approx. 6 square inches.  The filter mesh hole size is about twice the size of the tea strainer we have in the kitchen.

"I have installed two of these on my XJC and they look pretty neat.  It is easy to check the screens by undoing the screw tops and there is a spigot which is attached to a disc which sits at the bottom of the pot.  You use this spigot as a handle which lifts out the disc with the screen sitting on top plus the crap."

The Tefba housing is not transparent, so you can't inspect the element for accumulated crud without opening the top. However, by installing the Tefba filters in the highest horizontal portion of each upper radiator hose, owners have found that they can check the screens without draining any coolant first --and so are able to check them regularly.  The fact that the element is huge means it's not that important to check them very often anyway.

In the US, you can get Tefba filters from Fasterjags (page 716).

There have been at least three significant issues discovered with the Tefba filters.  The first is that the element didn't come all the way up to the cap; when the cap was screwed on tight, there was a gap between the top of the screen and the bottom of the cap.  Debris -- especially debris that floats -- could thus circumvent the screen and enter your radiator.

Ashcroft found an easy fix for the Tefba elements being too short: "the element does end about 3/16" below the cap, but the disc is about 5/16" below the in/outlet.  I just put a 3/16" thick O-ring under the disc, raises the screen to the cap."  Chip Wikan adds, "a trip to the local Advance Auto Parts found an O-ring, part # 64630.1, dimensions 30mm x 36mm x 3mm which elevates the "grudge" tray perfectly flush with the top of the filter."

This author went a bit farther and fashioned a thin strip of stainless steel sheet metal into a wavy shape and set it in the bottom of the housing before dropping in the tray with the screen on it.  This bit acts as a spring that holds the element against the cap.  One must be careful to shape the sheet metal so no edges dig into the plastic.

The second issue is that the screen is clearly shown to be formed into a V shape in the exploded view diagrams, but the one actually delivered in the filter is merely warped into a U shape.  In operation, this U shape can be blown up against the outlet side of the housing.  Ken Gray reports: "I decided to check mine after doing the equivalent of 6 or so Italian tuneups (testing the newly installed Crane system).  I found a distinct dish in the filter elements exactly the same shape as the exit hole."

If this happens, the effective screen area is reduced from the entire screen down to just the portion covering the outlet itself --and if there's any debris in there to speak of, flow is nearly entirely cut off, perhaps quite suddenly.  This is bad.  It is therefore imperative that all Tefba users carefully fold their screens into a crisp V shape as shown in the diagrams, which will prevent any such disasters.

The third issue is that the screen doesn't sit properly against the bottom of the tray, which can allow crud to slip under the screen and into the radiator.  This problem may be made worse by folding the screen into the crisp V shape.  The

Despite these issues, the Tefba filter has proven to be the item of choice.  All three problems are easily rectified once you know about them, and since you are reading this book, you know about them.

One other nice thing about Tefba filters: somebody out there must be listening, because many of the problems seem to be getting fixed.  The later models reportedly come from the manufacturer with a stainless steel spring attached to the bottom of the tray to hold the screen up against the lid.  And Richard Francis reports that the screen has been fixed, too: "Today's Tefba's are delivered with a stronger screen...shaped like a baseball field backstop...very difficult to bend and smaller holes."

The only remaining complaint about the Tefbas is that the cap sometimes becomes really difficult to get loose, which some owners blame on the lack of lubricity of long-life coolant.  Applying a little water pump lubricant or some such to the threads might help some, but you might also consider this when installing and arrange the filter such that you can get a big pair of pliers or an oil filter wrench onto the cap.  And, of course, don't overtighten the caps; Don Buresh suggests it's like installing an oil filter, "go 1/4 turn past seated and no more, otherwise it will be a real bear to get off."  Dave Harvey says, "I apply Teflon grease to the threads and gasket surface, the same stuff plumbers use on gas fittings.  This makes tightening and loosening the lids a much easier task.  And I use a strap wrench.  My strap wrench was originally intended for removing the oil filter on my (long gone) Ford Courier pickup.  It works very well in a confined space since it has a 3/8" socket drive."

The Tefbas are so popular with XJ-S owners that can I even forward suggestions on what upper radiator hoses to buy.  Al Askevold says, "I found two preformed hoses that can be used.  On the right side I used a hose from Napa p/n 8303 from the t-stat housing to the filter, and a short piece of 1-1/4" hose on the other end.  The 8303 Napa hose was used for clearance around my cold air intake mod, but should work for the OEM setup too.

"The OEM hose that I cut to fit for the b-bank is not the way to go!  After clamping everything together both inside corners on the oem hose were bent just enough to cause a restriction, not much but not a good thing for the b-bank.  So back to Napa, this time I came up with a Napa hose p/n 7737."

Brian Schultetus found another source of coolant filters:
Gano Filter Company
1205 Sandalwood Lane
Los Altos, California 94024
+1 (650) 968-7017

This company makes a filter that is essentially a conical screen in a tube.  The basic model is a clear plastic tube so you can see the filter getting crudded up and know when to take it out and clean it, but some people don't like plastic so they offer a brass tube model as well.  They also claim that the screen is made of the same copper alloy as the radiator itself, so it also serves as a monitor for corrosion.  And they point out that merely having the clear tube can provide considerable information on what is going on in the cooling system; you can watch the little "window" while the engine is running.

The filter comes in three sizes, and of course they expect most customers to buy one per car.  The V12 has two upper radiator hoses, though, so you will need two filters.  The hoses are 1-1/4" ID, which corresponds to Gano's "small" size filter.

If you're worried about flow rates through those screens, Damrel suggests using the next size up Gano filter, the "medium" size filter.  "I made up a couple of custom hoses and put the old hose over the radiator and thermostat housing nipples to make up the difference."  This author uses the small Gano filters with no problem, but it certainly couldn't hurt to be using the next larger size.

Gano filters do a great job of keeping the radiator clean, but because the element is much smaller than the one in the Tefba they must be cleaned out periodically to keep from becoming obstructions themselves.  Removal, cleaning, and reinstallation is a snap, except that it requires draining about one gallon of coolant and replacing it afterward.  If you have the later XJ-S with no radiator drain, this could prove a pain.  So, if you have the radiator out to be rodded (!) it's

Even if you have an earlier car with a drain valve, periodic cleaning could prove messy and wasteful of coolant.  Hence, the idea presented in the section starting on page 195 of providing a fitting with a piece of hose with a plug at the end is recommended.  This makes it very convenient to just drain a gallon into a clean jug, service the Gano filters, then put the gallon right back in.

Tony Glavocich points out that the clear Gano filters can be helpful in diagnosis: "If you have Gano filters, you might just tie some white string to the screen filter, then you can monitor when the stats are opening.  That is how I discovered my problem.  I was also able to see a difference in flow between the two sides by observing the string.  The string thing is something that I would suggest to anyone with Gano see-through filters."

There are yet other sources of coolant filters.  John Goodman says, "I noticed on the AC Delco website they have screw-on coolant filters (like oil filters).  Paper filter with mesh so if they do clog up the paper busts leaving the slightly coarser mesh to still catch the big bits..."

There's another product made in Australia by:
Coolfilter Australia
151 Bushmead Road
Hazelmere WA 6055

Unfortunately, one customer had problems with the Coolfilter product. "It consists of a conical plastic material which has a series of steps.  The idea is you cut it off at the appropriate shoulder to suit the ID of your hose.  I fitted new hoses and the there was no appropriate shoulder; one shoulder was too big and caused the filter to buckle and the next shoulder too small.  The step sizes go from 1.1" to 1.3".  The new hoses I have are 1.2" ID.  The Coolfilter is very flimsy and cannot push the hose out to accommodate the 1.3" step and of course the 1.1" step is too loose.

"Also, I believe the holes are too large (tea leaves would go straight thru), it would only filter out large particles.  The Coolfilter has slots which are 13mm long by 1.5mm wide tapering down to 1mm.  The slots are in between each size step and running lengthwise.  I have run the vehicle with the Coolfilters installed (as best as achievable) for about 50 kilometers and they have captured no crap at all.  Either I have a clean system or they pass the crap thru the slots and gaps created by the buckling of the OD."

Tom Bennett says, "Make your own filters!  I bought a couple of very fine mesh SS tea strainers, a little bit of cutting and shaping, ended up with 2 "chili" shaped strainers that fit into the top inlets of the rad.  Work great!  I open them up about once every 3 months, although the crud is getting less.  First time I looked, there was about a teaspoonful of crap in each!"

A fan tip rub may also be caused by a failure of the left side motor mount.  When stomping it in low gear, a lot of torque is applied to the drive shaft.  According to Newton, this means that the same amount of torque is applied to the engine/transmission assembly in the opposite direction.  The engine tries to tilt to the right, applying tension to the left motor mount that was really designed for compression only.  If this rubber mount is torn, the entire engine will lift right up off its mount, causing the fan to rub.

Mark D. Stoner did. "My yellow fan decided to explode one day when shifting at full throttle from 1st to 2nd gear.  Put a nice dent in the top of the hood along with shredding the steel fan shroud and blowing a huge hole in the radiator."

Lee Opausky wrote: "Yes, the yellow plastic fan is cracked at the front.  When questioned, the shop foreman of one prominent Jag dealership told me not to worry, the crack on his XJ-S is ½" wide!"  More proof that you can't trust the dealers for good advice.

Jim Isbell ordered a replacement fan, and reports that the fan he was shipped did not look like the original.  "It is black and has a flat center metal piece.  The old one was white (now yellow) and the center piece was dished.  The old one had a lower aspect ratio (short and fat) to the blades while the new one has the higher aspect ratio (long and skinny).  The black flat one makes up for the "dishing" by offsetting the plastic instead."  With any luck at all, this means that Jaguar has recognized the problem and redesigned the fan, and this new one won't have cracking problems.  By the way, some of us believe the original fan was yellow to begin with, not white.

The black plastic fan may be an improvement, but to be safer still it may be preferable to just go ahead and replace the belt-driven fan with electric fans as described beginning on page 219.

FAN CLUTCH TYPE --EARLY VS. LATE: The early XJ-S fan clutch mounts with one bolt, the later with four.  Mike Morrin points out that his ROM (Ed 4) appeared to have the two confused. "On page 26-3, section 26.35.21 appears twice, once titled "FAN AND TORQUATROL UNIT (Early Cars)" and then titled "FAN AND TORQUATROL UNIT (Later Cars)".  The diagrams and text for these sections appear to be transposed, as the section for "later cars" matches my 1975 car (as well as the illustration in the 1980 edition of the parts catalogue)."

On second thought, maybe not.  Morrin continues: "I am now sure that the version with the 4 bolts holding the clutch on to the pulley is the early version used on the carburetted XJ12 (and never on the XJ-S), as I now have one of these (XJ12) engines with fan clutch.  My "spare" 1973 XJ12 engine has a fan clutch with 4 bolts holding the clutch to the

So, apparently, this is what we have: The early XJ12 had a 4-bolt fan clutch with a metal fan.  When the XJ-S was introduced, it came with a 1-bolt fa clutch and a metal fan.  In 1979, this was replaced with a 4-bolt fan clutch with a plastic fan.

It it commonly acknowledged that the worst cooling problem the XJ-S has is not when running but after shutdown.  The small electric fan runs after shutdown if the thermal switch has it running when the engine is shut off, but once the switch cuts out --which it does all too soon, since it is reading coolant temperature at radiator outlet --it will not come on again.  700 pounds of hot engine plus hot exhaust manifolds and hot catalytic convertors tend to raise the underhood temperatures after shutdown considerably higher than they ever were while running, and there are indications that parts of the engine itself get hotter after shutdown as well.

There are three problems generally associated with post-shutdown heating: Dropped valve seats, hot start difficulties, and heat-stressed engine compartment components.  The exact mechanism of dropped valve seats is unclear, but several owners have suffered dropped seats after a hot shutdown rather than while running.  The other two problems are clearer, and result from the high temperature of the air surrounding the engine --and all the extraneous components that are heated by the air.  Since there is no longer fuel flow in the rail, the fuel sitting in it gets hotter and hotter, causing serious hot start problems that Jaguar has addressed with a coupla different types of fuel rail temp sensor providing fuel enrichment.  The post-shutdown underhood temperatures are clearly a key cause of deteriorated hoses, brittle wiring, short-lived electrical components, and a host of other traditional Jaguar afflictions.

This section includes several ideas for dealing with the post-shutdown temperatures.  Most address primarily the temperature of the air within the engine compartment, which may or may not have a significant effect on the temperature of the heads themselves in the vicinity of the valve seats.

HOOD VENTS: Just the ticket for letting the heat rise naturally out of the hood after shutdown.  It's a body modification, so it's discussed further on page 473.

ELECTRIC COOLING FAN BOOTSTRAP CIRCUIT: The electric fan includes a "bootstrap" circuit, so that if the coolant is hot enough for the fan to be running when the engine is shut off, the fan will continue to run until the coolant temperature switch shuts it off.  Once off, the bootstrap circuit drops out and the fan cannot start again, no matter what.

Other cars --notably Japanese and other FWD 4-bangers --have cooling fans that cycle on and off for quite a while after the engine is shut off.  Clearly, they are wired so that the fan will run if the thermostat calls for it, regardless of whether the ignition is on or not.  It is also evident that they come on --indicating that once they shut off the first time, they may still be needed again.  Probably the engine heat soaking through the compartment.

Why did Jaguar provide this bootstrap circuit, rather than just wiring the fan to run when needed like the Japanese cars?  There would be two possible results if the bootstrap weren't in there: 1) The fan would never come on after shutting off the first time --meaning that the bootstrap circuit was unnecessary; or 2) the fan would come on after shutting down, which means it needs to come on and the bootstrap circuit is contributing to the cooking of the engine parts!

The only plausible explanations: A) Jaguar was afraid the Lucas thermostat would fail in the on position and kill the battery; B) they didn't feel that a fan kicking on and off in the parking lot was in keeping with the proper Jaguar image; or C) they were worried about liability from someone having their fingers in there when a fan came on unexpectedly.  Stuart Barnes adds D) "Many car alarms are voltage sensing and although they can cope with a voltage rise (to allow an electric fan to run and then stop) a lot of the aftermarket varieties can't cope with the voltage drop that would occur when the fan came back on."

For those of us who are more concerned with the life of our machines, keep our fingers out of moving machinery as a force of habit, and don't have such alarm system concerns, it might be a good idea to rewire that circuit to run the fan whenever necessary.  It's easy to do: On the left side of the engine compartment is a small blue box that looks like a relay, but it's the diode pack (see page 224).  Pull the LG wire off of terminal 4 and connect it to a 12V power supply.

There is a 12V supply available at the solid brown wires at the headlight fusebox just a few inches forward of the diode pack.

Note that, if you have headlight washers and wipers, the blue box might not be the fan diode pack.  See page 224.

ENGINE COMPARTMENT AIR TEMP SENSOR: Another way to get the electric cooling fan to run longer after shutdown might involve adding an air temperature thermostat within the engine compartment --preferably high and rearward, where the post-shutdown cooking problems are the worst.  This thermostat could be set at a much lower temperature than the one in the coolant and still wouldn't come into play while the car is moving or the engine-driven fan is circulating air.  But if the air starts getting hotter after shutdown, it can come on --even if the coolant in the water pump isn't that hot -- and flow some cool air through the engine compartment.

Imperial makes a dandy little "Adjustable Thermostat for Electric Cooling Fans", number 226203, available at Discount Auto Parts.  It's really an air temp thermostat.  It has a remote bulb sensor and includes instructions for mounting right on the back side of the radiator core, but you could mount it anywhere --even on the underside of the hood!  The thermostat is adjustable from 248°F to 32°F, and the contacts are heavy enough to control fans directly without relays.

ELECTRIC COOLING FAN POST-SHUTDOWN TIMER: Michael Aiken's plan: forget relying on temp sensors and simply provide a timer that runs the fan for a fixed amount of time after shutdown.  Aiken used one of the existing 10minute seat heater timers to provide this fan operation, and provided the wiring scheme shown in Figure 12 which automatically starts the fan running on the timer whenever the engine is fully warmed up and shut off.  Aiken points out that this is not an unheard-of idea; the Nissan 300ZX uses a similar scheme with a 17-minute timer.

Aiken describes this scheme: "The timer is activated by grounding pin 1 and then releasing it.  It will not activate if pin 1 is held to ground.  I left the manual switch (on the side of the console) wired in so the light would show when the fan is on, but that is optional."  Having the pushbutton may have an additional benefit: you can push the button to force 10 minutes of fan operation whenever you wish.  This might be handy if, for example, you get stuck in downtown traffic; you can simply tell the fan to run continuously for 10 minutes rather than cycle on and off with the thermostatic switch operation.

"The capacitor is a 2000µfd electrolyte and the diode is 3 amp.  The capacitor attaches to ignition key 12V output in position 2 and 3.  This is important to keep the fan from coming on during startup (position 3)."  Ed. note: the wires that meet this criteria are white, as has been indicated on the schematic.  They are connected to terminal 3 on the ignition switch.

"When 12V is applied to the capacitor it charges through the diode.  When the ignition is turned off the capacitor discharges back through the relay momentarily (about .5 seconds) activating it and starting the timer relay.  The fan runs for 10 minutes and then shuts off.  The thermostat in the ground leg prevents the capacitor discharge if the engine is not yet warmed up.  The capacitor does hold the charge and will discharge later if the temp reaches the set temp --even several minutes after shutdown.  I set my temp at 180ºF."

The schematic shows the output of the timer (pin 4) connected through a diode to the wire from terminal 1 on the diode pack to the fan relay, so it will directly close the relay and operate the fan.  Radio Shack catalog number 276-1661 will serve nicely for this diode as well as the other one used in this scheme.  In this application on the timer output, the diode only serves to make the indicator light show that the timer is engaged.  If this diode is omitted, the system will still work just dandy but the light will be on whenever the fan is running, even if it is the A/C compressor control or the stock

If you happen to have one of the later cars where the A/C compressor does not bring on the electric fan (as Aiken has), you don't have to buy a new diode for this task; there's an unused one in the diode pack.  Just connect pin 4 of the timer directly to terminal 3 of the diode pack.

Aiken also points out that this scheme doesn't have to control the small stock electric fan; it could be used just as well to control an aftermarket electric fan, or anything else electrical you'd like to run for 10 minutes after shutdown.  The use of a marine bilge vent fan has even been suggested.  It's probably not a good idea to operate a large fan or multiple fans; it shouldn't take much airflow to keep the underhood temperatures within reason, and you don't want to strain the battery.  The fact is, the stock Jag small fan is probably perfect for this job.

Since Aiken used the seat heater controls, the schematic shows the timer and the pushbutton with indicator light as they appear in the Jaguar seat heater schematics.  Of course, if you'd rather leave your seat heaters wired as originally intended --or if you have an earlier car that doesn't even have seat heaters --you can simply buy a new timer from Jaguar, or perhaps a generic timer (or maybe the one from a Nissan!).  You can simply leave the pushbutton and indicator light (and the related diode) out of the circuitry altogether if you wish and connect terminal 30 of the relay directly to pin 1 on the timer.  Or, you can buy any generic momentary pushbutton switch; don't let the excessively complicated Jaguar illustration fool you, that heater switch is just a normal momentary single contact switch with a built-in indicator light.  If it's only the indicator light you want, you can skip the switch altogether and simply buy any generic 12V indicator and connect it to pin 4 on the timer and to ground and mount it anywhere convenient -- or you could wire it to one of the unneeded warning lights in the dash.

Aiken apparently left his timer where it was originally mounted behind the dash, but if you're installing a new timer you can pretty well choose anywhere to install it.  Other than 12V power --any brown wire --the only thing you really need is access to a suitable white ignition wire, and they are all over the car --even going to the EFI power relay in the trunk.  There is also one to the ignition system on the engine, so it's possible to install all of this stuff someplace near the fan itself --perhaps in front of the radiator, or in the compartment behind a headlight --and not have to run any wires into the passenger compartment, provided you don't want a pushbutton or indicator light.

The D-Jetronic XJ-S fuel system involves a fuel tank with a drain that feeds a small surge tank.  A screened pickup in the surge tank leads to a soft-mounted fuel pump just below and to the right of the spare tire.  The line leads to a fuel filter and then to two separate fuel rails on the engine, one for the left bank and one for the right.  A pressure regulator on each rail directs excess flow through a fuel cooler and then back to the tank.

The Digital P uses a similar system except that the two separate fuel rails were replaced with a single rail.  There are still two pressure regulators, but in this case one is a supply regulator and one is a return regulator.  Supposedly the return regulator, the one on the LF corner of the engine, is the only one that actually does anything.  While the D-Jetronic regulators held rail pressure constant, the Digital P regulators vary rail pressure with intake manifold vacuum and therefore have vacuum lines connected to them.

The earliest saloons are fitted with carburetors, which use much lower fuel pressure than EFI.  The EFI saloons have fuel systems resembling those in the XJ-S.  The most notable difference in the saloon fuel system, though, is that the Jaguar saloons have two fuel tanks and a switchover system so the driver can choose which tank to use.

In 1992 the XJ-S fuel system changed markedly.  The external fuel pump was replaced with a submersible pump inside the tank.  The fuel rails were redesigned to connect to the injectors with O-rings instead of short hoses.  The worthless supply regulator was omitted.

Besides the usual general concerns about fuel fires --fuel lines left in place too long until they rot, etc. --there are also a couple of specific worries:

EARLY D-JECTRONIC FUEL RAIL: The early Digital P XJ-S's (early 80's) had a problem with engine fires.  There was a recall to address the problem in which the fuel rail on the engine was replaced; the newer design is indicated by rectangular tubing, while the pre-recall rail was made of round tubing.  All Digital P XJ-S's were subject to this recall, but indications are the recall was not as conscientiously applied outside the US.  Unfortunately, word is that the recall is "closed" and dealers will no longer perform it.  If you have a Digital P with round tubing in the fuel rail, you probably should consult your favorite junkyard and collect all the parts that look different and perform the recall yourself.  Note that the D Jetronic still uses fuel rails with round tubing.

Leaking fuel in an engine compartment is remarkably difficult to ignite.  Usually there have been obvious odors and visible leakage for ome time.  Please do not ignore fuel odors; the XJ-S shouldn't have any.

MARELLI IGNITION WIRES: The later XJ-S with Marelli ignition also has a reputation for engine fires.  Peyton Gill reports on "an XJ-S that had a little pyrotechnics under bonnet.  I asked the guy about it and he said that the fire was put out within 30 sec (owner had a fire extinguisher) and the estimate to repair was $2000.00.  There was not that much damage.  The cause of the fire was the ignition coil wire was about 1/4 inch from one of the fuel injection lines (between rail and injector).  The ignition wire had been arcing to the line and eventually worked its way through.  I guess the physical damage and ozone created by the arc eventually broke down the line."

Julian Mullaney adds, "There was a recall for cracked injector hoses and injector bodies.  Ozone from the distributor leads causes the perished plastic.  The recall replaces the lead with a shorter one, and replaces the injector.  They looked up my car (vin no.) in their database and the fix had already been done a long time ago, however the problem persisted.

"The problem was ozone deteriorating the injector hose on the right bank second cyl. from the firewall.  It produces a cracked surface of the rubber hose.  You should look carefully for this, it's not easy to spot.  "The dealer said that they were instructed to look for visual damage to the hose and replace injector if needed.  "If" is the key word here.  However, if it looked good, they could get away with only changing the HT lead to a shorter one (thus not close to the injector) and leave the original injector hose.  This leaves the chance that damage could have occurred to the hose but it's not visible yet, leading to the following chain of events:

MTBE: Stephen Wood says, "We starting in Spring 1996 having a substance called MTBE --methyl tutol-buytol ethanol, something like that --blended with our gas to help reduce emissions.  Hopefully they will be taking it out soon, as there has been a major hubbub about it here.  You see, it also melts things, like fuel lines, carburetor gaskets, (especially the old rubber/cork type), fuel tanks, brazing material solder, etc.

"Last summer car fires were up significantly all over the state, including my brother's '69 Camaro (it was restored).  MTBE melted through the carb gaskets on his vintage Holley and poof.

"At that point it got serious, and I checked my fuel lines, and sure enough, they were going way squishy from the inside out.  In other cars we have seen it also has melted injector seals.

"If you ask the insurance companies they have had a slight increase but nothing to worry about.  No problem, right?  Wrong!  Most of the cars affected are cars that the insurance industry won't provide fire, theft and vandalism coverage on anyway.  If you ask the CHP and the firemen, they know that last summer was a major problem."

So, you need a new type of fuel hose, right?  "The problem with the hose issue is that the rubber manufacturers are not going to gear up for a California-only issue.  However, some of the new cars have fuel lines made out of a tygon derivative, a newer plastic that is more resistant to these blended fuels (New LT1-LT4-and LS1 GM motors).  I don't think there is a crossover app. as of yet, tygon is a bitch to work with and has the characteristics of polypropylene tubing, i.e., firm and not clampable.  You have to use special fittings with it.

"There is supposed to be some new silicone-based flexible "rubber like" fuel line coming out soon from Gates or

"I will have to take my gas tank out this summer, and have it boiled and welded or just put in a new one.  The corrosion around the outlet is growing and I think it is melting through the solder.  I may just JB Weld it or something."

FIRE EXTINGUISHERS: After reading this book, you have probably come down with a healthy dose of paranoia regarding fires in the XJ-S.  A fire extinguisher is cheap, and may come in handy.

Ron White had a fire in his car, and thanks to having a fire extinguisher in the trunk and knowing how to use it, his car survived with almost no damage.  "I have seen engine fires in other cars and have seen people make the mistake of flinging their hoods (these were American cars) open, only to have the fire flare up 5 or 6 feet because of the added oxygen.  I opened the bonnet just enough to get the nozzle of the extinguisher in, and gave it a good squirt.  I then cautiously opened the bonnet up and seeing no flames opened it up all of the way and gave it a real good squirt!"  White's extinguisher happened to be a Halon type which works wonderfully and leaves no crud on the engine but is bad for the ozone layer and is in the process of being outlawed.  Experts seem to feel that a common powder type fire extinguisher would probably work just as well, the only disadvantage being that you'd have a job getting all the powder out of the engine compartment afterward.

One more note: White's car is an '86, meaning it's late enough to have had all the updates to correct the early fuel rail problems and too early to be covered by the recall for the later cars with the Marelli ignition.  "It appears that the cause was a cracked body on an injector, and it was squirting fuel directly on the distributor!"  That fire extinguisher is sounding like a better idea all the time, isn't it?

John Napoli suggests a built-in system like those found on race cars: "It should be a lot easier to extinguish a fire within the closed confines of the engine compartment with the bonnet closed, and you could certainly react a lot quicker than, say, opening the bonnet, saying "Oh, sh$t", running for the boot, trying to find the fire extinguisher that is underneath all your luggage, meanwhile the bonnet is open and the flames are getting higher..."  Of course, keeping the extinguisher on the floor in front of the front seat may help.

Emile A. DesRoches says, "If anybody is really interested in a real "racing car" fire control system (sanctioning bodies require a system plumbed in to spray at the engine, fuel cell and driver's lap area), they can be obtained from such organizations as Racer's Wholesale in Atlanta.  From experience as an SCCA tech inspector, I can say that they may make a mess, but they work and clean up is inevitably less expensive than replacing a fried V12 motor."

FUEL ODORS: To state what should be obvious: Jaguars are not supposed to smell like fuel.

One excellent suggestion is to trot the car right down to your local Jaguar dealer, or anyone else with the equipment to test automotive emissions.  The testing equipment includes a probe that is inserted in the tailpipe to detect unburned hydrocarbons (fuel).  This probe is real handy for finding fuel leaks anywhere in the car.

There is a relay in the trunk through which the EFI controls the fuel pump; it's the one without a red paint mark on it.  You can remove the relay and jump connectors 30 and 87 in the socket to run the fuel pump.  This is useful for searching for fuel leaks without having to leave the engine running.  Of course, you'll kill your battery if you do it for too long.

FUEL ODORS IN TRUNK: The trunk smelling of fuel is a common problem with many common causes:

. fuel-soaked carpet padding (see page 235)
. leaking hoses either in the trunk or over the IRS (see page 235)
. leaking compression fittings (see page 236)
. someone installed the wrong type hose in your fuel system (see page 238)
. there may be a bad O-ring in the fuel filler connection (see page 244)
. a plugged or disconnected drain from the fuel filler compartment (see page 245).
. a tank that develops a hole by rubbing on a steenkin' rivet (see page 245)
. a tank that has developed stress cracks (see page 245)
. a tank that has simply rusted through (see page 245)

Note that you can greatly reduce the possibility of fuel leaks or odors by addressing all of these concerns at once!  Take the tank out, coat it outside and in, replace all fuel and vent hoses with new, and reassemble.  It would take a few days, largely because lining and coating the tank require several steps of cleaning and coating and letting them dry overnight.  If you're not willing to try lining the inside of the tank yourself, doing all the other tasks would still be worthwhile.

Don't overlook the possibility that fuel odors in the trunk aren't originating in the trunk.  The author had a leak in a line under the car, and couldn't smell it outside the car but it stank somethin' awful inside the trunk.  I couldn't even imagine how the fumes got into the trunk.  Likewise, a malfunctioning vapor recovery system (see page 259) that's releasing fumes into the bodywork up at the front of the car may result in the fumes migrating into the trunk.  In fact, even a cylinder misfiring and releasing unburned fuel out a tailpipe has been known to cause fumes to collect inside the trunk.

People who correct problems with the vapor recovery system often report that it cures odor problems in the trunk.  If the problem was a stuck-open (or missing) Rochester valve overloading the carbon canister and as a result odors were coming from the carbon canister up front and were working their way through the bodywork to the trunk, they may be truly cured.  Likewise, if the problem was a leak from the vapor recovery system somewhere, it may be truly cured.  But if the problem was a plugged vapor recovery system causing excessive pressure in the tank, the problems are not cured, they're just no longer as apparent.  The vapor recovery system is supposed to prevent excessive pressures within the tank, and if it fails the pressures may reach levels that force fuel through leaking fittings or even crack the tank.  If the vapor recovery system is fixed and the pressures are no longer excessive, there may be far less fuel coming through the leaks --but the leaks are still there.  And any cracks that may have started in the tank are still there, too.  If you could smell fuel, that fuel was getting out somewhere, and it would behoove you to find out where.

SMELLY CARPET PADDING: The fuel filter is the size of a Coke can and is located behind the spare tire in the trunk.  When this filter is replaced, it is all too easy to spill its contents within the trunk.  The nature of the foam padding under the carpet is such that once this happens, your trunk will smell of fuel for all eternity.  The only suggested fix is to replace the carpeting and padding.  It is recommended that before the filter is replaced, and before any repairs to the fuel system in the trunk are carried out, the carpet be removed.

When changing that filter, unscrew the mounting bracket from the floor first.  Then you can hold the filter over a catch pan when disconnecting the hoses.

LEAKY FUEL LINES: As described on page 243, there are several fuel lines that include a piece of hose in the middle of a metal tubing assembly.  When old, these hoses often weep fuel rather than burst outright.  In fact, they may leak so slowly that they never appear wet; the fuel evaporates faster than it leaks.  Just about the only indication of trouble is the odor.

Two of the hoses that need attention are not in the trunk, but rather under the car and over the rear suspension.  The line

Check all of these lines with the pump running, and replace any hose you even suspect of being the cause of odors.  Better yet, just replace the hose sections if they are older than ten years or so.

Both hose sections over the IRS are actually fairly easy to replace.  Both lines connect at threaded fittings at the forward corners of the trunk floor, and both have couplings just forward of the IRS.  Before removing the right side one, depressurize the fuel system, and before working on either, pinch the appropriate fuel lines in the trunk and in the engine compartment (if the tank hasn't been removed and the system totally emptied).

This author found the one on the right side a bit easier to do than the one on the left, because there were more other things in the way on the left side --but some of these things, like the handbrake cable, may switch sides on a RHD car so others may have different challenges.  On the author's '83, the fuel line assembly on the right side came out as a unit, so it could be rebuilt and reinstalled easily enough.

The line on the left side takes a little more thought.  First, there is a plastic clip up at the top of the arch holding it in place.  If it's not broken to begin with, it's easy enough to break it; it is only too apparent that it's not necessary to hold it in place.  Second, the short section of metal tubing on the rear end is hook-shaped, so it isn't likely to feed out over the IRS.  Instead, after disconnecting both ends of the line, pull it rearward a bit and use a razor knife to slice through the hose itself.  Then remove the rear section rearward and the front section forward.

To rebuild and reinstall it, start by cutting a piece of new hose a couple of inches longer than the original hose.  In fact, note how much of the straight section of the hook-shaped metal portion is exposed beyond the end of the hose, and cut the new hose longer enough to cover almost the entire straight section.  Install this new hose on the front metal section of the line with an EFI clamp, making sure that the screw portion of the clamp is positioned downward and a little inward because the top and outer side will be against the inside of the bodywork.  Stick a plug in the end of the hose, then feed the hose into position from the front until the end of the hose comes out on the back side of the IRS where you can get ahold of it.  Clean the entire straight portion of the hook-shaped section in preparation for having a hose slid onto it.  Put an EFI clamp over the tube, remove the plug in the end of the hose, then push the tube into the hose and continue to push until things begin to line up.  Loosely assemble the coupling at the forward end.  When the tube has been pushed into the hose far enough that the threaded end lines up properly with the fitting on the trunk floor, position the clamp near the end of the hose and tighten it down.  By using a longer piece of hose here, the clamp is located such that it can easily be tightened below the corner of the chassis and the screwdriver can be held within the wheel well.

When you tighten the threaded end into the fitting on the trunk floor, you will need to have an assistant hold the end of the line on the inside of the trunk in the correct position.  Failure to hold the lines in position while tightening will result in distortion of either the hose over the IRS or the hose in the trunk or both.

COMPRESSION FITTINGS: In the author's '83, there are seven places in the rear end of the car where a metal fuel line is attached via a brass nut and a brass compression seal.  Three of these are on the main fuel tank itself: the main line to the surge tank, the vent line from the surge tank, and the return line from the front of the car.  The other four are in two elaborate bulkhead fittings where the supply line and the return line run through the floor of the trunk.

These fittings are assembled by sliding the nut onto the tube, then sliding the brass compression seal onto the tube, then inserting the tube into the fitting and tightening down the nut.  As the nut is tightened, the brass ring is compressed onto the steel tube, forming a reliable seal and also securely holding the tube in place.  Typically, the thin-walled steel tube is soft enough that the compression of the seal necks the tube, although this isn't strictly necessary for sealing or retention.

The bad news is that these type connections are meant to be assembled once and left alone.  If you unscrew the nut, you can remove the nut/tube/seal assembly out of the fitting, but you cannot get the seal off the tube --and you'll only get the nut off if it can slide off the other end.  If you simply slide the thing back together and tighten it down, there's only a moderate chance it will seal; the tube and the compression ring apparently work-harden, and there's no further compression available to allow it to reseat.  Applying sealing substances is a waste of time, and can result in chunks of

The good news is that the brass compression seals themselves are common in the US and are available at any hardware store or industrial supply house.  They are also often available in auto parts stores, in the bins with brass fittings.  Note, however, that there is a similar type of compression seal intended for use with copper or plastic tubing, and the compression ring itself is a bit different; it has a collar around the middle.  It might work here, but obviously you might be well advised to seek out the same type as was originally used to ensure it seals properly in these fittings.

Suitable steel tubing is also available in sizes up to 3/8", sold in auto parts stores in straight lengths with flared ends and nuts in place; just cut the flares off and chuck the nuts, they won't work here, all you want is the straight length of tubing.

You can purchase a tool in any auto parts store that will help you bend metal tubing without crimping it.  Note that cheap tubing benders often don't work very well; it is recommended that you spring for a good one.  Also note that you'll want to put the bends in your tubing before you cut it to length.

You can make a barb for attaching a hose to the steel tube using a tool sold a most auto parts stores.  It's called a "double flaring tool", and its purpose is to make those flared ends that you just cut off the tubes you bought.  The intended use of the double flaring tool involves two steps.  The first step forms a little bulb on the end of the metal tube, and the second step folds the outer end of this bulb back inwards to form the double flare.  Forget the second step, just perform the first step, and it leaves a neat, professional-looking barb on the end of the tube for attaching a hose.  One example of this tool is the AmPro T73360.

Anyplace that sells the compression seals probably also sells the nuts that are used with them --but that won't help you.  This is a Jaguar, so the fittings are some oddball thread.  In the US, you'd go nuts (!) trying to find a new nut of the same thread; if you need a new nut, just go ahead buy an entire new hose assembly from Jaguar.  Fortunately, the old nuts are usually reusable; just cut the old tube in half to recover them.

When you assemble a compression fitting with a new section of tubing and a new compression seal, you'll know what they are supposed to feel like.  You can feel a smooth crush as the seal is compressed onto the tube./P>

"If it ain't broke, don't fix it" is a good credo, but you could actually justify removing those bulkhead assemblies on the basis of the weight savings alone.

I'd suggest you throw those bulkhead fittings as far as you can, but remember to save the nuts from them first; they might actually fit two of the connections on the tank itself --although that'd be an unreasonable expectation from the British, they probably deliberately made them different to make sure you couldn't connect the wrong line to the wrong place!

If your problem is that you've boogered up one of the smaller nuts threaded into the tank itself, you might be able to save yourself the trouble of trying to find such an oddball nut by simply performing this bulkhead fitting replacement and getting the nuts from there.

Finally, the big problem: the main line from the main tank to the surge tank.  On the author's '83, this is a hook-shaped 1/2" tube that screws into a 90º fitting on the tank.  I certainly hope they changed this design on later cars.  The incompetence of the designer was so awe-inspiring that you can't even get a wrench on that nut without removing the tank from the car!  Anybody exhibiting this level of skill should be operating a broom rather than a pencil --and only if you're not too picky about how clean the floor is.

This fitting is the most likely one to be leaking because of the hook-shaped tube.  Getting a hose connected to that tube,

So, once you finally figure out this is where your trunk odors are coming from, you need to get that fitting apart.  Drain the tank (see page 245).  Disconnect the straps holding the tank in place.  Insert some sort of broad pry bar between the gas tank and the deck it's sitting on and see if you can lift the tank up a bit.  If you can't, use a machete to slice through the foam under the tank so you can.  Once the tank is liftable, it's actually possible to get a box end wrench on the nut by sliding it on from the other end of the hook-shaped tube and holding the tank lifted as you maneuver the wrench to the nut and turn it.  Hence, you can fix your leak without totally removing the tank, disconnecting all those other lines, removing the battery tray, etc.

1/2" brass compression seals are actually not too difficult to find, but 1/2" thinwall steel tubing is.  The auto parts stores only carry steel lines up to 3/8".  You might try a place that carries parts for large trucks.  Other places that may carry 1/2" steel tubing, including hydraulic shops, typically have thicker-walled tubing --which will work fine in the compression fitting but is difficult to bend or to form a barb on for connecting the hose.

The solutions here come together.  First, you don't want to install another hook-shaped tube.  Instead, what you want to do is install a very short straight tube, providing a hose barb right there at the fitting on the tank.  Then you can use a longer piece of 1/2" fuel hose to connect it to the surge tank.  Hence, you probably already have the tubing you need - in the old tube.  Just cut off the old compression seal and cut off the hook end, leaving a straight section of steel tubing about 3" long.  Apply the old nut and new compression seal and install.  Be sure to clean up the outside of the section of tubing with some fine sandpaper so it forms a good seal.

Of course, if you try to use the double flaring tool to provide a hose barb on a tube this large, you may mess it up --and you have no backup tubing.  Solution: don't bother providing a barb here.  The maximum pressure this hose will ever see is about 3 psi, nowhere near enough to push a clamped hose off a smooth tube.

If your hook-shaped tube is too messed up to obtain a clean straight section from, you can use thicker-walled tubing since you're not bending it and you're not forming a barb.  The thicker-walled stuff might even be advantageous in providing a more secure attachment with more resistance to bending or deformation.

STINKY FUEL LINES: Believe it or not, one reported cause of fuel odors in the trunk is apparently the use of the wrong type fuel hoses.  They're not leaking; the odor seeps through the material of the hose itself.  You can tell this is the problem by wiping your finger on the surface of the hose, walking a few feet away, then smelling your finger.  If it smells like fuel, that's the problem.

FUEL HOSE MAINTENANCE: If you have any doubts about the condition of the fuel hoses in your car, replace them.  Based on experience from the online discussion list, it would be an excellent idea to replace all of the fuel hoses in the car at least once every ten years; you can do it every five years to be on the safe side.

In some locations, there is a fuel line assembly that consists of hose crimped onto metal lines; in such cases you can just buy new Jaguar fuel line assemblies, but it's cheaper to buy generic hose and install it in the existing lines with suitable clamps (see below).  The hardest part would be getting the original crimped fittings off, but the second time you do the job it'll be easier since you'll only need to loosen clamps.  Don't overlook the sections of hose in the lines looping over the rear suspension on each side of the car.

In other places, you will be replacing pieces of hose with clamps on the ends.  In yet other locations, you may need to replace hoses that don't seem to be attached at all --they are merely pressed onto the fitting.  Please read the following

FUEL HOSE SIZES -D-JETRONIC: Bernard Embden found that the nipples on the D-Jetronic fuel rail are measurably smaller than standard 5/16" nipples.  "Putting 5/16" hose on the Pre-H.E. fuel rail resulted in a less than satisfactory connection.  The clamps had to be tightened excessively and bunched the 5/16" hose just to prevent leakage at the required 30 lbs. fuel pressure.  Even in this unsatisfactory condition, the 5/16" hose could be rotated easily on the rail.  I fitted the 9/32" hose.  This was the only size hose that fit the nipple correctly."

FUEL HOSE SIZES -DIGITAL P: The D Jetronic fuel rail and injectors truly need 9/16" hose, a fairly unusual size.  The original hoses on the Digital P fuel injectors appear to be 7mm or 9/32" as well --but in this case it's the wrong size.  The injectors themselves are made by Bosch --and have barbs designed to fit an 8mm hose, a very common size.  The barbs on the square-tubing rail and on some of the lines to and from the rail are also designed to fit an 8mm hose.  When you have the old hose off, it is a simple matter to measure the diameter of the straight-sided portion of the barb between the ridges to confirm what size hose is needed.  5/16" is 7.93mm and will fit an 8mm barb just fine.

The problems begin when the novice mechanic finds out how easy it is to push the new hoses onto these barbs.  They just slide right on.  That just doesn't seem right, and smaller hose is purchased and crammed onto the barbs with great effort and sometimes even boiling the hose prior to installation or other extreme measures that are only too likely to damage the hose or shorten its life.

Resist such thinking.  The hoses are supposed to slip on easily.  Why would Bosch design an attachment scheme that requires lots of effort on anassemblyline?  When 5/16" or 8mm hose isused on the clampless connections on theXJ-S, they simply do not leak.  There is no problem there; the fuel leaks the car is plagued with come right through the hose when it dries up and cracks.

Some people have found 8.5mm hose --sometimes at a Jaguar dealer.  Don't use it on the XJ-S; there are no fittings on this car that call for this oddball size.

FUEL HOSE TYPE: The XJ-S features Electronic Fuel Injection, and EFI systems operate at higher fuel pressures than carburetors did: 30-50 psi vs. 5 psi.  Ordinary "fuel hose" was designed for 5 psi --do not use it anywhere in this fuel system.  Most auto parts stores now carry "EFI hose".  It is more expensive, but a fuel fire is no fun.  The basic generic EFI hose looks like standard hose; you will need to read the printing on the rubber surface to know you've got the right stuff.  Look for either "EFI" or "Fuel Injection" or some such clear indication of its suitability for fuel injection systems, or for a working pressure rating higher than 100 psi.

If you have clampless hose connections (see below), generic EFI hose will work fine --but there is yet a better idea.  If you find an industrial hose distributor or hydraulic hose shop, they can sell you what they refer to as "push-on hose", hose that was designed specifially for these type connections.  Push-on hose is available in two different styles: smooth rubber surface or cloth surface.  They both have basically the same specs; in fact, nobody seems to know why anyone would choose one over the other.  It probably has something to do with abrasion resistance or some such.

The rubber surface push-on hose usually has a bunch of markings on it, including a pressure rating in the order of 350 psi, but it probably does not use the term "EFI".  There is a spec number on there, and you're supposed to look it up in reference books to determine suitability for particular applications.  It is suitable for automotive EFI systems.

The cloth surface hose this author found has far less text on it.  Duh!  It's harder to write on cloth!  The letters are really big to be readable, and all it says is "WEATHERHEAD 5/16 H10005 D 09/14/98".  The pressure rating on this hose is actually lower than the rubber surface hose (250 psi) even though it looks a lot tougher than the rubber surface hose.  You cannot squeeze this hose flat with your fingers.  Weatherhead H100 series hose has a nitrile inner liner suitable for use with non-oxygenated automotive fuels.

Note that there are a few places on the XJ-S where one end of a hose is a push-on connection and the other end requires a clamp.  The push-on hose is suitable for these applications; it can be reliably clamped on suitable barbs.

The Weatherhead cloth surface hose is more expensive than the rubber surface: $2/foot.  Don't be intimidated by the fact that Jaguar wants many times that much for their "original" hose; it's no better, and it's arguably not as good.  Weatherhead is one of the most respected names in the industrial hose business.

Another good reason to be shopping at the industrial hose supplier is that you can buy this Weatherhead H100 hose in 1/2" size.  There are a couple of 1/2" fuel hoses in the trunk of the XJ-S, but there aren't many auto parts stores that carry 1/2" fuel hose.

Of course, you can buy fancier hose.  Bill Fernandez says, "There is a lot of stuff available out there, aero hoses, rubber, etc.  High quality cloth braided German fuel injection rubber hose is what I ended up using.  This is the same equipment used in BMW and Mercedes, they don't go bad period.  I have a 1975 CSi (BMW) with the original cloth braided hoses with 325k original miles and not a single leak or hint of gas yet.

"The H.E. Bosch injectors are designed to use slip-on rubber injector hoses.  The areo style will require lots of modification to both the injectors and the fuel rail to get them to work.  The areo stuff is very pricey and just not worth it aside from looks."

Hose to avoid: Based on several reports from owners, do not use Goodyear blue lined hose.  Vans says, "My Goodyear fuel injection hoses 5/16'' (blue lined) have failed in just 2 years.  They would only leak when side pressure was applied to the fuel rail or hoses, they would squirt out a small amount of fuel.  No leaks while running without side pressure.

"Just replaced all injector hoses with Dayco 7.9mm (5/16) from my local parts supplier.  While removing the Goodyear hoses some were able to just pull off.  When installing the Goodyear 2 years ago they were very tight and could not be pulled off.  This is not a job I want to do every couple of years.  My advise is to avoid Goodyear for these engines at all costs."

Ed Sowell adds: "I had the same problem with Goodyear hose.  I redid the rail with Gates hose, which most auto parts stores no longer carry.  NAPA does."

FUEL HOSE CLAMPS: Some fuel line connections, especially on earlier cars, came with crimped collars that compressed the hose against the barb.  If you remove a hose with a crimped collar, you can replace it with new hose with a clamp -- provided you use the correct type clamp.  If you live in the US and walk into an auto parts store and ask for a hose clamp, you will be handed a stainless steel band with a series of angled slots through it and a worm screw attached to one end.  These "aircraft type" clamps are excellent --for lines about 3/4" in diameter and larger.  Although they do sell small clamps in this style, they do not work well on hoses as small as the fuel lines on the XJ-S.  There are simply too many "corners" within that circle as it is snugged up, and although it may seal at first while you're looking it may leave local areas that aren't securely compressed against the fitting and will start leaking later when you're not looking.

If you live in the UK and ask for a hose clamp, you might get a "Jubilee" clamp or something similar.  These are also stainless steel worm screw clamps, but instead of angled slots in the band it has little raised lips for the screw to engage.  These are better than the US aircraft type clamps on small diameters, but still not good.

To assure a good, reliable seal, you're going to need some clamps that securely compress the hose onto the fitting uniformly all the way around.  While the worm screw types are not recommended, there are several other types that will work fine.  Many auto parts stores sell "EFI hose clamps", which consist of a steel band with a small screw and nut that draws it tight.  They come in various sizes, and you need to carefully select the size you want; these type clamps will only fit the size hose intended, you cannot just keep screwing them down smaller like a worm screw clamp.  Unfortunately, you're not likely to find these type clamps in stainless steel, so it is advisable to carefully apply anti-seize compound to the threads on that tiny screw if you ever want to get it loose later.

Sometimes EFI clamps are offered in a package with the hose; make sure you have suitable clamps on hand or can buy them separately before buying EFI hose without the clamps.  Jim Taylor says, "I replaced the originals on my (then) 16year-old '76 XJ12C.  I obtained two Volvo FI hose replacement "kits" (part number 273680-9).  Each kit contained the appropriate number of short rubber hoses and neat little black painted hose clamps (not worm gear type) for a Volvo six cylinder car.  This fix didn't cost very much.  My receipt (dated 3/4/92) shows I was charged the grand sum of $6.11 per

There is also a type of clamp that works similarly to the EFI clamp described above, except that it has two loops of wire in place of the steel band.  These seal pretty well, but they're not very pretty and they really mangle the hose.  They don't seem to come in stainless steel either.

Greg Price says, "The Series III XJ6 has some nice fuel injection hose clamps, and my local Jag tech recommends Mercedes fuel injection hose clamps."

Stefan Schulz says, "Here in the UK, Farnell offer stainless steel hi-torque hose clamps which are The Biz.  Highly recommended.  Farnell Industrial are on telephone [+44] 113-2636311."  Schulz adds that he does not recommend the fuel injection clamps from a Volvo.

Tom Mackie says, "I find most conventional "clamps" to be a little unsightly.  So..  There is a clamp used in the repair of shop air hoses as well as on oxy/acetylene hoses (if that's not a high fire hazard application, I don't know what is).  These clamps do not have a screw/nut on them.  They are a single usage item.  They are a formed metal band, with an outward flare/dimple/nipple (I have no idea what to call it) on each side.  These simply slide over the hose, are placed into position, then using pliers, these nipples are squeezed, compressing them, which in turn tightens the clamp.  No screw/nut sticking out, getting in the way, cluttering appearances etc.  Definitely not self loosening.  Removal is with side cutters..  Just snip off one side and bend it open.  These are cheap.. so making them disposable is not a big deal.  This I would use on the injector end.

"I was considering another crimp style, but for the fuel rail end.  There is what I'll describe as a "cup" shaped unit, which I believe is sorta an aeroquip fitting.  I have to confirm this yet, but I believe you could use any hose with the appropriate size "cup" and have it crimped into place.  The minor catch is that you either need the special tool which applies pressure to about 6 locations at the same time, or you have the fittings shop do it by taking them the fuel rail.  These are semipermanent, and removal is with a hack saw, which destroys the hose.  This is why I'm thinking of using these on the fuel rail side, and the removables on the injector side.  Again, no screws sticking out, etc.  Nice-n-neat."

Note that the problem of worm screw clamps causing leaks is not unique to the EFI fuel system.  One should also take note of the types of clamps used on the fuel tank vent system, the power steering hoses, the transmission cooler hoses, and just about anywhere else that small diameter hoses are clamped.  Leaks at some of these locations may be less disastrous than a fuel system leak, but you'd still rather not have any leaks.

CLAMPLESS HOSE CONNECTIONS: The section above describes what clamps to use on fuel hoses.  Now let's discuss not using them!  There are two types of hose barb used in the fuel systems on the XJ-S, and one of them must be clamped while the other should not be clamped.

With the barb shown at left, the hose is installed by merely pushing it onto the barb.  It works kinda like a Chinese finger trap; the hose slides on easily, but if you try to pull it off it grips onto the barb and won't let go.  These fittings typically come with a dished washer or cup that must be slid into place before pushing the hose on, but these items do nothing

Proper use of a hose clamp requires the smooth cylinder of the type shown at right for the clamp to compress the hose against.  If a clamp is applied to the barb shown at left, it will compress the hose against the points on the ridges and possibly damage the inner liner of the hose.  There are clampable barbs that have a series of small ridges in this clamping area, presumably to help ensure a reliable seal, but they are usually rounded and easily distinguishable from the large, toothy grips of the clampless barb.

Believe it or not, the non-clamped type provides a much more reliable seal.  This is apparently because it allows the rubber hose to flex and seals more securely as it does, whereas the clamped connection will often start to leak as soon as any pulling or twisting is involved.

Typically, you will know which type you're dealing with before removing the old hose by looking at what's on there from the factory.  If there's no clamp, it's the type that doesn't use a clamp.  If it's the type that needs a clamp, there will be some form of clamp --or a cup-shaped piece of metal that is "swaged" or "crimped" onto the end of the hose to compress it onto the barb.  The decorative cups on the non-clamped barbs sometimes look similar, but it is obvious that they are not swaged; in fact, you can spin them around with your fingers.

The problem, of course, with relying on the existing situation as an indication of barb type is that someone may have gotten in there before you and added clamps where there shouldn't be any.

Note that you may have a mix of clamped and clampless fittings.  The early D-Jetronic cars use clamps everywhere.  John Ashcroft says that his '80 needs clamps on the rail but not on the injectors.  On the author's '83, the entire injector/ rail assembly uses clampless fittings, but the connections at the fuel cooler still require clamps.

Regarding pressure ratings and the security of push-on connections: A shop frequented by this author has a tester, and in their spare time they test things to failure just for grins.  The 5/16" cloth-surface push-on hose described above was tested, installed as intended on a push-on fitting.  It held to 1200 psi, and then the hose ruptured near the end of the barb.  The push-on connection never leaked or came apart.

INJECTOR HOSE REPLACEMENT --D JETRONIC: Injector hose replacement on the D Jetronic is pretty self- explanatory: Loosen clamps, disassemble, reassemble with new hose, tighten clamps.  If there are crimped metal collars (you have original crimped collars after all these years?), you will need to cut through one side of each collar and spread it a little to get it off; replace the collars with EFI clamps when reassembling.  Ed Sowell adds, "It is not sufficient to tighten the hose joints just once.  I am absolutely sure they were all tight and non-leaking when I rebuilt the injection system last summer.  Yet, in April of this year they were nearly all loose.  I believe this is due to the hoses deforming under clamp pressure and setting in the compressed state due to high temperature.  Then they will be loose when the engine is cool."

INJECTOR HOSE REPLACEMENT -- DIGITAL P: This job is not self-explanatory since there are no clamps, but it's still pretty easy.  The guidelines below are for replacing the hose without even pulling the injectors, but you might want to remove them as a set to save your back and also to replace the injector seals at the same time.  Either way, you will need to depressurize the fuel system.  You will be spilling a little fuel, so take suitable precautions.  Disconnect the inlet and outlet lines to the rail, and remove anything that goes over the rail.

Cut all twelve old hoses through the middle.  Any fuel remaining in the rail itself will dump out, so you might want to choose a suitable hose to cut first and quickly aim it into a jar.  You might then try cutting a hose at the other end of the rail and blowing through it to clear out as much fuel as possible.  After cutting the hoses, lift off the rail, leaving the injectors in place.

Remove the pieces of the old hose from both rail and injectors.  Don't lose the dished washers.  Try to do as little damage to the barbs themselves as possible.  The basic idea is to use a razor knife of some sort --a boxcutter blade or utility blade, X-Acto knife, whatever --to "shave" down one side of the hose, cutting just deep enough to slice through

The problem, of course, is the dished washers get in the way.  You can only slice so far down the side of the hose before the blade hits the washer, leaving the last 1/8" of the cord uncut.  It's trying to get that last part cut, using a corner of the blade or whatever, where frustration sets in, and the frustration can result in damaged barbs.  Richard Fields says, "I used an X-Acto knife (available at any hobby shop) to remove the hoses, after fighting them with a razor knife.  The X- Acto blade I used was shaped like a cats-Jaguar?-claw and could get in behind the washers very easily.  It made cutting the hoses off a snap!"

Note that while the clampless barbs all are similar in configuration, the ones on the injectors are made of much softer metal than the ones on the rail.  You might want to work on the ones on the rail first so you get the hang of it before tackling the much-easier-to-damage ones on the injectors.

If the barbs get a little dinged up, believe it or not they can usually be repaired quite effectively.  The trick is to make sure there are no "notches" in the edge of each ridge, so that the edge of the ridge contacts the inside of the hose all the way around to form a leakproof seal.  If there's a notch, you can grip the barb gently with a standard pair of pliers while you rotate the injector (you probably need to remove the injector from the engine to do this properly) so that the teeth on the pliers scrape off the edge of the ridge all the way around until the notch is cleaned up.  You still don't want to use a clamp on this hose connection unless you had to clean the ridges completely off to get rid of notches --in which case you probably should spring for a new injector.

Others suggest not using a razor knife at all.  John Ashcroft says, "Used a electric soldering iron to burn the old hoses off of injectors with no damage to barbs."  Ken Gray elaborates: "You poke the hot tip of the iron into the fuel line just above the top barb and push it down the length of the fuel hose and into the seemingly useless cupped washer at the base where you just work the tip around a bit to completely severe the hose.  The whole process takes a few seconds due to the very hot tip of the weller.  You can grab hold of the barbs immediately after hose removal and they are barely warm. I would not use any other method now as the soldering iron works perfectly without any damage to the barb or internal plastics of the injector.  You do however need to use the correct soldering iron; I ended up using a Weller electric iron which seems to have a temperature control in the tip.  I must also say that I have not been able to reliably regenerate the tip for soldering purposes.  This is not a problem because the tips are readily interchangeable."

David Johnson suggests a wire wheel: "My plan of attack is to cut all the hoses in the middle between rail and injector.  Then I use my bench grinder which is set up with a wire rope wheel.  It makes quick work of the remnants of the hose on the injector and does not gouge the barb end.  The wheel's strands are flexible enough to get under the cup.  As for the rail I have an air die grinder which I use with a similar, though smaller and slower, wire wheel and it is simply a matter of abrading the material off.  Actually took me less than 3/4 hour to do all 12 recently."

Cut suitable 8mm or 5/16" (7.9mm) EFI hose into ten pieces 1-3/4" long.  Make doubly sure that all ten hoses are the same length; different lengths can cause problems with the clampless barb connections.  Install the ten pieces of hose onto the rail first; remember to put the dished washers in place.  Use no lubricants on either the hoses or the barbs; they should be assembled dry, and they should push on easily.  Position dished washers onto the injectors, and then push the entire rail down onto the injectors one bank at a time.  After pressing the rail down onto the injectors, pull upward forcefully on the rail to help the hoses establish a good grip on the barbs.  Leave the 1A and 1B hoses until last, and cut those hoses to whatever length seems to fit right.  Reconnect the fuel inlet and outlet, and then turn the ignition on for two seconds at a time for several cycles so the fuel pump can repressurize the system.  Start it up and check for leaks.

HOSE ASSEMBLY REBUILDING: Many of the lines (fuel, power steering, etc.) in the Jag consist of metal tubing with threaded connectors and a short length of hose in the middle somewhere, all sold under one part number.  When it's been in there too long and has dried up and started leaking, the section of hose can easily be replaced with suitable hose along with suitable clamps.  It is suggested that before you cut the original hose off, you place measured marks on the tubes on either side of the hose so that when you reassemble, the same overall length can be established.  You should

Some hose assemblies in the fuel system have clampless barbs to connect metal tubing to hose, similar to those fittings on the rail described above.  However, these may have a deep cup covering the end of the hose instead of the dished washer used on the injector hoses; this deep cup looks like a crimp collar except that it isn't crimped.  The deep cup can make it a bit more difficult to get the old hose off, since getting the razor knife on the hose will be all but impossible and getting a soldering iron tip in there will be no picnic either.  To make life easier the next time you replace hoses, you might want to order some of the dished washers used on the injectors, EAC7876, and reassemble the fuel lines with these instead of the cups.  That will also make disassembly easier this time, since you can just cut the cups off to get them out of your way.

The author's solution here worked well.  I used a hacksaw to cut these deep cups circumferentially, separating each one into a sleeve and a shallow cup --obviously being careful not to saw all the way through the hose and damage the barb underneath.  I was then able to simply slide the sleeve up the hose out of the way and slice the hose away using the same method as with the hoses on the rail with the dished washers.  When reassembling with new hose, I reinstalled the shallow cup (cleaned up a little) and discarded the sleeve.  The finished assembly looks good, arguably better than the dished washers at the rail.

If you get those cups off intact and intend to reuse them, note that when putting the new hose on you may have trouble telling if it's on all the way.  So, prior to assembly, slip the cup onto the end of the hose and mark on the hose so you'll know when it is fully inserted into the cup.  This is especially important with a really thick-walled hose like the Weatherhead cloth-surfaced stuff described above because it fits so tightly in the cup that it makes it very difficult to get on the barb.

FUEL FILLER CONFIGURATION: In the 70's, the fuel filler pipe on the XJ-S had a flange on it and was rigidly mounted behind the filler door with three screws.  This author's '83, however, has no flange; all it has is a small tang that engages a small bracket to prevent the filler pipe from rotating as the cap is tightened.  The same three screws are used instead to fasten a metal collar that holds a rubber boot around the filler pipe.  Hence the filler pipe is mounted flexibly; it can move around a bit since it is held in place only by the boot, an O-ring seal at the tank, the hose clamped onto its outside, and of course that little tang that prevents it from rotating.

With either design filler, the clamp on the hose connection to the tank is accessible from within the trunk by removing some carpet.  Then you can pull the filler out through the filler door after removing three screws.

On the later design, the filler itself inserts into the opening in the tank with a really fat O-ring for a seal, and then the entire assembly is enclosed in a short section of 2" hose.  If the fat O-ring works, the 2" hose only serves to hold the assembly together, not to contain fuel or odors.  This assembly might have been designed this way because Jaguar couldn't find a 2" hose that would positively prevent fuel odors.  Remember, the fuel-filler-to-tank connection in most other cars is underneath the car, not inside the trunk --perhaps for good reason.  If you have odors, you might consider pulling this assembly apart and replacing that O-ring, which is part number C46157.

FUEL FILLER CAP: ...is discussed on page 261 under the vapor recovery system.

FUEL FILLERS --SALOONS: The fuel fillers on the saloons are different from the one on the XJ-S.  They are a pair of decorative flip-open fillers on the top rear of the car --one for each tank, since there are two tanks.  Walt Osborn of

"In the past, this seal was serviced as the whole seal and holder that floats on the four studs; part #12685.  On series 2 cars the number was changed to RTC 196 for emission controlled cars.  In 1988 RTC 196 went NLS (No Longer Supplied).  Part #12685 (non-vented) has been available off and on...

"The seal can be easily replaced.  You can take the cap off the car or leave it on.  Use some pliers and pull the old seal out of its slot.  Go around the slot and bend the thin lip outward a little making the entrance to the slot wider.  Cut a piece of neoprene flat rubber 1/8" thick x 2-7/16" outside diameter x 1-1/2" inside diameter.  If you are worried about the rubber being compatible with current gasoline, there is an alternative.  There is a new gasket pair available for series 3 cars as aftermarket part #GCS/L.  Use the old gasket and mark the new gasket around the inside hole with a pen and cut the hole out with a razor blade knife, cutting just outside the pen mark.  Stretch the new part on, crowd it into the slot and bend the thin lip back down.  If you use the later gaskets there is a small hole which is ignored because it disappears under the thin lip."

FUEL FILLER DRAIN: Derek Hibbs says: "The answer for my fuel smell was simple: the fuel cap overflow pipe was disconnected and any spillage during refueling was draining directly into the boot/trunk instead of onto the ground.  Reconnected the overflow pipe and no smells (I also take more care when refueling)."

STEENKIN' RIVET: On the underside of the car there are numerous lines that are held to the car with little clips and rivets.  One of these rivets is in the panel the tank sits on, and sometimes the weight of the tank compresses the pad enough that the metal tank contacts the tip of the rivet.  After some vibration, the contact can wear a hole in the bottom of the tank.  Once the tank is drained and removed, it is a simple matter to patch the hole (there are types of epoxy sold that will work well) and find an alternate way of supporting the line under the car.

STRESS CRACKS IN TANK: Officially, the recall supposedly was to prevent excessive pressure/vacuum cycles on the tank, resulting in stress cracks.  Obviously, this is something else to check on your tank.

RUSTY TANK: Chad Bolles reports that the seal around the rear windshield starts leaking, and the water soaks the sponge under the tank and causes the tank to rust.  Chuck Sparks reports that external rust on the bottom of the tank where it sits on that foam is far and away the most common cause of fuel leaks in the trunk he has seen.  The author's car didn't have any leaks there, but it did have some rust --and there were no signs of any leakage from the rear windshield.  It's entirely likely that filling the tank with cold fuel --or just running the car, which chills the fuel in the tank via a fuel cooler -- may cause condensation on the outside of the tank, which runs down the sides and soaks into the pad.

FUEL TANK DRAINING: The way you're supposed to drain the tank is to remove a rubber plug in the floor of the trunk and loosen a drain plug in the bottom of the surge tank and allow it to drain into a container.  The drain fitting works kinda like a big brake bleed nipple; you don't need to remove it, just loosen it a coupla turns.  Unfortunately, the drain never lines up with the hole in the bottom of the car very well; you might want to consider enlarging the hole and using a larger plug.  Hopefully, one way or the other, you can push a short piece of 5/16" tubing onto the drain fitting to route it out the bottom of the car and into whatever container you'll be collecting it in.  Kevin Darling says, "An 11/16" wrench easily opened the sump drain from within the trunk."  While you're fiddling with that drain, you might consider upgrading it as described on page 253.

Using that drain works OK, I guess, but there is an easier way!  Remove the spare tire and disconnect the line from the inlet to the fuel filter.  Direct this line into a gas can sitting in the trunk.  Remove the fuel pump relay and insert a jumper

Of course, either way you drain the tank, it'll be easier if you drive the car until it's really low on fuel first.

FUEL TANK REMOVAL: The main fuel tank is located over the rear axle.  It is accessible by removing the spare tire and some other stuff, then pulling the carpet out.  Tank removal is pretty straightforward until you get to the last step.  The tank sits on a 1/4" layer of foam, and is often bonded to the foam from years of sitting on it so there's no way you can slide it out.  Chuck Sparks offers a solution: a machete!  Just slice through the foam from wheelwell to wheelwell, and the tank will come right out.  You're probably going to want to replace that foam anyway; if the tank has been leaking, it's probably smelly.

FUEL TANK LINING: The fuel tank in the XJ-S is made of stamped sheet steel.  This is a sorry choice of material for a fuel tank, and any automaker that chooses it should be ashamed --and that's most of them.  It'll start putting rust particles into your fuel system almost immediately.  After it's been doing that a few years, things get more serious.  It may develop leaks due to rusting from the inside out; it may develop leaks due to rusting from the outside in; it may develop leaks due to stress cracking; and it may shed enough rust scale from the inside surfaces to plug the fuel pickup, resulting in fuel starvation at high power, which in turn results in burnt pistons.

If you already have such problems, you need to do something --but if you don't have such problems, you might still consider making some preventative measures at some convenient opportunity.  A popular strategy --for owners of any old cars with steel fuel tanks, not just Jaguars --is to apply a coating to the inside of the tank.  Most such coatings will not only prevent future problems, but they will usually seal up minor leaks.  John Whitehead says "I have used gas tank sealer from Bill Hirsch Automotive (see page 700), with great success.  I put it in the fuel tank of my '67 XKE which had a number of pinhole-size leaks.  Previous attempts to coat the outside of the tank were not as successful.  The tank sealer is gasoline and alcohol resistant.  A quart can is sufficient as only a thin film is coated to the inside of the tank.  I am not sure of the product's chemistry, but it dries to a white Teflon-like film."  Obviously, major cracks or holes will require more extensive repairs.

Other sources of similar tank sealer materials include Red-Kote by Damon Industries, Renu (page 704), Eastwood (page 704), and Avon in England.  Most modern sealers claim to be suitable for gasohol, but you might want to ask to make sure.  Oxygenated fuels, octane boosters, lead substitutes, injector cleaners, and anything else you may be tempted to put in there are also things to ask about.  The Hirsch, Red-Kote, and Eastwood sealers (and perhaps others) use methyl ethyl ketone as a solvent, which means you need to avoid putting anything with MEK or acetone in it in your tank.  Note that, in the case of oxygenated fuels, lining the tank may be an improvement; MTBE will attack the brazing on a steel tank.

Several people have reported using POR-15 to coat the inside of their tank.  It may not be specifically intended for the purpose, but nobody has reported any problems.

You should be warned that lining your own fuel tank is not an easy job for the novice.  Obviously, the tank must be removed from the car, but that's not the hard part.  The inside of the tank must be scrupulously cleaned prior to applying the liner, and cleaning is a serious challenge on the XJ-S tank --even for shops with lots of experience cleaning and sealing fuel tanks.  The XJ-S tank has so many baffles inside that, looking into the filler and fuel level sender openings, you will not be able to see more than perhaps 1/4 of the total interior surface of the tank, even with mirrors.  You can just forget about brushing, scrubbing, sandblasting, or the like.  The only way you're gonna do anything inside this tank will be by putting things in, shaking it around, and pouring it out.

Bill Eslick: "Many years of racing (Midgets and Sprint cars) have given me opportunities to learn how to clean a fuel tank.  Solution: Three pint-sized cartons of BBs.  Pour them in the tank and shake the shit out of it.  If you are going to coat the thing then shake it dry.  Rinse with lacquer thinner, and shake again.  This is tedious but works remarkably well.  Be sure you use BBs; lead shot can get lodged in baffles, etc. because it's so soft.  Also, any errant BBs can be pulled out with a magnet."

A report from this author, who has tried BB's: if you put a BB in the XJ-S tank, you will be using a magnet to remove

Unless things are really bad in there -- lots of loose scale --most owners would be well-advised to use only liquids in this tank.  Still, this is not a simple matter of pouring out the gas and pouring in the sealant.  Mike Aiken provides the guidelines recommended for use with the Eastwood product:

1. Wash tank with hot soapy water, then rinse out with a garden hose.
2. Metal wash diluted in 2 gallons of water.  Slosh, 5 minutes a side, slosh.  This is supposed to remove contamination from surfaces and inhibit flash rust.  Says it contains alkali surfactants(?).
3. Rinse with garden hose.
4. 1/2 gallon of muriatic acid obtained locally.  Slosh until gray appearance.
5. Rinse with garden hose.
6. Rust remover (phosphoric acid).  Rotate until all sufaces are contacted and uniform gray appearance(?).  Dump out.
7. 1 quart of acetone obtained locally.  Slosh on all surfaces (no specified time).  Dump out.
8. Do step 7 again.
9. Sealer.  Rotate all around.  Let stand 8-10 minutes on each side.  Dump excess.  A white coating should exist on all surfaces of the tank.  Says it contains methyl ethyl ketone.
10. Allow to dry (open) for 48 hours before use.
"If you dumped all this crap in the ground you would have another "Love Canal".  It says to dispose of "stuff" according to local law."

The instructions that come with other products may not be as extensive, but they should be.  Simply applying a single cleaning product prior to lining may work on a new tank, but it's likely to result in troubles down the road if done to an old tank with a few years' accumulation of surface rust and gasoline varnish inside.  The lining may not stick securely in spots, then later peel off and plug up the pickup.

Aiken: "The key, I believe, is the first step (Ed. note: he means step 2), which is to get all the varnish and other goop off the metal.  Rust (and some metal) will be removed by the muriatic acid, but the acid will not remove non-metallic stuff.  The cleaner supplied by Eastwood softened but did not remove all the gasoline residual (varnish, etc).  Where I could see it I could scrap it off with a stick, so it was not yet removed.  So I added a step.  With most of the cleaner still in the tank, I added a gallon of acetone.  Sloshed it around then let it sit for about two hours, then sloshed it again.  It worked.  If you see anything but gray metal (maybe some rust and corrosion is OK) the process will fail.  The muriatic acid will not remove non-metal stuff, and the liner will only adhere to pure etched metal."

The steps above describe a "metal wash" with "alkali surfactants", but in reality any automotive cleaner/degreaser that can be poured into the tank, sloshed around, and drained out will work well.  The objective is to get any varnish and goo out, so make sure that you accomplish that.

The muriatic acid is for getting the major metal corrosion off.  Muriatic acid is available at building supply stores (it's used to clean brick walls) and at swimming pool supply stores (used to control ph in pools).  The concentration commonly available is 20º baume, which is a suitable strength for this job.  Most shops --as well as the guidelines above --suggest using a half gallon, but on this tank a full gallon is advisable because the interior of the tank is so convoluted that there may be spots you don't get to with less liquid inside.

Muriatic acid is nasty stuff; Aiken says, "muriatic (hydrochloric) acid is potent and very caustic.  Emission of chlorine gas is lethal.  You must wear rubber gloves and a mask and be outside."  Arranging to be upwind is helpful, too, even if it requires a fan.

Phosphoric acid is available in several products for treating surface rust, including Ospho and Right Stuff De-Ruster,

Note that there should be no rinsing with water past step 5.  The residue of the phosphoric acid treatment is removed with the acetone.  After rinsing and draining (several times for maximum effect), any remaining acetone will evaporate completely in minutes, leaving the tank clean, dry, and ready for lining.

Tip: each time you put a liquid in, you're gonna have to drain it out.  And there is only one opening into the XJ-S tank that will drain the last pint or so, and that's the fitting for the main line to the surge tank -- the one that's intended to be a drain.  All the other openings are nothing but frustration, nothing ever seems to pour out of them except when you don't want it to!

A popular idea is to use heat --either to make the various cleaning agents or acids work better, or merely to dry the inside of the tank after rinsing.  If a really big oven is available, this might work pretty well --but the more common procedure is to use a torch to heat the outside surface of the tank.  One should be aware that this method might be perfectly workable on other tanks that are mere cans, but on the XJ-S tank such torching will clearly have more effect on the outer shell than on the baffles within.

Also note that you will only be able to visually inspect or physically touch a small percentage of the inside of an XJ-S fuel tank.  That means that you must rely on liquids to accomplish everything you need to accomplish.  Trying to scrub the areas you can see will only keep you from being able to judge the success of your work by looking at the areas you can see!  Treat the entire tank the same way, and then you can conclude that the entire tank is done when the visible areas look done.

When the liner is poured in, you need to slosh it around to coat all the inside surfaces and drain out the excess.  Good luck!  First off, the stuff doesn't really "slosh" since it's a little too thick; it might help to dilute the liner with some MEK or acetone prior to pouring it in.  Even if you render it sloshable, it's still difficult to coat all those internal baffles; as you rotate the tank over and over, the fluid pours past the baffles without really getting up on them.  Of course, the baffles are not a leak concern, but you would like to prevent them from rusting anyway.

When you open the tank up to drain the excess liner, you can just prop it up and let it pour out --and it'll pour for two hours.  Alternatively, you can just drain for five minutes --getting most of what you will ever get out --and then tip the tank over to let the remainder run back across surfaces inside to make the coating a little thicker.  If you will tip the tank to a different position every few minutes, you can avoid the lining puddling in any one place.

Of course, while you're lining the tank, it would also make sense to line the surge tank --which is easier to do, although again it's not as easy to drain as you might think.  The drain plug in the bottom won't drain the lowest half inch of liquid!  You have to tip and tilt the surge tank to get everything to drain out of the big pickup opening, and all the liquids like to flow around the opening rather than draining out it.

And you might also want to consider lining the vapor separator, although it's a bit tougher because the biggest opening into it is a 5/16" hose connection.

If all this sounds like too much for the do-it-yourselfer, there are places that will do it for you.  You can usually find a local shop that does this sort of work, although the one found by the author had never heard of phosphoric acid, had been applying liners over bare metal with surface rust for 25 years.  For a more reputable shop, you can contact Moyer's Fuel Tank Renu (page 704) about shipping your tank to them for work.

Although this section was written with the XJ-S coupe fuel tank in mind, it's probably equally applicable to the convertible and cabriolet.  The Hess & Eisenhart is another animal, since it has two tanks; the upper one is a modified version of the coupe tank and the lower one is completely custom.

FUEL TANK COATING: As mentioned above, a common cause of fuel leaks in the XJ-S is rust on the outside of the tank --specifically, the bottom.  Therefore, even if you're not interested in lining the inside as described above, you might want to tackle the job of making sure the outside doesn't rust.  The tank still has to come out, but beyond that this

Note: when you first remove the carpet and look at the tank in place, what you may think is rust may be the remnants of the glue that once held the carpet in place.  Be sure you're really looking at rust before you panic.

FUEL TANK REPLACEMENT: The author, having gone through the tank lining process, has arrived at a few conclusions:

1) I'd never do it again.  Rather than fiddling around with all this work, I'd just take the tank down to a local fab shop and have them make me an entirely new tank out of heavy gauge aluminum.  The cost is reportedly comparable to buying a new tank from Jaguar, but if you buy a new tank from Jaguar you still end up with a rust-prone steel can.  While making the new aluminum tank, I'd omit those stupid threaded compression fittings and just provide barbs for connecting hoses.  I'd probably have a new surge tank made while I was at it, and completely change its configuration so as to better locate the pump and an in-hose pickup filter.

2) I consider the entire idea of making automobile fuel tanks from steel to be irresponsible at best.  Aluminum should be the minimum specification, if only to minimize rust problems.  From an automobile manufacturer, though, I would expect a mass-produced version of the fuel cell commonly used in racing.  Racing organizations wouldn't consider a simple steel tank acceptable, and with good reason: they're an obvious fire safety hazard.  It wouldn't cost auto manufacturers $20 more per car to provide a similar level of safety in street cars --far less than air bags or ABS brakes cost.

FUEL LEVEL SENDER: It's discussed on page 594.

FUEL TANKS: This section is of no use to coupe or later convertible owners, but it is reportedly difficult for H&E owners to find information on how this system works so a description is included here.  According to Mike Cogswell, "In order to make room for the folding top and its mechanism H&E had to take the standard tank and cut part of it off.  It would appear they literally cut the tank and welded in a sloped section.  To regain fuel capacity, they added a second tank under the parcel area, basically where the rear seat would have been in a coupe.  The upper tank is about 14 US gal. and the lower is about 11.

"As you know, the standard tank has a sump from which the high pressure fuel injection pump draws its fuel.  Since the second tank is lower than the first H&E added two concentric hoses.  The larger outer hose allows fuel to gravity drain into the lower tank from the upper (which is where the filler neck is located.)  Consequently, the lower tank is always full until the upper tank goes dry.  Meanwhile, a small submerged pump constantly pumps fuel from the bottom tank to the top tank via a small tube that is located in the center of the large drain hose.  The fuel is dumped into the upper tank's sump, where it is available to the main fuel pump.  The submerged pump can pump fuel faster than the engine consumes it, but any in excess of the sump capacity will drain right back into the lower tank.  Both pumps only run when the ignition is on and the standard pump circuit is energized, so all the regular safety interlocks still work."

Tim Blystone points out that since parking the car nose-down on an incline will cause the fuel to drain toward the forward tank and away from the sump, the auxiliary pump might not keep up when the tank is less than half full.  "All of the early tank designs will stall on a sufficient incline."

"H&E went through a couple of different configurations.  The main difference is the dams added in the interior of Jags

FUEL TANK LEAKS: This author has only laid eyes on one H&E convertible, and that one was literally pouring fuel out the bottom of the car.  Steve Wilke says, "I've heard stories from a couple of informed sources that Jaguar Cars repurchased a large number of Hess & Eisenhardt convertible conversions, and these cars were then shipped elsewhere; Brazil was one of the target countries that was mentioned to me.  Seems that a large number of the H&E conversion fuel tanks weren't made properly, and had a propensity for splitting their seams and producing a very pronounced fuel smell.  When the owner would call the dealer to report this, they'd say something like "Really?  Where is this Jaguar?".  Then they'd send over a flatbed truck, load up the car, and hand the owner a check.  Perhaps Brazil has a much lower population of suit-hungry attorneys than the States do.  I would expect the population of H&E's in the States to be quite small indeed by this point."

If you have an H&E with a leaking tank, there's certainly no need to ship it to Brazil.  It's a fairly simple matter to fix a leaking fuel tank, or even to simply take it to a local welding shop and have them fab up a replacement tank in heavyguage aluminum with whatever fittings and connections you desire.

FUEL GUAGE: see page 595.

FUEL HEATING PROBLEMS: The stock Jaguar fuel pump moves far more fuel than the engine normally needs with the excess returned to the tank.  Since this heats the fuel somewhat, a fuel cooler is included in the return line, using the A/C freon circuit to provide cooling.  On the H&E, however, the problem is exacerbated by the fact there are two pumps running full time, coupled with the fact the car is a convertible so the top may be down and the A/C off on warm days!  Tim Blystone: "Normally this presents very little problems until the A/C goes on the fritz, or you have one of H&E's earlier designs.  If it is summer, the top is down... the A/C system is off.  No cool fuel.  Vapor lock from hell."

FUEL SYSTEM MODS: Tim Blystone: "My modification puts the plastic hose from the H&E fuel cell directly into the supply for the sump tank.  A new and longer piece of hose is required.  Fuel is pumped by the H&E pump directly into the Jag sump tank and bypasses the need for the tank to be gravity filled.  There is a return to Jags original main tank from the sump tank so there is no excess pressure in the sump.  The result is a fuel system that doesn't have the H&E problem with steep inclines or die dead in the middle of a hot southern day."

Another idea might be to do away with the surge tank and main fuel pump altogether and (somehow) connect the pump in the lower tank directly to the engine.  The fuel in the upper tank can then simply gravity-feed to the lower tank and stay there.  Basically, the lower tank would serve as the surge tank.  The return line from the engine doesn't require alteration, it can continue to feed into the upper tank.  The vent lines from the surge tank can simply be plugged, allowing the existing vent lines from the two main tanks to work as intended.  Benefits include more luggage space in the trunk!  Before doing this, one would need to ensure that the fuel pump in the lower tank can actually provide the flow and pressure required by the engine.  If necessary, just replace that pump with one of known capacity --one from any large V8 with EFI, for example.

GAS CAPS: The single fuel filler on the H&E is the same as the two on an XJ6.  You can read about these on page 244.

In fact, it's common enough that it even caught Jaguar's attention.  This pickup screen plugging is a very rare example of a problem that has been recognized and addressed by Jaguar.  In Issue No. 2 of the XJS Bulletin, Ray Ingman of Classic Spares, Inc., reports that Jaguar issued a replacement pickup screen with a considerably larger screen area.  The part number is CBC5649.  Anyone working in the area should definitely upgrade.

Ingman apparently doesn't think a lot of this fix; his impression is that the larger area won't prevent it from plugging, it'll just take longer.  He may be right, but he might not be.  For one thing, the suction at the screen is a function of the screen area, so a screen with more area will have less suction at the surface --so maybe the junk won't have as much tendency to stick.  Another possibility: It may be that the larger screen has so much area that it's effectively unpluggable --you could cover the entire surface with crud and it would still be able to pull enough fuel through the nooks and crannies between chunks to maintain flow and keep running.

John Goodman owns a 1989 XJR-S 6.0 litre: "I have just cleaned out my sump tank, no signs of a filter!"  Who knows, maybe Jaguar decided it was more trouble than it was worth.

There is some experience to indicate that the plugged pickup problem is often accompanied by a failed fuel pump.  Perhaps the plugged pickup causes the pump failure.  Be aware that when you find the pickup problem you may also have to replace the pump before the car runs right again.  Apparently, if you can hear the pump whining when driving, you can count on it.  Perhaps the cost of this pump is one good reason to check the pickup before you have problems.

OK, you're thinking to yourself that you don't have the symptoms of a pickup problem, but you'll now be able to recognize it if it happens and know how to fix it when it does.  John Himes would probably suggest you think again.  If the sump pickup can get plugged badly enough to shut down the engine, what happens when it's plugged a little less than that?  Let's say it's just a little bit plugged, not enough to affect engine operation at 60 MPH but enough to start limiting fuel flow at full power.  Just as you're really getting into the interesting areas of the speedometer, the pressure in the fuel rail starts to drop off.  The engine starts to run lean just when it can do the most harm; lean mixtures at full power are a recipe for disaster.  And you're into the open-loop range of operation, so the oxygen sensors are not able to correct the lean mixtures.  Himes was cruising along at 140 MPH, and the next thing you know he was facing several months of down time and several thousand dollars in mechanic's bills to fix a couple of burned pistons.  Now, lemme ask again: are you sure your fuel pickup is in good shape? In fact, everyone with the earlier style pickup screen should definitely upgrade; go ahead and order the part now.

Kevin Darling claims that his car starts more easily since he cleaned up his pickup, and has a lower, more stable idle.  Neither of those effects can be easily explained, but improvements are always welcome.

There is, of course, another way of dealing with the problem: discard the OEM screen altogether and install an inline screen in the hose between the surge tank and the pump.  This would have the advantage that, once this screen had collected a lot of crud, you could clean or replace it and get the crud out of the system once and for all.  With the OEM setup, you're probably leaving a lot of crud inside the surge tank even when you clean it as best you can.  Also, with an inline screen you may be able to pinch the lines and service it without having to drain the surge tank.  Finally, if you get a screen assembly with a clear housing, you'll be able to see if it's dirty.

The line between the pickup and the fuel pump is 1/2", and finding a fuel filter or screen assembly with 1/2" fittings may be difficult --and you certainly don't want to step down to smaller fittings, since the entire objective is to minimize restriction in this suction line!  Keep looking; Chad Bolles says NAPA carries fuel filters with 1/2" barbs.  This author found a suitable unit a local parts store; it's a Wix filter, number 33299.  Less than ten bucks.  It has an all-metal housing.  It's a pretty compact unit, helping ease installation a bit.

Andrew Holley found another one: "Has 1/2 inch fittings and looks just the thing for keeping the crud out of the system. The part no. is 202711 (Volvo)"

There are also various types of high-performance or specialty filters that might be used.  Holley makes a unit called a Volumax that includes a cleanable 60 micron screen element.  It comes with either 8AN or 3/8" hose barb fittings that screw into the housing, but 8AN is 1/2" so you might be able to find 1/2" hose barb fittings to screw into the housing.

Heavy equipment places that work on trucks and bulldozers may have suitable filter assemblies that can be fitted with cleanable screens, but they are usually big industrial contraptions and will be difficult to locate in the XJ-S.  They also have threaded connections, so you'll have to install some suitable fittings for connecting the hoses up

Another possibility, of course, would be to tee together two or more 3/8" filters.  Finding suitable 1/2"-to-3/8" tees may be harder than finding 1/2" filters, but once you've put it together it'd be easier finding replacement filters.

You'll need some 1/2" fuel hose --another challenge.  EFI hose is not necessary, this is a low-pressure application.  But finding any fuel hose in 1/2" size may require visiting an industrial hose shop rather than an auto parts store.  See page 239.  You also need to get some clamps; EFI style clamps would be great, but 1/2" hose is big enough that regular worm screw clamps work just fine.

The OEM fuel hose goes from the pickup tube to the pump inlet, only about four inches with a 90° bend --too close to put this filter in between.  Instead, use a new piece of 1/2" hose to make a big circle from the pickup tube barb CCW past the pump inlet, down, back to the right, up, and back left into the fuel pump inlet.  Then install your filter anywhere in this loop that's convenient.  Probably three feet of 1/2" hose total, but absolutely no sharp bends.

Wrap some foam around the metal filter so it won't rattle and clang against the floor or battery support.  I used the 1/2" foam tape used for sealing doors.  After encircling each end of the filter with foam strips, I added some electrical tape to hold it in place.

FUEL PICKUP -SALOONS: Saloons --either XJ12 or XJ6 --don't have a surge tank, but they nevertheless have the same problem with clogged fuel pickups, one per tank.  Without having read this book, Chuck Sparks came up with a remarkably similar fix as that described above, fitting two generic fuel filters in the lines between the tanks and the selector valve.

FUEL SUPPLY MONITORING: From a fail-safety point of view, the surge tank pickup situation is bad.  Regardless of which pickup screen you have installed or how often you clean it, there is really no way to know if it's plugged until you notice the symptoms -- and the first symptoms are likely to be low compression readings in a couple of cylinders!

Of course, a plugged pickup isn't the only possible cause of lean running under hard throttle.  A failing fuel pump, an obstructed fuel line, or a fuel filter overdue for replacing are other obvious candidates.  Whatever the cause, the result will be the same: if you run it hard, you're gonna be buying new pistons.

Oh, c'mon, the problem can't be that serious!  How come other cars aren't burning pistons at full throttle all the time? Well, obviously because their fuel systems weren't designed by Jaguar engineers.  On most cars, nobody ever even has to think about the fuel supply; it's just there, and it works.  The concept that an engine could run lean because of a plugged fuel pickup strikes owners of other cars as laughable.

Of course, you could resolve to never drive the car hard --but why else would you own a Jaguar?  A better solution would be to have some indication that the fuel supply is holding up before you burn pistons.

Two methods come to mind.  The first would be to install a fuel pressure gauge or sensor in the rail.  Robert Dingli says: "I bought a VDO fuel pressure gauge for about Aus$40 and connected it to the fuel rail where the cold start injector was once supplied.  I believe any pressure gauge designed for hydrocarbons would be suitable and other brands sell for much less.  My gauge is mounted in the engine bay as I am paranoid about high pressure fuel entering the cabin.

"There are a couple of things to note about connecting the gauge:

-use high pressure fuel line and fittings.

If you have the Digital P system, ideally you'd use a gauge that reads the difference between the fuel rail pressure and the intake manifold pressure.  Since the fuel pressure regulators are referencing manifold pressure, this should result in a steady reading at all operating conditions and any variation is a sign of trouble.  If you use a regular guage that references ambient atmospheric pressure, the fuel rail pressure will go up and down as the intake manifold vacuum varies, so you will have to monitor both and do a little math to make sure things are operating properly.

For most intents and purposes, a pair of air/fuel meters (see page 37) is a better idea than a fuel pressure gauge.

SURGE TANK DRAINING: In theory, the easy way to drain the surge tank is to pinch off the line from the main tank to the surge tank and run the pump, which will pump the fuel through the fuel rail and back into the main tank.  You don't even have to hotwire the fuel pump relay; you can just start the engine and let it run until it stalls.

Good idea in theory, but in fact may not work too well.  As described below, the return line from the engine doesn't simply go into the main tank, but rather goes through the tank and is directed into the vent connection for the surge tank.  Running the pump will circulate the fuel from the surge tank around and back into the surge tank, and you will have to run the engine until it burns all the fuel in the surge tank.

So, pinch off the vent line too?  Bad idea, because then the pump would pull a vacuum on the surge tank and cavitate long before it empties the surge tank --unless your surge tank has been fitted with the JLM 2163 vent kit mentioned below, it which case this might work fine.

Forget that method; there are other perfectly workable methods that are very easy.  The intended method of emptying the surge tank is to clamp the main line from the main tank, and then remove the rubber plug in the floor underneath the surge tank and open the drain in the bottom of the tank (see page 245).  Since the vent line actually opens near the top inside the main tank (as opposed to where it looks like it goes) you only need to make sure the fuel level is below that level so it sucks air instead of fuel.  Just plan on this job when the tank is less than half full.  Of course, you can do it when it's full; it's just that you will first have to drain the main tank down to the level of the vent before the surge tank will empty.

Another way to drain the surge tank is to pinch off the main line from main tank to surge tank, disconnect a line from the fuel filter and direct it into a gas can sitting in the trunk, and remove the fuel pump relay and apply a jumper between terminals 30 and 87 in the socket to run the pump.

Of course, one way to drain the surge tank is to drain both the main and surge tanks; that way you don't have to pinch off any hoses.  See page 245.

SURGE TANK DRAIN UPGRADE: Somewhere along the line, the drain plug in the surge tank changed from C41803 to CBC4518.  The newer drain plug is magnetic, while the earlier item was a simple plug.  If you are working in the area and find no magnetism in your drain plug, you definitely should opt for a replacement; any particles that stick to that magnet are particles prevented from plugging the pickup screen.

The 1988 Jaguar Parts Catalogue lists only the first part number, but later editions apparently confused things a bit.  Wally Magathan says, "According to my parts manual, RTC9900CA, Jan 1989: on page 2D 05, there is a diagram of the sump tank, with the drain plug part annotated as having been replaced by a magnetic plug.  One puzzlement, however: the diagram is indicated to pertain to cars equipped with 3.6 engines only.  There is no diagram labeled for use with 5.3 engines."  Kevin Darling responds: "This puzzled my local Jag dealer as well.  But the RTC9900CA parts book is wrong, since both my 1985 and 1990 V-12's have the sump tank."

Supposedly the CBC4518 plug will fit all the earlier cars.

If you're cheap, of course, you could always simply drop a magnet into the surge tank while working on the pickup.  It might be more challenging to clean, but it should do just as good a job of keeping ferrous particles off the pickup screen.

SURGE TANK VENTING: The vent line from the surge tank doesn't go to the vapor separator, as one might expect. Instead, it connects back into the main tank about 2" above the bottom.  However, this is not a simple opening into the tank.  Inside the tank, this fitting continues as a tube that makes a couple of bends and terminates with an open end pointing upward a couple of inches from the top of the tank.

Meanwhile, the fitting for the return line from the engine compartment is at the bottom left rear corner of the tank. Inside the tank, this fitting continues as a tube that runs across the rear of the tank --there are actually a couple of clips brazed to the inner surface of the tank to hold the tube in place --and then bends upward and terminates with a 180º hook that pokes its end down into the opening of the pipe from the surge tank fitting described above.  The connection of the two pipes is not liquid-tight; if you tip the tank over and pour a liquid into one of the fittings, it will leak out of the connection within the tank.  But it doesn't appear to be a very loose fit; the tube from the return line appears to nearly fill the opening in the end of the tube from the surge tank vent.

In other words: the fuel returning from the engine compartment passes through the main tank but really goes directly back to the surge tank, with a leaky connection inside the main tank to allow air to bleed out or something.

Mike Morrin provides a possible explanation for this Rube Goldberg: "Let's say you are nearly out of fuel, with a little fuel still sloshing around the bottom of the main tank.  You park, with the engine running on the side of a road with a lot of camber so that all the fuel runs to one side of the tank.  The main outlet from the tank is now above the fuel level.  The engine can keep running (or restart) for as long as there is fuel in the surge tank.

"With the arrangement you describe, the engine can keep running until all of the fuel in the surge tank is burned in the engine.  If the return pipe just went to the main tank, the fuel circulated by the pump would all end up in the main tank, and the surge tank would be empty in a minute or so."

Apparently something about this system didn't work as intended, though; in Issue No. 2 of the XJS Bulletin, Ray Ingman reports that Jaguar issued a kit to provide an additional vent for the surge tank, JLM 2163.  The kit includes a replacement pickup tube that features a vent connection.  A line from this connection is simply teed into another vent line up near the vapor separator.

Ingman describes the incentive for this fix as a "problem of fuel vaporization within this tank under adverse, e.g. hot, climatic conditions.  This results in flat spots and hesitation in engine performance."

SURGE TANK VENT CONNECTION: There are three threaded fittings on the fuel tank in the '83 coupe.  The main drain line from the tank to the surge tank requires a 13/16" wrench and the return line from the front of the car requires a 19/32" wrench --both readily available at most hardware stores.  However, the fitting where the surge tank vent connects to the main tank requires a 1/4" Whitworth/5/16"BSF wrench.

FUEL PUMP CONTROL: On both the Digital P system and the earlier D Jetronic, the fuel pump is controlled by the EFI ECU via a relay in the trunk.  The ECU contains a circuit that determines whether or not the engine is actually running and shuts off the pump if it has been motionless for more than a coupla seconds.  You can observe this circuit working by turning on the ignition without starting the car, and listening to the pump run; it should shut off in a couple of seconds.

Note: there have been some reports that owners have gotten the idea that they are supposed to wait until the pump stops running before starting the car.  This is not the case; the fuel pump control circuit is only provided as a safety device.  When starting, the key should be turned from off all the way around to start promptly.

The fuel pump control circuit is unreliable in the 6CU ECU, and sometimes will fail to keep the pump running more than

If you'd like to test this circuit to determine if this is your problem, simply remove the fuel pump relay in the trunk (the one without a red mark on it) and put a jumper into the socket connecting terminals 86 and both 87's.  This will allow the pump to run whenever the ignition is on.  If the car now runs perfectly, the fuel pump circuit in the ECU (or the relay itself) was the problem.  AJ6 Engineering, Beckman, or any other place that repairs ECU's should be able to fix this problem for far less than the cost of a new ECU.

If you're willing to risk the odds that you will be in an accident where you are knocked unconscious, a fuel line is severed, and something ignites the leaking fuel, you can leave this jumper in place permanently -- but a better idea would be to cut the orange wire from the 85 terminal in the socket and connect it directly to ground and reinstall the relay.  That way, the relay will continue to handle the heavy current to the fuel pump instead of pulling it through the ignition switch, as is done with the 86-to-87 jumper.  Note also that if you happen to have a leaky injector, turning the ignition on without starting the engine can fill a cylinder with liquid fuel, causing considerable damage the next time the starter is engaged.

You might also consider upgrading to the later 16CU ECU.  See page 296.

The voltage to the fuel pump, unfortunately, is a far more serious concern.  The fuel pump provides a constant flow of fuel.  The engine takes what it needs, and the excess is returned to the tank.  As long as the engine is at low power, most is being returned to the tank, and a reduction of pump capacity would go unnoticed.  When the throttle is floored, however, a fuel pump working at low voltage won't provide enough fuel to keep up, and the engine will run lean - precisely when the EFI system is in "open-loop" mode and desperately in need of enrichment.  The inevitable result will be burnt pistons, in short order.  What's worse, it's quite possible you'll spend thousands of dollars rebuilding the engine without ever figuring out why you burnt pistons -- and hence may do it again the next time you floor it.

Now, today, before the next time you hammer that gas pedal, go out there and measure the voltage across the terminals on the fuel pump itself.  You'll have to remove the spare tire, the trunk carpet, and a couple of panels to get at it, but it's not difficult.

At idle, the voltage should be at least 11V.  Better yet, have someone hold the engine at 2000 rpm.  At that speed, the voltage should be at least 13V.

If it's not, fix it.  For analysis, you can use the same VOM while you're there to determine where the voltage losses are --in the ground connection, in the fuel pump relay itself, in the wiring from the battery to the fuel pump relay, in the wiring from the fuel pump relay to the pump.  In the XJ-S, all these items are within a couple feet of each other in the corner of the trunk.  In the saloons, the battery is up at the front of the car, so testing each part of the circuit is a bit more involved.

Better idea: just forget the testing and replace everything.  Run a new 12-gauge wire directly from the battery post to the fuel pump relay.  Run a new 12-gauge wire from the fuel pump relay to the fuel pump.  Run a new 12-gauge wire from the fuel pump to ground.  Make sure you're providing good connections to the fuel pump relay socket, not just splicing into the existing wires near the terminals --the existing connections where the terminals are crimped onto the wires may be the problem!  If the voltage at the pump terminals still isn't what it should be, replace the fuel pump relay itself - that's the only thing left it could be.  All of this could be done in perhaps an hour for ten bucks worth of wire, connectors, and a relay.  Money well spent.

FUEL PUMP NOISE: A noisy fuel pump is a very common complaint.  The two most common causes, though, are not the pump's fault.  The first is a problem in the mounting.  The pump is supposed to be mounted in foam rubber and connected at both ends with flexible hose so that it can vibrate without transmitting sound into other parts of the car.  However, its near-vertical mounting often allows the entire pump to slide downward through its mounting until the outlet barb, within the hose, is jammed hard against the trunk floor.  This allows the vibrations to be conducted directly into the structure of the car.  To prevent this, the author wrapped a piece of soft rubber around the pump and held it securely to the pump body with a hose clamp.  The pump could then slide downward only until this rubber contacted the mount, and could not slip any farther.  Problem solved.

Ed Sowell has a related problem: "Mine was really noisy for a while.  Then I found some jerk had put a floor jack under the boot floor pan, pushing it so that it ran into the pump.  Got quieter when I pounded the floor back down."

The other likely cause of pump noise is a plugged pickup or other restrictions on the suction line to the pump.  See FUEL PICKUP on page 251.

FUEL COOLER -1992-ON: Richard Mansell quotes from a Jaguar publication that was sent to him: "It is titled "Technical Guide -The New XJ-S 1992 Model Year Preliminary Information".  In it there is a paragraph about the fuel cooler deletion, it says:

"With the introduction of the in-tank fuel pump, the fuel cooler is deleted.  This affected the characteristics of the system so that a muffler is added in the line to reduce noise and vibration."

"I wonder why adding an in-tank fuel pump should allow the deletion of the fuel cooler.  It also says in another section:

"As a result of the deletion of the fuel cooler, it is necessary to introduce a redesigned hot start system.  The thermal vacuum valve fitted to pre-92 MY vehicles is replaced by the following components:

1. Fuel rail temperature switch.  The electrically operated switch enables the fuel rail pressure to be increased when the fuel temperature exceeds 70 degrees Centigrade at hot starting.
2. 45 second timer module.  The timer limits the time for which the increased fuel pressure is applied.

FUEL PUMP: John Goodman reports: "The latest XJ-S's had pumps inside the fuel tank, so Jaguar may have done this for noise related problems.  I suspect that these pumps are lower output because the '93 model XJR-S had twin in-tank pumps, and must be ordered in a matched pair."

FUEL PUMP REPLACEMENT: Noel Keefer found that somebody had already replaced his in-tank fuel pump with a Walbro.  "A WALBRO pump ought to be available at NAPA, for cheap.  It was a perfect fit."  Note that, when you take the old pump out, you'll find it encased in a housing.  You have to open the housing up; the Walbro fits inside where the original pump was.

FUEL PUMP WIRING: Nigel Sly, who owns a '93 4.0, reports on a fuel pump wiring issue: "Pull the fuel tank and remove the pump cannister/housing, then prise that apart, remove and replace the pump.  Took me about 5 hours all in all.  Just the pump unit will cost about $100.  Don't celebrate at that cost, when mine failed it was the connector which had toasted, apparently a design fault.  New pumps have a different connector, which will not fit the female connector in the evaporative flange."

"First, cut off the connector from the pump, and then solder on an extra 2 to 3 feet of wire to the pump cables, this gives room to allow the pump to be refitted without the evap flange getting in the way.  Pop out the through connector which goes through the evap flange (black in colour), cut the right angled bit off the connector, and then drill a small hole down through the connector, which will allow the pump cables to be passed through.  Fit the connector back into the evap flange, and fill the connector with mastic/sealant to seal the hole.  You will probably need to remove the connector from the external harness as well, unless you can find a matching connector to fit to the pump cables.  If cannot find matching connector, cut the connector from the external harness, and then fit matching connectors to the external harness and the pump cables."

"I tried for weeks to get the original pump connector, even tried the makers of the connector, only to be told it has been out of production for years.  Jaguar had the pump connector, and hence the evap flange changed in 1994, mainly I think because of numerous failures of the original connector.

"Incidentally, the tank does not need to be completely removed from the car; it needs to be moved back about a foot in order to get access to the evap. flange.

"A replacement pump (in canister), complete with new redesigned evap. flange, and new harness is about $900, but now as rare as rocking horse s**t, you might see them listed on various sites, but stock is zero."

Sly may be satisfied with his fix of running the wires through the flange and sealing them up, but in general this type of thing is not a good idea.  It's possible to end up with leaks through the wires themselves, vapors or liquid passing between the copper conductors and the insulation.  In general, this type of problem calls for a liquid-tight bulkhead connection, something that the pump plugs into on the inside and the harness connects to on the outside.  Better electrical supply houses should be able to provide such connectors, but make sure they're compatible with fuel and ethanol.  If all else fails, you could conceivably make such a thing by embedding straight pieces of solid brass in the sealant and then connecting the leads to them on the inside and outside.  You might even use connectors to hold the brass pieces in place while the sealant sets up.

Alternatively, you could make one small hole per conductor, and install a small bolt and nut with insulating washers.  You must make sure that the head of the bolt seals against the insulating washer, otherwise you will get a leak along the bolt threads.  It may prove a challenge to get the electrical leads connected without causing a leak.

FUEL PUMP PLUGGING: Noel Keefer reports: "My '92 [42,000 mi] has two screens prior to the pump.  It produced the proper pressure and adequate volume for shop tests.  But it couldn't go fast very long, maybe 5 minutes.  Pulled the pump from the tank and the two screens were clean.  So was the inline filter.  All were perfectly clean.  However the pump, a Walbro!, has about a 1/4 inch intake with a screen finer than the two prior filters.  It was dirty.  I carved the screen out because I'm not particularly fond of removing the tank when I have 3 filters preceding the pump.  Now I have 2 followed by the inline and a screen on the return!

"Some may say now the pump is in jeopardy.  My answer: ''So what?''.  If the external filter is ever going to be more than a splice in my fuel line let the D*** dirt get to it.  But tank removal is now going to be less frequent, if ever."

Rory McKenzie reports: "My friend Mike Dallaire ('92 xjs v-12) told me his in-tank pump fried out and he had to do similar work.  He said when he pulled the in-tank fuel filter out, it was all clogged up with the remnants of little polyethylene ''packing pillows'' which had not been completely removed between the shipping and installation phases."

VAPOR RECOVERY SYSTEM: When the car is running and drawing fuel out of the tank, there must be a vent system to allow air into the tank to prevent a vacuum from being created.  It is no longer acceptable to merely have a small hole in the gas cap; such methods allow fuel vapor to escape into the atmosphere all the time, whether the car is running or not, and would contribute to air pollution.  Raw gasoline is a serious air pollutant, and besides that it smells bad.

Unless you live in California or somewhere else where they have intelligently-designed gasoline pumps, you pump 20 gallons of fuel vapor out into the air every time you pump 20 gallons of liquid gasoline into your car.  It is simply inexcusable that, decades after the public became aware of the problems of air pollution, every filling station in America doesn't have the same vapor recovery filling systems that California has.  But, back to discussing the fuel tank vent system in your Jag.

Avoiding polluting the air via a properly-designed fuel tank vent scheme is easy and doesn't hamper the performance of the car one iota.  The only disadvantage to the owner is in the initial cost of installation, but since the car comes with the system from the factory and has therefore already been paid for, there is no reason to remove or disable it.

In simplest terms, a "vapor recovery system" connects the fuel tank vent to a carbon canister.  Air can flow freely through the canister into the fuel tank, but when vapors from the fuel tank try to escape through the canister they are absorbed by the activated charcoal.  Of course, the charcoal can only absorb so much fuel.  Therefore, whenever the engine is running, there is a system by which the engine draws fresh air through the canister.  This draws the vapors back out of the charcoal and burns them in the engine.

When the car is not run for extended periods of time, the amount of vapor generated in the tank could be considerable.  Gradual changes in ambient temperature and barometric pressure would cause the vent system to "breathe", running a large amount of vapors through the canister.  To absorb all this vapor, the canister would have to be prohibitively large.  To reduce the amount of vapor the canister has to deal with, there is a "2 psi valve" in the vent line between the fuel tank and the canister.  This valve will allow air to flow in either direction, but only after a certain pressure or vacuum has been reached.  If the contents of the tank expand and try to escape out the vent, it will prevent any flow until the pressure reaches 2 psi or so, and then it will allow it to pass to prevent damage to the tank or hoses.  Similarly, if the contents of the tank contract and try to draw air in through the vent, the valve will prevent any flow until the vacuum reaches a set value -- usually lower than the pressure value -- and then it will allow it to pass to prevent the tank from collapsing.  As a result, the vast majority of the smaller expansions and contractions do not open the valve at all, and the amount of vapor the canister must absorb is greatly reduced.

I am sorry to report that the vapor recovery system on the XJ-S is unreliable.  Many owners have reported problems, usually indicated by a large "whoosh" but often dismissed as normal until the gas tank cracked or other dangerous symptoms arose.  Fortunately, if the symptoms are recognized and addressed promptly, it's never difficult to make the system work as it should; it's simply not that complicated or expensive to fix.

VAPOR RECOVERY SYSTEM --AFTER RECALL: The original XJ-S vapor recovery system pretty well followed the description above.  However, there was a tendency for the tank to develop stress cracks from excessive pressure fluctuations as well as indications it did not vent as well as intended (including numerous complaints about fuel odors), so there was a recall to address the system.  In general, the recall involved the installation of a "Rochester valve" in place of the 2 psi valve.  David M. Johnson: "The Rochester valve (Part CBC 7714) is a cylindrical disk (approx 2 inch diameter) with an inlet from the fuel tank vent pipe and outlet for the vent to connect to the carbon canister.  A third outlet at the top is to connect to the manifold vacuum."  A Rochester valve works the same way as the 2 psi valve when the engine is off, but when the engine is running the vacuum signal pulls the Rochester valve wide open to freely vent the tank.

The recall also installed one or two (depending on VIN) vacuum-operated purge valves to provide a positive purge when the engine is running.  The left side throttle butterfly housing was replaced with one that had suitable taps for controlling the Rochester valve and purge valves.

For those who have disconnected the vacuum lines from the butterfly housing and want to reconnect them properly, I can give this guidance based on the dealer instructions for the recall that installed the system in the first place: Among the two vacuum hoses that go from the butterfly housing to the area in front of the left wheel well, one is supposed to have a black and white delay valve in it, hanging in the vicinity of the coolant header tank.  A hose from the black side of this delay valve should be connected to the front port on top of the left butterfly housing.  The hose with nothing in it should be connected to the rear port on top of the butterfly housing.  Of course, there were several variations on this system as applied to different cars, but I think that description should cover most of them.

The carbon canister, the Rochester valve, the purge valves, and the associated plumbing are all located forward of the left front wheel; remove the forward panel of the inside wheel well to inspect.  The only part of the vapor recovery system not in this location is the vapor separator, which is high in the right side roof pillar on the coupe.

I am sorry to report that, after the recall has been applied, the vapor recovery system in the XJ-S is still unreliable.  The installation of the Rochester valve sounds good in theory, but unfortunately the Rochester valve itself is apparently extremely unreliable.  When it fails, it apparently fails jammed shut, which is the worst thing that can happen to a vapor recovery system.

CARBON CANISTER OVERBOARD VENT: When the recall was applied to the vapor recovery system, one change done was to remove a hose that vented the carbon canister out the bottom of the car.  It then just opens into the bodywork cavity.  This demonstrates an interesting attitude; of course, if the system is working as it should, there shouldn't be any odors coming out of this opening.  But if, on the off chance, some gasoline vapors make it through this canister, you might be happier if you installed a new hose venting it overboard.

VAPOR RECOVERY SYSTEM -- CHECKING: If your XJ-S has the Rochester valve, the first check is quick, simple, and clear: with the engine running, open the fuel cap.  There should be absolutely no "whoosh" or any other symptom of pressure equalization.  If there is a whoosh, either the Rochester valve isn't working, or the system is plugged somewhere.

The second test requires more judgement.  When the engine is shut off, the Rochester valve becomes a 2 psi valve, and a small pressure or vacuum can build up in the tank.  After parking for some time, a little whoosh is to be expected, but too much is too much.  Too long is not the concern; typically, a nearly empty tank will whoosh for a long time (lots of air space inside) while a nearly full tank results in a very brief whoosh.  The concern, though, is not the duration but rather the severity.  David M. Johnson says, "A huge whoosh and an oil canning sound means the valve is not working -

Another sign of trouble: no whoosh at all.  There is a remote chance that the fuel in the tank has remained at the same temperature since shutdown and hasn't developed any pressure or suction at all --but that's really unlikely, especially if the car has been sitting in the hot sun.  Generally, if you don't get a whoosh when the car's been sitting a while, either the Rochester valve is stuck open --which may sound acceptable but it's really not, it'll quickly saturate the carbon canister and then you'll have fuel odors, not to mention what you'd be doing to the environment --or there's a leak in the system somewhere, which obviously could cause odors, fires, you name it.

In the US, the duration of the whoosh involves the little trap door in the filler that prevents you from inserting a fuel nozzle dispensing leaded gasoline.  Since you can no longer buy leaded gasoline, nozzle notwithstanding, this thing is a relic of a bygone era and could be removed without concern.  But if it is there, it effectively restricts vent flow when the cap is removed, and may make a short whoosh into a longer whoosh.  Conversely, if the trap door is gone, a long whoosh may seem deceptively short.

If your car doesn't have the Rochester valve arrangement for some reason, whether or not the engine is running makes no difference; either way, there should be a small whoosh.

BACKUP FOR ROCHESTER VALVE: The entire point of the Rochester valve is that the tank should be freely connected to the carbon canister when the engine is running.  It is a simple matter to make sure that happens: just tee into the vent lines before and after the Rochester valve and connect up a solenoid valve to bypass it.  Connect the solenoid valve to a switched power source so it is energized whenever the ignition is on.  That will ensure proper venting when the car is running.

To ensure proper venting when the engine is off, you can install a 2 psi valve in another bypass around the Rochester valve.  If you don't have a 2 psi valve, you can probably get one from just about any car in a junkyard; most cars use a simple system similar to the pre-recall scheme in the XJ-S.  Or perhaps you can buy a Jaguar part, CBC6820.

Of course, once you have the 2 psi valve and the solenoid valve working together, you could eliminate the Rochester valve.  If it jams open, that'd be a good idea.

Obviously, another option would be to install a second Rochester valve around the original.

FAILSAFE FOR VAPOR RECOVERY SYSTEM: There are reportedly several different gas caps used on these cars; some OEM, some aftermarket.  Some of them are a total seal, but others have a pressure/vacuum relief valve built into them to serve as a safety in case the vapor recovery system gets plugged.  Good idea!  If your gas cap is a total seal type, you might want to replace it.  Note that if you have the pressure/vacuum relief valve type, it may defeat the whoosh test described above; you'll only get a small whoosh when removing the cap even if the vapor recovery system is totally plugged.

If somebody has drilled a hole in your cap, you definitely should replace it.

FUEL FILLER UPGRADE: The fuel filler on the XJ-S --at least this author's '83 --is the old style that turns 1/4 turn.  Not only is this a lousy design, but it's also difficult to secure; Jaguar offers a locking variety, but believe it or not their locking gas cap is officially not supposed to be used in the US --it doesn't seal as it should and therefore won't meet EPA emission requirements.  Roger Bywater says, "Most lockable caps have a tang which engages with the underside of the filler neck so the sealing arrangements are probably unable to withstand any significant vacuum or pressure and are just able to stop fuel sloshing out."

On later models, Jaguar made the door over the filler lockable, which eliminated the need for a locking gas cap.

Walter Acker IV points out that it is a simple matter to ditch this dinosaur and install a modern filler from a junkyard.  The filler on his '76 is different than the later designs (see page 244), but the general idea should apply equally well to either type.  Just peruse the local junkyard until you find a car with a modern tighten-until-it-clicks fuel filler cap on a

"I checked with the state of California smog reps and they said that it is not a legal modification so if it is detected by a smog rep then the car may not pass smog in CA."  Damn shame these guys are so picky, since this cap upgrade will improve the car's emissions.  "The smog police will give you a problem but the normal smog techs just remove the cap and see it is threaded and test it without ever calling the officials for clarifications."

"The one thing that I like is the fact that when you go to a parts store they have a new style of gas cap.  It is called a Prevent which is a pressure release type so that you can release pressure buildup before there is a problem when removing the cap for fuel filling."

Note that you need to pay attention to how high the new cap sits; you don't want to go through the entire modification only to find that the filler door won't close.  And having to hack a side off the new cap will reduce the esthetics of this upgrade considerably.  Note, however, that the tighten-until-it-clicks cap can merely be turned a couple more clicks if the problem is a corner or something that obstructs the door.

Bernard Embden --who owns a '78, also with the earlier flanged-type filler pipe --reports: "A visit to the junkyard resulted in the removal of the fuel neck and cap from a 1987 Ford (hacksawed the fuel pipe right out of the trunk-lucky no sparks).  I cut approx 2 inches from the filler tube, and the same from the Jaguar fuel filler pipe.  Keep your existing flange that mounts the pipe to the body.  You will need to modify it somewhat.  Make your cuts dependent on whether you will keep the existing flange or not.  Off to the welder.  Two trips later (he had no way to pressure test the weld) and I was ready to install.  The Jaguar filler pipe is quite large, approx 2 inches I.D.  The Ford pipe is 2 inches O.D.  This made the welding quite easy because one pipe fits inside the other.  Remember to change the tank gasket (large "O" ring thingmajij).  No leak, no drips, no fumes.  One of those projects that made so much sense that I should have done this years ago."

Regarding finding the right one in the junkyard, Embden says, "Most filler pipes started small and stayed small.  However some started larger and then became small.  On these you only need the first few inches so it doesn't matter."

This author made this upgrade, but my '83 has the later style filler pipe with no flange.  I believe this makes the upgrade easier, since you don't need to worry about the alignment of the flange when you have the two pipes brazed together.  And, without a flange, if the cap ends up too high for the door to close you merely loosen the clamps and slide the filler pipe a little farther into the tank.

David Low points out that the XJ40 has the tighten-until-it-clicks type of filler, and suggests that it may be adaptable to the XJ-S "if you're handy."

A locking gas cap for the tighten-until-it-clicks type filler is readily available, and appears to seal just fine.  These later caps won't ding the paint as badly when you drop them, either, since they are plastic and weigh less than the old metal 1/4-turn caps.

VAPOR RECOVERY SYSTEM --MAINTENANCE: The vapor recovery system, including the carbon canister, is normally maintenance-free.  Activated charcoal can absorb and release fuel vapor forever, it doesn't wear out or get "full".  However, there are filter elements within the canister (after all, it is an air intake) that may eventually get clogged, and the carbon itself may eventually get contaminated with fuel additives or other non-petroleum substances, so it is recommended the canister be replaced once in a great while.

If you're really a skinflint, the carbon canister can be opened and the filters replaced.  There are two, one at the top of the charcoal and one at the bottom --you must dump all the charcoal on a newspaper or something.  Both filters can be neatly replaced with coffee filters.  The canister can be held shut with aluminum tape when reassembled.

The carbon canister itself has an opening on the top to atmosphere, and three fittings on the bottom (note: the canister may be mounted upside down, so top may mean bottom and vice versa).  The fitting labeled T is connected to the fuel tank, via the appropriate valves and the vapor separator.  The fitting labeled P is the purge line to the engine.  The fitting labeled C is capped off; it originally was the connection for venting the float bowls of the carburetors, but they are history.  Note: if you fit carbs, do not simply open this fitting and try to use it; a screen has been omitted inside as well, and you will draw carbon granules into the float bowls.

One of the possible causes of the common fuel odors is the location of the canister in the XJ-S.  On most cars, it is located in the engine compartment where any escaping fumes will simply be blown away by the flow of air through the radiator.  But in the location in the bodywork forward of the left front wheel, there is no such flow.  The vapors may gather in the bodywork and eventually work their way to the passenger compartment.  Of course, there aren't supposed to be any fumes escaping, so this is a secondary problem.  However, it might be a good idea to connect a length of hose to the atmospheric vent on the canister and route it out the bottom of the car.

Another possible failure mode is that the engine is not properly purging the canister.  If the engine is not drawing air through the canister when running, the canister will quickly become saturated with fuel and will cease to absorb, and any further fumes coming down the vent line will escape to atmosphere.

VAPOR SEPARATOR: In the XJ-S, there are several vent lines from the fuel tank.  They all are routed to a small vapor separator high in the bodywork to the right and above the fuel tank.  This small metal contraption is intended to allow most fuel vapor to condense and drain back into the fuel tank.  The vent line to the canister is routed from a point high in this separator, so fuel vapors must be very determined indeed to make it past this point.

Note that the vapor separator has been blamed for many problems.  Since it is steel, it is prone to rusting.  If a hole rusts through it, fumes will be vented into the bodywork.  Also, rust particles may fall inside it and plug the tiny vent passages and hoses.

VAPOR RECOVERY SYSTEM --INCORRECT PLUMBING: David M. Johnson owns two H&E's, and reports: "I found that on both of my cars the fuel vent systems were plumbed incorrectly (not done by my local dealer).  The carbon canister under the front left wheel arch is connected to a vent pipe from the fuel tank, and a vent pipe to the PCV valve next to the LHS air intake.  The two vent pipes were wrongly connected, i.e. the fuel tank vent was connected to the valves for PCV pipe (two valves operated by vacuum from the LHS manifold), and the PCV vent pipe was connected to the Rochester valve that should be connected to the fuel tank vent.

"So what's the big deal?  Well, the valves that would normally operate the PCV valve only open under vacuum when the engine is running.  When parked and sat in the sun the tank cannot vent!  I tested these valves with 10 psi and still the valves would not open.  The tank is now a sealed container with fuel vapor inside!  There are only two things that can happen:

(a) The tank will build up a severe pressure and will rupture in time due to fatigue at the weakest location.  A pressurized gas vapor canister in my car/garage does not give me a good feeling!
(b) If you are lucky, one of the vent pipe/fuel connections will leak to relieve the pressure and cause a fuel leak and/or a fuel vapor smell.  I am still not keen on this option with the car in my garage!
"If the tank is connected correctly to the Rochester valve, the valve will open at approx. 2 psi to relieve the pressure in the tank, and also opens under vacuum.  This stops the tank venting under all conditions and hence does not overwhelm the carbon canister.

"Of course my vent works perfectly now, no gas smells and no severe pressurization of the tank, just a small woosh

"This recall was Hess specific (recall (C002) XJ-S purge kit (Feb 1990).  If you check the recalls on XJ-S 86-91 you will find there were similar problems with the regular XJ-S but a different fix.  The mod was estimated to be 4.35 hrs for later Hess cars to install Kit JLM2046 and conduct a fuel system integrity test.

"The diagram (figure 6, page 8 of 23) showing the valves and carbon canister connections is not very clear because the fuel vent pipe connections are only partly shown, but the PCV pipe vent connections are clearly shown.  I deduced these pipes were incorrectly attached by testing all the valves to determine how the vapor system functioned.  I called the Jag dealer the next day to get a copy of the fuel vent recall, and hence confirm the connection was incorrect.

"I do not think the two cars were fixed by the same dealer for the recall.  One car is from New York, and the other is from California.  That is why I suspect other cars could also be connected wrongly!"

IDLE SPEED ADJUSTMENT: On each butterfly housing, there is an adjustment screw that a lever contacts when the throttle is at idle.  These are not to be used for setting idle speed.  If they have been disturbed, the linkage must be readjusted as described on page 271.

Underneath the rear end of the left intake manifold there is an aluminum housing with two hose connections; one that goes up to the back end of the manifold and one that goes forward to the air filter housing.  This contraption is called the auxiliary air valve, or AAV for short.  Just below the connection leading to the air filter housing is a bolt.  This bolt, believe it or not, is the idle speed adjustment.  The bolt itself obstructs an air passage, so the farther the bolt is unscrewed, the more the passage is opened, and the faster the engine idles.  It's not real convenient to get to, but a ratchet and a long extension with a swivel at the end will do it.

Some suggest polishing a bit off the OD of the outlet fitting/cylinder to change the press fit to a slip fit, and then retain it with screws through the side of the housing.  This makes it a bunch easier to get apart next time.  A little sealant would

John Ashcroft of Melbourne, Australia, says, "H&H Spares do a c/o for $90 AU, trade price; they have someone rebuild them so the bits are available somewhere.  Put one of their exchange units in about 5yrs ago and it's still working fine."  See page 727 for H & H Prestige Spares.

AUXILIARY AIR VALVE --CHEAP FIXES: If your AAV isn't sticking but exhibits the "tired" behavior described above, Roger Bywater suggests a fix: "It does seem that the range of movement can change with age possibly due to very slight leakage from the bulb.  In such cases it is quite feasible, after assessing the amount of correction required, to just press the top further into the casting body in a vice (with a socket or tube over the bulb) to get the thing operating back in range.  Obviously it has to be checked in boiling water before and after and it needs to be done with care because it is all but impossible to get it back if it goes in too far.

"Don't go blaming Jaguar or Lucas for this valve and its foibles, although most of them run for years without trouble.  It was a Bosch invention."

Faced with a completely failed AAV, Jan Wikström simply started the car and let the AAV suck a small rag into the opening in the air filter housing to plug the port.  If the rag is small enough, it could conceivably plug the port without interfering with the warm idle adjuster.  Of course, if it's too small it'll pull it through the port and into the engine.  I'd suggest something around 2 inches square.

With a little more disassembly, you can do a better job of plugging it.  Take the hose off the inlet fitting and jam a plug in there.  By making the plug short enough, you should be able to push it past the warm idle passage, which comes off the bottom of this passage, and plug the cold idle port only.

Really cheap and easy: jam a cork into the hole into the opening in the air filter housing.  The problem with this is that it will suck through the distributor vent scheme like crazy to maintain idle.  Still, if you have a problem on the road, this might be a quick fix until you get home and can do something better.

All of these last fixes, of course, completely eliminate any idle boost when cold.  Interestingly, several owners have reported that this doesn't seem to hurt anything!  The V12 will idle at 300 RPM with no problem.  Some cars have another means of boosting the idle when cold, namely the supplemental air valve at the front of the right intake manifold.  This thing stays open for 45 seconds on US-spec cars and 15 minutes on UK/Euro spec cars to compensate for a disabled vacuum advance at idle; you might consider re-enabling that vacuum advance at idle (see pages 304 and 135) while leaving the idle boost functional.

Finally, of course, an entire separate cold idle scheme could be provided; John Napoli says, "just get one or two vacuum solenoids.  Wire to toggle switches, pipe the air thru an inline fuel line filter (or plumb to air box) and go to town.  These thingies are real cheap.  Get generic units unless you have some Jag take-offs in your junk box."  For fancier work, you could install temp switches in the coolant circuit to operate these solenoids automatically.  By using different temp switches, the idle could drop in steps as the engine warms up and the solenoids shut off in sequence.

IDLING ON ONE BANK: Kurt Hill has a very early XJ-S, and the AAV plumbing looks like the illustration in Section 19.20.16 of the ©1975 ROM or Fig. 3.52 in the Haynes manual --which don't resemble the plumbing in the later cars at all.  In this early layout, there is a tee on the outlet of the AAV, with one fitting connecting to the crossover pipe while another connects to a hose that goes forward underneath the left side intake manifold and connects into it from the bottom.

Hill's problem was that the car ran great at speed, but idled on the right bank only --and flunked an emissions test big time because the EFI system was still squirting fuel into the left bank that wasn't firing.  It turned out that a PO had replaced the hose from the AAV underneath the left manifold with generic hose, and since it has to make a 90º turn, it kinked as soon as manifold vacuum was applied to it.  Since this is not only the idle air supply to the left bank but also the crossover pipe, the left bank got no air.  Since this hose was hidden under the manifold, it was a difficult problem to

The easy fix: replace the hose with a molded hose with a 90º bend in it, which is what the car originally came with.  Better fix: install a metal spring inside the hose to prevent collapse.  Better fix yet: replace the hose with a section of copper piping with a 90º elbow, and connect it at both ends with really short pieces of hose.

Those with later cars don't need to worry about running on one bank at idle (unless they have Marelli ignition!), because the crossover pipe is no longer part of the AAV plumbing but a separate entity.  But any hoses under manifold vacuum are always cause for concern for sucking flat.

OVERRUN VALVES: If the throttle is closed at an elevated RPM, the manifold vacuum can exceed that normally found at idle.  Under such high vacuum conditions the fuel/air mixture being introduced into the cylinders, even at the proper ratio, can be so rarified that it cannot be reliably ignited with an ignition spark.  If that cylinder full of unburned mixture is then exhausted, it dumps quite a load of raw hydrocarbons into the atmosphere.  However, as Roger Bywater points out, an even worse result (from the car owner's standpoint) is what happens when the mixture is later ignited within the exhaust system; it can blow the mufflers open.  This igniting within the exhaust is what causes the "backfire" upon deceleration that is characteristic of some cars -- mostly pre-EPA cars.

"The purpose of the over-run valves is to limit the vacuum that the engine can generate on the over-run because it was generally considered that when vacuum exceeds about 22" Hg the charge density is so low and contaminated by exhaust residuals that combustion ceases to take place effectively.  The over-run valves therefore ensure that any mixture entering the engine is dense enough to fire."

At the front end of each intake manifold on the Jaguar V12 is either a blank-off plate or a little housing with a stub hose connection to the air filter housing.  The little housings contain the overrun valves.  They are a spring-loaded poppet valve that should open only when the manifold vacuum is higher than a set amount more than idle vacuum.  Basically, this limits the manifold vacuum to a level where ignition is reliable.  It also tends to make the engine feel as though it has no "compression" on deceleration --basically, the throttle is being opened a little.  In fact, on some other automobiles, the same effect is achieved by physically opening the throttle.

Does your car have overrun valves?  Apparently, it depends on whether or not your EFI system incorporates another method of addressing the same problem: overrun cutoff, in which the fuel injectors are shut off under deceleration (see page 274).  Bywater: "When the EFI V12 engine was first introduced it had over-run valves and did not have over-run cut off.  Cut off was introduced in some markets in about 1977-8 and the over-run valves, being no longer necessary, were therefore deleted on the respective cars.  I cannot be sure from memory if US Federal emission cars were included but it is possible that they continued without cut off.  All manual transmission cars continued with over-run valves because they did not have cut off as it caused unpleasant driveline shunting.  Manual ECUs also gave slightly different low end fuelling being able to run at full throttle below the stall speed of a torque converter.

"Cut off on the D-Jetronic system was effective at all temperatures unlike later Lucas Digital cars in which cut off was inhibited at low temperatures, necessitating the return of over-run valves.

"I think it is correct to say that if a D Jetronic engine has over-run valves it would not have over-run cut off, unless of course someone has swapped the ECU at some time.

"In fact, the over-run valves were notorious for losing spring pressure and causing a high or erratic idle speed.  The practical solution was to just tighten the nut about 2 turns."  Basically, adjust it just tight enough that the valves are closed at idle --which can be confirmed by putting a finger over the hole in the filter housing with the engine idling.  "Setting the over-run valves by checking with finger over the hole is as good as any method.  As long as they don't leak at idle but work when you blip the throttle and release it to create an over-run condition they will be OK.  You will probably hear them anyway.  Again from memory I think they were meant to start to open at 20" Hg but by their nature they are more a sort of progressive leak rather than a step change device so manifold vacuum could exceed this value to a small extent."

ACCELERATOR PEDAL --EARLY MODELS: Mike Morrin says, "The Jaguar pre-HE service manual seems not to have been updated from 1975 to 1981, which is fine for my car, but I have seen a few things which are obviously wrong for most of the pre-HE cars.  A minor example of this is the RHD accelerator pedal assembly: The only type shown in the manual was only fitted to the first 200 cars."

THROTTLE CABLE --ELECTRICAL PROBLEMS: Ron Brock says, "The starter was acting as though I had a low battery.  After replacing the battery to no avail, I started in on the starter.  The car would crank over fine sometimes and other times it would barely turn.  After receiving several "tips" about checking the electrical connections, I went thru them from the battery forward.

"My problem became clear one night in the garage, I was attempting to start the car with the bonnet up, and it was just dragging.  It was then that I noticed a whiff of smoke coming off the back of the engine.  I walked around to the front of the car to determine what was "smoking," it was the throttle cable, and was it hot (by the way this also solved my sticking throttle problem).  It seems that the engine was grounding itself thru the throttle cable.  I was unable to remove and clean the standard grounding strap at the engine, so I added a second strap that I purchased from NAPA for $4 and the car has been fine.  Absolutely amazing.  I would seriously recommend that anyone have starter/charger problems explore this cheap and easy fix first." See page 555.

THROTTLE LINKAGE BUSHINGS: There is a throttle shaft on each side of the engine, parallel to the heads, that transmits throttle motion to the butterflies.  The rear end of this throttle shaft, along with some linkage, is supported by a plate bolted to the rear of the intake manifold.  There is a rubber bushing in the plate for the shaft to turn in.  This bushing is probably shot -- British nonmetallic parts again.  This bushing will dry up, crack to pieces, and fall out, leaving the throttle shaft to wallow around in the opening.  In fact, this is another example of a 100% failure mode in the XJ-S; if you haven't already replaced the bushings, they are probably bad right now.  The effect on the throttle operation is not good, as it tends to screw up the sync of the two butterflies with each other and with the throttle pot in the turntable.  There are also reports that this problem can have adverse effects on emissions tests, especially if one bushing is gone and the other is still on the job.

The part number for the original Jaguar rubber bushing is C34388.  However, I don't think anyone in their right mind would recommend the original bushing --it's rubber, for heaven's sake.  Rubber throttle linkage bushings are a relic from cars with rigid linkages from the pedal to the carbs; since the engine moved around on its mounts, some means had to be provided to connect the pedal on the car to the butterflies on the engine without the engine's motion affecting the throttle position.  The solution was to have one rotating shaft with one end mounted on the car and the other mounted on the engine; the pedal was connected to a lever right next to the mount on the car, and the butterflies were actuated by a lever next to the mount on the engine.  The pedal twisted the shaft which opened the butterflies, and engine motion would rock the shaft back and forth without twisting it.  Rubber bushings were needed at the ends of such shafts to isolate engine vibrations from the rest of the car, and to allow the small angular motions of the shaft without any binding.

None of this applies to the XJ-S.  The motion of the engine relative to the car is dealt with via a throttle cable.  The linkages where the bushings are used involve shafts that are mounted at both ends from the same intake manifold, so there is no relative motion.  Totally rigid bearings will work fine.

This application really begs for nylon bushings, but bronze bushings would probably work just as well if you can install them so they wouldn't rattle or jingle.  The shaft is 5/16", and the hole in the plate is 1/2".  With a little looking, it should be possible to find a suitable generic bushing to use here.  A bushing with a single lip will work; retention won't be a problem since it is effectively trapped.

Replacing this bushing looks difficult; it appears to require removing either the throttle body or the linkage support plate, either of which is a pain.  You may choose to remove the linkage support plate, since it will permit you to fiddle with the bushing installation away from the car --or take it with you when shopping for a bushing.  If you go this route, make sure to have two EAC2650 gaskets on hand for each side; see page 42.

David Littlefield describes a shortcut: "I was able to replace both my bushings today in my '88 XJ-S without removing

"Once I had the rod out of the car, I was able to move the pinch bolt even further back--past the knurled portion and right against the shoulder.  I then took the new bushing to my bench grinder.  I carefully ground down almost all of the lip on the beveled side.  I put the bushing on the rod, then fitted the rod back in the car, pushing the rearmost end in first and then putting the ball end in the throttle body fitting.  I then pushed the bushing into place, while still on the rod.  Removing almost all of the beveled lip on the bushing allows the bushing to be pressed into place while on the rod, since distortion of the inner diameter of the bushing is minimal.  Replacing the spring clip behind the spacer and resetting the pinch bolt completes the procedure.

"As stated in the book, a bushing with a single lip will work since the bushing is effectively trapped.  There are no real worries about the bushing slipping back on the rod because the spacer and spring washer hold it in place.

"I used the factory bushing for this procedure, but I see no reason why it wouldn't work with others."  Littlefield gets two demerits for replacing a British nonmetallic part that failed with another part just like it --but at least, using his method, it won't be too difficult to replace them again.

Jeff Elmore offers a different shortcut: "I remembered someone saying that it was easy if you did (something) and slid the shaft back through the throttle housing.  Well, after some contemplation, I figured he meant removing the screws from the shaft-to-plate and sliding the plate out of the shaft and sliding the shaft forward through the housing.  Well, it worked like a charm and the bushings were replaced in about 20 minutes."

If you'd like to try a more expedient fix, John Napoli describes a method he credits to Gerry Duff: "We just cut a couple of pieces of rubber hose.  Slipped right onto the shafts, and is the right OD.  No tools or disassembly needed.  Been working fine for almost a year, and when they wear out 5 minutes to do it again.  When the repair was done, the rubber hose sections were left long enough so that they could be turned around if excessive -and quick -wear was realized until a more conventional repair could be effected.  Last week I asked the owner how it was holding up.  He pulled the hoses, and stated that there was no visible sign of wear at all --he had never needed to turn 'em around."  Note: this author tried using this method on a friend's car, and couldn't get it to work.  It apparently requires a particular type of hose we didn't have on hand; we were trying to use fuel hose, which was a little too fat to fit through the hole properly and tended to "walk" off the shaft when the throttle was moved repeatedly.  Napoli suggests that the hose used with success may have been vacuum hose.

As Leslie Winfield discovered, a generic bushing with no lip will work if you can figure out how to hold it in place -- and can make installation almost as easy as Duff's fix.  "I purchased a 1/2 inch x 5/16 inch bronze bushing 1 inch long, and two 1/2 inch outside snap-rings.  I ran a 5/16 bolt through the bushing, pinched it with a nut & chucked it in my drill press (poor man's lathe).  I shaved about .005 inch off the OD with a flat file, used a hacksaw with a 24 tpi blade to cut a groove about 3/32 of an inch from each end deep enough for the snap-ring, and then cut the bushing into two halves.  With a little fiddling, the snap-ring can be threaded to the inside of the support plate, the bushing can be slid over the shaft and through the hole in the support plate (grooved end first), and the snap-ring positioned into the groove on the bushing.  The bushing is now captured on the shaft, and almost no play is observed with this setup.  It doesn't look too bad, cost $1.07, and it should last as long as my '79 XJ-S does."  Of course, if you happen to have purchased bushings with a flange, you can still use this method by cutting the groove in the opposite end from the flange.  While buying these bushings, you might want to buy a spare one in case you ever need to replace the thingy in your Lucas distributor -- see page 142.

Home Depot offers a nylon part that can be installed exactly the same way that Winfield installed his bronze bushings. It's stock number 30699 87298, described as "1" x 1/2" SPACER -NYLON".  All of Home Depot's "nylon spacers" are marked for their OD and length, with no marking on the package at all about their ID; there are several ID's available, including 1/4", 5/16", and 3/8", but other than the stock number they are all marked the same.  If they happen to be out of the 5/16" ID bushings, you could purchase the 1/4" ID bushings and carefully drill them out.

After bushing replacement, the linkage should definitely be adjusted as described below.

THROTTLE LINKAGE ADJUSTMENT: If the butterfly stop screws have been disturbed, the linkage bushings have been replaced, or any other tinkering has been done that could mess up the linkage adjustment, it should be readjusted.  Also note that several owners have found that a rough idle cleared up when this procedure was undertaken, even though one wouldn't expect it to make any difference; the crossover pipe should deal with any imbalance between sides.

I'd like to simply dump the description of this procedure off on the repair manuals since any decent repair manual would provide a step-by-step procedure that's easy to follow, but unfortunately the procedures described in the ROM (Section 19.20.11 followed by 19.20.05 --not 19.20.25, as is indicated in Step 10 even though such a section doesn't exist) is only barely discernible and the one in the Haynes manual (Chapter 3, Section 47 followed by Section 37) is bloody awful.  I will endeavor to explain the process here more clearly.  In further developments, the mid-90's cars with OBD II required much more careful adjustment to avoid fault warnings.  TSB #19-36, dated 10/95, says: "Diagnostic Trouble Codes (DTCs) may be set if both throttle valves are not synchronized to begin opening at the same time.  The Manifold Absolute Pressure (MAP) sensors will detect a difference in pressure between the two intake manifolds, which leads to the setting of DTCs.

"The most common codes found are: P1106 P0106.  The following DTCs may also be set: P0107, P0108, P0125, P1107, P1128.  Poor throttle valve synchronization may also cause customer complaints of poor driveablity and idle quality."

TSB #19-36 provides improved procedures for adjusting the throttle linkage on the OBD II cars, but it can be applied to all V12's with EFI.  As a result, these improvements have been incorporated into the following descriptions of the adjustment procedures.  Joe Bialy and Richard Mansell provided some interpretations of this TSB.  Mansell says, "I suspect there are different TSB's for the different models.  I guess the contents are the same but for a start the throttle pedestal is different on my '96 XJ12 compare to the XJ-S I owned so the picture with the TSB is different."

The linkage requires five distinct adjustments, which must be done in order because each affects the others.  Proceed as follows:

Before starting, remove the air filter covers and elements.  It is highly recommended that you clean the throats before proceeding, using some sort of solvent (see THROTTLE STICKING below) to get the areas where the edges of the butterflies contact the housings nice and clean.  Rather obviously, check the condition of such things as the linkage bushings (see above) before doing the adjustment.

Disconnect the crossrods from the throttle pulley by prying them off the ball joints.

Loosen the locknuts and turn in the butterfly stop screws until they don't interfere with the butterfly motion.  Make sure the stop screws turn easily enough to turn with your fingers; if they're hard to turn, you may need to take them out and clean up the threads.

Loosen the clamp on the lever at the rear end of each butterfly shaft, directly below the crossrod attachment.  This lever is clamped onto a splined section of the butterfly shaft, and since the clamp takes on some toothiness the first time it's tightened it tends to move in snaps.  While holding the butterfly closed move the lever at least one snap in the open direction, both to ensure you have the clamp loose and to make sure the stop within the linkage here isn't interfering with the butterflies closing.

Adjustment 1: Loosen the screws holding each butterfly disk in its shaft, gently press the butterfly closed so that it makes secure contact all the way around, then retighten the screws.  This centers the disk in the opening.

Adjustment 2: Set the butterfly stop screws.  This screw prevents the butterfly from quite fully closing; if it closed completely, it could easily jam, especially with temperature changes such as shutting off a hot engine and then trying to start it the following morning.

To adjust the stop screw requires a 0.002" feeler gauge.  The earliest Jaguar repair procedures specified a 0.004" (0.105 mm) gauge, but after 1978 it was changed to a 0.002" (0.05 mm) gauge -- which works fine for the earlier cars.

Insert the feeler gauge at the bottom, push the butterfly firmly closed on it, and give the feeler a little tug so the butterfly

While pulling gently on the feeler, turn the stop screw with your fingers just until the butterfly starts to let go of it.  Try it a couple of times until you get the feel of the process, at least well enough that you can do both sides the same way.

Without moving the stop screw from this position, take your fingers off of it and put an open-end wrench on it.  Tighten down the locknut while holding the stop screw still with the wrench.

From the TSB: "An improved factory procedure for setting the throttle stop screws, using an air flow measuring gauge, was introduced during the 1994 MY production of V12 engines.  All 1995 MY V12 engines are set at the factory using this method."  Many garages actually have this air flow measuring device since it is indispensible for syncronizing SU and Zenith Stromberg carburetors.  It should work fine here, although you might need to remove the inner half of the air filter housing to be able to get it to sit on the intake properly --and then you'll need to plug the bolt holes, since they create a vacuum leak.  If going this route, you should set one butterfly stop screw per the directions above and then set the other butterfly stop screw to flow the same amount.

Adjustment 3: Adjustment 3 is officially to position that lever against its own stop, take up all the backlash in the coupling under the butterfly stop screw, then tighten that clamp back down.  However, it moves in snaps --you'll never get it to clamp down exactly where there is no backlash.  So, hold the butterfly against its stop screw and move the lever towards its own stop until it snaps as many times as it's going to.  Tighten the clamp down.  When done, the linkage at this corner of the engine should have a bit of backlash: move it one way and it opens the butterfly, move it the other way and it sits on its own stop, and there should be a little movement in between.  Again, make sure the stop in this linkage isn't what's stopping the butterfly itself.

Adjustments 1-3 should be performed on both sides of the engine, and obviously everything should end up as close to the same from one side to the other as possible.  If nothing seems to feel the same way on the second side as it felt on the first, you probably should start over and do them both again.

Adjustment 4: Adjust the throttle crossrods.  Obviously, you will need to put them back on for this procedure.  Graphite lubricant is recommended in the ball joints, but it is not recommended that you lube them now; the powder might interfere with the adjustment.  Rather, adjust the crossrods then snap them back off to apply a little graphite.

Position a spacer 2mm (0.079") thick between the turntable and its idle stop.  A 2mm allen wrench works if you have one, but whatever you use try to make sure it doesn't fall down into the nether regions somewhere.  The spring tension will hold a 2mm allen wrench in place during this job, but jus the same it'd be a good idea to either tie a string to it or at least have the other end over the turntable pedestal itself rather than hanging out over the cliff.

Loosen the locknuts on the crossrods and adjust each link such that the butterfly is just starting to open with that 2mm spacer in place.  The thread on one end of each crossrod is LHT, so with both locknuts loose you can just turn the rod itself to make it longer or shorter.  They even provide a knurl to help you turn it easily.

"Just starting to open" is a bit tricky; if you have good light, you can carefully watch the lever lift off the stop screw on the butterfly.  However, a better idea is to install that .002" feeler gauge between the lever and the stop screw and allow the return spring to hold it.  Position it so it's hanging over the throttle body rather than straight up.  Now turn the crossrod just until the feeler gauge falls down against the throttle body.

Tightening the locknuts requires three hands: one to hold the 1/4" wrench holding the ball socket still, one turning the 5/16" wrench to tighten the locknut, and a third to keep the crossrod from turning as you tighten.  If you have a third hand available, a pair of pliers might be preferable to expecting to hold the crossrod still with fingers.  If you don't have a third hand available, a pair of vice grips will work if you carefully prop them on the fuel rail.

Make sure the ball sockets end up properly oriented 90° to each other when the locknuts are tight.  The flats on the one at the turntable end should be horizontal and the flats on the one at the outboard end should be vertical.

When done, check your work: put that .002" feeler gauge in the butterfly stop on each side (or one in both sides, if you

Also make sure the two butterflies open as close as possible to the same time.  If they don't, the TSB allows an additional 0.030" of turntable travel to get the second throttle to move off its stop.

Adjustment 5: Loosen the locknut on the full throttle stop screw on the throttle pulley, and back the stop screw away.  Hold the pulley in full throttle position, noting that the butterflies are both full open.  Adjust the stop screw until it just touches the pulley and retighten the locknut.  This stop screw merely prevents stress on the linkage while the engine is at full throttle and the kickdown switch is in operation, and is not meant to restrict full throttle.

Ensure that the throttle moves freely through the full range of motion.  Finally, check for no gap at the turntable stop with the throttle in the closed position.  If the cruise control cable is too tight, it can restrict the throttle linkage moving fully to idle.

You will need to warm up the car and readjust the idle speed, since the butterfly stop screw positions have been altered.

THROTTLE STICKING: Apparently, all cars have occasional problems with throttle sticking due to buildup on the butterfly itself.  A butterfly cleaning procedure from Randy Wilson: "You are cleaning the throttle plate and surrounding area.  The edge of the butterfly and the area of the housing right around it will be covered in black goo.  Prop the throttle open and wipe the stuff out with a rag.  Use the weakest solvent you can to get it clean.  I start with a "WD-40" grade oil, and go to carb cleaner if it's really bad.  Oven cleaner is out.  Sand blasting is not needed or recommended.

"Warning: Some non-Jag cars, notably later Fords, have a teflon coating on things in an attempt to reduce this problem. Most solvents will damage this coating."

THROTTLE LINKAGE LUBRICATION: Jan Wikström says, "The ball-joints shouldn't be lubricated at all, unless you want to give them a dusting with Teflon or graphite.  The reason is that grease hardens and oil or grease picks up dust from the air, increasing linkage wear and friction.

If you wish to understand or troubleshoot the Jaguar XJ-S electronic fuel injection system, it is highly recommended that you obtain a copy of "Understanding Electronic Fuel Injection, Ignition and Engine Management" by Roger Bywater and available from AJ6 Engineering (page 713).  The book is written as a primer on EFI in general, but since Bywater's expertise comes from years of working for Jaguar many of the examples presented happen to be Jaguar systems.  Often, it seems he is talking about these cars in particular.

According to Dick White, "There is a book ‘Bosch Fuel Injection and Engine Management' which I found very informative.  It contains many references to Lucas." It is available from EWA (page 724), among other sources.

FUEL INJECTION SYSTEM TYPES: The 1976-80 XJ-S used a type of Lucas fuel injection system based on the Bosch "D-Jetronic" design.  From 1980 on, the cars used a system referred to as a "Digital P", also based on a Bosch design.  The two systems are completely different.  Among the differences: The earlier D-Jetronic system used a trigger board within the distributor operated by a magnet in the rotor; the later Digital P system simply derives its triggering from the ignition pulses.  The D-Jetronic has a "throttle switch" in the turntable on top of the engine that provides an on

The D-Jetronic has no oxygen sensors, lacking the sophistication for feedback control.  The North American Digital P has two oxygen sensors, one in each exhaust downpipe, and Roger Bywater reports that the ECU will control the mixture in each bank separately.  The Digital P systems in countries without emission regulations had the feedback capability omitted from the ECU, and had no oxygen sensors.

Bywater elaborates on the various systems: "D-Jetronic ran from 1976 to 1980 in the XJ-S but, just to confuse things, ran until 1981 in the saloon.  Digital P 6CU first appeared in July/August 1980 on the 10:1 compression flat head engine rated at 300 b.h.p. in the XJ-S.  Most XJ12 saloons continued with the earlier 9:1 D-Jetronic engine until the arrival of the H.E. engine in July 1981 but a few saloons were fitted with the 10:1 engine and Digital P.  I understand that the improved fuelling accuracy of the Digital P EFI system was what made the higher compression engine viable.

"The 10:1 engine performed very well and was certainly the most lively version of the 5.3 ever produced but there were two things which could make it a bit fragile at sustained high speed.  Firstly the cooling ability of the radiator was a bit marginal, secondly the distributor build quality was not too good and we measured errors of up to 10 degrees excessive advance at 6000 revs, which is obviously likely to cause trouble.  Not surprisingly, there were tales of piston failures on German Autobahns.

"Those early 6CUs triggered from the coil negative terminal and the ECU was protected internally from the high voltage firing spikes by a 100K resistor in the input circuit.  This was not necessary with the Constant Energy system introduced for the H.E. and was replaced by a link.  Another important difference, apart from the fuel requirement of the 10:1 engine being different from that of the later H.E., was that full load fuelling was set into the mapped fuelling values so there was no need for a separate full load enrichment switch circuit.  This means that fitting an ECU intended for an H.E. car to one of these engines is likely to magnify any tendency to burn pistons because the full load condition will be excessively weak.  A number of people have found this out the hard way.  Strangely the ECU seems to survive the high voltage firing spikes despite not having the protection resistor.

"The H.E. engine arrived in July 1981 in both the XJ-S and XJ12 saloon so that is when D-Jetronic really ended."

INJECTOR GROUPING: The wiring harness is set up to operate the injectors in four sets of three.  Within the ECU these circuits are combined to form two sets of six.  In the early D-Jetronic systems, each set of six injectors included three on each bank, and this injection pattern is explained in great detail in the repair manuals.  However, in the later Digital P systems (which include oxygen sensors), each group included all six injectors from a single bank so the ECU can monitor the oxygen sensors separately and control the mixture of each bank as a group.

OVERRUN CUTOFF: On the Jaguar V12, some EFI systems feature overrun cutoff and some don't; see the section on overrun valves on page 268.

When the foot is all the way off the throttle but the engine speed is well above idle, the pilot is clearly not interested in power; any fuel provided is a waste of fuel and an unnecessary contribution to emissions.  So, if the ECU detects that the throttle is at idle and the RPM is above some set point (1500-1800 or so), fuel to the injectors is totally shut off.  As the RPM drops past another set point nearer to idle speed (1100-1300 or so), the fuelling is turned back on to provide a smooth transition to idle --or to rev it back up to the cutoff RPM.  Roger Bywater: "It's easy enough to check on the car by just flicking off one throttle pushrod and opening that throttle to lift the speed without the throttle switch being moved (assuming the switch is set correctly)."

Regarding which EFI systems have overrun cutoff, Bywater says "...all 6CUs do indeed have over-run cut off above approximately 1500 r.p.m. but it is activated not only by a closed throttle signal from the throttle potentiometer but also by the vacuum signal.  On a Federal 6CU cut-off commences at nominally 17.5" Hg and fuel reinstates when the vacuum falls to 15" Hg.  Cut off on European versions is active over a wider vacuum band which also varies with engine speed.

"16CUs only need the throttle closed signal to activate cut-off above the required speed."

This feature can easily confuse the novice mechanic that may not be familiar with it.  What will sometimes happen is that the car is running poorly, and the idle screw will have been opened up to maintain a reasonable idle speed.  Then the problems with the engine are corrected, and the engine then tries to idle faster --but hits the cutoff RPM, shuts off, drops back to the cut-in RPM, kicks back on, and sits there cycling up and down indefinitely.  The mechanic thinks he has really screwed something up this time and begins all sorts of ill-conceived corrective measures when all he really needs to do is close down the idle screw a bit.  It's even more confusing, of course, when the overrun cutoff feature is temperature dependent so it doesn't cutoff when the engine is cold but starts cycling upon warmup.

Another common cause of trouble is the infamous auxiliary air valve (page 265).  The car is running fine one day, but the next day the auxiliary air valve sticks open and the engine starts ramping up and down upon warmup.  The mechanic drives himself crazy trying to figure out the ramping, while what he really should be looking for is the cause of the high idle.

For the overrun cutoff feature to work right, the ECU clearly needs to know the throttle is at idle.  On the D Jetronic, there is a special contact in the throttle switch for idle.  In the Digital P, the throttle pot must be adjusted properly (page 297).

EFI GROUNDING PROBLEMS: Michael Neal sends this experience: "...the radiator had been replaced and a ground for the fuel injection harness at the right front of the engine compartment had not been re-secured.  It had blown two ECUs before I found this.  I don't know why but it took the ECU a week or two to blow.  After I replaced the ground and ECU there were no further problems."

Reportedly, if the engine clearly is running very rich or possibly won't even start because it's too rich, it's time to start looking for grounding problems in the EFI wiring.  John Napoli relates one experience: "Although ground to the ECU was one of the many things we had checked early on, the owner later went further and checked the ECU connector.  He found an intermittent ground on pin 1 at the connector.  This pin, according to our schematics, should ground to the frame of the car at the ground points near the battery.  This wire was identified in the loom and a splicer to ground added.  The car started fine and at this point is OK."

ELECTRONIC CONTROL UNIT: The following is a list of the ECU part numbers, hopefully mostly correct.  Thanks go to Jeffrey Gram, AJ6 Engineering (page 713), and other sources.  D-Jetronic: Type 3CU LRZ103 and LRZ113? Digital P: Type 6CU catalyst version: DAC 2597 and DAC 3586 non-catalyst version: DAC 2596 and DAC 3062 Type 16CU catalyst version: DAC 4118, DAC 4585, DAC 6335, and DAC 6337  These are the low compression version - presumably 11.5:1 non-catalyst version: DAC 4119, DAC 4478, DAC 4586 and DAC 6336  These are the high compression version - presumably the 12.5:1

Additionally, there is a low compression non-cat version: DAC 6338.  For one year (1981), the XJ-S had Digital P EFI on a pre-H.E. engine.  Clearly, the fuelling maps for such a car would differ from those for the later H.E., and the ECU's would not be interchangeable.  It's not known if any of the part numbers above apply to the pre-H.E.  Digital P.

Note also that the Marelli ignition system provides a cleaner signal to the EFI system, so the ECU's fitted to Marelli ignitioned cars have less filtering in the signal input circuitry.  This may help account for the profusion of 16CU part numbers listed above.  The pre- and post- Marelli ECU's are not interchangeable.

Richard Mansell quotes from a Jaguar publication on the changes for the 1992 model year:

"The new fuel control system, the Lucas 26CU, replaces the 16CU and provides the following benefits:
-Improved starting performance at all temperatures.
-More efficient engine operation during warm up.
-A diagnostic facility which stores fault data for later retrieval.
-Low quiescent current drain.
-Eprom socket to allow modifications.
-JDS diagnostics serial link.
-Fuel used output.
-Enhanced software.
-Enhanced limp home capability.
With the pre-facelift ECU, (Lucas 16CU), one injection is delivered per engine revolution.  In the facelift condition, the Lucas 26CU, there are three injections per engine revolution.  The number of pulses is reduced to one per revolution after a set number of injections.

After-start enrichment -The enrichment is now coolant temperature dependent.  It decays away over a number of engine revolutions instead of over a time period and is no longer linked to cranking fuelling so that better calibration is achieved.

Acceleration enrichment is reduced; calibration is improved; over enrichment is bettered in the occasions where the driver opens the throttle very quickly.

Full load Enrichment -Where full load enrichment was determined by vacuum operated switches sensing inlet manifold depression, it is now determined by throttle potentiometer position and engine speed.

There is a single 2.5 bar mini fuel pressure regulator instead of two."

Roger Bywater continues: "The 26CU controller introduced in 1991 for 1992 model year was superseded by the 36CU type part way through 1993.  36CU was the next stage of development of the 16CU, 26CU theme and was itself superseded at the end of 1994 by the much more advanced Pecus / Nippondenso system of full engine management."

The people at John's Cars (page 717) say they will test your ECU for you, free of charge.  They are confident you will eventually be buying something.  They add, however, that since testing requires a car, there may be a few days' delay until they have a car with the correct system on hand for the testing.

Of course, you can probably learn a lot yourself if you have a friend with a car similar to yours.  Swap the ECU's and see how many problems go with them.

If your ECU gives up the ghost, please see the comments under Performance Mods (page 310) before spending the major $$$$$ for a new one.  Also, you might want to contact AJ6 Engineering listed on page 713.

If you wish, you can open the ECU easily enough; it is a simple cover-body-cover sandwich with several screws holding it together.  Note that a couple screws have aluminum caps that serve as a tamper indication; it might be wise to inquire about policies regarding exchanging an opened unit before opening.

Take precautions to avoid static electricity discharges while inside this unit.  Usually, it is sufficient to keep one hand on the chassis while working.

EFI WIRING HARNESS TROUBLESHOOTING: Matthias Fouquet-Lapar suggests "one thing I would do is to put in fixed resistors for the various sensors direct at the ECU connector" to find out if there's a problem in the harness.

INJECTOR CONNECTORS --D JETRONIC: The connectors on the early cars are a simple plug that inserts into a rectangular recess on the injector.  If you need new connectors of this type, Ed Sowell says you can get them at NAPA. "They have what they call "harness rebuild" parts which is a selection of connectors and pigtail wires with various

housing 2-17411 (this is the plastic connector body)

contact 2-17421 (this is the pigtail with the connector attached-- 2 req'd per connector)

Also discovered that NAPA has the contacts themselves without the pigtail wires."

INJECTOR CONNECTORS --DIGITAL P: Apparently Bosch decided the simple rectangular plug wasn't secure enough, so they developed a much more sophisticated connector for the Digital P system.  These connectors are a rectangular hard plastic box that fits around the connector on the injector, and they have an external spring to provide snappage.  These connectors simply pull off, although they can be a real bear sometimes.  It might not be a bad idea to apply a little grease or something to that spring or the little point that it snaps around to help get it off next time.

These same connectors are also used on the Digital P temperature sensors.  According to Peter Cohen and others, NAPA offers this connector in parts or as an assembly.  The assembly, with pigtails hanging out, is part number 2-17424.  In parts, the numbers are
Housing - 4 per box 2-17416
Spring Clips - 25 per box 2-17417
Terminal Ends - 25 per box 2-17418

Michael Bucklew says, "The NAPA parts did not fit due to the lip around the bottom that holds the spring clip.  My plugs do not have the lip around the bottom.  The NAPA parts were $14.49 each for the plugs."  It's unknown if Bucklew's comments apply to the pigtailed assembly, the individual parts, or both, but at that price who cares?  That's too much.

Rue Palmer says the problem is that is apparently the wrong NAPA part number.  The connector you need is NAPA part number 2-17427.  He describes this as a "Wired Housing (a wired connector minus the spring clip).  I had to use the spring clips from the old injector connectors because the new connectors don't come with them."

Lucas lists the parts this way:
housing 526 8917 comes in packages of four
contact 526 8918 comes in packages of 25
spring 526 8930 comes in packages of 25

The Lucas parts, as would be expected, fit fine; this author used them on my harness rebuild.

It appears that the complete connector with pigtails is the most common way to find these parts.  Discount Auto Parts also carries Caltherm, item number 08653, "GM Multi-Port Fuel Injector Connector".  Costs less than two bucks each. Cohen: "Other vendors are:

Conduct tite: Fuel Injection Repair Socket #85850
Dorman: Connector kit #643-463"
John Robinson adds, "Beck Arnley makes an OEM copy connector w/pigtail: 158-0017."

Ed Forman says, "I looked at several parts stores, found some that looked like they would work at an Auto Zone store.  But the back stuck out too far and hit the plate that holds the injector in place.  In desperation I went to a Jag dealer, they had the same type as the Auto Zone store.  But I found the right ones at an Auto Value store.  They are made by Parts Master part # 84059, they work great.  About $3.00 each, that's better that $12.50 at Jag."

Patrick MacNamara says, "Best deal I have found on the injector connector housings is from Del City.  They were only $1.03USD each and are complete with 6" pig tails, #73522.  No boots though."  MacNamara ditched the pigtails since he wanted to use high-temp wire, which meant he needed terminals separately: "The terminals for the injector housings are available from your local Volvo dealer at about $.75CDN each (Cable terminal #V0978258-2).  The terminal connectors from Volvo are nifty two piece quality looking terminals and don't look as cheap as the ones installed by Del City with their pigtails.  They have the double OEM crimp with one on the insulation and one on the actual wire which if I understand correctly should negate fatigue.  The terminal crimp part seems to be referred to as an open barrel arrangement necessitating special crimping pliers."

So, Patrick, why didn't you get the housings from Volvo as well?  "I had purchased one to trial fit it to the Jag injector.  They are of a superior design in terms of positive locking with a nice button for release as well as being made from what looks like high impact resistance plastic.  Unfortunately the button release and lack of half moon cut out negates the fit onto the angled injector port."

None of the above items seem to include the rubber boot that covers the joint between the wires and the plastic connector.  Gregory Wells says, "Wurth markets the rubber boot and as with all Wurth parts, they're expensive.  I think the Wurth part number is 5-7120, but I'm not real sure of that.  Wurth distributes hardware and shop supplies to repair shops via independent salesmen and as far as I know does not distribute to the retail market, so if you want to chase these down call import repair shops to see if Wurth calls on them."

Rue Palmer says you can get the boots from NAPA: "Harness Boots (for those who want the original rubber boot-2 per box): 2-18414"

MacNamara adds, "Boots are also available from Volvo at $1.84CDN each (Housing cover #V0967340-1).  These fit the Del City Bosch connectors very well but are slightly shorter than the Jag OEM ones.  They are also much sturdier looking."

If you can't find the boots, screw it; the harness will work just as well and just as long without them, and probably look just as good or better.  Keen Young says, "My solution was 1/2" shrink tube over 1/4" shrink tube.  Put them both on the wires, solder on the connector, slide the small tube up to the connector, slide the large tube over the small one and over the connector, heat.  If you look really closely, you can tell it's not factory.  Got the tubing at the local surplus store for $.20/foot."

RECOMMENDED READING: Roger Bywater wrote the definitive guide to the D-Jetronic system, published in Vol. 2, No. 2, Jaguar Quarterly (now Jaguar World --see Kelsey Publishing, page 723), 1989.  It is highly recommended that owners of cars with this system obtain a copy of this article.

TRIGGER UNIT: D-Jetronic cars have a "trigger unit" inside the distributor that provides a signal to the EFI system to trigger the fuel injectors.  It is mounted just under the distributor rotor and is activated by a magnet in the tail of the rotor.

The trigger unit originally fitted inside the distributor had magnetic reed switches and a three-wire connector that plugs into the EFI wiring harness.  These type trigger units were later superceded with a replacement trigger unit that uses Hall effect circuitry instead of reed switches for improved durability.  The Hall effect trigger unit has a fourth wire, separate from the connector, this fourth wire must be connected to a 12V power source that is switched on with engine ignition.  Unlike reed switches, the Hall effect circuits require a power supply.  Three-wire units are no longer available.  By now, most of the original three-wire trigger boards have probably been upgraded to four-wire.

Reportedly, the official Jaguar procedure is to connect the fourth wire to the white wire at the ballast resistor.  This, in fact, should provide the proper switched 12V source -- on paper, anyway.  However, Ray Reynolds reports that the 12V available at the ballast resistor was so noisy that it caused the injectors in his car to fire wildly, resulting in flat spots and even stalling at some throttle positions.  He simply reconnected this wire to a more reliable 12V source and his problems cleared up.

TRIGGER UNIT TESTING: If you have the Hall effect unit, the testing procedure in the ROM won't work.  However, either the reed switch version or the Hall effect version are supposed to provide the same signal to the EFI system, so it's still easy enough to test --you just need to make sure that it has 12V power and a ground connection when doing the testing.  And you need to test it in place and using the rotor to activate it; it doesn't matter if it'll work with some magnet you're holding in your hand, if it won't work with your rotor, it won't work.

There are four wires.  The one that provides 12V power should be obvious; it's not in the connector with the other three.  Of those three, the center one in the connector is a common ground; it must be grounded during testing to complete the 12V power circuit.  The outer two are normally open but get very brief closures to the common ground as the magnet in the rotor passes over the trigger unit.

To test, connect leads to these three wires without unplugging the connector.  You can unplug the connector, tie small test wires to the terminals, and plug it back in.  Or you can just jam straight pins through the wires and connect your VOM to the pins.  Turn the engine over and watch for brief closures, once per cycle, between each of the outer wires and the center common wire.

TRIGGER UNIT CONNECTORS: Peter French claims to be one of the few people that still has reed switches in his car rather than the Hall effect sensor.  "I also had a good problem earlier with the 3-way connector to the injector switches.  The centre (0v) pin had two wires going to one pin and they were "over-crimped".  One wire had broken such that the reed switches had no common return unless the idle switch contact on the throttle switch was closed.  Net effect was that the car would start and idle fine but cut out as soon as the throttle was opened!"

TRIGGER BOARD SCREWS: As mentioned on page 140, Richard Dowling tapped out the holes in the distributor body to take M4 screws.  "My trigger board had 4 special rubber grommets with holes to take the screws.  I had no trouble with putting nylon M4 screws through."

ROTOR: Yes, the distributor rotor is an ignition system part --but in the Jaguar V12 with D Jetronic EFI, it's also a fuel system part since there is a magnet in the tail of the rotor to trigger the fuel pulses.

Mike Morrin reports: "Beware, there are two types of D-Jetronic distributor rotors.  The ones with the narrow magnet (P/N 54422422) only work with the old style trigger units, the ones with the wider magnet (P/N 54400048) appear to work with both old and new trigger units."

MANIFOLD AIR PRESSURE (MAP) SENSOR: One man's pressure is another man's vacuum.  Yes, the conditions within the intake manifolds on non-supercharged engines are commonly referred to as vacuum, but engineers normally refer to air pressures in terms of absolutes rather than relative to atmospheric, so the sensor measuring the air pressure within the intake manifolds is referred to as the "Manifold Air Pressure" sensor.

Mike Morrin: "I would strongly recommend that all owners of cars with this system periodially check the manifold vacuum sensor for internal leaks.  I stress this because when I needed a replacement for mine, I was told that new units are no longer available for the "early" calibration systems, and so I needed to find a good used one.  This resulted in me driving around London (I was officially in the UK on business) for 2 days sucking on manifold vacuum sensors at all sorts of dodgy Jaguar parts shops.  Of the dozen units I saw, only 5 did not leak, and only one of these was the correct

"The sensor is the aluminium cylindrical thing right in the front right hand corner of the engine compartment.  The test is simple, disconnect the center hose from the tee piece between the manifolds (above the distributor) and suck on it as hard as you can, there should be no hissing sound from the sensor unit.  Then stick your tongue over the end of the pipe while releasing the vacuum in your mouth.  The hose should stick to your tongue for several seconds before it (the hose) drops off.

"Internally the sensor has a barometer bellows, but there is an extra brass (?) diaphragm which provides the vacuum seal.  This diapragm flexes every time the manifold vacuum changes and it is not surprising that metal fatigue sets in and causes a split around the outer edge.  This is an example of Bosch design which would make Lucas look good (if Lucas had not insisted on sticking their name over the Bosch logo!).

"If the sensor is leaking, then the engine will be running rich, particularly at part throttle, but this varies depending on the size of the split in the diapragm.

"I did attempt to repair my faulty manifold sensor, both by adding a rubber diaphragm and by soldering up the split in the brass diaphragm, but both of these repairs resulted in a significantly lean mixture."

Roger Bywater of AJ6 Engineering (page 713): "If there is a break in continuity to either winding on the pressure sensor the entire system will be dead.  Really all that most people can do is check the two windings for isolation and resistance (nominally 350 ohms between terminals 8,10 & 90 ohms between 7, 15) and the assembly as a whole for a vacuum leak.  Obviously that will cause excessive richness at light load whilst full load will be unaffected, although in practical terms a minor leak may not be all that important.  Electrical failure is extremely rare and I don't suppose the aneroid bellows fail very often, unlike the full load diaphragm on the European version which is prone to splitting around the edge (which can be repaired by careful soldering in the early stages.  These devices come apart quite easily once the 4 rivets are drilled out.  The pressure sensor being effectively a variable inductance transformer, function testing would entail firing pulses or low voltage AC through the primary winding and measuring what happens at the secondary.  In fact the most practical way to test one is to link it to an ECU on a bench rig representing the vehicle installation (such as we use) and measure injector pulses at different loads at a set speed.  Obviously not many people will be able to use either method."

D-JETRONIC REPLACEMENT: Roger Bywater of AJ6 Engineering (page 713) says "it is not that bad a system and shouldn't be that troublesome really if it is properly set up (correct throttle balance is vital).  Although odd bits like trigger boards and pressure sensors do fail occasionally, and injectors tend to jam if exposed to water contamination, the ECUs don't often go wrong (unlike early H.E. 6CUs) and really the wiring and connectors are the main problem areas as they age.  It is a lot easier to go over the connectors, cutting back the wires and soldering them to the terminals, than to strip the lot out and install a new system.

"If the system is beyond economic repair and really does need to be replaced then I would have thought that by far the easiest route would be to simply fit all the hardware, including manifolds, plumbing and Constant Energy ignition, from any H.E. engined car from 1981-88 and use a 16CU controller (1986-91) and have us install the correct program for the early flat head engine (Super Enhanced option available).  This setup has been used successfully on a number of V12 E types converted from carbs to EFI and has the great advantage that all the parts are familiar and easily available.

"Aftermarket ECUs sound great but in practice involve a lot of time and effort to get right and would be hard to justify for a standard engine.  It would definitely involve rather more than "just wiring in a new processor" and any improvement in performance or fuel effcicency would be minimal.

SCHEMATIC CORRECTIONS: In the Haynes manual 478/49015, you should mark Fig. 10.124 and 13.92 at the thermotime switch #298 to show a ground connection on the line at the bottom between the heater and the contact.

Also note that the thermotime switch contains a thermal switch and an electric heater.  The schematics make it look like a relay.  It should show a resistance rather than a coil.

Note also that Section 19.22.32 of the ©1975 ROM shows a schematic of the cold start injector system that is poorly labelled at best.  It shows "12V" connected to 86C via a WR wire, when it would have been much clearer to mark the wire "from starter relay" --there's no power on it except when the starter is engaged.  The thermotime switch is at the bottom left, unlabelled and no innards shown.  The cold start injectors are at the bottom right, unlabelled and no innards shown.  The cold start relay is at top center, unlabelled with the innards shown incorrectly; since it shows five terminals including an 86C, it is evidently attempting to illustrate the system with a bootstrap circuit (see below), but there are no internal diodes shown and there is no internal connection to terminal 86.  Ken Gray and Roger Bywater claim the illustrations in the same section in other ROM's such as the early XJ12 ROM show the non-bootstrap relay (four terminals) largely correctly.

COLD START RELAY VARIATIONS: Basically all of the schematics showing the cold start injector system on the D Jetronic EFI system show the cold start relay as a simple relay: one coil and one contact, 4 terminals.  If the car is really wired that way, the cold start injectors will only operate while the starter is engaged.  This makes good sense; once the starter is released, it can be presumed that it's because the engine has fired and therefore there is no more need for the cold start injectors to be spraying.  In this configuration, the only reason the thermotime switch cuts off after a few seconds is to prevent flooding in case the owner holds the starter on for a long time.

Ken Gray says the early cars were wired differently, though: "In reality, (76 model XJC5.3 Oz spec & also 75 Daimler Double Six brit spec.) the relay is a five terminal relay.  It has two internal diodes, and the extra contact is labelled 86C.  Diode 1 goes from 86C to 86.  This allows current to flow to the relay coil from the start relay ie when the engine is cranking.  Diode 2 goes from 87 to 86.  This allows current to flow into the relay coil from the main injection relay to allow the cold start injectors to stay energised after the starter has been dis-engaged.  Diode 1 blocks any current from feeding back to the starter solenoid once the starter key has been released.  The thermotime switch opens after it has timed out and the injectors are de-energised."

Basically, what Gray is saying is that the relay has a built-in bootstrap circuit; once it has been energized by the starter being engaged, it will hold itself energized even after the starter is released until the thermotime switch shuts it off.  If your car has such a relay, the schematics should be altered to look like Figure 14.

Interestingly, while the Jaguar cars with this system were reportedly connected this way, it would actually make more sense to connect the wire to the heater in the thermotime switch to 87 on the cold start relay instead of 86.  It would function exactly the same way, but there wouldn't be as much current going through the diodes.  Roger Bywater found schematics of other cars with similar Bosch EFI systems that were wired that way.

The diagrams that this schematic revision might apply to are as follows: In the ROM ©1975, the "Fuel Injection Schematic" following Section 86, and whatever diagram shown in section 19.22.32, as discussed above.  In the Haynes manual 478/49015, Fig. 10.121, 10.124, 10.129, 13.92, and 13.96.  Check your own car, and if it has the relay described, mark the appropriate schematics accordingly.

Gray: "The relay is a Bosch manufacture with the Lucas sticker stuck on the side.  The Bosch number is 0 332 003 028 - 12V, 10A.  The Lucas marking is 25RA which I think is the series (not serial) number, because all the relays that are in the same can configuration bear this number, and 33353A which I believe is the important part number."  Gray goes on to point out that the Haynes manual clearly shows the 5-terminal relay he's talking about in Fig. 3.50.  He claims this relay is also illustrated in his XJ12 ROM; "My ROM is the red covered Jaguar XJ12 /Daimler Double Six version.  Publication Part No.  E190/4."  Section 19.22.31 of the XJ-S ROM ©1975 shows the cold start relay, but not clearly enough to indicate how many terminals it has.

If your car has the relay Gray describes, it will be a large metal can that looks similar to the starter relay with individual wires connected to spade terminals and it will have a terminal labelled 86C.  If your car has the simpler system illustrated in the schematics, it may have 5 terminals but one will be labelled 87a or some such; there will be no 86C.

Roger Bywater isn't thrilled with the bootstrap concept used here: "I know what can happen when the cold start injector(s) are allowed to spray with the engine running.  A weak 'spit back' can ignite the fuel from the cold start injector which then becomes a rather noisy blow lamp inside the manifold.  A single plenum engine would immediately stop then would easily restart probably without the condition even being recognised.  A V12 could have one bank 'lit up' inside but the other bank would keep it running, after a fashion, until the thermotime switch trips out when things revert

COLD START PROBLEMS: William F. Trimble says, "My Haynes manual for the V12 (yeah, I know ... :-) suggests to remove the thermo-time switch altogether if you have cold-start problems."  This author's Haynes manual says "A problem can occur on 1980 models causing stalling immediately after cold start.  This can be overcome by removing the cold start relay..."

John Braybrooks says, "I have a 1982 XJ-S in Victoria, British Columbia, Canada.  I keep my car in a garage and one recent winter my son drove it out so that he could use the garage space to work on his 1929 Model A.  When he finished he returned the Jaguar to its rightful location.  Next day my wife also moved the car to facilitate sweeping the floor and again returned it.  Next morning when I tried to start the car there was no life.  I called local Jaguar specialist, Paul McKay, and he immediately diagnosed the problem as flooding.  He came to my house and replaced the spark plugs which were the least difficult (5) and we were then able to get the engine running on those cylinders, later more and more came on line until all was well.  He informed me that this was a characteristic of this engine and it was not unusual for the dealers to experience this problem with brand new vehicles loaded on and off transporters during the winter.  Under the right conditions the cars would not start when delivered to the dealer.  Paul warns that if this does occur and you are able to get the engine running of a few cylinders do not "gun it" otherwise the unburned fuel will be burnt in the catalytic convertors and the excessive heat could cause a meltdown.  If I have to move my car for very short periods in cool weather I now always let the engine run until it is thoroughly warm."

Roger Bywater explains: "That's a familiar story.  Back in the early 1980's they had new H.E.'s doing that even in our mild winter after being shuffled around the factory car parks a few times before delivery.  That's why they got rid of the cold start injectors after a period of just having the connectors taped back for the dealers to hook up before delivery to the customer.

"Whilst it may be the case that the H.E. V12 is more prone to cold plug fouling than some other engines, doing repeated cold starts in very cold conditions without getting to even part warm is maybe asking a lot of an elderly car probably with shaky HT leads and things.  If I had to move any car, not just a Jaguar V12, repeatedly in severe conditions I would at least let it run to near fully warm every other time then rev it up two or three times to make sure it was clear."

FUEL SUPPLY SCHEMATIC CORRECTION: Fig. 3 on page 19-3 in the ©1982 Supplement and Fig.13.18 in the Haynes manual as well as the same diagram in the Handbook purport to illustrate the fuel supply system for the Digital P.  In fact, it's quite accurate --if you never had the fuel rail recall performed on your car.  Since all cars should have had the recall done, the left half of this illustration should look like Figure 15.

There are now two pressure regulators (although the bottom one in the illustration is actually the only one that regulates pressure), and the cold start injectors are gone.  Note that for the 1992 model year, Jaguar went back to having a single pressure regulator.

Fig. 4, 18, 20, and 21 and sections 19.60.01, 19.60.03, 19.60.04, and 19.60.05 in the ©1982 Supplement as well as Fig. 13.13, 13.14, 13.22, 13.23, and much of the text in Chapter 13, Sec 5 in the Haynes manual likewise reflect the pre-recall fuel supply system.

HOT STARTING: The fuel cooler works great when the engine is running, but is worthless after the engine is shut off.  The heat rising from the engine heats the fuel in the rail, which is not moving.  If the engine is started about a half hour after shutoff, it may have difficulty starting.

Jaguar has provided two different fixes for this problem.  Both involve a temperature sensor in the boss on the left side of the fuel rail; the boss has no opening into the fuel, but the sensor has a copper bottom that presses against the rail to sense the temperature.  The boss itself seems to exist on all XJ-S H.E.'s, since a recall replaced the rail after the hot fuel problems were found.

The earlier type sensor is electrical, and is connected in line with the inlet air temperature sensor for the EFI system.  The later type sensor has vacuum connections, and is connected between the intake manifold and the left side fuel pressure regulator.  At least one of these sensors has been known to simply fall apart, but owners have had some success simply gluing them back together.

If your car doesn't have either fix (or if it does but still has difficulty with hot starts), there is a work-around for the hot start problem.  Turn the ignition key on and off several times before attempting to start, allowing the fuel pump to run for two seconds each time.  This will flow cool fuel from the tank into the rail.

CLOSED-LOOP OPERATION: The earlier D-Jetronic EFI systems were strictly open-loop.  This means that the ECU contains a schedule of values (a "map") for how much fuel the engine gets at a given operating condition, and that's final.  The Digital P systems in markets that did not limit emissions likewise were open-loop only.  For North America and other markets where emissions were regulated, however, the Digital P system featured a closed-loop fuel control.  There is still a map providing "baseline" fuel scheduling, but there are also oxygen sensors in the exhaust system that monitor the exhaust for excess oxygen.  If an oxygen sensor finds excess oxygen, the ECU presumes the engine is running too lean and trims the fuel scheduling a little richer.  If it doesn't find excess oxygen, it presumes the engine is running too rich and trims the fuel scheduling a little leaner.  The oxygen sensors are essentially an on-off device --they either detect oxygen or they don't --so the closed-loop control mode is neurotic, always either correcting one way or the other; it is never satisfied.  When operating normally, it is constantly cycling from a hair rich to a hair lean and back again.  As a result of this constant feedback correction, the engine is always kept very close to stochiometric fuelling in this mode.

Oxygen sensors are also known as Lambda sensors; Lambda (.) is the Greek symbol generally used to denote relative air/fuel mixture, with .=1 corresponding to stochiometric, .>1 meaning lean, and .<1 meaning rich.

Of course, stochiometric is not necessarily ideal.  For max power, you'd like it a little rich.  At max power, it'd better be a little rich, because running near stochiometric is a good way to burn pistons.  So, there are two switches --a roller microswitch on the turntable and a vacuum-operated switch nearby --either of which will kick the EFI system out of closed-loop mode at high throttle.  This causes it to run on the baseline map with no trim, which is of course designed to be a little rich just for this purpose.

COLD START INJECTORS: The schematics in the manuals show that the cold start injector system was carried over to cars with the Digital P EFI.  However, the only Digital P cars with cold start injectors today are apparently the 10:1 compression ratio pre-H.E. models.  H.E. cars don't ever seem to have cold start injectors; some early cars came with them, but they were all removed when the fuel rail was replaced on a recall.  The square cross section fuel rails now used on H.E.'s has no provisions for cold start injectors; there is a different square cross section rail with connections for cold start injectors that was retrofitted into the 10:1 cars.  Some early H.E.'s may still have a harness and a relay in there doing nothing.  Early H.E.'s have little covers over the holes in the intake manifolds where the injectors once were, while later cars don't even have the holes.

If you have an H.E. with no cold start injectors, you can scratch through the cold start injection system consisting of the thermotime switch 298, the cold start relay 299, and the cold start injectors 300 on the following schematics: In the ©1982 Supplement or Supplement A, the diagrams on pages 19-1 and 19-2.  In the Haynes manual 478/49015, Fig.

Roger Bywater of AJ6 Engineering (page 713) reports that the 1983-87 3.6 AJ6 engine with Lucas 8CU EFI has a problem with worn engines.  A worn engine draws less vacuum at idle, but since the 8CU bases fuelling on manifold pressure, it believes that the lower manifold vacuum means the engine is drawing more air and responds with more fuel -- making the engine run overrich.  Since these cars lack Lambda sensors for trim it cannot correct itself, and the car runs worse and worse.  Bywater says owners complain of "shunting" in trailing throttle, bad idle, and failing MOT tests due to excessive CO in the exhaust, even though the engine is not really all that tired and rebuilding doesn't appear justified.  Of course, at full throttle the wear problems are insignificant and the engine runs fine.

Bywater suggests that disconnecting the vacuum advance from the throttle edge tapping and connecting it directly to intake manifold vacuum --and readjusting the idle mixture and speed accordingly --may help as a temporary measure if the engine isn't too bad.  For a more permanent fix, AJ6 Engineering offers an ECU modification wherein a trimmer screw is added that can be used to correct for engine wear -- and can be corrected back in the event of an engine rebuild.

John Goodman reports that the XJR-S has Zytek ignition and sequential fuel injection --see pages 172 and 721. "It is essentially the same injection system off the '80's group "C" Le Mans race cars.  Jaguar made a big thing about publicising it.  But I suspect TWR had a load of spare bits left over and needed something to do with them!"

"Also there are two power resistors on the R/H front inner wing.

"I thought Jaguar's claims for improved fuel economy was bullshine, but it is more economical than my previous H.E."

Emile DesRoches says, "The XJR-S Product Support Manual lists special software along with a serial port connector whereby a laptop computer can be connected to the Zytek engine management computer (unique) fitted to the XJR-S to perform various diagnostic, calibration functions.  Apparently this software was originally provided to dealers upon request from Jag North America for repairing these beasts."

Goodman: "The ECU can be reprogrammed with different fuelling and timing if only we had the software! And it is not Jag Dealer software, they only have the standard tune parameters!"

The later cars come with JDS (Jaguar Diagnostic System) or OBD II (On-Board Diagnostics version II) as legislated by the California Air Resources Board (CARB).  When those fault codes appear they can cause consternation --that's what they're for.  The owner's handbook provides a list of codes, but of course it never seems to provide enough real guidance.  Hopefully some of the reports included here will help.

Defective relays and/or their connections are a known cause of fault codes, as mentioned in the section on relays

Charles Randle says, "I was out to my dealers today and read up on the EPA ordered recalls for all 6.0 V-12 cars.  With a '94 XJS with JDS, all I get is a replacement of all major grounding connections.  But all 95-96 OBD II cars get a free Oil and Filter change; and replacement of all EPA components that have set an OBD II code.  Also the EPA warranty has been extended to 150K miles.  So if anyone out there hasn't registered their after market car with Jaguar as the present owner; don't pass this up.

FF 3 --COOLANT TEMP SENSOR: Mark Barker reports on his 6-cyl: "Trip computer displays "FF 3" (Coolant temp sensor failure), when the electric fan motor is dying.  Just happened this evening.  I suppose coolant temp is related to cooling fan.

"Certainly was the motor --brushes gone.  I mean gone, too.  Big pile of black dust fell out of dissasembled motor followed by broken bits and pieces sticking to magnet.  Found some brushes in scrap motor I had, oiled the bearings.  Back together, no more "FF 3".  Strange, but true."

FF44 AND FF45 --OXYGEN SENSORS: Sam Emrick says, "Late-models (at least) seem to have a common problem with bogus O2 sensor failure code reported (FF44 or FF45).  My '94 had this problem."

Charles Randle talks about a recall: "It plainly says for my JDS codes that FF44 and FF45 codes are being caused by poor grounding connections rather than bad O2 sensors.  I wish I had known that before changing them out a few months ago."  Since grounds are a common cause of trouble in the Jaguar XJ-S, just go ahead and add a ground strap as suggested on page 555.

FF67 --SECONDARY AIR INJECTION SYSTEM: Charles Randle says, "My '94 6.0 started having FF67 set a couple of months ago.  I read up on it in the ROM, which tells me just enough to understand a dozen things that may cause the problem.  However, there is one ambiguous sentence that is a large gray area, so I took it to my local dealer after talking to the Lead Technician on the phone.  The simple things I could check myself I did.  I determined the Air was coming on and apparently in the right (as printed) sequences.  The tech spent an hour verifying this on the JDS, and called Mahwah.  Two days later they faxed a "Decision Chart" and a possible problem/solution.  It seems the PMCF on all the 6.0's might have come from the factory with the PROM set too sensitive.  During any of the secondary air functions the PROM is looking for a certain voltage from both O2 Sensors.  If it doesn't see a signal of this magnitude, it sets FF67.  And that is all it does.  It doesn't go open loop or any other deregulating function.  The bottom line is, the dealer gave me the "Decision Chart" and said I really didn't want to pay him $78.00 an hour to verify 3 pages of decision charts.  He also gave me a mail for service procedure to send the PMCF to Delphi Diesel Systems for testing and installation of a less sensitive PROM.  To date I haven't either completed the Chart or contacted Delphi.  The JAGUAR NA procedure when the cars were under warranty was to have the dealer ship the PMCF to Mahwah, who then sent it to Delphi and it was returned to the dealer COD for work/parts/shipping.  For the time being, I am resigned to ignoring the FF67 and dumping the code each time I won't be using the car for a while.  There is no way to disable the PMCF signal without disabling future serious codes that you might want to be notified of."

Michael Hahne concurs: "My '94 XJ12 has the same FF67 deal.  I replaced the O2 sensors and had the recall done, and it still shows up once in awhile.  I talked with several knowledgeable folks who said it's probably clogged Air Injection rails.  It's a nasty job to clean these out, but hardly necessary for the kind of driving we do.  It's mostly an emissions thing.  I've driven mine that way, occasionally clearing the FF67 code, for 10's of thousands of miles.  No troubles.  I drive my '94 XJ12 from Chicago to New Orleans almost monthly.  My car now has ~90,000 miles.  I drive it daily to and from work, a round trip of ~160 miles.  Just drive the beast, and don't worry."

FF69 --DRIVE/NEUTRAL SWITCH: Alan Baker says, "This is a common fault on the XJ40's of that era, (they use

Gregory Wells adds, "I was always told the FF69 involved the way the key is turned to start the car.  If you grab the key and turn it to the start position in one motion, the FF69 can be set.  If you grab the key, turn it to the run position and pause for just a brief moment before continuing on to the start position, the code won't set.  I was told that the ECU circuitry would not "see" the voltage level it was looking for if you passed through the run position quickly, rather than pausing briefly, and this is what triggers the FF69 code.

"This isn't supposition, as we have many, many reports from customers that this procedure does keep the FF69 from being set.  The nice thing is that it costs nothing to try it."

CLEARING FAULT CODES --6-CYL: Gary Penovich says, "On a ‘94, you can clear the fault code from the ECU without disconnecting the battery.  It's a piece of cake.  Open the dash trim panel that's underneath the passenger airbag by pulling down on it.  Unscrew the passenger heater vent cover.  Remove the small trim panel from around the heater vent.  You should see a purple connector attached to a yellow(?) wire.  The connector has only one conductor in it, and it isn't connected to anything.  Short that conductor to ground for 3 seconds.  It will clear the fault code.  The process may be the same for all AJ6 powered XJS, perhaps AJ16 as well.

"I have actually moved the connector outside of the trim by running the wire through the vent cover.  Now, I can access it simply by swinging the dash panel downward.  It comes in handy after disconnecting sensors while the engine is running.  The ECU will flag a fault even if the key is on with the engine off!"

If your car is too old and tired to pass a required emissions test, you should have it corrected.  However, if you don't have the time or money to get this done right now, John W. Himes makes the following suggestion: "I add a gallon of denatured alcohol to the tank.  This makes a very clean burning fuel.  The car does not run as good with that in the tank, but it passes emissions very well."

Harry Trafford says, "I have used 99% isopropanol at 12% with some success.  Brings down the CO%.  Yes, the percentage is high and the idle had to be adjusted to keep running, but these were desperate people.  I had them add 46 oz. to make 3 gal. of premium.  After the test, they just bought more gas to dilute the alcohol and readjust the idle."

"I used 2-propanol because it's what was available at the time.  I also had methanol, but it's corrosive and not a good thing to put in British cars."

Alcohol tends to be hard on some rubber products in the fuel systems of earlier cars, and British non-metallic parts have enough trouble without adding to their woes.  Therefore, it is not suggested that you use this method more often than necessary.

Another idea used by some is to retard the timing a bit before the tests.  You can't retard the timing by turning the distributor on a car with Marelli ignition, but Jaguar thoughtfully provided a jumper that can be pulled to operate the Marelli ignition system on a slightly more retarded map.

Trafford continues, "I bought a CO analyzer, too.  It's a "Gunson's Gastester".  This unit is not a professional system, and you need a lot of patience because it must clear to 0 after you make any adjustment.  Says it reads in 1 minute, but I gave it more.  It looks and feels cheap, but it worked for me by just following the directions.  It's made in England."

"Here is the address for the guy that sells the "Gunson's Gastester" CO analyzer in Pennsylvania.  He will answer your e-mail.

Ray at: r.d. enterprises, ltd.
290 Raub Road, Quakertown, PA 18951 USA
phone: +1 (215) 538-9323 fax: +1 (215) 538-0158
e-mail: rdent@rdent.com

CARBURETORS: Replacing the EFI with carburetors is not recommended.  Carburetors have several disadvantages: First, a standard carburetor does not correct for changes in altitude, temperature, fuel density, or other variables that make an engine run at less than optimum performance.  Corrections usually require an excessive amount of complication in the carburetor design.

Second, since the carburetor relies on a pressure reduction due to drawing air through a venturi, there is always a flow restriction due to the venturi.  Using a carburetor with a larger venturi reduces the loss, but the airflow at idle is so small that they have difficulty drawing fuel consistently, and a rough idle and poor low speed performance is the result.  The American solution was the progressive 4-barrel, which uses one set of venturis at low speed and an additional set at high speed.

Third, carburetors tend to have problems ensuring proper fuel/air mixtures at all cylinders.  With most arrangements, the corner cylinders on a V-8 tend to run leaner, because the path for the fuel/air mixture to get to them is more convoluted, and the fuel gets left behind and drawn into a nearer cylinder.  Such problems would be even more serious on a V12.

Problems occur when a cylinder runs lean; burned pistons usually result.  In the old days, the engines would simply be adjusted rich enough to avoid any problems.  When environmental regulations and fuel efficiency demands rendered this solution unacceptable, the incidence of burned pistons increased.

The time-honored solution to this problem was multiple carburetor systems.  The intake path for each cylinder must be similar, and sometimes even a dedicated barrel for each cylinder was used (Webers, etc.).

Obviously, fixing all these problems simultaneously would involve a truly elaborate carburetor system, possibly requiring multiple, progressive barrels for each cylinder.

EFI systems generally come in two types: throttle-body and multi-port.  Each type will correct the first and second problem of carburetors, because all EFI systems automatically correct for variables and no EFI requires a venturi.  The throttle-body system, which consists of a single injector in the same housing as the butterfly valve, shares the same distribution problems as carburetors, but is much simpler and cheaper than multi-port.

Multi-port EFI, what the Jaguar comes with, is the ideal fuel supply system.  Since the injectors serve each cylinder individually, there is little chance of a cylinder not getting its share.

The only disadvantage of EFI is the difficulty in modifying it --which, of course, the EPA considers an advantage.  However, contacting AJ6 Engineering (see page 713) will likely alleviate all such concerns; they will modify ECU's for very reasonable fees.

EFI SYSTEM REPLACEMENT: Electromotive Inc. (see page 716) makes a system called the TEC-I (TEC stands for Total Engine Control) that replaces the EFI computer and the entire ignition system as well.  It's got more modern and comprehensive electronics than the Jaguar original, including an optional knock sensor.  Also, it is programmable using a PC-compatible computer, allowing the owner to customize the operation to suit his needs.  It's not cheap; but if your ECU has already died and you're looking at the cost of the Jag original to get running again, it starts to look cheaper.  And if you're having ignition problems as well (this system renders the entire distributor superfluous, you might as well put in a blank-off plate), it starts to look downright reasonable.

If you are performing serious engine modifications, this system is just the ticket.  Since it can be calibrated, you are not restricted to the original response curves on your non-stock engine.

AJ6 Engineering (see page 713) also makes replacement EFI systems and components, and will modify the stock ECU on an exchange basis.  According to Jeffrey Gram, "if experimenting was wished they could do a single EPROM version , which has up to 8 MAPs.  It would be possible to switch between the MAPs if the ECU is depowered between switches by means of a "dial".  AJ6 do such programmes to experimenters which then have 8 maps to choose from trying to find the best setting."

Scott Horner found an aftermarket system in New Zealand:

"From them you can buy the ECU, Ignitors, Injector Ballast and Tuning Module (a handheld LCD interface) & the Crank Angle Sensor...  You still need to supply a lambda sensor (aftermarket Bosch will do), and the coils...On my car, we used VN Holden Commodore (Australian GM car) coils, 2 coil packs.  The Holden uses the Buick 3.8 liter engine, so it's presumable the coils would be available in the US in some form.  I have heard these coils only last about 20,000km, but we'll see.

"Any 3 or 6 pack coil combination would do, I have heard Audi have a very tidy solution..."

Robert Dingli reports: "Here in Australia there are many, many aftermarket injection ECU's available.  I've tested many of them in cars and on the bench and have found most of them to be garbage.  Common faults are production quality, lack of temperature compensation and other instabilities, and general difficulties with setting up a system from scratch.  Basically you get what you pay for.  A $2000 Motec or Autronics unit is highly recommended over sub-$1000 Injec, Linx EMX, Microtec or Haltec.  The expensive units also control ignition.  The Motec, Autronics and Haltec require a portable PC (to be added to the cost if not available) to make proper adjustments.

"As far as "high performance" chips are concerned, I'm rather skeptical as to their worth.  The problem (??) with modern day EFI systems is that they are very close to optimum, being a fine balance of performance, economy and exhaust emissions.  Some of the chips available advertise that the systems will still comply with pollution levels.  The specs reveal that power increases are only in the order of a few percent for most cars."

"Systems where chip changes may actually make a noticeable difference are:

-Systems with electronically-governed rev limits.
-Racing use where pollution isn't a concern.
-Turbo cars where the electronically-governed boost limits are raised.
-Electronic ignition systems without knock sensors where the timing maps can be advanced to take advantage of better quality fuels.
-Electronically-controlled auto gearboxes where upshift points are raised.
-Older poorly-calibrated systems, e.g.  SIII XJ6 Jags set up for cold climates but being run in warmer climates."

According to Ken Wallace, "If you live in a regulated area the smog police will not approve of any of this even if it improves your emissions.  You can have your installation certified, but this is very expensive like more than $10,000 from what I hear."

Robert Gee adds a warning about aftermarket EFI systems: "I worked for a car manufacturer who made their own injection systems (Rover MEMS).  One or two people had fitted MEMS to their own cars, mostly for competition use. One guy had a modified peugeot 205 GTi with one in.  He had spent a fortune on the thing.

"Now, given that this guy had access to rolling roads, vehicle calibration experts and the like, the driveability was never perfect (an important Jaguar feature -low throttle response crucial on an auto).  Also he went through about 3-4 tankfuls of petrol doing the calibration (not too bad at US petrol prices I suppose - more than the cost of an ECU at UK

"To cap it all, when he came to sell the car it was quite hard since it was non-standard and hence not supported by any garages.

"Put it this way, I could have converted my XJ-S 3.6 to full sequential injection with fully programmed ignition for next to no cost - but preferred to keep it standard and I probably would not have got it any better than the Lucas P digital.

"If there one thing I learn't at Rover it's that the low throttle drivability is what separates a good car from a bad one and it also takes about 95% of the engineering effort.  Anybody can make a car which goes well at full throttle -and I suspect it's the latter market at which the after market fuel injection systems are aimed."

FUEL INJECTOR ORIENTATION: Strictly a cuteness mod here.  Of the 12 fuel injectors on the XJ-S, some have the electrical connector pointing rearward and some have it pointing forward.  If you wish, it is possible to reorient any fuel injector to point either rearwards or forwards, even the two front ones --the connector will easily fit under the arc of the fuel hose.

To reverse the orientation of an injector is not easy unless you happen to be replacing the hoses or the rubber seals, in which case it's a snap.  While the large rubber seal is off or the hose is disconnected, take the plate that retains the injector off and flip it over.  Twist the injector around on the hose.  The wiring harness will usually reach either side of an injector, but note that some harnesses are really brittle and fiddling with stuff like this may be asking for trouble.

There's not much good reason to do this.  Perhaps you have an idea on how to make it easier to get to the spark plugs.  Or, maybe just for a symmetrical look, you'd like the front 3 on each bank to face rearward and the rear 3 on each bank to face forward.

The tubes on the air rails insert into holes in the intake manifolds leading some to believe it's somehow involved with the intake system, but it's not; the lines go through the intake manifold mounting flanges into the heads and terminate within the exhaust ports.  The purpose of the air injection system is to provide oxygen in the exhaust stream to enable the catalytic convertors to work.

AIR INJECTION PUMP: Roger Myers reports that the air pump on the XJ-S can be replaced with a GM unit.  Take the old one to your local parts shop and ask them to give you one just like it.  Chuck Sparks says that A-1 (a rebuilder) lists it as part number 32128.

GETTING THE AIR INJECTION SYSTEM TO ACTUALLY WORK: John Napoli adds, "I have had the opportunity to see the air rails from Jag engines --both 6 and 12 cylinder versions.  Very often, the cars have brand new air pumps and diverter valves and hoses --so someone spent a good penny replacing all that stuff.  And on every one, the air rail tubes (where they stick into the head) were completely coked up.  You would need some really ambitious air to get through all this!!  Moral of the story: if you are going to maintain your air pump system, don't forget to do the obvious and simple and remove and clean out the air rail tubes.  Otherwise you are just wasting time and money."

You'll also probably need to clear out the passages within the heads.  There's nothing complicated about those passageways, they are straight shots into the exhaust ports.  You can clear them out with a drill.

AIR INJECTION PUMP CONTROL: Roger Bywater says, "the 2-3 seconds delay on the diverter valve was because of a controlled leak across the actuator diaphragm which allowed the valve to progressively reapply air injection while the manifold was still under high vacuum.  I seem to remember that removing the neoprene cover nipple from the actuator stub pipe prevents this leak from building up a balancing vacuum on the reverse side of the diaphragm, thereby totally disabling the air injection system.  We sometimes made use of this to take a before-catalyst gas sample from the air rails, fittings having been added for that purpose.

"In fact there can be more to this diverter valve business that is not readily obvious and it can have advantages even with over-run cut off.  In the over-run condition the injected air from the pump becomes quite a high proportion of the total through-put so if no fuel were present, as would be the case with over-run cut off, the catalyst would lose temperature quickly.  Having a diverter valve to temporarily dump the excess air gives the catalyst an easier time, with less steep temperature cycling and helps to maintain catalyst effectiveness when the fuel reinstates."

AIR INJECTION PUMP WASTE OUTLET: On the H.E., the air pump only delivers air to the exhaust system during warmup; once the engine is warm, it wastes the air into the right side air filter housing.  Michael Aiken points out that it is plumbed "to the engine side of the filter.  Unfiltered air is being pumped directly into the engine -and this is very dirty air coming out of this pump!  I would recommend that the wastegate tube be removed from the air cleaner housing and the opening in the housing blocked."  Aiken adds that the filth coming through this line was actually visible on the inside surface of his air filter itself.  He also points out that, in addition to the dust that the air injection pump may be pumping into the intakes, the pump itself is junk and may start pumping bits of itself into the intakes at any time --rust particles, bearing bits, whatever.

It's possible that the waste line was routed to the filter housing to reduce noise, but if noise is a concern it should nevertheless be rerouted to the intake side of the filter housing, not the engine side.

AIR INJECTION NON-RETURN VALVE: Roger Bywater: "The reason for the check valve in the air rail was not because exhaust back pressure could exceed the pump pressure, but to prevent exhaust backflow into the pump if the drive belt should fail."

Bruce Battles says that the Jaguar non-return valve "without the T-splitter is a GM part (check valve) Part # STI AV7. Just keep your T-splitter and install on the new GM check valve."  Chuck Sparks provides a couple more part numbers: Tomco 17001 and Std Parts AV-7.

AIR INJECTION SYSTEM REMOVAL: Removing this system is not recommended, as this would be a modification of an emission control system and would be illegal in many areas.  Too bad, too; this system accounts for a great deal of plumbing under the hood as well as a belt-driven load on the engine.  And on the Digital P cars, it only functions when the engine is cold --the pumped air is wastegated after the engine warms up to prevent interference with the operation of the oxygen sensors.

Eliminating the load would be easy: just gut the air pump so it only serves as an idler pulley.  The existing check valve will prevent any backflow from the exhaust tracts into the gutted air pump.  And there's little chance an emissions inspector would ever notice.  Eliminating the clutter and weight is more involved: removing the air manifolds and piping, plugging the holes in the intake manifold, and replacing the gutted air pump with an idler pulley.  The emissions inpectors are more likely to notice this if they look under the hood.  None of this will affect a tailpipe test, though, since such tests are typically done with the engine warmed up.

If you chose to install an idler pulley in place of the air pump, there are lots of pulleys available for use on automobiles; you can ask for an idler pulley in any auto parts store and be presented a choice of several.  You'd need to fab some sort of bracket to position it, and remember that you'll need to adjust the belt tension with it.

The neatest pulley installation would result from using genuine Jaguar parts.  Peter Smith: "I removed my air injection system and used a jockey pulley to carry the V-belt.  These pulleys were standard equipment on English cars which did

The 1987 Jaguar Parts Catalogue lists the part numbers:

EAC4185 Pulley
C37886 Hub
EAC3042 Bearing
C23128 Setscrew
EAC3041 Bearing Holder
C37875 Bracket

The pulley used as an idler is the very same part number that's used on the air pump --so you can skip buying EAC4185, just use the one you have.

You can also probably skip buying the bracket C37875 if you're willing to add a couple of inches of spacers around the pivot bolt for the air pump.

John Napoli offers a suggestion for plugging the air injection holes in the intake manifold: "Buy 1/4" nail anchors from Home Depot.  They are aluminum and look like a large pop rivet.  Get them 1" long.  Cut them back to 5/8" long with a band saw or hack saw (only cut the body, don't worry about the ‘nail').  Put the two o-rings from each air tube on the shank of the anchor.  Smear on some engine-grade silicone.  Insert into the manifold and hammer down the nail all the way.  Omit the ‘plates' and retighten the intake manifold to the engine.  Looks great and works great."  This mod is likely to require an extra washer or two on each stud, since the studs may not be threaded far enough to tighten the nuts down on the manifold flange with the plates omitted.

Napoli: "Here is the info on the nail anchors I used -- the ones I got at Home Depot:

Star Anchors and Specialty Fasteners
1/4" by 1"
2615-32178 (part number)
31916 26096 (number under bar code)

"This is for a box of 40.  Enough for 3 V12s and 1 Opel Kadette."

Michael Aiken's local Home Depot apparently carries similar anchors in a different package: ""Red Head" light-duty anchors.  They are 1/4" x 1" hammer-set anchors used for anchoring to concrete.  They are easy to install just as John says.  They come in a package of 14 --perfect for a V12 as long as you don't screw up more than two.  I have two spares.  The part number is 11234.  They are in the fasteners dept."

An addendum to Napoli's idea: While Home Depot only carries 1" anchors, 3/4" long hammer drive anchors are available at some other hardware stores, usually in the bin right next to the 1" ones.  Since the flange on the intake manifold is about 7/8" thick, these anchors can be used without cutting them shorter.

If you set about removing pump, valving, plumbing, and rails with the engine in the car, you will find it very difficult indeed to remove the pipe that goes from right behind the air pump along the bottom right side of the engine and emerges behind the turntable.  Some have resorted to ripping this pipe to pieces to get it out.  The easiest solution is to simply leave it there.  If you ever have the right side exhaust manifolds off for some reason, you can remove it then.

REPLACING THE AIR PUMP WITH A GM ALTERNATOR: If finding or fabricating an idler pulley to replace the air pump is too fiddly for you, note that installing a GM CS130 alternator in place of the air pump is easier and probably cheaper.  This replacement is described starting on page 580.  The GM alternator not only serves as an idler but also eliminates the need for the Lucas alternator and its V-belt in the process.

AIR INJECTION --6.0 ENGINE: Charles Randle says the air injection system in the 1993-on 6.0 engine is different; "Suggestions like do away with the system with an idler pulley is not an option."

MANIFOLD/DOWNPIPE NUTS: The nuts that hold the downpipes to the manifolds look like an extra long nut.  They actually contain a self-locking helicoil, a special type of helicoil in which a couple of the coils near the center are deformed to provide some friction when turning.  These helicoils are held within the nut by a staking on each end that deforms the thread just beyond the end of the helicoil.  Whenever these nuts are removed and reused, it is recommended this staking be checked, and re-staked if necessary.

The helicoil design means the parent metal of the nut is thinner than normal nuts.  This is countered by the nut being so long.  If overtorqued, these nuts will split lengthwise, and internally grip the socket used to torque them.  If this occurs, of course, the nut must be replaced.  The stud is a normal fine thread, so a normal nut will fit.  It is recommended that a stainless steel or brass nut be used due to corrosion problems at red-hot temperatures, and a locknut or lockwasher be used since a normal nut lacks the self-locking feature of the original.  Obviously, a locknut that uses a nylon insert for self-locking is unacceptable.

Thomas Alberts says, "I have purchased the long nuts with the helicoil inserts from a Jag dealer, but since then I've seen them at Western Auto hanging on the pegboard in a bubble pack."

Some auto parts stores sell "stud nuts", nuts intended for use on exhaust manifold studs.  Generally, they are longer than normal nuts and made of solid brass (no helicoil insert).

Another type of nut that looks right is the coupling nut sold in hardware stores for connecting lengths of threaded rod together.  These are typically coarse thread, but even if you replace the stud these nuts would probably not work well.  They are generally mild steel, so they aren't very strong and will corrode something fierce on an exhaust manifold.

Getting the exhaust manifold/downpipe nuts on and off seems imposing, but it usually can be done easily enough.  The two outer nuts on each side can usually be loosened from above with a box end wrench and a lot of patience, and the two inner nuts can be loosened from underneath the car with a socket, universal, extensions and ratchet.  Michael Minglin suggests, "For the outside studs I bent a box end wrench into kind of a "Z" shape so I could slip one end over the nut from the top of the car.  I welded an old socket onto the other end so I could use another wrench for leverage, and use a torque wrench to put it back together."

An even better idea: find a 9/16" "distributor wrench".  These wrenches are designed to tighten and loosen the bolt underneath a distributor on American cars, and therefore have a deep zig-zag to them.

Be sure to use anti-seize compound when assembling, whether using original nuts or substitutes.

Jaguar provides four threaded holes in each header.  In later cars, only two studs are used.  If the threads in one pair of holes get boogered up, it should be possible to install studs in the alternate two holes, and rotate the loose collar on the downpipe 90° and reinstall.  Rob Warnicke says his '73 XJ12 had studs in all four holes per downpipe, eight per bank: "I don't know when the changed the set up.  I was surprised when I tore into my 87 and only had half the hardware to deal with.  The new flange and the old flange are essentially the same, with the new one having two fewer ears on opposite "corners".  They work the same, just with fewer bolts.  One would think that since Jaguar dropped it down to two per exhaust manifold, you could delete two on the older cars as well. "

TRANSMISSION/EXHAUST PIPE BRACKETS: When considering the mounting of exhaust pipes, it must always be kept in mind that the engine moves around on its mounts.  When power is applied in low gear, the entire engine/transmission assembly can tilt significantly to the right.  Typically, exhaust systems are rigidly mounted to the exhaust manifold and unsupported from there to the rear of the car, where they are supported by soft rubber mounts. The intention is that the pipes will flex enough over this length that the engine can move without damage or fatigue.

The XJ-S, of course, has a problematic transmission mount (see page 342).  Problems with the transmission mount can cause the engine to move more than intended, increasing the stress on the exhaust system.

The XJ-S also has several joints in the exhaust system around the catalytic converters, which happen to be in the middle of the unsupported span.  These joints can vibrate loose under the stress.  Add to this the fact that the catalytic converters themselves get very hot when running, and are made of a high-temperature, brittle material.  There are reports of the catalytic converters actually cracking within about 50K miles.

Jaguar's solution is to add a pair of small brackets from the torque converter cover to the pipes.  The intention is to render the portion of the exhaust system between the manifold and the catalytic converter rigidly attached to the engine/transmission assembly, thereby seeing no stress.  The flexing of the system would have to occur from this point rearward.

This solution is mediocre at best.  On earlier models, the torque converter cover is made of sheet metal; it is not strong enough for this load and generally ends up pretty mangled.  The fix also causes noise; some of the vibration is transmitted to the sheet metal cover, adding a tinny sound to the car.

Later, a beefier cast cover was used.  This may represent a solution to the problems, or at least part of one.

EXHAUST PIPE UNIONS: The three-bolt flanged joint in the exhaust pipe just forward of the rear axle is a very interesting device.  The seal within it serves as a sort of ball joint.  The angle of the pipes at the connection can be changed by tightening some of the flange bolts while loosening others.  This enables corrections to alignment so the exhaust system doesn't bang against anything.

Unfortunately, few muffler shop weenies have ever seen such a feature.  If they just zip the nuts on those bolts with the air wrench and proudly announce they finished the job in under 30 minutes, it's not likely things will line up.

If you have disassembled your exhaust system at this point and need to reassemble it properly, you will find it most helpful to have an assistant --or a jackstand, if you are short of assistants --hold the forward end of the rear muffler up in its proper position while you tighten the three bolts on this fitting.  When you think you are done, grab the pipe and give it a good shaking.  If it bangs anything, you're not done.

EXHAUST SYSTEM ASSEMBLY: Jan Wikström sends this procedure for assembling each side:

1. "Hang the bent pipe in place.  Make sure the insulating compressed-fibre bead is in place inside the rubber.  Smear Loctite exhaust joint compound in the joint and offer it up to the flange.  Do the screws up looser than finger-tight.
2. "Insert the second muffler and engage its hanger.  Smear the Loctite stuff on the sliding joint and join it up.
3. "Push in a finger-thick stick (conveniently brought by crazy dog) on each side of the tail muffler to jam it in the centre of its asbestos-lined pocket.
4. "Push the bent pipe clear of the brake calipers and jam in another stick between the pipe and the bleeding nipple.
5. "Shove the front muffler over and up until it sits right with another finger-thick stick between it and the heat shield. (memo: get a bone for the helpful dog)
6. "Look at the tail muffler to check that it isn't sitting too high or low through the see-saw action of the pipe.  Waggle the pipe accordingly.
7. "While holding everything in place, tighten up the flange bolts about half tight.
8. "Fit clamp and slot cover piece, liberally smeared with you-know-what.  And do up the sliding joint about half tight.  Check that both hangers have ample space for the pipe to move.
9. "Remove all sticks, hold your breath and check clearances.  If the exhaust can shake normally on the hangers

"The Loctite stuff is great; when the heat comes on, it foams to maybe three times its volume and makes a tight seal.  A tap with a hammer will break it when you want to open the joint."

IMPROVEMENTS IN LATER DESIGNS: Stefan Schulz reports: "I've just replaced pipes on the left side of my car's exhaust system.  Observations:

"Jaguar seem to have realized that some of the exhaust parts weren't brilliant and actually made some improvements, to wit:

. The intermediate pipe now has an extra kink so that it no longer prevents access to the gearbox sump bolts.
. The locating pin arrangement for the over-axle pipe has changed so that it now looks a lot more reliable.  Stress is distributed over a much larger cross-section of the hanger-to-pipe joint now.
. The old band clamps used in various places were labelled "Aeroquip".  Presumably that points at use in flying equipment.  Which is a scary thought, as both which I removed used Nyloc nuts -not a smart thing to do on a hot exhaust system!  The new band clamps are actually different part numbers and sizes for different locations, and they are designed like the mothers of all clamps.  Extremely strong and wide -get the genuine Jaguar part for a change.  Well worth the money."

HEAT SHIELDS: The Jag seems to have them everywhere: those hokey little pieces of sheet metal that seem to do nothing but get in the mechanic's way.  Not so!  While some performance cars are designed to go fast for the magazine road test and never see 100 mph again, the Jaguar is designed for the Autobahn --not just 140 mph, but 140 mph all day.  Under these conditions, the exhaust manifolds and downpipes can get red hot.  Items that hot radiate heat (emit heat as infrared light -you can feel it from a distance).  The belts, electrical insulators, boots, hoses, O-rings, etc. (all of which happen to be black) absorb this radiant heat and cook.  The heat shields are not there for passenger protection or to aggravate the mechanic; they are necessary to prevent the rubber and plastic parts from destruction.

Particular attention should be paid to the heat shields around the catalytic converters, because they get hot even when you're driving slow.  If these heat shields are not in place, the boots on the steering rack ($$$!!!) won't last long.

Heat shields are no more complicated than they look.  You can easily make them out of scrap sheet metal.  Hoses and the like can actually be provided considerable protection by merely wrapping them with ordinary aluminum foil.

HEAT SHIELD BOLT SEALS: The heat shields over the exhaust manifolds on the H.E. are held on by two bolts of different sizes.  The larger rear bolt is actually a plug for a port into the exhaust tract, presumably because Jaguar used the port in past models or anticipated the need for such a port at one time or another.

This fat, stubby bolt is sealed with a copper washer.  If your local auto parts store has a rack of red cards titled "Help!", it probably has a package of two sealing washers that are the correct size: number 66265, "Brake Hose Bolt Washers", ID = 33/64", OD = 45/64".  These same seals fit the banjo bolt under the oil pressure sender -- see page 46.

CATALYTIC CONVERTORS: According to Randy Wilson, the XJ-S has "two different types of catalysts in series.  The first cat after the engine is a three-way.  The second is a single function reduction cat."  Since it is a dual exhaust system, there are two of each for a total of four catalytic converters.

There is a honeycomb insert in the downpipe, immediately adjacent to the exhaust manifold.  This is part of the catalytic converter system.

Note that sometime in the 90's, perhaps with the introduction of the 6.0 in 1994, the catalytic convertors were upgraded with new designs that are far less restrictive.  These new models reportedly do not have the honeycomb within the

CATALYTIC CONVERTORS --MELTDOWN/FIRE: When a cylinder fails to fire, the unburned charge of fuel and air is pumped into the exhaust system.  If the catalytic convertors are up to temperature and operating, they will "burn" this mixture, and get hot as a result.  If there's a lot of misfiring going on, there is a risk of a serious fire starting at the cats and possibly destroying the entire car.  Roger Bywater expounds at length on this concern: "Back in the 1970's when I was working in Emission Control Dept. at Jaguar one of my responsibilities was complying with Japanese Heat Damage Tests.  Amongst other things this meant having a catalyst overheat warning system (via a thermocouple in the cat) and the test procedure called for one spark plug to be disabled while idling to prove the system worked.  The mixture from the dead cylinder would then be burnt in the catalyst which would obviously get a bit hot.  On the old oxidising catalyst systems this was not unduly dramatic, but even so because the carb XJ6's had the cat well back under the car, if driven any distance in this condition, they could end up with the rear seat springs popping through the top of the seat!

"Now when we started using Lambda sensors on the 4.2 EFI engine the situation changed alarmingly.  When a plug was disabled the Lambda sensor would detect the spare oxygen from the dead cylinder and the system would react as if the fuelling was too weak so swung to the rich limit in trying to correct it.  The catalyst now would be getting a supply of air and extra fuel and would start to glow in no time at all, even at idle.

"Of course the main reason the cat got hotter on the 4.2 EFI with Lambda was not so much because of having feedback as because it was a lot nearer the engine than had been the case with the oxidising cats.  Also one cylinder out on a 4.2 6 cyl puts through a lot more fuel than one out on a 5.3 12 cyl so the 4.2 cat had a lot more to burn.

"In fact on the carb engine with oxidising cat we had to disable 2 cylinders to provoke the cat to overheat enough for the test.  On the EFI with a 3 way cat one cylinder was more than enough and we had to keep reconnecting the lead periodically during the test to stop the cat rear cone temp going over 1000°C, and remember this was at idle!!!

"I am sure this is far from unique to Jaguars and is made worse by the presence of a pressurised fuel supply with the potential to make sure almost any underbonnet fire will have catastrophic consequences.

"Really if any catalyst car develops a misfire it should not be driven.  It is a bit like when the oil warning light comes on driving another couple of miles could prove to be very costly!  It is perhaps realisation of this sort of problem that prompted California ARB to come up with OBD & OBD2 with the requirement for really powerful fault monitoring techniques."

See page 161 for warnings on how faults in the Marelli ignition system can burn your car to the ground and page 169 for how overheating cats can cook the Marelli crank sensor.

CATALYTIC CONVERTOR TEMPERATURE MONITORING: The regularity of the Marelli distributor rotor failures (see page 161) has resulted in suggestions for monitoring the temperature of the catalytic convertors in hopes of avoiding expensive damage.  This plan has a distinct advantage over monitoring the various possible causes of overheating, since it will alert the driver to overheating problems in the cats irregardless of whether Marelli is at fault or something else.  A jammed fuel injector, a faulty fuel regulator, ECU problems, any number of things can cause a catalytic convertor to run hot, and with a large engine such as the Jag V12 it doesn't take too large a problem to cause some serious overheating.

There are lots of ways to monitor cat temperature.  Some sort of fusible link --perhaps even homemade, like out of silver solder or something --could be installed on or near the cats that would melt and break a circuit when the link's melting temperature was reached.  Some sort of bimetal strip or coil could be used to open and close a contact at a certain temperature.  A thermocouple or two could be installed in, on, or near the cats.  There are optical sensors that will detect and measure infrared radiation.  For a really half-assed indicator, a pair of normal insulated wires could be twisted together and installed so that a hot cat would melt the insulation and cause a short.

The first problem is figuring out what temperatures we're talking about.  Bob Gallivan forwards a guideline: "This is

In Japan and the Middle East, catalytic convertor temperature monitoring systems are required by law --so you may be able to obtain the necessary parts from Jaguar.  Richard Mansell says, "Browsing through the '87 XJ-S parts manual I have found the bits and pieces used for the catalyst monitoring on the Japanese spec cars.  They appear to use a catalyst mounted thermocouple, DAC1226, along with a little black box, DAC6943, known as "Module-catalyst switching".  Also listed on the same page are sensor-thermal, DAC1043, which appears to be bolted to the floor although it does not say where.  There is a harness, DAC3573, to plug it all together."

Andrew Corkan and others have pointed out that you can "buy a commercial dual-needle exhaust temperature monitor from Summit Racing.  About $250 US, works but has a big goofy dial you will have to mount."  See page 720 for Summit.

Michael Aiken suggests, "If people are serious about monitoring cat temperature there are relatively inexpensive probes and gauges -they are used on snowmobiles to monitor exhaust gas temp for tuning.  They even have digital gauges.  They can be found at any snowmobile (motorcycle) shop or snowmobile catalog.

"I looked into a setup in a catalog I have.  A dual analog Westach gauge (one 2" gauge, two needles) goes for about $85, a 3" gauge is $100.  Two probes ($30 ea) would be $60 for a total of $145 to $160.  The two needles in the gauge point at each other and should register the same under normal operating conditions.  One rising significantly above the other would indicate a problem!  The probe is mounted in a 3/16" hole with a stainless steel clamp (no welding).  The gauges read from 400°F to 1600°F.  The only problem I see is the leads to the gauge from the probe are only 4 feet long.  It's not far from the exhaust in a snowmobile to the gauge panel."

Corkan again: "A DIY thermocouple option accessible to everyone might be to get K type thermocouples (~$20 each). Then get a specialized thermocouple amplifier (Linear Tech #LT1025 is a cheap option, ~ $10 each) and wire the output of the amplifier to a comparator (a cheap one from Radio Shack) that will turn on a light when the amplifier output goes above a certain point."

Since there may be some question about just how hot is too hot, John Arthur suggests, "What we need is a reference temperature.  Fortunately the excellent design of the car means that one has already been provided at enormous expense.  That's right --the other cat!  What is needed is a measurement of the difference of temperature between the 2 cats.  There are industry standard thermocouples that are used in labs and workshops for measuring oven temperatures.  Some are simple and could be clamped to the outside of the cat and others have a threaded boss that would be best screwed through the exhaust just behind the cat.  Connect 2 of these thermocouples, one per cat, back to back and the voltage developed across the ends will be proportional to the difference between the temperatures of the 2 cats.  You have to take the thermocouple wires back to the electronics but they are available with a length of 2 metres which should be enough.  These things are reasonably linear and a temperature difference of, say, 300º Celsius would give an output of around 12 millivolts.  Some enterprising electronics guy could doubtless produce a simple amplifier that would enable a warning light or buzzer to sound.  Two amplifiers and 2 gauges and you could read the actual temperatures.  There are even ICs available which compensate for the slight non-linearities of the thermocouple.

"I have found a reference to Analog Devices AD595 as a thermocouple amplifier for Type K thermocouples.  However these cost over 12GBP plus tax in 1996.  A simple generic op. amp. such as a 741 or equivalent would cost pence/cents and do the same job of alerting you to a major temperature difference."

Note that monitoring only the difference in temperature may not be a good idea, since failure modes other than the Marelli rotor failures may threaten both cats equally.  The typical cause of high cat temps is a misfire, and a misfire on both banks can cause cat overheating on both banks.  In fact, such a failure mode is described on page 168.

CATALYTIC CONVERTOR NOISES: Gerald Foster reports, "The dealer is turning out to be not so dumb.  If I had gone with them I would have saved buying a power steering pump and water pump the independent dealer sold me. (Yes, a bad cat can sound like a grinding power steering pump)."

CATALYTIC CONVERTORS --CHECKING: Greg Maddison suggests that you can visually check the front cats for plugging by disconnecting the pipes between the first and second cat, unscrew the oxygen sensors, and insert a small light into the hole.  "I used a small Mag light with the shade removed."  Looking into the back end of the cat, you should be able to see the light through the core.

CATALYTIC CONVERTOR REBUILDING: Greg Maddison says, "The original Jag parts are $800 each so you can see how changing all four would be quite an investment.  I found a company that rebuilds them for much less than new ones cost, they are called Jag Services."  See page 694.

AFTERMARKET CATS: LaRue Boyce says, "Caution on the aftermarket cats! Both pieces were not "true" and couldn't be joined together without a lot of modifications."

GENERIC CATS: Generic cats are available from J. C. Whitney for, like, fifty bucks each.  Sure, you have to figure out how to plumb them up, but considering the cost difference you have plenty of incentive.

CATALYTIC CONVERTOR GUTTING/REMOVAL/REPLACEMENT: Catalytic convertors are not inherently particularly restrictive in an exhaust system; in a properly-designed system, removing the cats has very little effect on performance.

Unfortunately, this is not a properly-designed exhaust system.  The general concensus is that the stock exhaust system on the XJ-S is very restrictive, and the cats are a key part of that restriction.  Simplest fix: take off the downpipes and cats and bash all the innards out of them and reinstall.

Of course this will reduce the restrictions considerably, but for the optimal flow it'd be nice to have smooth pipes instead.  One possibility is to replace the US-spec downpipes with the European versions that have no catalytic honeycombs inside.  Unfortunately, they don't have oxygen sensor ports either, and it'd be nice to maintain those.  However, oxygen sensor ports are commonly available from places like Jeg's (page 717) or Summit (page 720) and can be welded into the downpipes.

If you must face the emissions inspector, neither of those options will be acceptable.  There are others that might be, however.  First, you could consider fitting some aftermarket catalytic convertors, preferably something broad and flat to fit under the car and less restrictive than the originals.  Or, you could consider retrofitting the later OEM cats to the early car!  According to John Napoli: "I happened to be at my local Jag dealer as someone was taking delivery of a new pair of V12 head pipes.  I noticed that these pipes did not have the corrugated metal inserts in each of the four down tubes.  These inserts are ostensibly part of the catalyst system, and are present on many V12s (including my '82 XJ-S H.E.).  Anybody who has seen head pipes with these inserts in place would reasonably conclude that they add a lot of restriction to the exhaust.  The replacement pipes I saw today have a different shape to the cats --more streamlined and seemingly smaller than the cylindrical cats on the head pipes with the inserts.  The parts man said that both types of pipes are available (with the inserts and without), both are fully certified smog-wise, and that the design without the inserts is considered a better performer because of the reduced back pressure.  The downstream cats are required with both designs.  I did not inquire as to price, but it seems that anyone replacing their cats should consider these replacements, as the Jag V12 rewards you for anything that helps it breathe better."

EXHAUST PIPE TIPS: The XJ series Jaguars have a unique style of tip on the exhaust system, a sort of S-shaped extension that places the outlets right out on the corners of the car.  This is not a mere styling feature; these tips were supposedly designed to correct a problem with exhaust fumes recirculating back into the car.  The shape puts the outlets out into the airstream coming around the car rather than into the dead air space behind the car.  If you wish to replace

Of course, the aerodynamics are significantly different between the various XJ models and all of them have the S-shaped tips.  While the fume problem may be the case with some of them, it's not likely to be the case with all of them.  Some people claim to have no problems, while others complain bitterly of the odors.  Pay your own money, take your own chances.

You might not really want to replace them anyway.  The generic pipe tips available locally are usually cheap chrome-plated steel, and the chrome comes off quickly and the steel underneath rusts away to nothing.  The stock Jaguar tips are made of stainless steel, so there is no plating to flake off.  No matter how dirty they get, they can always be made to look new again with a little work with some Comet cleanser.

J. C. Whitney offers stainless steel exhaust pipe tips, basically a 9" long straight piece of stainless steel pipe cut off either straight or at an angle at the end and held in place with two setscrews.  The ones to fit "1-5/8" to 1-7/8" OD pipe" will fit the stock XJ-S muffler nicely; catalog number 12xx0949U for the straight cut end, 12xx0952Y for the angle cut tip.  Note that the outlets on the mufflers are turned down slightly, so these tips will not sit horizontally but will angle downward a bit.

TAIL PIPES: Ernie Laprairie reports: "Just had two dual-tip Pacesetter resonators installed instead of the bulky Jag style.  Looks great and still quiet, only about 8 inches long plus chrome double tips on each side."

ADDING A CROSSOVER PIPE: One typical performance enhancement to dual exhaust systems is to add a crossover pipe: a connection between the two exhaust streams to permit each exhaust pulse to escape through both systems.  This idea has been used with dramatic results on V8's, and many cars come with them from the factory.

There may be precious little performance improvement from adding a crossover to a V12, though.  First off, six cylinders per bank results in smoother exhaust flow than four, so the pulse flow benefits of a crossover are smaller.  The exhaust pulses on a V12 alternate between banks while there are successive pulses on the same bank on a V8, which is another reason the crossover helps the V8 so much.

There is another reason to consider a crossover, though: sound.  Without a crossover, the note from each pipe is that of a six-cylinder; with a crossover, each pipe sounds like a 12-cylinder.  The Series III E-type was fitted with a crossover pipe, and Roger Bywater claims it was strictly to make the car sound proper.

To avoid screwing up the EFI, a crossover should be installed after the oxygen sensors.

A crossover has two disadvantages: First, it can make the exhaust system, already a pain to work on, even more difficult to assemble and disassemble.  Second, being able to check the exhaust from each bank helps with engine fault diagnosis.  Both of these problems can be minimized by including a flat face flange in the crossover, and making a flat blank-off plate that can be bolted into the connection when doing engine analysis.

Summit Racing (page 720) offers "balance tube kits" for less than $50.  These require no welding to install; simply cut sections out of each pipe, install tees with clamps, and install a connecting pipe with clamps.

MUFFLER REMOVAL: AJ6 Engineering (page 713) offers a pair of "Silencer Substitute Pipes" to eliminate the mufflers forward of the IRS.  They claim a 15-20 hp gain for this change; they also mention the inevitable change in exhaust note.

Members of the xj-s@jag-lovers.org discussion list generally report that removing the mufflers forward of the IRS and replacing them with straight pipes or less restrictive mufflers results in only a slight increase in sound, and the sound that results is pleasant.  However, removing the mufflers rearward of the IRS and replacing them with straight pipes or less restrictive mufflers usually makes the car unacceptably loud, and the sound is not pleasant.

If your objective is the sound, consider modifying the intake system first as described on page 108.  The sound that

LARGER PIPES: AJ6 Engineering (page 713) offers a "Large Bore Exhaust System" and claims improvements of 2025 hp.  They mention that this may only be justifiable if the entire system needs replacement anyway.  Keisler (page 718) also offers a package.  Both systems include downpipes that lack the catalytic convertor that's integral with the OEM downpipes on US-spec cars.  Martin Karo says, "You can (and I did) section in a flat performance cat in the long straight pipe section."

Scott Horner, who has an extensively modified XJ-S, says, "I have 2-1/4" pipes the whole way from the exhaust manifolds to the outlets....You do have to be careful adjusting these for clearance thru the cage, but I was able to bleed the brakes at the weekend without any problems whatsoever..."

AJ6 notes the inherent difficulty with fitting anything really big through the IRS.  If you're that kinda guy, you can forget about ground clearance and just run some big pipes under the IRS.  This also eliminates several bends in the piping, further reducing restriction.  The Keisler system supposedly goes this route.  Note that the IRS subframe is mounted on rubber and moves around a bit, so pipes going under the IRS should not be attached to the IRS --unless attached with rubber mounts.

Roger Bywater of AJ6 Engineering adds that they also offer "a new V12 extractor exhaust system that is cheaper and better than a conventional large bore system for road use."

PIPE INSULATION: A performance trick popular with competitors is to thermally insulate the exhaust system.  This keeps the heat in the exhaust gases rather than permitting it to escape through the walls of the pipes and into the engine compartment or under the car.  The result is an improvement in exhaust flow, and thereby an improvement in performance.  In the case of a V12 Jaguar, there is another very significant benefit: lower underhood temperatures.

There are a couple of ways to accomplish such thermal insulation, including wrapping the pipes, coating the pipes, and coating the pipes on the inside.  Wrapping the pipes is probably the cheapest option, but it can be difficult to accomplish in a cramped engine compartment with convoluted manifolds.  It's also potentially dangerous.  Brian Schreurs says, "I must advise against traditional "header wraps".  If oil gets on them somehow, they can catch fire.  It's happened in my F- body club." Back in the old days, the wraps were made of asbestos.  "It could be that the wrap itself didn't catch fire; it just acted as a handy absorber for the leaking oil, and only the oil burned.  I don't care to learn which one it is on any of my cars."

Wrapping also makes the manifolds themselves run hotter, because they're not getting the air cooling on the outside.  This might be harder on heavy cast iron manifolds than on headers; Tom Bennett says, "The material I had thought of using is Cool-It from Therma-tec, just read the back of the box, DO NOT USE ON CAST IRON MANIFOLDS!"

Ed Hyatt says, "According to my books on turbocharging, header wrapping is only acceptable on race cars.  Because of the additional heat stresses they place on the header, deterioration is greatly accelerated and cracks are common.  Distortion was also severe and common.  It was discovered that after a header was removed, it could not be used again because it was distorted too much."  Coating might not cause the same issues simply because it's not as effective.  Coating on the inside has the opposite effect, helping the manifold run cooler.

The XJ-S was originally fitted with a Borg-Warner Model 12 automatic transmission, but in 1979 this was replaced with the GM400 automatic.  According to Ed Sowell, "If it's a BW12 the dipstick/filler neck will be at the left side of the engine bay."  The dipstick/filler is on the right side with the GM400.

In the mid-70's reportedly 352 XJ-S's were fitted with 4-speed manual transmissions and the official Jaguar repair manual dedicates an entire section on maintenance, but there is precious little information available on that tranny for inclusion in this book.  The XJ-S's fitted with the six-cylinder AJ6 engine were available with a 5-speed, but there is no info herein on that tranny either.

OVERHEATING: An automatic transmission generates waste heat as a result of the "slipping" of the torque convertor.  It always slips; more at low rpm and less at higher speeds, but the only way it won't slip at all is if there's a "lock-up torque convertor" fitted -- popular on some modern transmissions, but not on the GM400 or Borg-Warner transmissions used in the XJ-S.  There is a cooler provided to deal with this waste heat; it's in the end tank of the radiator, and therefore rejects the transmission heat into the engine cooling system.

If there are faults in the automatic transmission, it can greatly increase the amount of waste heat generated.  David Hodges had a transmission that he knew was malfunctioning, and before he fixed it he did some careful testing.  With calibrated temperature sensors in each bank of the engine, he drove 125 miles at various continuous speeds.  Then he installed a small transmission cooler and made the return trip under nearly identical driving and weather conditions.  He showed conclusively that, with known transmission faults, the small transmission cooler lowered the engine temperatures significantly --from just a few degrees at low speeds to as much as 18°C above 100 mph.  Hodges adds: "At idle with the separate transmission cooler the engine cooling fan (electric) runs for shorter periods of time before it switches off and the gap between switching back on is most definitely longer."

Hodges' conclusion: "Bearing in mind the V12's tendency for overheating and the trouble many have in curing it, a faulty transmission could be leading many up the garden path.  I only noticed the initial problem with the gearbox whilst driving very hard.  It makes you wonder if a gearbox that is 'iffy' and has gone undetected could be contributing to the overheating problem so many have experienced."

There is much discussion on keeping the GM400 cool on page 336.  Much of what is said may apply equally to any automatic transmission.

SHIFT CABLE --ELECTRICAL PROBLEMS: William F. Trimble reports: "The Jag would not start --nothing when the key was turned to the start position.  Shortly thereafter smoke started coming out of the shifter quadrant on the console.

"We took part of the console apart and found that the shifter cable had melted, freezing the car in park.  A check underneath revealed that the lockout switch and wiring looked OK, and that there were no obvious problems with any of the wiring under the car."  Eventually, the problem was found: a loose ground cable.  "The high current load imposed by the starter could not get through the loose ground cable.  The current chose the next best available route, which was through the shifter cable to the body."  This problem is reportedly common enough that some parts clerks are familiar with it.

Avoid this problem and install an additional ground strap.  See page 555.

BORG-WARNER/GM400 BOLT PATTERNS: The bolt pattern for the transmission/engine attachment is the same for the BW12 and the pre-1993 GM400, and apparently was the same for the Series III E-type with manual transmission.  However, when the GM400 was incorporated, the dowel pin arrangement was changed.  Robert C. Warnicke: "I have a '73 pre-H.E., '84 H.E., T400 and BW sitting in my carport.  The bolt patterns appear to be the same.  The H.E. has two dowels on the back that are much bigger than the dowels on the pre-H.E.  At least one of these dowels is in a different place as well.  I don't know how important the dowels are with all the bolts, but one will have to be removed off the pre- H.E. for the T400 to fit, and the other will be loose in the T400 hole unless something is fabbed to make it fit tight."  It is possible to remove the dowels and bolt a transmission to an engine despite dowel pin conflicts.  However, the alignment of the engine/transmission mating may not be as good.  If misaligned, the flexplate may flex at each revolution, and will quickly fail.

Scott Horner points out there is also a difference in the end of the crankshaft.  The crank that mates to the GM400 has a relatively large pilot diameter in which the protrusion on the front of the torque convertor sits.  The crank that mates to the BW12 has a smaller pilot diameter.  When faced with this problem, he was able to machine the stub on the front of his GM400 torque convertor to fit the BW12 pilot hole on the crank.

BAND ADJUSTMENT: Michael Neal offers this tip: "If you attempt your own band adjustment on the B/W don't overtighten them.  The car will come to a very sudden halt.  A quick adjustment: tighten them finger tight and back off the adjuster 3 flats."

WARMING UP THE TRANSMISSION?: According to a tip passed on from the Heart of America Jaguar Club, if you have a Jaguar with a Borg-Warner automatic transmission (pre-1979 XJ-S), you should let the car idle in neutral for 10 - 20 seconds before driving.  This is because a one-way valve that prevents fluid from draining from the torque converter is unreliable, and the torque converter may have drained.  The fluid pump does not function in park, so it must be in neutral to do any good.

FLUID: If you have the early XJ-S with the Borg-Warner automatic, the owner's handbook specifies Type F fluid.  However, there are reports that some Jaguar dealers refill these transmissions with Dexron anyway, because they feel their customers appreciate the smoother shifts resulting from the slipperier fluid.  This might not be a good idea, since firmer shifts cause less wear.

REPAIR MANUALS: Craig Sawyers says, "I rebuilt my GM400 using just the ROM.  However, I wish I'd bought Ron Session's book on "The Turbo Hydra-matic 400" -tells how to take all variants to bits and overhaul using "real world" tools.  Includes performance tuning too."

Richard Chapman adds, "I have it and it gave great insight into the internals.  Some of Ron's suggestions do not seem to get acceptance in the industry it would appear."

George Balthrop suggests "Haynes Techbook 10360 "GM Automatic Transmission Overhaul", which covers both the TH400 and the TH700, provides information on the function of this transmission, special tools, in-car repairs, testing & trouble-shooting, full overhaul & modification."

GM400 AUTOMATIC TRANSMISSION INTERCHANGABILITY: It is well known that the later XJ-S's are fitted with the GM400 automatic transmission.  What is less known is that this transmission (through 1992) has a housing designed specifically to mate with the Jaguar V12.  Because the GM400 has an integral bell housing, a GM400 from any other car will not fit.

The innards are interchangeable, though, so even though it's not easy to replace your transmission, it is easy to have it rebuilt.  It's not even particularly difficult to remove (as transmissions go) and there are several access panels under the interior carpet to make maintenance easier.

If the tranny is apart, it is recommended that the sprags be replaced with high-performance aftermarket models.  The Jag is hard on even the trusty GM400, and has a tendency to tear it up.

As a result of a complete revamp, the 1993-on 6.0 liter V12 has a standard GM engine/transmission bolt pattern.  Cars with this engine come with a 4-speed version of the GM400 called the 4L80E; the E means it is controlled electronically.  It cannot easily be retrofitted to earlier cars.  The earlier basic 3-speed GM400 was posthumously renamed the 3L80.

GM400 -MINOR DIFFERENCES: John Goodman reports: "I may be wrong here, but I think Jaguar revised the tranny a few times throughout its history.  My '88 car shifted much faster with less "slurr" than my friend's '84."

Richard Mansell says, "The Collectors guide does mention that "the GM400 transmission was recalibrated for improved responsiveness" from 88MY."

Goodman adds that the GM400 in the XJR-S has different shift characteristics.  "The factory-modified GM400 came as standard on the 6.0L XJR-S from '89 to '93 Part no.  SPE 1027.  The owners handbook says "JaguarSport modified shift points".  In my car ('89) I would consider under normal driving the shifts to still be quite soft, under hard acceleration they are by no means harsh, but seem to be a little quicker.  However, what is noticeable is its ability while in drive to kickdown into first at higher road speeds, (up to about 38-40 mph); this is quite useful."

"The bell housings are different because it no longer needs the Marelli speed sensor.  The valve body is changed and recalibrated and a different spring in the rear accumulator (whatever that is).  The XJR-S manual and all the other related bumph I have collected makes a big point of stating it is unique."

Richard Mansell says, "As well as suspension mods the SportsPack modifies the gearbox change points.  This means that the car will change down into first at up to 49mph (standard GM400 -30mph) and down into second at up to 98 mph (standard GM400 -85mph).  During full throttle kickdown acceleration the car will also hold first up to around 64mph and second until around 105mph."

Besides these functional differences, there are also physical distinctions --including the shape of the pan and therefore the shape of the gasket that fits.  John Himes: "If you are looking to fit a new filter or shift kit on your General Motors Turbomatic 400, check the serial number for the date of manufacture (first 2 numbers), or at least the shape of the pan.  Pre-88 models are a little different than 88 and newer."

DEXRON II/III FLUIDS: John Horner passed along this info from "an applications specialist at Texaco's lubrication division.": "Since Type A, Type A Suffix A, DEXRON, DEXRON-II and DEXRON-IIE fluids are obsolete, customers with transmissions calling for any of these earlier vintage fluids should use DEXRON-III.  DEXRON-III fluids are designed to be back-serviceable for automatic transmissions used in passenger cars and light trucks manufactured since 1949.

"There are a few synthetic DEXRON-III ATFs available but they may be hard to find.  They are also more expensive than mineral-based ATFs.  Synthetic transmission fluids basically share all the same advantages that synthetic motor oils enjoy over conventional mineral-based oils.  These include improved low-temperature fluidity, oxidation stability and reduced volatility.

"Compared to the old Type A fluids (and even newer generation fluids such as DEXRON-II or IIE), a mineral-based DEXRON-III fluid will help prolong the life of a transmission.  DEXRON-III fluids retained the low-temperature

"For your information, and as a point of reference, when GM introduced DEXRON-III fluids they increased the drain interval to fill-for-life under normal service and 50,000 miles for severe service."

John T.  Horner adds: "Mobil lists a Dexron type synthetic ATF.  Check the web site at:

If durability is more important to an XJ-S owner than the gentle shifts, use of alternative fluids (see page 327), boosting the line pressure (see below) or installation of a "shift kit" may be in order.

RAISING THE LINE PRESSURE: Tim Blystone sends this idea in response to the suggestion of using Type F fluid on page 327: "The F-Type fluid is somewhat thinner and is supposed to allow the tranny to shift faster and more positively.  It does no harm and neither have I ever been able to see any good it does either.  I would rather use Dexron 3, remove the pump and replace the pump pressure spring with a new red spring.  Used in Corvettes.  This will raise line pressure and make the whole thing shift more positive."

GM400 TRANSMISSION MODS: Helpful sources include B&M Racing (page 714), TCI (page 720), and Turbo Action (page 720).

GM400 TRANSMISSION SHIFT POINT MOD #1: The 5.3 liter Jaguar V12 was designed prior to the fuel crunch of 1973 and has "over-square" engine dimensions --the bore (90 mm) is considerably larger than the stroke (70 mm).  Such a design is conducive to high performance at high RPM and is therefore ideal for racing applications, but results in poor low end torque.  However, to optimize fuel economy, it is best if an engine is turning rather slowly, so the stock GM400 automatic transmission is set up to keep the V12 in the RPM range where its performance is poorest.

The point at which the GM400 shifts is determined primarily by a governor that responds to engine RPM, and is varied by two things: 1) a vacuum modulator that makes the car upshift promptly when vacuum is high (light throttle); 2) an electrical switch on the throttle linkage that forces the tranny to downshift, and remain in lower gears until 5000 RPM, when the pedal is pressed all the way to the floor ("kickdown").

The vacuum modulator is a bolt-on device on the right side of the transmission.  Some of these modulators are adjustable by removing the vacuum hose and inserting a straight blade screwdriver into the vacuum fitting.  Turning the adjustment changes the preload on the spring, therefore altering the shift points.

The vacuum modulators are available in several sizes, and since they are a standard GM part, are found in any auto parts store for reasonable prices.  In general, the smaller they are, the more vacuum required to make the tranny upshift, so the longer the car will remain in the lower gears.  Of course, it is recommended that you make sure to buy one that is adjustable.

Alan Jenks "fitted a B&M adjustable vacuum modulator (B&M #20234).  This fits all TH400's."

Rather than buying a smaller modulator, Greg Meboe modified his existing one: "I needed to increase the spring pressure against the diaphragm.  I did this by collapsing the modulator body around part of the spring in a vise, effectively shortening the working length of the spring.  I imagine I took about 30% of the travel out of the spring.  This had the effect of increasing the effective spring rate.  The vacuum modulator modifications produce an upshift between 500 and 1500 rpm's higher than before, depending on throttle position."

GM400 TRANSMISSION SHIFT POINT MOD #2: For absolute maximum performance, shift points should be selected that surround the peak on the horsepower curve --without exceeding the redline, of course.  The engine should be allowed to run past the power peak, so that when shifting the engine doesn't drop back too far below the power

The published stats rate the Jaguar V12 at 5000 RPM.  With the large steps between gears on a three-speed transmission, the engine should be taken to the redline of 6500 before shifting to optimize performance.

The GM400 slushomatic transmission, of course, was designed with the 1950's-design pushrod V8 in mind.  Not only does it normally shift at relatively low rpm, it absolutely refuses to allow the engine to rev beyond 5000 rpm; it will shift at this point even if you have selected low gear with the lever.  The above modification to the vacuum modulator will not affect the limit where the GM400 will force a shift.

The governor assembly is contained under a sheet metal cover on the right rear side of the transmission, and there is an access cover under the carpet of the XJ-S to get to it.  If you remove the governor and grind a little weight off of each of the counterweights, the engine will shift at higher RPM under all conditions.  This modification will allow the engine to run faster than 5000 RPM, where the stock GM400 will force a shift no matter what.

It may make sense to modify the governor as described, and install a large vacuum modulator to keep the light-throttle shifts at a reasonable RPM.

According to Chad Bolles, the GM400 in the 1991-92 XJ-S was programmed differently than earlier cars, providing higher RPM shifts under power, better downshifting, and holding low gear forever if the shifter is held in 1st.  It may be possible to retrofit the changes into earlier cars (replace the governor, etc.) or to buy the later transmission and retrofit it.

GM400 TRANSMISSION SHIFT POINT MOD #3: If you want serious performance from your XJ-S, install one of the many available "shift kits" for the GM400.  Keep in mind when you select your kit that your objective is to allow higher RPM shift points at full throttle (when the kickdown switch on the throttle cable is activated) or when manually shifting; High RPM shifts when taking it easy are of little benefit and will hurt fuel economy and passenger comfort.  Many shift kits offer more firm shifting, some shift at redline at all times (!) and some even render your car a 3-speed manual.

Most shift kits can be installed by simply lowering the pan from the transmission and removing the valve body within.  Replace a few springs and the like, and reassemble.  See the notes on page 326 regarding the differences between pre- and post-1988 GM400 transmissions.

Alan Jenks reports on a "‘Shift Improver Kit' from B&M Racing to the Turbo Hydromatic 400 automatic transmission.  There are two kits, one for pre-1988 TH400 (B&M #20260) and one for post-1988 (B&M #20261).  The kit can be fitted in two forms, either ‘heavy duty' (stage 1) or ‘street/strip' (stage 2).  Stage 1 provided firmer shifting without compromising the quality of the ride, which is what I wanted."

Per Chad Bolles: B&M makes a product called a Transpak, "with this you can set up the trans to shift like you want, from very hard, to normal street."  B&M also makes a Racing Kit, "this is a race very hard shift kit (neck snapping)."  Finally, in what should probably be listed as GM400 Transmission Mod #3A, there is a replacement valve body.  "The B&M valve body changes the shift pattern to 123NRP instead of PRN321."

Jim Hall says, "I installed a TransGo competition shift kit recently.  In addition to very positive shifting, it has the added benefit of allowing downshifts to 2 and L at any speed.  I'm delighted with it."

Jim Cantrell says, "The TH400 in modified form normally has a whine in first gear.  This is the planetary gears.  I don't really understand why, but installing a shift kit seems to increase the whining.  It is considered normal behavior and at least on the one I have, has gone nearly 100k miles with no problems."

Jan Wikström had his local tranny shop "lock up the freewheel on 1st gear, which gives me respectable engine braking and a better "feel" in the really low-speed twisty bits.  Caution: it's now possible to engage 1st at any speed..."

Paul Burke reports on "some information regarding "tweaking" of the GM400 box.  It describes removal of four of the six balls, shift improver plate (different valve body transfer plate) and plugging one of the passages.  The article was in Musclecar Review, February/March 1997 starting on page 58."

TORQUE CONVERTOR REPLACEMENT: First off, you might wish to note Roger Bywater's comments on the stock GM400 torque convertor on page 33.

There are torque convertors available that have a higher "stall speed", which sorta means they engage at a higher RPM.  This is wonderful for the Jaguar V12, but does require removing the tranny to change.  According to Thomas E. Alberts, "B&M tells you to try for 500-750 RPM less than the RPM at peak torque."

Michael Kenrick reports that the torque convertor from a 3.8 Buick Regal Turbo can be used to provide a more suitable stall speed.

According to Chad Bolles, the later model XJ-S uses the HI-Stall convertor. "It is the same converter used in the 427 L-88 and LS6 and LS7 Chev, flash stalls around 2600-2800rpm, the difference being the Jaguar converter has 6 lugs on it where the Chev has 3."  He adds that a Chevy convertor may be used in the Jag, leaving the other three bolt holes unused.  Reportedly, some GM torque convertors use six bolts as well.

Bolles also explains the difference between stall speed and "flash stall".  Stall speed is the RPM the engine runs at continuously if the brake is held and the accelerator is floored in gear.  Note: this is very hard on the equipment, and causes a lot of heat in the transmission; such tests should only be done for a couple seconds, and the car should be driven around at normal speeds for a while afterward to allow the transmission fluid cooler in the radiator to cool the transmission back down.  "Flash Stall, hold the brake, trans in gear, quickly mash the acc pedal, watch the Tach, it will flash to about 2500-2800 rpm, but if you just hold the brake and ease the acc pedal down the converter will not reach the same rpm before it tries to spin the rear tyres.  Don't ask me why, I just know that that's how it works."

GM400 RATIO CHANGE: Thomas E. Alberts says, "...I agree that the standard gearset is poorly matched to the XJ-S...  Note that the modified gearsets, like TCI's, lower the second gear ratio as well as first.  Observe:

TH 400 TCI gearset
1st 2:48 2:75
2nd 1:48 1:57
3rd 1 1

I think it would make a very nice improvement and without any sacrifice of top end speed."

ADDING OVERDRIVE TO THE GM400: John Goodman has heard about "overdrive units manufactured by American Overdrive Inc. designed for autoboxes, GM400 included?  This effectively changes your GM400 into a six speed.

"Two possibilities here would give much better acceleration.  The unit can be supplied with the internals reversed so you have underdrive first, underdrive second and underdrive top.  Or install a lower axle ratio and leave the overdrive in and switch it out for "Sport Mode"."

TH700R4: One way to deal with the shortcomings of the GM400 or BW12 is to replace it with the more modern TH700R4.  One large benefit is that the TH700R4 will provide much better performance from a standing start: the torque convertor provides a larger effective reduction, and first gear is much lower than the GM400's 2.40:1.  Plus, it has four gears, including an overdrive 4th.  The overdrive 4th can enable the installation of a lower final drive ratio, making the get-up-and-go better still without sacrificing the top end cruise.

John's Cars (page 717) provides the adapter hardware necessary to fit the TH700R4 to the Jaguar V12 5.3.  Scott Horner says that Dellow (page 715) does as well, and Chad Bolles of Jaguar South (page 717) announced his adapter: "Just think, XJ-S'ers: 30% lower rpm at 80 mph --that means about 1900 rpm.  Gas mileage up around 20 to 30%.  0-60 times in the 6 second bracket.  Tyre smoke from the stoplite.  A loss of about 30 to 50 lbs by getting rid of the Turbo 400."  XK's Unlimited (page 697) offers a "conversion kit".

If you have the ‘94-on 6.0 V12, you probably don't need an adapter; the TH700R4 will probably bolt right up, since those engines have a standard Chevy bolt pattern.  You probably aren't as interested in the swap, though, since the 6.0 also comes with the improved 4-speed GM400 and enough torque for respectable takeoffs.

MANUAL TRANSMISSION: The shift points, cruise speed RPM, fuel economy and top end can all be optimized by replacing the GM400 or BW12 with a manual transmission.  This is a major task requiring the installation of flywheel, bell housing, clutch, clutch pedal, console modifications, speedometer fiddling, etc.  Changing the final drive ratio (differential gears) should be considered, since 5-and 6-speeds generally have an overdrive top gear and the final drive ratio is already tall enough.

Jaguar did make a few XJ-S's with a 4-speed manual transmission, but these were early cars.  The transmission and clutch were similar to those used in the SIII E-Type, but those cars are valuable today.  Trying to obtain the hardware needed to convert your XJ-S to a manual transmission from either source is likely to be difficult and expensive.  Besides, you end up with only 4 gears.  For most people, it makes more sense to adapt a modern 5-or 6-speed from some other model car.

The author of this book has performed this modification on his car, using a 5-speed Borg-Warner NWC transmission from a Camaro and making a lot of components from scratch.  Now such a task is much easier, because you can purchase many of the necessary components or even entire kits for this conversion.  General info for those considering such mods follows, much of it provided by Mike Frank.

There are five transmissions commonly considered.  One is the Borg-Warner NWC 5-speed, which comes in Camaros, Mustangs, and several other vehicles; it has an integral shifter (no external linkage), and there are a couple different locations for this shifter.  Reportedly the Mustang shifter configuration is better for the XJ-S than the Camaro configuration.  This tranny is adequate for a stock XJ-S V12 but may be marginal if extensive engine mods are done.  There are lots of ratios available.

There are 5-speed conversion kits using the "JT5" transmission, which is supposedly the same thing as a BW NWC only different.  Only conversions for E-types and other older Jaguars are mentioned, but since the E-type SIII V12 is included, it may be possible to figure something out for the XJ-S.  JT5 kits are offered by Terry's Jaguar (page 696) and Vicarage (page 704).

Another possibility is the Borg-Warner 6-speed used in the Dodge Viper and the later Firebird, Camaro and Corvette models.  It has some advanced features such as carbon composite synchros.  This is a massive tranny, and will probably handle whatever a Jag V12 can be made to dish out.  There are a wide variety of ratios available.

The third possibility is a Getrag 5-speed.  It is supposedly also adequate for all conceivable uses.  The Getrag is a novelty in the US, but is reportedly fairly common in Europe.  SNG Barratt (page 696) offers kits using this transmission; again, only E-types are mentioned, but the SIII V12 is included.

The fourth possibility is the Tremec 5-speed, described by Jim Swarr: "Tremec is owned by Dana Corporation which is well known worldwide for its transmissions and rear axles.  The Tremec 3550 and TKO is their performance line of transmissions.  Tremec made the famous Ford "top loader" 4-speed.  This is a modernized version of that with an overdrive.  It has a heavy duty aluminum case, rollerized gears and internal rail shifter.  The gear ratios are 3.27, 1.98, 1.35, 1 and .68 .  The only gear ratio option is a .82 overdrive.  It is a very strong transmission; I have one in a customer's 750 hp drag car.  I would suggest that you use the TKO because it has a bigger input shaft and output shaft.  A bellhousing needs to be fabricated (welding a plate to a stock bell) for your car to fit a Ford transmission, or if you can adapt it for a Chevy 4-speed I can convert the Tremec to fit into the Chevy bell.  If you have any more questions please call me at 610-489-4029 anytime after 10:30AM EST."

Concerned about the toploader's reputation for notchy shifting, Inder Singh says, "In a followup question on the subject, Mr. Swarr assures me that Tremec has made a number of improvements to its shifting characteristics."

Keisler Automotive Engineering & Electric (page 718) offers a kit using the Tremec TKO, and Conversion Components Ltd. (page 715) offers a Tremec kit.

The fifth possibility is the Toyota Supra transmission --but apparently there is confusion about which Toyota Supra transmission.  There are three general types.  The first type is generally referred to as the W58, although technically there were W55, W57, W58, and W59 transmissions differing chiefly in ratio only.  This transmission is described as "an all-alloy case 5-speed and can be distinguished by 9 bolts and 2 dowels holding the box to its bellhousing."  There are four possible stick positions: 18", 19", 20-1/2" and 21", as measured from the front of the box.

If you get your own Supra W58 tranny from a junkyard, note that before installation it is recommended to remove the front cover of the transmission which holds the input shaft bearing and the input end of the layshaft and replace the light-duty layshaft bearing with a generic industrial-duty bearing of the same size --a five-minute job.  Reportedly the bearing that's in there has 8 balls, and the generic bearing will have 12.  Winston Good reports: "After much trouble I thought I should include the part number that I found to do this 5 minute job: KOYO BLO6307NR C3.  The box I got says 6307.  I believe the NSK number is HR6307NX.  All the specs are at the NSK website.  Mine took longer than 5 minutes since the press is at the machine shop."

Dellow (page 715), sells kits to install a W58 in a Jaguar.  Note that, despite the fact that Dellow is located in Australia, getting all the hardware needed from them might still be cheaper than buying the transmission itself locally.

Dellow also offers some Supra 4-speed boxes.

Conversion Components, Ltd. (page 715), also offers 5-speed kits using Toyota Supra gearboxes.  They modify the shifter location to make it more ideal for installation in the Jaguar.

There is also some history of the Toyota "steel case" 5-speed from Celicas, Crowns, Coronas, Cressidas, etc., being used in Jaguars with success, even though it is described as not quite as strong as the Supra.  This tranny has 7 bolts holding it to the bellhousing.

W58 transmissions have a long and glorious history of successful use in Jaguars with 6-cylinder engines.  They have also been used behind V12's and the owners have been happy with them -- at least, up until they broke.  There are reports of failure.  If a V12 has a Supra transmission behind it that hasn't broken yet, the W58 may in fact be up to the task, or maybe the owner has just been lucky so far --or maybe it isn't a W58.  Which brings us to the second type of Toyota Supra transmission.

According to Tony Bryant, the W58 was only used in non-Turbo Supras and a 2L Twin Turbo model sold only in Japan.  From 1986 to 1993, the 2.5L Twin Turbo and 3L Turbo were fitted with the R154 transmission.  "The R154 has huge & wide gears.  It has inch deep ribbing all over the case.  It is 50% heaver than the W58.  Makes the W58 looks like a dinky toy.  There is no parts interchangeability.  Not even close.  I've had them both apart at the same time.  A friend with a Tremec came over to have a look.  He said the Tremec has noticably smaller gears."

The third type of Supra transmission is the V161 six-speed used on the 3L Twin Turbo from 1993 on.  Bryant: "The V161 is different again, apparently even stronger than the R154."

So, if you're considering putting a Supra transmission in your XJ-S, there are people that will suggest a W58 transmission and even outfits that will sell you a kit to use one.  But, really, if you're going to that level of effort and expense, it really only makes sense to insist upon the R154 or V161.

Once you decide on a tranny, there are details to deal with.  John Napoli tells us about Tilton (page 720): "They cater to the racers.  They sell a full range of bellhousings for the V12 that accept popular manual transmissions.  You can even get a small-diameter, multi-plate clutch with a small, reverse-rotation, gear reduction starter that mounts backwards on the bellhousing, alongside the transmission.  Imagine --starter changes in the XJ-S without removing exhaust pipes, and from inside the car!!  Be still my heart."

Jaguar made a lot of manual transmission XJ-S's --with the AJ6 engine.  Still, maybe some parts would be helpful for the V12 conversion.  Chad Bolles reports, "The pedal box from the 5sp XJ-S will fit any XJ-S, but the problem is it will

Vintage Jaguar Works (page 697) offers a pedal box with clutch pedal and master cylinder.

AJ6 Engineering (page 713) suggests that the ECU needs the overrun cutoff disabled "to avoid driveline shunt at low speed."  AJ6 Engineering also can remap the fuelling to deal with wide open throttle below 2000 rpm --a situation that simply cannot exist with the A/T so the original map may not have been optimized all that well in this realm.

One final note: The mid-80's US-spec XJ-S EFI operates in closed-loop mode in D and in open-loop in P or N.  There's a reason for this; it can develop an unstable idle in closed-loop without the load of the torque convertor.  If you install a manual transmission, you may need to operate in open-loop all the time (which is terrible for fuel economy) or find some other way to switch from open-loop to closed-loop.  Or, you can operate in closed-loop all the time and work to minimize the idle instability; upgrading to 3-wire oxygen sensors might help.  Adjusting the idle mixture trim on the ECU may help.

Yes, the transmission mount in the Jaguar XJ-S deserves its own section in this book.  This mount would have made Rube Goldberg proud.  The design utilizes a spring to take the weight of the transmission, as opposed to the rubber supports used on most cars.  It also has a vertical post assembly containing a "special washer with rounded edges" within a rubber bushing.  This assembly allows a very limited range of motion: some vertical travel to allow the spring to work via the post assembly sliding up and down within the bushing; very little horizontal or axial travel, since the special washer fits snugly within the bushing; and a little tilting (torque reactions) via the special washer behaving as a ball joint within the rubber bushing.

The desire to use a spring doesn't adequately explain the complexity of this assembly, however.  It's possible that there was also a safety objective.  In the 70's Volvo was advertising that their transmission mounts would guide the engine under the car in a front-on collision instead of the engine coming into the passenger compartment, and perhaps Jaguar had similar intentions in mind.  The part that connects to the bottom of the center post is sometimes called a "collision plate", although it's also called a "tie plate".  Perhaps crash safety is a plausible explanation for the complexity, but it's certainly not obvious how this design makes the car any safer in a crash.

Note: If you disassemble the mount and lower the transmission significantly, Thomas E. Alberts suggests you take care that the top of the engine does not damage the heater valve.

If you have the mount apart, consider servicing the driveshaft U-joints while you're there.  See page 348.

RUBBER BUSHING & SPRING CUP REPLACEMENT: Finding the rubber bushing (CAC3227) or the rubber spring cups (CBC2517) in place and intact appears to be a rare occurrence.  They are often missing, damaged or mislocated, evidence of previous mechanics working in the area who didn't understand how the support goes together.  Even if the parts were installed properly, they are often severely deteriorated, sometimes to the point where there's little evidence they were ever there beyond a puddle of rubbery goo in the bottom of the spring support.  Some people claim their original parts were made of foam rubber, but apparently this is a material breakdown of the solid British rubber that makes it crumble so as to appear to be a deteriorating foam material.

To properly install a new rubber bushing requires removal of the spring support; you cannot simply jam the rubber bushing in from below.  With the spring support removed, install the rubber spool into the center boss so that one lip of the spool is on top of the support and one lip is within the recessed opening on the bottom.  It should be securely snapped in place in the boss.

If you are disgusted with the lack of durability of the spring cups, you can easily make substitutes by slitting rubber or vinyl tubing lengthwise and slipping it over the end coils.  Note that there are supposed to be spring cups on both ends of the spring, but apparently the upper one is difficult to get in so mechanics leave it out.  John Whitford, installing a new CCC6759 spring, says, "There were seats on both ends of the spring I pulled out.  The top one had been badly mangled by the motion.  I left off the top seat when I refit the spring.  I tried to fit it (by itself) around the raised part of the spring retainer and it was stretched and distorted when I got it all the way around.  I'm sure the spring popped out of the old one and then chopped it up.  Everything went back together just like the book and as of the first test, I'm clunkless."  Maybe the new spring was designed long enough to be used without the upper cup.

Paul Hackbart notes that John's Cars (page 717) offers replacement bushings and spring cups: "The transmission mount bushing from John's Cars is no different in design.  Both the bushing and the cup at the end of spring are for sale in polyurethane."  Polyurethane would seem too stiff for the bushing, but LaRue Boyce says, "I put in the John's Car bushing last month and it works great."  Since this bushing must be squished to be installed in the support boss, having it made of something as stiff as polyurethane would obviously make it more difficult to install.  Boyce adds, "...it is a little difficult.  I tried a vice, etc., but the only way I could get it in was to use lots of oil on the bushing and angle it in and press with a flat screwdriver.  Not very scientific but it finally went in.  Mine works great and I have no complaints, much better than the handful of part that fell out.  It appears to be made of the same stuff as John's steering rack bushings."  Note that, if you must lube it to get it in, it'd probably be a good idea to use a special lubricant made for polyurethane since some hydrocarbons will attack polyurethane.  Hackbart adds, "The trans. mount bushing from John's Car's does not come with that special red grease used with polyurethane however.  It is the same type of grease included with rebuild kits for brakes; you can get it at any auto parts store."

XK's Unlimited (page 697) also offers polyurethane spring buffers and center bushings.

POLY BUSHING FAILURES: Paul Hackbart also reports on a failure mode of the John's Cars bushing.  If the transmission is forced to the upper limit of travel (such as by running over something that hits the bottom of the tranny and knocks it upward), the washer (double washer on the GM400 mount) at the bottom of the post --which is supposed to provide a bump stop limit to upward travel by hitting the bottom end of the bushing --can actually push the center portion of the bushing right through the boss on the spring support, shearing off the outer flange of the polyurethane bushing and leaving it rattling around the bottom of the post.

This problem may actually occur with the stock rubber bushings as well, we just wouldn't know it because they end up in too many pieces to figure out what happened.  Such shear damage could probably be avoided with either type bushing by replacing the bottom washer with a fender washer with a larger OD, so that it contacts the full surface of the end of the bushing rather than just the center portion of it.  Since the outer portion of the flange will be put in simple compression in such a configuration, it should render the bushing safe from shear damage.  Note that the washer used shouldn't be too big or it might contact the inside surface of the "dome" on the tie plate and make noise.

Note also that the reason the GM400 mount uses a double washer is probably to limit the upward travel to about 1/16" less than it would be with a flat washer, so if you're installing a flat fender washer you should do something to similarly reduce upward travel.  One idea would be to cut the sleeve on the post about 1/16" shorter and install a small 1/16" thick washer on the post under the flat fender washer (just above the tie plate), which would work.  Another idea would be to cut a large rubber disk out of a truck tire inner tube, put a hole in the center, and install it on the post around the lower sleeve.  That way, when the transmission moves upward, the flat washer will hit the bottom end of the bushing with a thin layer of rubber in between, softening the impact and limiting the upward movement.  Most of the time, this rubber disk will simply sit on top of the bottom washer and do nothing.  If the hole in the rubber disk is made just a hair smaller than the OD of the sleeve, it can be pushed onto the sleeve and will stay in place by itself while you install the rest of the parts.

TRANSMISSION MOUNT SPRINGS: Mike Morrin: "The BW12, GM400 and manual springs are different parts; the BW12 spring is painted black/yellow, the GM400 spring is painted black/red.  The manual transmission spring is black/blue." See more info on the GM400 spring on page 346.

This author owns a car that came with a GM400 transmission, so the section on that mount is more comprehensive than this one on the BW transmission mount.  The concept behind the BW mount is obviously similar to the mount used in the later GM400 cars, so it is recommended that the BW owner go ahead and read the section on the GM400 transmission mount and study the illustration.  Maybe later versions of this book will contain a similar illustration of the BW mount.

We're not totally helpless on the BW mount, though; following are some notes.  While the center post in the GM400 mount is attached to the transmission with two bolts through an aluminum base plate, the center post for the BW is a simple double-ended bolt that threads directly into the transmission case.  A dish-shaped spring seat is held in place by the BW post, while the base plate of the GM400 post serves as its upper spring seat.  Since the BW post doesn't have the shoulder that the GM400 post has, an additional sleeve must be used above the "special washer" to provide the proper shape for the bushing to slide up and down against.  Fig. 1.7 on page 24 of the Haynes manual, as is typical, leaves one of the two sleeves and the special washer out altogether.  However, Fig. 1.12 on page 29, although showing the mount for a manual transmission, shows the two sleeves and special bushing correctly.

The upper end of the rubber bushing impacting the base plate of the GM400 post provides a downward bump stop limit to the mount's travel, but the BW post doesn't have a base plate so a special "double washer" is installed between the uppermost sleeve and the hex on the post itself to serve as a bump stop.  As shown in the illustration on page 345, the surface of the GM400 base plate is not flat but rather a bit conical, perhaps to soften the blow when the rubber bushing hits it.  The double washer used at the top of the BW mount has a similar shape, as Mike Morrin describes: "It is 2 washers spot welded together, the first is a 1/8" thick flat washer with 1/2" ID which fits the spigot, and a 2" OD.  The second has a 3/4" ID which just fits over the sleeve, a 2" OD.  The second washer however has a profiled thickness which is 1/4" thick near the centre and tapers down to a thickness of 1/8", 1/4" from the outside edge, and is flat from there out.  The same part is used on the BW66 in the XJ6."

Don't get confused by the various diagrams and exploded views, many of which are incorrect.  Mike Morrin says, "The problem is that the XJ-S and e-type parts books show the double washer on the top, but the XJ12 parts book shows the double washer on the bottom.  I have seen them assembled both ways."  Fig. 1.7 in the Haynes manual likewise incorrectly shows the double washer at the bottom.

Both the GM400 and the BW mount schemes have a washer at the bottom end of the post to serve as an upward bump stop limit to the mount's travel.  The one on the GM400 is a "double washer", but it's not like the one described above; it's a simple matter of two flat washers welded together.  The bottom washer installed on the BW post is a simple flat washer.

I'm sure you've been following all that perfectly, so I don't need to explain how to assemble the mount --but I will anyway.  For cars fitted with the BW automatic, the double washer must be positioned on the post before the spring support is installed, since it cannot be inserted through the bushing later.  Mike Morrin says, "I sat the double washer on top of the bushing"; this may be an excellent method, since the spring support isn't all that heavy and if the double washer falls off you can simply try it again.  After the spring support is bolted in and the jack is removed so the tranny is sitting on it, the order of parts installed on the post is sleeve, rounded-edge washer, sleeve, double washer, collision plate, nut.

The Borg-Warner transmission mount was complex enough, but when the same idea was adapted to hold up the GM400 transmission it got even more confusing.  A picture is worth a thousand words here.  Exploded views abound but many seem to be missing a few parts, which doesn't help someone trying to figure out how it goes together.  Figure 16 is a section drawing of the assembly, in hopes that it will be of some help.

Note that almost everything in this diagram is attached to the transmission itself, which means it moves up and down with the transmission as it bounces on the spring.  The only parts in this diagram that are motionless relative to the chassis are the spring support, the bushing within it, and the bottom coil of the spring.  There is a major support plate rearward of the spring support that is not shown in this diagram for clarity, but it's one of the most obvious things in your way when you're under the car.

Also note that the two rearward arms on the spring support attach to the support plate with 1" spacers.

SPRING: Michael Neal reports that the GM400 tranny support spring (CAC2327) does not hold up well, and recommends it be replaced every 30,000 miles (when the tranny fluid and filter are supposed to be changed).  Apparently it gets weaker as it gets older.

Peter Cohen reports that the springs changed part numbers a few times, perhaps indicating Jaguar's attempts to improve this thing's durability.  "CAC2327 superceded to CAC2327/1 and then superceded to CAC2327/1*"  He reports that the CAC2327/1* "is a thicker coil!!!"

John S. Whitford says, "I bought a new spring because the one I pulled out was only 3 9/16" high.  Jaguar has a new part no.  CCC6759 for the spring and it was exactly 3 3/4" high.  It even had paint codes on it like the front road springs do.  Blue and Violet.  No clue what they mean though."  Neal responds: "That is the number of the only spring I've been using for a few years now.  It is the latest and greatest unit but still collapses easily."

John's Cars (page 717) offers a replacement spring that is supposedly better than the Jaguar springs.  Brian Radovich of John's Cars: "The only difference I spec is a high silicon steel which has a much better tensile life than the Jag bit."

Unfortunately for John's Cars' reputation, the vendor making springs for them reportedly made a batch of the springs out of the wrong wire, making the springs too stiff.  This may seem counterintuitive, but imagine how your car would ride if you installed springs in the suspension that held the car up in the air and the suspension hard against its stops.  This is exactly what happens here; the transmission mount only has about an inch of travel and the spring is supposed to support the weight of the tranny in between the stops (as shown in Figure 16), but the overstrong spring held the transmission up against the upper stop.  This, of course, causes all the vibrations of the engine/transmission assembly to be conducted directly into the chassis.  Owners who installed the faulty John's Cars spring have had to disassemble their transmission mounts to reinstall the stock spring.  A stiffer spring could be used provided it is also shorter so that it still holds the transmission in the correct position, but such was not the case with this spring.

Radovich found the problem and corrected it, so you should now be able to get a usable spring from John's Cars: "I will warranty any spring I have sold - and any poly mounts that have suffered as a result."

GOT A COUPLE EXTRA WASHERS? There have been several reports of washers being found between the vertical post and the housing of the transmission (see Figure 16).  Reportedly, with the mount assembled correctly it was still possible for the forward U-joint on the drive shaft to hit the support plate, causing a "clunk".  The washers were added between the post and the transmission housing to hoist the transmission by the thickness of the washers, just enough to eliminate the clunk.

GM400 TRANSMISSION MOUNT REASSEMBLY: The two rearmost pan bolts should be double-ended bolts with the head in the middle, so that after installing the pan there are studs available for holding the forward bracket in place.  If such bolts are missing and unavailable, normal bolts can be used by inserting suitable washers between the bracket and the pan.  The washers should total 3/16" thick.  A better idea might be to thread nuts onto studs, screw the studs into the tranny, and then tighten the nuts to hold the pan on securely while leaving the other end of the stud to hold the tie plate in place with a second nut.

While apart, the spring support (CAC2438) should be cleaned to remove all the crud that has collected in it.  The crud often appears to be the dissolved remains of the original rubber parts, but we will endeavor not to draw any conclusions about Jaguar's materials engineers.  The crud must be removed to allow the spring and lower spring cup to seat

The transmission must be jacked all the way up into the tunnel before the spring support is installed.  Once the spring support is securely bolted into place, then the jack can be lowered, allowing the transmission to sit on the spring and the center post to protrude through the bottom.

Easier said than done, of course.  With the transmission jacked up hard against the tunnel, bolting the spring support in place may still be difficult.  Paul Hackbart came up with a nifty solution, but you need to have one of the better floor jacks to do it: "Larger jacks have a removable/floating circular dish piece that raises the car.  Well (Dummy!) simply remove disk leaving 3/4-1" hole.  The long bolt goes straight through the hole as the mount is jacked/pressed up and is perfectly balanced allowing you to tighten all 4 mounting bracket bolts.  So, allow one jack and 2x4 to hold up tranny under sump and your larger one with dish removed exposing hole to jack up mount."

Once the spring support is bolted in and supporting the tranny and the jacks have been removed, the assembly of the parts on the center post is as follows: the first item to be installed should be a special washer that has rounded edges, C29011; it will need to be crammed into the rubber bushing somewhat.  Next is the sleeve, C30157.  Third is a part that looks like two washers welded together; it should be installed with the larger opening facing upward.  Then the tie plate is installed, followed by the large self-locking nut; there is no washer directly under the nut.

If the special washer C29011 is missing, a 1/2" splitring lock washer bent flat will serve.

Two small spacers should be installed between the tie plate and the forward bracket.  If they are missing, 3/8" washers totaling 1/4" in thickness may be used.

After assembly, there should be no more than 3/4" between the tie plate and the bottom of the spring support.  Check that the transmission moves freely on the mount; since the spring is soft, you should be able to bounce the entire engine/transmission assembly up and down a little with your hands.  If it appears to be immovable, something is not right.  It also should not clunk when moved.

Gerry Halpern had a howling noise coming from the transmission area on acceleration. "I got a copy of the assy drawing from a local parts guy and reinspected it again this weekend, frankly hoping to find somthing that I had installed incorrectly.  Alas, I couldn't find a thing wrong.  Laying there on my back looking up at the trans mount I pushed upward to make sure that I got movement; sure enough, it seemed to move OK.  However, I decided to loosen the 4 bolts holding the mount, then moved the trans up and down.  I could see the mount move and realign itself.  Voilà! I could now move the trans quite freely up and down.  I tightened the mount bolts and sure enough problem solved.  Point to be made is that the trans mount should be positioned so that the mount can be moved easily up and down against the spring pressure.  Two of the bolts are awkward to get at with the exhaust in place and there is a great deal of tolerence in the bracket slots making it easy to misalign."

Keeping in mind that the engine/transmission is entirely supported and positioned by the two motor mounts and the transmission mount, misalignment of the transmission support might be due to problems with the motor mounts.  If the transmission support doesn't wanna line up, maybe the thing to do is loosen the motor mounts and see if you can realign them.

VARIATIONS: On page 49 of the Haynes manual, there is a picture labelled "49.5A Aluminum spigot bolted to transmission" (all the photos in the Haynes manual reflect parts from a Daimler Double Six with a GM400 transmission, obviously pre-1985).  The post shown in Figure 16 is steel, so if this spigot is really aluminum it's something different.  It also appears to have the entire external shape of the post incorporated in the post itself, so there's no need for a "special washer" or a sleeve.  Mike Morrin says, "The GM400 mount in the pre-H.E. parts book shows the spigot with the ridge machined into it, there being no part numbers for the "special washer" or sleeve."  If that's actually the case, the reassembly instructions above are correct except that you can leave the special washer and sleeve out of the order.  On the other hand, maybe what you really want to do is find the later design steel post; it's unlikely the design was changed without a good reason.

Sometime in the 90's, the post design was changed again.  This final configuration had the external shape of the early aluminum post so no special washer or sleeve is needed, but it is made of steel.

Paul Hackbart says there also may be a difference between the way the steel posts are constructed.  They all consist of a steel shaft pressed into a cast aluminum base, but some have a set of splines visible around the edge of this press fit.  This may reflect a problem with the shaft breaking loose and turning while the mechanic was trying to tighten or loosen the self-locking nut --but it's also possible that all post assemblies have splines and it's just that some extend up far enough to be visible.

TRANSMISSION MOUNT SUBSTITUTION: If you simply cannot figure out how to get the transmission mount back together despite all the guidance above, there are ways to substitute a more simple and basic mount scheme.  John's Cars (page 717) offers a "no-nonsense" transmission mount, but you might not even need that; Chad Bolles says, "The extension housing for the Turbo 400 in your car is nothing but a Chev part.  On my car I removed all the nuts, bolts, brackets, and the rest of the crap.  I went to Parts America (Western Auto) and found a rear mount that fit a Buick, had two (2) holes in it and one stud.  I then made myself a new rear crossmember, and reassembled the whole deal.  Now I can change trans fluid without removing the rear mount."

Of course, Jaguar didn't provide such an involved mount scheme for nothing.  One of their reasons was that a spring absorbs vibration better than a block of rubber.  Imagine, if you will, how well your car would ride if you took the springs out of the suspension and replaced them with big blocks of rubber.  Dan Jensen says, "I cannot comment on the GM 400 mount offered by John's Cars.  I can comment on the effect of a TH 350 in my '83 XJ6 with the John's Cars rear transmission mount for this unit.  There is noticeably more vibration transferred to the car.  While John's claims this should not be the case (transmission the cause?), I prefer the factory mount."  Other owners, however, claim they cannot feel any degradation in smoothness with the John's Cars mount --perhaps because their original mount was assembled incorrectly!  We'll never know for sure; you'll have to take your own chances if you decide to go this route.

SLIP JOINT ALIGNMENT: Craig Sawyers suggests that when removing the rear suspension, it's easier to just yank the drive shaft apart at the slip joint than to unbolt it from the final drive unit. "There is a pair of arrows stamped on the two halves so you get the splines aligned and end up with a balanced driveshaft.  Both halves are balanced dynamically at the factory.  The arrows are faint; I marked mine before disassembly, before I noticed the arrows after cleaning it up."

UNIVERSAL JOINTS: The XJ-S was clearly not designed with ease of servicing the forward drive shaft U-joint in mind.  Applying a grease gun to the zerk fitting, as well as removing the drive shaft itself, require the transmission mount to be removed; if you have it out anyway, you may wish to address the drive shaft.  However, drive shaft inspection also requires that the main support plate be removed.  Jaguar provided two bolts up within the tunnel to make sure this task was as unpleasant as possible.

According to Chad Bolles, the U-joints in the drive shaft are a GM standard, and Spicer 5-153X or Tru Cross 153 will fit.  The U-joints in the rear axles are also a standard; Spicer 5-160X or Tru Cross 160 will fit.  All of these should be available at your local auto parts store.

Some mechanics claim that having a grease fitting on a U-joint does more harm than good.  In theory, if the seals in the U-joint are any good, it will never need regreasing; if the seals are bad, regreasing won't help for long.  And undisciplined use of a grease gun is the best way to destroy the seals.  Even if you're careful with the gun, it's more than likely that the grease injected will all go to one bearing and leave the other three ungreased; it's a path-of-least-resistance kind of thing.  If you believe all that, you might as well choose replacement U-joints that have no zerk fittings and save a couple bucks.

FLANGE BOLTS: The flange bolts are occasionally found to be loose.  Craig Sawyers: "Yup.  Par for the course.  However, the 15000 mile service for the car says "Check tightness of propshaft coupling bolts", so Jaguar obviously recognises that they loosen.  Actually, I think it more likely that the bolts stretch slightly.  While you're under the car, check the ones at the other end (gearbox).  Betcha they're loose too."

It's also very important that the self-locking feature of the nuts is in good order.  These bolts are too short to attain any sort of anti-rotation action due to bolt stretch, and lock washers aren't used here.  If the nyloc nuts turn too easily on the bolt threads, replace them.

REAR SUSPENSION/DIFFERENTIAL REMOVAL: It's discussed on page 384.

DIFFERENTIAL TYPES: The XJ-S has apparently been fitted with at least two different differentials ("final drive units" for you Brits).  From 1976-1985, the differential was a Salisbury 4HU Powr-Lok that came with either 3.07:1, 3.31:1 (1976-1982), or 2.88:1 (1982-1985) ratios.  From 1985-1987, a 2.88:1 Dana unit was used.

GREASE (ZERK) FITTINGS: Unlike the newer American "low-maintenance" cars, the Jag has zerk fittings all over the suspension.  Periodically it should be gone over with the grease gun, but please be conservative.  It is tempting to grease fittings too often and to pump too much grease, which will destroy the seals or gaiters on the joint.

The following is a list of the grease fittings on the car:

• All six universal joints --good luck getting at the forward one on the drive shaft (see page 348).  The protective covers on the rear axle U-joints have openings for greasing, but they may not line up.  You can relocate them as necessary.
• All four corners of the flat plate under the differential (lower swingarm inner joints).  There are holes in the plate for access to the zerk fittings.
• The needle bearings in the lower pivot joint of the rear hub carriers; the fittings are just inside the rear wheels at the bottom.
• Both front hubs.  The fitting is on the side of the hub near the outer cap.  With some wheel designs, the wheels do not need to be removed.  Rumor has it these fittings have been deleted in later cars.
• Both upper front ball joints --remove the front wheels for access.  If these ball joints have been replaced with XJ40 ball joints, there are no grease fittings.
• Both lower front ball joints.  The fittings point inward, underneath the car.  If these ball joints have been replaced with XJ40 ball joints, there are no grease fittings.
• Steering rack -- see note on page 374.
Also, the rear wheel bearings should be greased by removing the small cap on the hub carrier and spooning a little grease into the hole.  Don't overgrease, because the excess merely spins out and coats the inside of your wheels.

The pre-1983 Jaguars also had zerk fittings on the tie rod ends, but the later cars were fitted with "improved" tie rod ends with no such fittings.

The ball joint zerk fittings are designed with a relief system to prevent the grease gun from applying too much pressure.  Under the fitting itself is a plastic washer that covers the relief hole.  When the joint is full of grease, any additional greasing will force the plastic washer to bend, allowing the grease to come out adjacent to the fitting itself.

When installing the zerk fittings on these ball joints, note that overtightening the fitting onto the plastic washer will deform the washer and open the relief hole.

Michael Neal sends this tip on lubricating the lower ball joint: "If the grease comes out from behind the plastic washer as soon as you apply it then the passage is plugged.  The best way to clean the passage is to remove the lower plate and zerk fitting.  Ream out the passage and apply some grease to the cup before reassembling.  The grease in the passage hardens after a relatively short amount of time and plugs the passage."  It is possible to remove this cup and clean it out without getting involved in the access and rebuild procedures discussed on page 366; Put a jack under the spring pan on the A-arm and jack it up, bend back the locking tabs and unbolt the cup, clean it out, regrease, and bolt it back on with the same shims in place.

Craig Sawyers pointed out that it might also help to unload the ball joint.  James Berry says, "The grease finally went in, as Craig Sawyers suggested, if the car is jacked and the weight is taken off the hub.  With the grease gun attached to the zerk, under pressure, the hub was moved right and left until finally the grease gave up and went where it was supposed to (I think)."  It can be surprisingly difficult to get grease into this joint, even with the taper pin disconnected from the hub carrier!  The pressure of the grease itself tends to press the ball against the upper ball seat, totally sealing off the path the grease needs to pass through.  It may work best to have the weight of the car on the wheels and turn the steering back and forth while greasing -- if you can figure out how to accomplish that.

See the note on lubricating the water pump on page 212.

Don't overlook the zerk fittings themselves as a possible source of trouble.  Each zerk fitting has a tiny spring-loaded ball check valve to allow grease in but not out.  It is susceptible to corrosion and jamming.  They are also easily damaged by impact.

RIDE HEIGHT: XJ-S owners are often concerned about whether the car is actually supposed to sit that low, or if something is wrong.  The ROM describes a check, but it presumes you have original tires with full tread.  It also presumes you have "slip plates", devices you set the front tires on so they can slide around and not bind the suspension travel.  The following is a derived procedure that subtracts the tire rolling diameter out of the equation in order to determine if your car is sitting at the "correct" ride height for the tires you have on it, and all it requires is a level section of concrete.

Position the car on level ground with nobody in it, no heavy stuff inside or in the trunk, a full tank of gas, the emergency brake off and the shifter in N.  Push the car back and forth a few feet.  When pushing rearwards, push on the front bumper and deliberately bounce the front of the car a little while pushing.  When pushing forwards, push the rear bumper and deliberately bounce that end as well.  This is to make sure the car is fully settled in its position.

Measure the height to the center of the front wheels.  With any luck, they should be the same, but if they vary slightly determine the average.

Subtract 6-3/8" from this height.  This gives you the correct height above the ground for the flat bottom of the cross member between the front wheels.

If all four tires are the same, use the same front wheel center measurement (do not measure the height of the center of the rear wheels) and subtract 4-7/8".  This will give you the correct height above the ground for the edges of the plate between the rear wheels with a full tank of gas.  If all four tires are not the same, what do you care what the correct ride height is?

So much for the "correct" ride height.  Now, to describe what you actually have, a story from B.  J.  Kroppe: "My former supervisor (a Jaguar employee) did vehicle packaging for the F-Type.  He started with XJ-S drawings and came across some things which didn't add up.  So he went to the assembly plant and measured some XJ-S vehicles and compared them to the drawings.  He discovered that the cars being produced (this was mid-late 1980's) were very much lower than the drawings said they should be.

"After some investigating he learned that over the years more features had been put on the car, making it heavier, but springs had not been changed to accommodate for the added weight, thus causing the lower ride height in the actual cars vs. what the drawings were saying."

In practice, it appears the XJ-S may ride about a half inch lower than the "correct" ride height, even when new.  If yours is significantly lower than that, however, it's probable that either the shocks or the springs need replacing.

SAGGING FRONT END: If your Jag seems to be riding low on the nose end, a likely culprit to check is the front shock absorbers.  The XJ-S uses gas shocks, in which the damping fluid is held under pressure by a small amount of gas within the chamber.  A side effect is that the pressure causes the shock to try to extend.  This extending force helps raise the car a little, especially when the suspension is soft.  The Jag was designed for these shocks, and if they lose pressure, the nose sags.  Since the pressure may be lost while the fluid is still present, the low nose may be the first sign of failing shocks.  Of course, the rear shocks are also gas type and may cause the same problem, but it doesn't seem to happen as often.

If the front sags and the shocks aren't the problem, see Craig Sawyers' comments on rust problems on page 372.

SHOCK ABSORBERS: To check the front shocks, jack up the car and remove the front wheel.  From inside the engine compartment, remove the locknut, nut, rubber doughnut and seat from the top of the shock absorber.  Then reach into

The traditional tests of shock absorbers involving pushing the car down and noting its recovery or noting the car's reactions over bumps are not entirely applicable to modern gas shocks.  If a gas shock loses its gas charge, it may still appear to pass these tests; if it still has fluid in it, it will still provide some damping.  The damping effectiveness is greatly reduced, however, and will get much worse over a series of bumps.  And, as noted above, the car's ride height will be affected.  There seems to be no substitute for disconnecting the shocks and checking them by hand.  Checking the rear shocks will require a spring compressor to remove the springs from the shocks.

The original shocks on the XJ-S are Boge.  Shocks are also offered by Unipart, Spax, Armstrong-Girling, Bilstein, Monroe, Gabriel, KYB, and Koni, some of which are actually reasonably priced.  The only consistent reports received by this author regard the Gabriels --consistently negative.  They should probably be avoided, despite their lifetime guarantee.

Monroe, sold by NAPA and many other auto parts outlets in the US, used to offer reasonably-priced, serviceable shocks for the XJ-S.  However, reports are that they came up with the "Sensatrac" design and it went to their heads, and their prices are no longer reasonable.

Terry's Jaguar Parts (page 696) offers some "competition gas-filled shock absorbers" with adjustable spring supports and spherical bearing mounts.

Matthias Fouquet-Lapar points out that Bilstein is now online:

CLUNKS -FRONT: If something in the front goes "clunk" when you drive over a bump, check the rubber bushings on the top of the front shock absorbers.  British non-metallics again.  Any generic rubber shock bushing will do, and will do better than the original.  David Littlefield says, "Generic replacement bushings are available in the "Help!" section of your local auto parts store.  Look for the area with a variety of parts on red cards.  The part number is 31018 and they come two to a pack.  The pack also says "Ford/Mercury" on it, so if you can't find the "Help!" products, perhaps you can ask for a Ford/Mercury replacement.  You will need two cards (or four bushings altogether).  I paid $2.58 per card at Pep Boys.  I would describe them as being about the size and shape of a medium sized mushroom cap; only, of course, with a hole through the center.

"Replacement is a breeze.  I did both sides in a little over an hour.  The biggest operations are jacking up the car, removing the tire, and removing the hinged side of the air filter on each side.  Removing the old bushings and installing the new ones is a straightforward and simple procedure."  Note: you can easily compress and release the shock while you're there, thereby checking that it's in good shape -- see page 355.

"The old bushings were the consistency of foam rubber after five years and about 25,000 miles.  These were Jaguar replacements done after the car had traveled 32,000 miles over four years on the factory installed bushings.

"Bottom line: About $5.00 and an hour and a half of my time for a fix that should hopefully last a long, long time.  This versus about $25 in parts and $75+ in labor to the dealer for a fix that would last, at most, about 30,000 miles."

Note that the XJ-S has steel washers that fit between the bushings and the chassis; purpose unknown, but it won't hurt to put them back in with the new bushings.  Littlefield says, "The real purpose of the washers seems to be to let you know your bushings are bad by clanking around and driving you nuts until you replace them!"

Some people want to know just how much to tighten the nuts when putting in new bushings or new shocks.  The answer: all the way.  The posts on top of the shocks have a shoulder, and the nuts should be tightened until they sit down on this shoulder.

Another common cause of clunks is loose diagonal supports across the top of the engine compartment.  Make sure the bolts at both ends are tight.

Also check for a failed subframe mount.  When the rubber within the mount is torn but still in place it would seem that it shouldn't make any sound, but it does.  There are two doughnut-shaped mounts at the front, and two V-shaped mounts near the steering rack.  If the rubber is torn or otherwise damaged, they should be replaced.

FRONT SUSPENSION CHECK: You may be confident that your front suspension is just fine, but this test is so quick and easy you might as well try it.  Stand beside the car and grab the top of a front tire and shake it vigorously in and out.  If everything is OK, the only thing you will feel is the flexing of the tires, and you will hear nothing.

If you feel any slop, or you hear a "clunk" back and forth, your front suspension is not up to snuff.  You should check the following items, which are discussed in more detail below:

1) Adjustment of the wheel bearings.
2) Condition of the ball joints, upper and lower.
3) Wear groove on bottom of front axle.
4) Bushings at inner end of upper and lower swingarms.
5) Front subframe mounts.

Perform this test and correct any problems noted before having your car aligned.  The repair or replacement of ball joints, tie rod ends, swingarm bushings or subframe mounts normally requires realignment, and it's a shame to have to do it over.

Peter Havas says passing the shake test doesn't necessarily mean all is OK: "The suspension is too heavy to give any accurate indication by shaking it.  Okay, if we're talking metal to metal, then yeah give it a shake.  But a dried out bushing, frozen on the inside won't move.  Bad lower wishbone bushes don't display any bad behaviour at all when pushed around.  I would suggest:

"Uppers: Remove the wheel.  As the bushing is a mushroom shape and protrudes from the yoke of the wishbone, check that the lip holding the metal backing plate is not torn or worn to the point that you can peel it back from the plate.  The plate at the end should be uniformly held in by the rubber.  Check for obvious cracking, and if the bushing is rust coloured, or seems to seep rust from the mating surfaces around the yoke, or the backing plate.  Insert a longish bar diagonally through the upper wishbone, and flex the fitting to check for any undue movement, water seepage, or cracking.

"Lowers: On the steering wheel side (rhd or lhd) check that the rear bushing is dry.  If it is oil soaked, dig around the nut to see of the bush has become spongy.  For the other bushes: ensure that the wishbone is centered on the fulcrum, and no rubber is protruding around the castellated nut.  Remove the split pin and nut on the front two bushes, and check that there is no rust between the fulcrum (carrier) and the bush.  With the car supported on jack stands, put a length of 2x4 under the lower wishbone and lift while an assistant checks that there is no play in the bushes.  If no assistant is available, feel for play or obvious shifting when the suspension is moved.  Using the same longish bar from the upper test pry the wishbone directly away from the fulcrum to see if there is any play.

"The lower bushes, especially in the front, tend to freeze to the fulcrum and "squash" for lack of a better term.  The constant chaffing heats the rubber so it starts to come out around the nut on the end.  Usually after many miles, the set of the wishbone on the fulcrum is evident.  It really starts to show when someone has changed to nice sticky tires, and the suspension is doing all the work it can.  Because of their tendency to freeze up, they often don't display any movement at all when static, and people tend to pass them up: "If it ain't broke don't fix it.""

It should also be noted that, contrary to common belief, a car will not periodically require realignment for no good reason.  If a car was correctly aligned at one time and no longer is, it is because parts are either worn or damaged, and merely realigning without addressing those parts is unwise.

FRONT HUB REMOVAL: Michael Neal suggests the brake caliper not be removed when pulling the hub, to avoid fiddling with steering lever shims (see page 435).  Instead, unbolt the disk from the hub by inserting a socket through an opening in the dust shield.  Then, remove the hub leaving the disk in place.

That works, but really fiddling with the shims isn't bad.

If you do separate hub and rotor, it's probably a good idea to mark it first so you get it back together the same way.  Couldn't hurt, and may help avoid brake shudder problems.

FRONT WHEEL BEARINGS: According to Chad Bolles, the XJ-S uses standard front wheel bearings, available in any auto parts store.  The pre-1977½ XJ-S outer is an A-2, the inner is an A-6.  The 1977½-up car uses A-13 for the inner, A-12 for the outer.

FRONT WHEEL BEARINGS/SEALS SERVICE INTERVAL --ABS-EQUIPPED CARS: Bruce Segal reports from Canada: "Jaguar was recommending that the front wheel bearing seals be replaced every 15,000 mi (24,000k).  At the same time the bearings should be looked at and replaced if there is any evidence of water ingress.  I don't know if this applied anywhere besides Canada.  We found that after going to this procedure front wheel bearing failures disappeared."

Stefan Schulz provides a possible explanation: "It could well be the likelihood of contaminant ingress that causes Jaguar to specify the change interval.  The grease seal at the inside of the front hubs was changed with the advent of ABS.  The pre-ABS grease seal looks like it will properly do the job, since it sits firm in the hub casing and its sealing lip rotates (and presumably experiences friction and wear) over the relatively smooth surface of the stub axle.  The post-ABS

"I have had my XJ-S for almost three years and 42,000 miles now.  R&R'd stub axles and front wheel bearings when I bought it and bearings again about 10,000 miles ago.  They needed it."

Segal again: "In my environment (winter, salt, water ) the new type seals do not provide a long term solution --thus Jaguar Canada's very short replacement recommendation.  We've found that quite often the bearings had started to rust front the salt water getting past the seal."

If you have an ABS-equipped car, perhaps while you have the hub off for an overhaul it'd be a good idea to polish up the contact surface on the hub to help seal life.

FRONT AXLE WEAR: The inner races of the inner front wheel bearings tend to turn on the axles.  As a result, they eventually wear a groove in the axle, on the bottom where the load is.  This allows the wheel to wobble even when the bearings are adjusted properly, and your Jag starts driving like a Pontiac.

To check for problems, remove the front hubs and check the stub axles for a wear groove.  Run your fingernail along the bottom of the axle from the upright outward.  If your fingernail catches at all, the axle should be replaced.

According to Richard Griffiths, the inner race is supposed to rotate on the axle.  This distributes the wear evenly around the inner race rather than concentrating it on the bottom.  "With proper lubrication, heat treat and tolerances etc., the effect of a "walking" inner race on the axle is a beautiful mirror-like burnished surface, not galling and wear as some have noted."

Well, there's little an owner can do about heat treat or tolerances, and on the XJ-S inner race rotation is clearly a problem --and bearing wear is not a problem.  So it makes sense to ensure that the inner races will not turn by using Loctite 640 or some similar high-strength bearing retaining substance.  This may shorten the life of the bearing by some negligible amount according to some engineer's theories, but in the real world it will positively eliminate the wear on the stub axle.  Use it on the inner race of the outer bearing, too, since it has been known to have the same problem.  Adjust the front wheel bearings as described below.

FRONT WHEEL BEARING ADJUSTMENT: Section 60.25.13 of the ROM, Step #4, indicates that the front hub bearings should be adjusted to attain end float measurement of 0.002"-0.005" (0,05mm-0,15mm).  However, Technical Service Bulletin 57-15 revised the end float spec to 0.001"-0.003".

If you don't happen to have the type of dial indicator needed to measure end float, this author recommends the following procedure: Tighten the retaining nut to perhaps 20 ft-lb while turning the hub to make sure everything is seated properly.  Loosen the nut then spin it back on until it seats, normally a very distinct point; continue to tighten about 1/10 of a turn while turning the hub.  Fit the lock and install the cotter pin.

This may seem tight, and in fact may be tighter than the official Jaguar procedure (measuring end play) would result in. Any bearing expert will tell you that proper operation of a roller bearing requires some preload.  When tight, the weight of the car is distributed among the rollers.  When loose, the slop allows the load to be taken by only one or two rollers at a time, and the unloaded rollers may slide rather than roll.

Another method that has been suggested is to tighten the nut to 25 ft-lb while rotating the hub and then back the nut off one flat.

If you're using Loctite on the inner races as suggested above, you might opt to apply the Loctite to the inboard race, assemble, tighten the nut to 25 ft-lb while rotating the hub and leave it there long enough for the Loctite to set.  Then pull the nut and outboard inner race back out, apply Loctite there, and then do your final assembly and adjustment.

Note that having the bearings adjusted too loosely -- as well as having a grooved front axle, as described above -- would be detrimental to seal life.  And the seals on the ABS-equipped cars may be marginal already, as mentioned above.

FRONT WHEEL BEARING CAPS: Apparently, some bearing caps are a total seal, while others have a small hole in the middle.  It is suggested that if you have wheels that don't keep dirt out of this area, put a small piece of aluminum tape over the hole.  Or, just pry it off and take it down to the local auto parts store and buy a generic replacement.

CHECKING OF BALL JOINTS AND TIE ROD ENDS: To test joints such as these, it is helpful to find a convenient way to "shake" them, or to move them in such a way that will cause them to slop one way and then the other.  In the case of tie rod ends, this is easily done by moving the steering wheel back and forth just a little.  With ball joints, if the front tire shaking described under FRONT SUSPENSION CHECK on page 362 caused a "clunk", that same motion will work for this test.

This test requires two people.  Place a single finger on the joint in question in such a way that one side of the finger is against the hardware on one side of the joint, and the other side of the finger is against the other side.  While holding this position (may be difficult, since the car should be sitting on its wheels) another person should provide the shaking motion.  If the joint is OK, no motion can be felt between the two parts.  If the joint is loose, a human finger will easily detect the slop.  Typically, any slop at all is unacceptable, the joint should be replaced.

With either ball joints or tie rod ends, though, the more common indication that the joint needs replacement is that the protective boot is torn open.  On the joints on most cars, the boot is not replaceable, and the joint will last as long as the boot --so when the boot goes is when the joint gets replaced.  This is true of the Jaguar tie rod ends as well, but not necessarily the ball joints; since they have replaceable boots, it's possible to keep replacing the boots until the joint itself wears out.

ANTI-SEIZE COMPOUND: See description on page 29.  This note is to point out that many suspension components involve tapered fits, such as the ball joints and the front axle in the hub carrier.  It is suggested that anti-seize compound be used on the tapers themselves as well as the threaded nuts.  It does no harm, and can make the assembly much easier to get apart in the future.  In tapered fit applications, care should be taken to ensure the entire fitting is thinly coated, since the anti-seize compound will not be spread during assembly as it is on threads.

BALL JOINT GAITERS: The gaiter used on the original Jaguar ball joints is a Rube Goldberg assembly in itself, and the parts are available separately.  The gaiter itself (C43216) is a clear flexible plastic item, with a steel ring molded into it to make the small opening fit snugly around the ball shaft.  The gaiter fits into a plastic collar (C22970) which the Haynes manual calls an "insert", and a rubber ring (C22969 --looks like a skinny O-ring) fits into a groove on the gaiter to hold it snugly into this plastic collar.  The plastic collar snaps onto the ball joint itself.  If you are replacing the gaiter and don't have a rubber ring, you can simply tie the gaiter to the plastic collar with some wire.  The same gaiter assembly is used on both upper and lower ball joints.

Note that the plastic collar only goes on one way.  There is a barely-perceptible ridge around the ID on one side, and that side must be installed toward the ball joint.  The ridge snaps into a groove on the ball joint, leaving the collar situated such that it can be rotated on the groove.  If you try to install it upside down, you will have to jam it hard against the housing and you may still not manage to get it to snap into place correctly.

In the Haynes manual, Chapter 11, Section 10, steps 2 and 3 tell you to remove the retaining ring, gaiter, and collar separately.  You may be able to remove these three items together as one part --or as a handful of chunks, as is typical.  However, during reassembly it may be necessary to install them separately because the collar can be a bit of a challenge to get snapped onto the ball joint.

This author's experience is that this transparent gaiter has a life expectancy of less than five years.  The clear plastic turns dark brown, then rots and falls out in crumbs.  As with any grease-filled assembly protected by a boot, once the gaiter rips open and sand and water get in, the ball joint itself is quickly ruined.  Since the gaiters are available separately, you can make the ball joints last almost indefinitely by replacing the gaiters before the old ones get rotten and rip open.

The gaiter provided in the QH lower ball joint rebuild kit (see below) is different than the original.  It is a solid black rubber item with no metal reinforcement.  A metal clip is provided in the kit to be used in place of the rubber ring on the large opening.  The QH kit does not include a new plastic collar, which leads to a question: are you supposed to reuse the original plastic collar, or are you supposed to use this gaiter without the collar?  It really doesn't work well either way.  Here's what seems to work best: using a small pair of snips, carefully trim the flange on the side of the collar that ends up inside the gaitor down to about half its original breadth.  Now the black rubber gaiter will fit it properly.

The black gaiters in the QH kits are also British, and don't seem to last much longer than the clear plastic Jaguar originals.  They dry rot and start cracking at the seams.  In addition, they are rather poorly designed; they are a simple dome shape with a hole in the top, and this shape doesn't really flex properly when the ball joint is swivelled to one or the other extreme position.  The pulling to one side tends to pull the small hole around the tapered post hard enough to stretch it open and allow dirt to get in.  Fortunately, this gaiter works well enough in the nearly centered positions where the joint spends 99% of its time.

Chuck Sparks suggests that a thin layer of red Girling "rubber grease" (see the discussion on brake caliper assembly on page 428) be applied to the inside surface of the gaiters prior to assembly.  The idea is that this coating might help keep the grease from your grease gun from contacting the rubber the gaiter is made of.  Since the two may not be compatible, keeping them apart may make the gaiter last longer.  Well, maybe a shaky theory, but applying the red grease couldn't hurt.

There are better solutions to the gaiter situation here.  One would be to find a non-British gaitor from some other application that fits.  Mike McLaughlin says, "Once again I'm reminded of a product out of marine catalogs...  There are available several sizes of black, flexible bellows that may be far superior to the automotive product.  They are used to route the marine steering arm, throttle and gearshift cable ass'ys through bulkheads to the outboard engine and in some applications, house a u-joint and/or exhaust gasses to the outdrive (volvo, mercruiser).  A poke about in a marine supply house may well reveal the ideal product..."

If you can't find a good gaitor that fits, you can fabricate your own gaiters from shoe leather or inner tubes or something.  It's really not difficult, and it's especially not difficult to do better than the OEM items.

The best solution, though, is to replace the ball joints in entirety with the XJ40 items as described on page 368.

LOWER BALL JOINT ACCESS: The overhaul procedure in 60.15.13 says to disconnect the brake line and the tie rod end.  Both are unnecessary unless you really prefer to work on the bench.  Obviously you need to be careful not to stress the brake line.

The Haynes manual, Chapter 11, Section 10, Step 1 tells you to remove the stub axle carrier as described in Section 8.  Section 8 tells you to remove the brake caliper and the hub/disk assembly, both of which are unnecessary for ball joint work.  It also suggests separating the upper ball joint from the stub axle carrier, but if you're not working on that ball joint at this time it would obviously be much easier to separate it from the A-arm by removing the two bolts and keeping track of the alignment shims.

You can pretty much ignore the directions in the repair manuals and simply follow the following steps.  Obviously, start by putting the front of the car on jack stands and removing the road wheel.  The steering must be turned back and forth a couple of times, so it's really easier (and safer) to lift the entire front end of the car and place on stands rather than trying to lift just one corner.  Note that the car will probably get lifted off those jack stands at various points in this process and set back down on them.

Once the lower ball joint is apart, there will be nothing to prevent the road spring from snapping the lower swingarm downward around its inner mount bushings.  To keep the car's weight on that spring, support the suspension with a jack under the outer corner of the spring pan on the lower A-arm.  Stay away from the lower ball joint.

Before disconnecting the upper ball joint, you need to make sure there's no load on it.  This is important when taking it apart, but it's even more important when reassembling; it's really difficult to insert the bolts in the holes while lifting the car with one hand!  If the rubber bumpers in the upper A-arm are on their stops, the road spring may be pulling the A-arms down and applying tension to the upper ball joint.  Jack the lower A-arm up until the spring is compressed far

Once you know the upper ball joint is unloaded, separate the hub carrier from the upper A-arm.  You can remove the nut and use a ball joint separator to pop the tapered pin loose from the hub carrier, but if you're not planning on servicing that upper ball joint it's easier to simply remove the two bolts holding the joint to the A-arm (make sure to note where the alignment shims go).  You'll need to turn the steering a bit towards that side to get the outboard bolt out.

Tilt the top end of the hub carrier outward to get access to the nut on the lower joint ball pin.  Loosen the nut a few turns but don't remove it.  You need to loosen the nut far enough to get past the nyloc insert so the nut turns freely; once the tapered pin is popped loose it's free to spin, which may make it difficult to remove the nut if it won't spin easily on the threads.

Use of a fork-type ball joint separator on the lower joint will not only destroy the old gaiter, but the plastic ring and the upper ball seat as well.  The fork type separator doesn't work very well here anyway; better to have the screw-type separator on hand.  Even better, usually you can get it apart without using any separator tool; jam something between the inner corner of the hub carrier (right next to the lower ball joint) and the A-arm, and forcefully rock the upper end of the hub carrier outward.  Once it pops loose, the hub carrier will fall, and if it still has the brake assembly on it it's quite heavy; that's why you loosened that nut but didn't remove it!

If you're careful, you can accomplish all this without disconnecting the tie rod or the brake line; it might help to turn the steering wheel one way or the other.  Of course, this implies you're willing to rebuild the ball joint right there.  If you prefer to carry the hub carrier to the bench, obviously you'll need to disconnect the tie rod and brake line and bleed the brakes once you've reassembled everything.

If you separated the upper end by unbolting the ball joint, use one of the upper ball joint bolts to connect the inner end of the upper ball joint to the outer holes in the upper A-arm.  This provides a convenient support for the hub carrier once the lower ball joint is apart.  If you popped the pin loose at the upper ball joint, you can slip it back together and install the nut loosely, or use more conventional means such as hanging the hub carrier with wire.  Once the hub carrier is supported, you can remove the nut on the lower ball pin entirely and proceed to rebuild the ball joint.

LOWER BALL JOINT REBUILDING: The original lower ball joint is a rebuildable assembly, with parts books showing part numbers for the individual components; apparently there is no single part number for the overall assembly. Before the advent of the XJ40, Jaguar offered a rebuild kit for the lower ball joint, part number 12803.  That's not a misprint; for some reason, there is no C or other letters before the number.

The lower ball joint from the XJ40 (the 1988-on XJ6) is a one-piece throwaway item (see below) that will replace the entire ball joint assembly on the XJ-S, and costs less than the Jaguar rebuild kit.  Hence, Jaguar reportedly no longer makes such a kit, and authorized repair shops merely replace the joint with the XJ40 item.

However, an aftermarket parts company, Quinton Hazell, makes a rebuild kit for the original rebuildable ball joint; the part number is QSJ221RK or something like that.  QH's prices for this kit are much more reasonable than the Jaguar parts prices ever were, and it is cheaper to use this kit to rebuild your ball joint than to install the new XJ40 unit.  It's still a better idea to go with the XJ40 joint, though, because it comes with a better gaiter.

The original, rebuildable lower ball joint is assembled with shims to provide a properly snug fit between the ball and the socket.  It should be noted that these shims are intended to provide a proper fit at assembly, not for removing the slop from a worn joint.  If a joint develops slop, it should be rebuilt with new parts or replaced entirely, not merely readjusted.

The ROM, Section 60.15.04, describes re-shimming the lower ball joint without disconnecting it from the stub axle carrier, but frankly this is questionable; you will have a difficult time determining the correct snugness of that ball joint without being able to manipulate the ball pin by hand.  Besides, you probably need to replace the gaiter while you're in

When rebuilding the lower ball joint, don't lose the shims that come out.  Although the QH kit includes shims, there may not be enough to provide all new shims.

Bernard Embden suggests: "I found that, under pressure, grease was spitting out between the shim and one lower ball cup.  Putting a straight edge against the ball joint surface at the knuckle revealed an uneven surface which had to be trued up before completing the rebuild.  I believe that these lower ball joints are subject to a lot of abuse as the car runs over debris, etc.  Checking with a straight edge should be part of any rebuild."

It is recommended that you trial-assemble the ball joint dry (no grease) in order to establish the correct shimming.  It's amazing how grease can make a sloppy joint feel tight.

Thoroughly grease the ball and socket parts prior to final assembly.  Although the joint has a zerk fitting, its use is no substitute for proper greasing at assembly.

LOWER BALL JOINT SUBSTITUTION: As mentioned above, the lower ball joint from the XJ40, part number CAC9937, will replace the original ball joint on the XJ-S perfectly.  This ball joint is made by Lemförder in Germany; the Lemförder part number is 030 260 004 834.  It has no grease fitting, it's not rebuildable and the gaiter is not considered replaceable (not available separately) --but it's still the better choice in ball joints!  The gaiter built onto the Lemförder ball joint is an excellent design, shaped like a bellows to allow the joint to move back and forth without stressing the rubber or pulling open a gap.  It also has metal spring rings at both ends to hold it snugly to the joint.

So, your choice seems to be: replace the gaiters on the original ball joints every five years, or replace the entire joint with the XJ40 part and forget about it for some time -- perhaps ten years anyway.

The XJ40 lower ball joint also provides a bit more clearance for aftermarket wheels.

When installing the XJ40 ball joint, the shims from the original joint are not used.  They were only needed to provide internal clearance in the rebuildable joint.

When replacing the rebuildable ball joint with the XJ40 ball joint, note that the upper ball seat of the original ball joint must be removed.  It's a metal ring, and it actually looks like it could be an integral part of the hub carrier, but it's not; it's pressed in from below.  Charlie Marino suggests using the old ball pin as a tool for removing it; "I placed the ball end of the ballpin on the upper seat from the top and hit downward into the seat with a hammer.  About 4 medium hits drove the seat out through the bottom of the stub axle carrier."

UPPER BALL JOINT REPLACEMENT: The official repair manual calls for "Steering Joint Taper Separator JD.24", but we don't need no steenking separator!  Put the car on jackstands and remove the wheel.  Put a jack and block of wood under the lower ball joint and jack it enough that the rubber bumpers on the upper A-arm are not touching the subframe.  Loosen the nut on the upper ball post several turns, but do not remove it.  Lower the jack so that the rubber bumpers sit on the stops and the full spring force is applied to separating the joint.  If you're lucky and the previous mechanic used anti-seize compound on the taper, you'll hear a pop as it comes loose.  If more difficult, a little judicious tapping on the side of the hub carrier may help.

Make sure to note where the shims are located between the arms and the ball joint.  Even if you plan to have the car aligned, at least it will drive better on the way to the shop.  The shims are supposed to lift right out, but they weren't made quite right; they tend to catch the bolt on the inner corner on the hook-shaped end.  If this corner is filed slightly, reassembly will be easier.

UPPER BALL JOINT SUBSTITUTION: On the original XJ-S upper ball joint C23024, the gaiter C43216, plastic ring C22970 and rubber ring C22969 are exactly the same parts as those on the lower joint -- see the discussion on page 365.  This means the gaiter is replaceable as it is on the lower joint, but it also means it will need replacing on a regular basis.  Other than gaiter replacement, this ball joint is not rebuildable like the lower joint.

As with the lower ball joint, the XJ40 upper ball joint CAC9938 (made by Lemförder) is a better choice; in fact, many parts houses may automatically ship you this part when you order an upper ball joint.  The gaiter on the XJ40 upper ball joint is just like the one on the XJ40 lower ball joint: not replaceable, but a much better design than the XJ-S gaiter.  Like the XJ40 lower ball joint, the XJ40 upper ball joint has no grease fitting.  The Lemförder part number is 027 260 005 834.

UPPER BALL JOINT --SLOPPY MOUNTING: Walt Osborne of Vintage Jag Works (page 697) points out that the original upper ball joint on XJ's was mounted with a pair of long 3/8" bolts while the XJ40 upper ball joint is mounted with long 10mm bolts.  As a result, when the XJ40 upper ball joint is installed in an earlier car using the original bolts, there is about 0.020" slop in where it will get positioned as the bolts are tightened down.

This is not exactly the world's most pressing problem.  Wherever the ball joint is when it is snugged up, having the car aligned will deal with it.  There are only two situations where this slop can have a detrimental effect: 1) If you hit a pothole so hard as to slam the ball joint against one limit of this slop or the other --move it despite how tight the bolts are holding it still --it could affect your camber. 2) If you work on your front suspension for some reason and unbolt the ball joint and reinstall it, it may not end up in exactly the same place.  In either of these cases, we're talking about a worst-case scenario that the ball joint will relocate by 0.020" -- barely noticeable.

However, Osborne also points out that fixing this slop is pretty easy.  Merely drill out the holes in the swingarms to 10mm, file the openings in the four alignment shims per side a hair bigger, and install the XJ40 ball joints with 10mm bolts.

First challenge: finding a 10mm drill bit.  In the US, good luck!  Fortunately, you can forget it.  Mal Stewart reported, and this author has confirmed, that 10mm bolts will fit in the holes in the swingarms without drilling.  They're snug --in a couple of places, I had to polish the inside of a hole a bit with sandpaper --but you certainly won't need to use a 10mm drill bit.  I did opt to chamfer the edge of the hole under the bolt head to make sure the head seated properly.

Second challenge: Finding suitable bolts.  Of course, you could try getting the OEM bolts for an XJ40 from Jaguar.  Osborne suggests using generic 10mm bolts of the correct length with the head of the outboard bolt rounded off for clearance as the original bolt was.

The two bolts are different lengths.  100mm is just about perfect for the inboard bolt; I found that Grainger (page 711) has both 100mm and 105mm bolts, with the 105mm bolts being significantly cheaper!  They work fine, the extra length is no problem.

You'll probably have to buy 80mm bolts for the outer bolts, but 80mm is too long; the correct length for the outboard bolt is about 68mm.  You might get away leaving the bolt 80mm long, but it might catch on the brake disc dust shield near full steering lock, so just to be safe cut the extra off.

You will probably want Grade 8 bolts for this job --but metric bolts are not rated the same way as SAE bolts.  What you want is Class 10.9, which is essentially equivalent to Grade 8.  Don't get confused by metric Class 8.8, that's essentially equivalent to Grade 5.

I had difficulty finding 10mm nuts in Class 10.9, so I used Class 8.8 nuts.  The strength of the nut is nowhere near as important as the strength of the bolt in this application.  The Class 8.8 nuts are available in many places; I found nyloc nuts at Home Depot.

You don't care if the bolts are regular, fine, or extra fine thread as long as the nuts fit the bolts.

I had to file the alignment shims a bit to get them to fall into place properly.  The slots are big enough to fit the 10mm bolts, but it won't fit both at the same time!  The solution was to file the slot on the inboard end of each shim a bit deeper, so it gets a little closer to the other slot.  It took perhaps 30 seconds with a round file.

Both the bolt heads and the nuts I used fit 17mm wrenches.  That's considerably larger than the 9/16" OEM bolts and nuts, and raises clearance concerns with the outer bolt.  After installation and before reinstalling the wheel, have an assistant turn the steering lock-to-lock while you watch the hub carrier rotate around the upper ball joint.  The clearance conditions vary somewhat with suspension extension, so place a floor jack under the lower ball joint, lift it up a bit, and

Here's an interesting option: replace only the inboard bolt on each ball joint with the 10mm bolt, leaving the original 3/8" bolt in the outboard location.  The single 10mm bolt will eliminate all the slop in the horizontal direction and half the slop in the vertical direction --but the horizontal direction is the only direction that affects alignment.  This will save you having to buy 80mm bolts, shorten them and round the head, and worry about clearance.

Bob Higgs has another method: "You can do as I did, that is to take a strip of .010" stainless steel shim, wrap it around the 3/8" bolt making a tube shape and inserting this in the upper ball joint mounting hole.  You can then use the old 3/8" bolts, no drilling no filing no rounding off required."

Sounds simple enough --but Higgs doesn't tell you where to obtain .010" stainless steel shim stock.  You can buy it at Grainger or MSC or similar industrial supply outfits.  It ain't cheap --but if you're looking to save money you could get the non-stainless stuff.  FYI, the ball joints are a bit more than 1-1/8" wide, so that's how long your tubular shims will need to be.

Higgs also fails to mention exactly how you "wrap it around the 3/8" bolt making a tube shape".  This task is definitely easier said than done.  Maybe there's a special tool available somewhere, but if you're working with normal hand tools you'll probably end up wishing you had just sprung for the 10mm bolts.

One option there would be to cut a strip of stainless steel shim stock about 1/4" wide and several inches long and wrap it spirally to form the shim you need.  Since it's just taking up space, the spiral form will work just as well.

Another idea would be to get some thin-walled metal tubing, such as brass tubing from a hobby shop, with an ID of 3/8".  Since the OD of such tubing is usually some even amount larger --the OD of the brass tubing from a hobby shop will be 7/16" even --you can then just use a 7/16" drill bit to ream out the hole in the XJ40 ball joint.  Slide the tubing into the hole and mount the ball joints with the original bolts.

FRONT SWINGARM BUSHING CHECKING: The front swingarm bushings may be checked using similar methods as the ball joints, except that the bushings include some rubber so there will be some slight motion even in a perfectly good joint.  Usually, the best indication that a swingarm bushing is bad is that some of the rubber is hanging out of it.

LOWER SWINGARM INNER BUSHING REPLACEMENT: Craig Sawyers provides some insight into removal of the lower fulcrum shafts on this elite precision automobile: "Be prepared for a very sweaty hour or two.  Get yourself a four pound lump hammer and batter the living daylights out of it.  Be of strong heart and right arm -the SOB's will come out.  They rust into the metal sleeve in the bushes.  Once it starts to move, you will need a long drift to continue driving it through the hole in the suspension (I used a loooong ocket extension I have).

Of course, the bolt will be mushroomed at the end after the abuse you offer it, and you'll need two new ones -they are about £15 each."

"After I spent a cheerful day exercising my arm, and patience, removing mine, I happened to be at the Jag dealer.  I was collecting some parts, and chatting to Colin (the workshop head).  In the background there was this fearful BANG, BANG, BANG then a rest pause, then BANG, BANG...

"Good grief, Colin - what on earth are you guys up to?"

"Front lower wishbone shafts -sometimes takes hours of that treatment before they move.  Sometimes we even have to take it in shifts as each of us tires...."

Uhhhhh, do I even have to suggest that anti-seize compound would be a good idea when reassembling?

Clay Merritt suggests a saw: "Once you drop the crossmember you can get to the fulcrum shafts with a reciprocating blade, then tap them out from inside."

Doug Dwyer presents a counterpoint: "I've done this job on two Jags and the fulcrum shafts came out with a few taps.

If my experience means anything I wouldn't automatically assume that they'll be seized in place."  Actually, being patient and tapping lightly may be the secret, as really beating on it is only likely to swell the shaft and make it more difficult to get out.

SPRING REMOVAL: If you're working on the lower swingarm bushings, trying to adjust the ride height, or any of several other operations, you will need to remove the front road spring --safely.  Needless to say, it is a very strong spring, and care must be taken to either gradually release the compression on it or to hold it securely compressed so that it cannot break loose.

Ideally, you should use a spring compressor that fits this assembly, but that may be difficult to find --the front spring mounts on the XJ-S seem designed to confound most standard spring compressors.  The official Jaguar tool is a threaded device that goes up the middle, but is reportedly so large and bulky that it requires the car be on a lift, not merely on jackstands.

Carlos Artal says, "Get a thick, long threaded rod (size unimportant, but as thick as you can).  Get 6 large washers that will fit on the rod, and are at least 5cm diameter.  Finally; get some nuts for the rod (if the rod is as thick as mine, the nuts were size 16 metric).  I got 4, and you'll see why.

"On the upper part of the x-member, just put some rag under the washers (3) and insert the rod vertically, then insert 2 nuts from the top, so they rest on the washers.

"From the underside, use 2 little blocks of wood, which fit into the "circular pan" the shock base has, and then put on the other 3 washers, and 2 nuts.

"To disassemble, just tighten the lower nuts until you can undo the bolts in the pan."  Then back the nuts down to lower the pan until the spring is completely free.  "Just one warning!; when you think the spring is completely sprung, keep on going, these puppies are big and dangerous (my first one jumped 2 meters!)

"To assemble, with the same setting as above, the problem is that the spring will make the pan wander from side to side.  I used 3 thin rods as "guides" for the entire pan."  Others use long bolts or threaded rod screwed into the holes in the swingarm as guides, but note that having anything threaded tends to make the pan hang up on it; it's better to have something smooth.

Dennis Kindig used a similar procedure, and offers these variations: "You may want to fiddle with a piece of bar stock cut at the proper angle and placed between the washers on the rod and the spring pan to help align the pan with the wishbone.  There is an angled section of cylindrical bar stock on the "official" tool ($420 US, by the way) that accomplishes that.  I also found that wedging the rod (I used a socket stuffed in there) so that it stayed at the outer end of the oval hole in the spring pan gave me more leverage (it pulls to the inside under tension)."

Joe Bialy describes a totally different spring removal method: "Use three pieces of threaded rod about a foot long each.  3/8-24 fine thread.  Remove three pan bolts, install the rod with nuts to hold it all together.  Remove the other 3 bolts.  Slowly and uniformly back out the nuts on the three rods.  The pan will back out with them.  Reverse the process to install."  The problem, of course, is finding threaded rod in fine thread; Bialy says McMaster-Carr (page 711) carries it.

Other suggestions include tying the spring in the loaded position while it's sitting on its wheels and then jacking it up - please be very careful tying it, and make good and sure whatever you use is strong enough for the job.  And keep your body parts outta the way anyway, just in case it breaks loose.

Michael McLaughlin says, "Herein is the no brain / no pain / no danger / no unusual tools (requires two jacks and a nut splitter) front spring liberation.  Find the complete story at:

SHIMS: The steering lever attaches to the hub carrier with two bolts.  At the rear (longer) bolt, there is a shim (it looks like a thin washer) that goes between the steering lever and the brake caliper.  Don't lose it!  Omitting this shim at reassembly screws up your alignment and distorts the steering lever.  See the further discussion on these shims on page 435.

STEERING COLUMN INSTALLATION: If you have lowered your steering column, Rob Reilly sends this tip for reinstallation: "When putting back the steering column use a little rubber cement to hold all the washers in place.  Leave the bolts loose and pull the column back about 1/4" before you tighten them; if you don't, you will get binding in the lower column universal joint and bumpy steering."

STEERING COLUMN: The Jaguar Parts Catalogue lists the "upper steering column" as a safety item; it's designed to collapse in a collision.  Apparently you're not supposed to fiddle with it, just replace it as a unit.  Richard Dowling says there is a plastic section in here designed to absorb energy in a crash: "The plastic shaft appears to be moulded in situ since it has spigots of plastic sticking out of it which lock it in position since they engage in small holes in the tube.  These are effectively shear pins, since a moderate force on the plastic shaft will push it up the tube."

He found his to have been already sheared, he expects as a result of work he was doing in the area.  "It was a year ago so I do not recall exact details, but the jist of it was that at some stage I had probably sheared off the pins trying to get the universal joint splines to line up at the bottom end of the column.  That can be hard work in a very confined space, but I am no Tarzan hence it is obvious that the shear pins are not real strong.

"Most of the mechanism is hidden inside the outer case of the column assembly.  Design details are nonexistent in the ROM, and fig. 11.34 in my Haynes manual is the best illustration.  You can figure out how to pull the complete assembly apart, no rocket science, but it is fiddly.  If the shear pins are shot the column is still useable, since friction tends to hold the plastic shaft in position.  It will not ride up the column, since the universal joint and bearing at the bottom prevent this.  However, when my steering wheel became sloppy ( not dangerously, just a little disconcerting ) I found the bottom bearing had dropped out of the column outer casing since the plastic shaft had migrated downwards.  You can see in Haynes' fig 11.34 a plastic bush just above the splines.  The bush is a push fit in the bottom end of the column outer case, but it can drop out if the shear pins let go.  This appears to be the only problem from failed shear pins.  However, it needs a quick fix because if it drops too far it may bind up the 2 universal joints in the lower part of the steering.

"The fix is to take a wormdrive clip that will clamp on the lip of the bush which is the same OD as the column case.

This way you can almost clamp the lip to the case, but to make it better buy a flimsy clip and try and bend the edge of the worm drive clip down so it acts as a shoulder to go over the lip.  Maybe with a strong clip you could put a few saw cuts around one edge and bend it down easier to make a shoulder.  This is an improvisation with column still in car.  If the column is out of the car some other improvisation will be even more secure."  Another idea might be to use the worm screw clamp to hold another strip of metal securely to the outer diameter of the housing and bend the edges of that strip down over the lip of the bushing to hold it in place.  All of this can probably be done with the column in place, no need to take it out.

"One tedious way to fix this may be to strip the column assembly down again and put a few small screws or roll pins through the tube holes to hold the plastic inner shaft, sufficient to hold the plastic in place while remembering they have to shear in a crash."

STEERING RACK LUBRICATION: According to the John's Cars catalog, using the zerk fitting on the steering rack does more harm than good, and they remove them during their rebuilds.  Others have reported no problems, but obviously one would be well advised not to get carried away with the grease gun.  Stefan Schulz reports: "Perhaps even Jaguar realized that eventually, mine (CBC5708) doesn't have that fitting any more."

STEERING RACK LOWERING: Contrary to the instructions in the manual, the steering rack can be lowered far enough to work on the mount bushings without disconnecting either the hydraulic lines, the tie rods or the steering column.  The only difficult part is access to both ends of the three mounting bolts.

The steering rack is mounted on slotted holes.  You'll have to trust me on this, because they're not slotted far and the entire slot can be hidden behind the flat washers under the bolt heads.  The intent is to be able to position the rack properly with respect to the lower A-arm mounts, and there is a special Jaguar tool used to check for proper position when reinstalling.  Presuming that you don't happen to have this tool laying around the house, it is suggested that you carefully mark the position of the mounting bolts within the slotted holes prior to unbolting the rack.  When reinstalling, simply put it back where it was.

Any time the steering rack is lowered for inspection or repair, it is wise to disconnect the bolts mounting the power steering cooler to the subframe.  The pipes on this unit are very fragile, the hoses are short and often stiffened by age and heat, and a new cooler is of course more than $100.  It can generally be repaired by any reputable radiator shop, however.

Chuck Sparks suggests that, while the rack is down, you spread the bosses on the subframe a bit to ease reinstallation.  Install a piece of 5/16" threaded rod through a boss with a flat washer, two nuts, and another flat washer in the middle.  Spin the nuts outward until they are holding the flat washers against the sides of the boss, then continue to turn them to force the sides apart.

STEERING RACK MOUNT BOSS CRACKING: John Smith suggests you check the front suspension subframe for cracking around the steering rack mount bosses while you have the rack lowered.  "The kerbside (passenger side) mounting was cracked along the inside (closest to car centre) 2 inch vertical weld to the subframe and also the half inch horizontal weld on the subframe lip.  In other words, the inner vertical of the mounting bracket was broken away from the subframe."

Smith's local Jag supplier, as well as others, suggest this cracking is due to the stiffer aftermarket rack mounts.  It can't be directly due to the stiffer mounts, since they won't change the loads on that boss --in fact, they probably reduce the impact stresses since the rack isn't banging around in there as it does with the OEM bushings.  However, the cracks may be caused by installers using the bolts to pull the sides of the bosses in to meet the aftermarket bushings rather than space them properly with 5/16" fender washers.  Or, since the car is actually driveable for a change, the driver may be driving it harder.  Whatever, the possibility of cracked bosses is certainly no excuse for sticking with the crappy OEM bushings; have a welder repair and reinforce those bosses if necessary.

STEERING RACK MOUNT BUSHING REMOVAL: John's Cars offers a rental tool for removing the original bushings from the rack.  It is extremely helpful, especially when working with the rack hanging under the car where a bench press won't help.

You can improvise such a tool using two 3/8" drive sockets (one with an OD a hair smaller than the bushing, one deep and large enough for the bushing to fit inside it), a long 5/16" bolt or piece of threaded rod with nuts and washers.  It's not always a snap, though; getting them to stay aligned and not cock sideways or jam can be a challenge.  John Tompane says, "I was experiencing what others reported, the 'pusher' socket was getting out of line.  My solution -I purchased two bronze thrust bearings at the hardware store for a couple of bucks.  These look like top hats from the side, or a cylinder with a shoulder.  This fit into the 1/2" socket and did two things, one it kept the 1/4" bolt in alignment.  Second, the shoulder rests firmly on the back of the socket providing a solid base to torque the nut/bolt.  Result = worked like a charm.  Without the bearings I wasted hours trying to get the easy one out (passenger side) and quit for the night.  After getting the bearings, all three came out in a snap."

Jim Warren went another route: "I used the two socket method.  I ground the thrust edges of the pusher to remove any roundness.  There is very little of the bushing outer sleeve to push on, and with the factory rounded edges, the socket can easily get cocked slightly and not push squarely."

Another possibility: You can cut through the rubber and remove the guts of the original bushings and then use 1/2" drive sockets with a 1/2" bolt!  Or 3/8" drive sockets with a 3/8" bolt.  Either should hold the tools together and aligned more securely than a 5/16" or 1/4" bolt through 3/8" drive sockets, and obviously you'll have less concerns about strength with the heavier bolts.

Not everyone has to work so hard, though.  Tom Bernett says, "The two socket method worked splendidly for me -no tendency for the pusher socket to get cocked at all.  I don't know if it helped, but after the initial tightening of the bolts/sockets, I gave the bolt head a firm smack with a hammer as a little encouragement to break whatever bond there might be.  This is the kind of job that you expect to be a real problem.  I pictured hours under there with hammers/chisels/drills/saws/etc.  You can imagine my delight as I watched all 3 bushings slowly slide out one by one."

A method to avoid: Some people cut the rubber and center sleeve out, leaving only the outer sleeve, then insert a hacksaw and cut through the sleeve on one side; the sleeve can then be collapsed and removed easily.  If done carefully enough, it appears to work fine, but a small nick on the aluminum boss on the rack can cause a stress crack later.  Using a drill or other means to destroy the original bushing involves similar risks.

Another method to avoid: using a hammer.  You're just asking for damage to that aluminum rack.

An obvious method to avoid: Heating the aluminum up to get the bushings loose.  Unbelieveable as it may seem, some people are willing to try this.  The facts that the housing is aluminum which conducts heat very well, the seals inside are rubber, and a rebuild costs as much as a three-day ocean cruise for two apparently never occurs to them.

STEERING RACK MOUNTS: Even if the original Jaguar steering rack mount bushings in your car are in fine shape, the steering response is awful.  The stock mounts are very soft, which by itself is not necessarily bad.  However, for some reason Jaguar chose to position the mounts parallel to the steering forces, so they are loaded axially (shear) rather than radially (compression).  See Figure 18.  There are bumpers (flat washers with a layer of rubber on one side) on either side of the mounts to limit the side-to-side motion of the rack.  This design results in a nonlinear response: When you turn the wheel gently, the steering is somewhat unresponsive, since the mounts flex and absorb most of the steering motion.  When you turn hard enough that the bumpers are contacted, the steering suddenly becomes much more responsive.  The inconsistency of response makes it difficult to steer smoothly, especially when driving hard; the car seems indecisive about how much it wants to turn.

Besides providing lousy response when new, the OEM mounts are also known for a lack of durability, and of course when they come apart they come apart all at once.  Ray Johnson says, "everything was fine and then the next thing I knew I was tacking a 4200# sailboat down the highway."

On the XJ-S discussion list on the Internet, this author mentioned the possibility that this inconsistent response might actually be dangerous, especially with drivers that never drive hard and therefore are taken by surprise in the first panic situation they encounter.  Of course, the first panic situation may rip the mounts apart --but do you really care exactly why the mounts don't work right in the first panic situation?  Jim Downes responded: "Many (too many) moons ago when I was a student, I worked part-time at a Jag/Rolls dealership in Ireland.  Occasionally, a customer's Jag would be towed in after a very bad crash.  Most customers complained of an apparent loss of directional control during (as Kirby correctly identifies) a 'panic' situation.  In almost every case, the bushings were worn and behaved exactly as described above.  Absolutely all of the senior mechanics there felt that the bushings were dangerous after a few months of use."

The solution is to replace the steering rack mount bushings with ones that are not merely stiffer but of a totally different design.  This modification is so common that virtually every aftermarket business dealing in Jaguar stuff offers a kit.  The John's Cars design (see page 717) subjects the elastomers to compression only, and eliminates the inconsistency in the steering response.  They use polyurethane, making the mounts stiff but not totally rigid.  The entire kit is about $50, and well worth the money.  A similar kit is the Mackay Sure Trak A1598U, available from BPI (see page 692).  XK's unlimited (see page 697) offers a kit of slightly different design made of delrin, but the function is similar.

Folks, please take this recommendation seriously: even if the stock bushings have not yet failed, even if they are brand new, replace them with aftermarket bushings as soon as possible.  If you are determined to keep your car "original", please yank those original junk bushings out and carefully box them away for future concours events, and install some good mounts for any actual driving you may do.  Downes concurs: "Regardless of perceived 'quality' of feel, when I move the wheel expecting a twenty degree turn, that's what I want, not fifteen or twenty five degrees depending on side-loads, braking loads, road camber or any of the other variables that can influence the 'mood' of the original bushings."

The stock assembly includes a sheet metal U-channel that fits around both bushing assemblies on the driver's side, holding the whole mess together as you offer it up to the car.  When you lower the rack, this piece might stay up there; pull it out, it's helpful for installation.  The aftermarket bushing set from John's Cars includes a new one of these pieces -- very nice, since the old one might be a little mangled.

Because there has been some confusion due to inadequate instructions provided with these kits, one thing needs to be made very clear: when these aftermarket bushings are installed, they should fit snugly within the bosses on the subframe.  There should be no gaps or spaces whatsoever.  If the boss is wide enough that the bushing assembly fits with space left over, some 5/16" fender washers should be installed to fill the gaps.  The mounting bolts should be tight, compressing the boss (Slightly! That's why you need to add fender washers if necessary!) onto the ends of the metal tube within the bushing.

Jaguar itself offers a stiffer mount scheme in its "SportsPack", using one normal mount (CAC 1635) and two special ones (CBC 5928 or CBC 9107).  While an improvement, this scheme still maintains the lousy shear-loaded design, and it is still a better idea to get the aftermarket kits instead; they are easier to install (no press fit required, since there is no shear loading) and a good bit cheaper.

The urethane (red) mounts don't last forever, however.  Lee Opausky reports: "Installed 5 or 6 years and 40 M km ago, John's poli bushing failed in the last 3 weeks at a very rapid rate.  The steering wheel yesterday went to a "full half turn/no change in direction" mode from somewhat loose steering 3 weeks ago.  This part was very good to us for many years since it first replaced the "British rubber" and I have no probs with the quality of the part.  What I find intriguing is the rapidity of the failure with practically no warning signs.  3 mos ago I had these guys out when the rack had to be lowered to install a new starter, and a visual did not reveal any signs of fatigue.  Now they are literally mushed with only the outer rim in one piece - like a slice of orange peel.

"The poli bushings were of orange color and gave excellent service for 5 or 6 years.  No oil or other chemical came into contact with these parts (clean car) and all 3 seem to have been affected at the same time to the same extent."  Of course, one wouldn't expect just one or two to be affected; when the rack decided to move sideways, it must take out all three to do it.

Larue Boyce: "I installed John's Cars steering rack bushings in my '91 in in January of 1998 at 98,368 miles.  I replaced them with the black ones from Welch Jaguar in Dec of 2001 at 140,439 miles when I replaced the rack with a rebuilt from Coventry West.  I think the bushings did a great job and were worn out after 42,000 miles along with the heat from the motor and Florida.  The bushings had worn, discolored and the end pieces separated into several "O" s."

So far, durability seems to be an issue in urethane aftermarket mounts but not delrin (grey) mounts, and may be due to this being a poor environment for urethane.  Jim Cantrell says, "The melting point is about 350°F and the maximum recommended service temperature is 250°F.  Above this temperature, the esters boil out of the matrix and brittleness follows.  However, they rate poor in resistance to hydrocarbon exposure, acids, synthetic lubricants and hydraulic fluids.  Could be something there in the engine compartment besides heat that degrades the material."

Bolles suggests that instead of replacing the original mounts, you merely insert washers on either side of them to reduce the side-to-side travel; washers from mag wheel lug nuts work well.  This makes the original mounts last indefinitely, since they hardly move.

Another idea may be to cut out some hard rubber pieces --preferably with some cord for strength, like old tires or drive belts --to install on either side of the original mounts, providing a compression member to restrain the side-to-side motion.  Make sure to fill the space, leave no gaps; for the rack to move at all, it should be compressing material.  You might consider removing the OEM rubber-faced washers on each side of each mount and installing fender washers instead along with a broad flat chunk of hard rubber the same or larger OD as the mounting lug and perhaps 1/4" thick.

Since the three mount bushings work in unison, the stiffness of the rack mount system can be controlled by altering just one, two, or all three mounts.  However, this author recommends you treat all three bushings the same so as to distribute the load equally on all three mount lugs on the rack rather than concentrating the load on one or two lugs.  An alternative idea is to stiffen the two mounts on the driver's side and allow the one on the passenger's side to remain flexible; some suggest this will minimize stresses due to differences in thermal expansion, allowing the passenger's end to "float" a bit while the driver's end remains firmly anchored.  It's not likely there are any significant stresses due to

STEERING RACK MOUNT BOLTS: If you happen to be working on the rack with either the engine or the front subframe out of the car, you may be able to put the bolts in any way you wish.  But for the benefit of those who work on the car later, please install the upper mount bolt on the driver's side from the outside inward, and the lower bolts on both sides from the inside outward.  This makes it much easier to install or remove the rack with the engine and front suspension in the way.

If you must replace the mounting bolts, be careful not to use bolts that are too long.  When complete, be sure the upper bolt on the driver's side does not protrude too close to the engine block, since the engine moves on its mounts and will beat against the bolt.  And the lower bolts should not protrude too closely to the lower A-arms, since they are likewise mounted on rubber and may move during operation.

STEERING RACK REMOVAL: If you have to totally remove the steering rack, one problem is how to remove the pinch bolt that connects the steering column swivel joint to the tower shaft.  Remove the oil filter first, then turn the steering wheel until the pinch bolt is positioned where you can get at it.

Also note that the pinch bolt must be completely removed for the swivel joint to be disconnected from the tower shaft.  The tower shaft has a recess the bolt fits through; merely loosening it will not permit removal.

You might find it helpful to carefully mark the relative position of these parts prior to disassembly.

STEERING RACK TOWER SHAFT SEAL: This seal is prone to leakage.  John's Cars (see page 717) offers an aftermarket seal that is supposedly better than the original.  It better be, it's quite expensive.

Len Olsen offers another option: "OEM or aftermarket kits no longer include original 'steel cup' style seal.  New type frays quickly.  Better than original can be purchased from Autozone, included in kit #7910 (cost $10).

"Power steering kit #7910 is for a 1980 Chevrolet Camaro, 350 V8, 5.7 liters.  The number stamped on actual seal in the kit is '1 PC 7808195', but AutoZone says that as far as they know it is only available as part of kit.  Take my word for it, it is better than original for the XJ-S (or any Jaguar sporting the same rack and pinion assembly) being that it is slightly oversize and "beefier".  It's been in there 18 months, after wearing out 3 other types of seals in quick succession.  Burrs, debris, etc. helped 'do in' the others, but this one's tougher.

"AutoZone had told me that that the unidentified "Powercraft" seal kit #7910 was from a '85 Chev 350ci truck, but it also showed up on their system for a 1980 Chevy Camaro.  Oh well, go figure!  It worked for my Kitty."

Tom Bennett adds another: "Go to your local seal store and ask for an oil seal with the following #22-30-6mm.  The I.D. is 22, O.D. 30 and the height is 6mm; this is 2mm more in height than the Jag "New" style but I can assure you fitting it is no problem at all!  The particular seal I bought was blue and flexible, no idea what the material was, not rubber though!  Cost about $3."  Reportedly, one problem associated with the tower seal is incorrect installation by driving it too far into the housing.  Be sure not to drive it any deeper than it needs to go.

STEERING RACK REBUILDING: Judging from the experience of other XJ owners on the Internet, you're going to need a rack rebuild sooner or later.  They start leaking power steering fluid out of the boots.  Replacing the boots won't help, they have deliberate drain holes in them!  They're not supposed to hold fluid, they just keep dirt out.  The fluid is supposed to be kept in the rack by seals on each end of the power piston itself.  If the boots are filling with fluid, rack rebuild time.  Of course, there are products on the market that you can supposedly pour into your power steering system to stop leaks, but these will be a temporary fix at best.

There is a "seal kit" available for the steering rack.  Note that reportedly the tower shaft seal is not included in this kit; check with your source and order the tower shaft seal separately if necessary.

A high percentage of people who have rebuilt their own steering racks have reported failure on the first try, and all for the same reason: when installing the rack bar through the seal on the driver's side end of the rack, the teeth on the rack bar ruined the seal.  This typically results in ordering an entire new seal kit to obtain this one seal, and greater care the next try.  The repair manual calls for wrapping the rack with tape prior to sliding the seal over it; apparently this is the minimal precaution, experience says to lube it up as well and exercise extreme caution during assembly.  It has also been suggested that the seal and the part it mounts into be slid over the rack separately and then assembled, since installation in the housing makes the seal more difficult to work with.

Even with care to not damage that seal on installation, your rack rebuild still might not be successful; you may still have fluid in the boots within seconds after startup.  Gregory Wells of Coventry West, Inc. (page 693) says, "We rebuild a large number of Jag racks each month and we find that the wear causing the leaks is usually not just the seals; the sealing surfaces wear, too.  And unless these are checked and dealt with in one way or another, the rack will probably leak immediately or sooner than you'd like.  Modern elastomer seals tend to wear the metal sealing surfaces more than the old natural rubber seals.  We have polishing equipment we use to polish the seal surfaces; if they are too worn to polish out the grooves without reducing the diameter of the shafts below what we feel are minimum specs, we replace the part from the usable spares pile."

POWER STEERING BOOST REDUCTION: Many drivers object to the inert feel of the overboosted power steering, and seek ways to reduce the assist.  One of the simplest cures is to install a smaller diameter steering wheel; Momo and others make aftermarket wheels and adapters.  The owner of a later car, of course, has a driver's side air bag to contend with.

John Goodman points out that the XJR-S has reduced power assist, and it may be possible to retrofit the valve body onto the steering rack in the regular XJ-S.  "I don't think the racks have changed much, the valve is probably interchangeable.  Reduces assistance by.... well, you need two hands to turn the wheel at standstill, normal round town corners are OK.  On the road it is noticeably heavier but much improved.

"SPC 1034 is the part no. for the rack valve from an '89 parts list.

"SPC 1286 is the part no. for complete rack from '92 parts list.

"SPC 1158 is the part no. for the rack valve again '92 parts list.

"The rest of the steering is std.  Front springs/shocks are unique XJR-S items though."

The XJ-S owner is advised to only consider the boost reduction mods after replacing the rack mounts with aftermarket items.  The rack mounts are the cheaper mod, they will usually provide the feel the driver is looking for --and they make it easier to take the rack in and out to make further mods like the valve replacement.

STEERING WHEEL ALIGNMENT: If your steering wheel is cockeyed when driving in a straight line, your problem may be in the relationship between the steering wheel and the rack, or between the rack and the front wheels.  Jaguar has provided a nifty method of determining which.  If you remove the grease fitting from the steering rack, a dowel (or special Jaguar tool no. 12279) can be inserted to engage a notch in the rack.  When the notch is lined up with the grease fitting hole, the rack is centered.  The steering wheel can then be lined up properly.  Once this is done, a misalignment when driving straight (be sure you're on a level road, and not in the right lane of a road that is crowned) calls for correction at the tie rods.  If the correction is minor and you are confident that the alignment is otherwise OK, this can be done by carefully marking both tie rods and adjusting both of them the same amount.

Franck Guilloteau says "that "special tool" can easily be replaced with a screwdriver (torx T20 for example) that has the same ID of the zerk (sp?) grease fitting on the steering rack -remove the fitting, insert the screwdriver -move the wheels until it drops in a rack groove - the rack is centered!"

TURNING RADIUS: Dan Jensen reports, "I recently replaced the power steering racks in my '83 XJ6 and '84 XJ-S with rebuilt units.  After changeout, I noticed a significant, and undesirable, increase in the turning radius on the XJ6.  This often made it difficult to make U-turns without backing up, and complicated parking.  A check with my local Jag specialist revealed the source of the problem.  Some point along the line, Jag added rack travel limiters as part of the inner ball joint lock tabs.  These were apparently installed to preclude potential rubbing of the tires on front end components after Jaguar changed the recommended tire size from 205/70 to 215/70.  I don't know if this applied to the XJ-S as well, which had 215/70s specified.  By pulling back the inner ends of the rack boots, I could see the thicker locking tabs.  I unscrewed the inner ball joints and replaced the wide tabs with the narrower tabs.  This caused no noticeable change in toe-in since the thickness of the locking tab between the rack and ball joint is the same on both varieties of tabs.  This was a 10 minute job and fully restored the tighter turning radius I was used to.  I have not noticed any rubbing of tires on components with the 215/70's on the car.  If others have what feels like a wide turning radius, you might want to examine one side of your rack to see what tabs are used.  Apparently rack rebuilders are not always careful about the VIN number and rack changes, but I cannot see how the limiters served any real purpose and, in fact, created a bit of a hazard in my case when making U-turns."

POWER STEERING PUMP: According to XKs Unlimited, there have been three different power steering pumps used on the XJ-S.  Prior to 1976½, the part number was C28457, and the pulley was retained by a single nut in the center. From 1976½-1980, part number C45540 was used, and the pulley was bolted to a hub on the shaft with three bolts. Also, the high pressure line connection is sealed with an olive, visible when the hose is removed.  From 1980 on, part number EAC3167 was used and this pump looks just like its predecessor except that the high pressure line is sealed with an O-ring.  This last pump is referred to as the "metric pump".  The same three units were used on other Jaguars of similar years.

The XJ-S power steering pump is a standard GM Saginaw unit.  However, it is uncertain whether the Jaguar system operates at the same pressure as a GM; so, if you replace the original unit, it is suggested that you remove the pressure control valve from the Jaguar unit and install it in the new one.  The pressure control valve is easily removed by removing the outlet fitting and shaking the unit until it falls out.

POWER STEERING PUMP TENSIONER BOLT: The eye end of the threaded tensioner for the power steering pump is held to the engine with a double-ended bolt, C36196, through the timing chain cover.  Several people seem to have one problem or another with this bolt.  Peter Havas says, "I happen to be past master at this one, having had my pump come adrift at eye-watering speed.  The beast is a long bolt, with a 13mm head 8mm shaft, fine thread.  I had mine shear off at the front cover.  My fix was to purchase a length of 8mm threaded rod, and insert it into the hole, then double nut the bolt to the front cover, and finally re-assemble the eye bolt adding another nut at the end."  Note that on early cars, this is probably a 5/16" UNF bolt instead of an 8mm.  Craig Sawyers: "Watch the nut though; the old one on mine was (uniquely) BSF thread.  The new replacement one was UNF.  Don'tcha just love it?"

Havas: "As an aside, check the two big bolts holding the pump bracket to the engine.  My back bolt sheared off completely."

POWER STEERING FLUID: According to the owner's handbook, you're supposed to put the same type fluid into the power steering unit that you put into the automatic transmission.  This is interesting, since the early cars with the Borg-Warner automatics called for Type F fluid while the later cars with GM400 automatics call for Dexron 2D or III, and the power steering system didn't change.  Apparently any ATF will do in the power steering system.

Apparently Type G fluid was called out in some owner's handbooks for the power steering.  "Type G is an obsolete designator for Dexron.  It's so obsolete that nobody remembers what it was."

See the discussion on Dexron ATF's on page 326.

On the other hand, maybe you shouldn't use any sort of ATF in the power steering system.  Jeb Boyd says, "I do believe you would be better off using power steering fluid in your power steering system.  I was led to believe a few years back when they were experimenting with various formulae for ATF that the additive that was P/S compatible was no longer in ATF.  I have been using power steering fluid exclusively ever since with no problems."

Joe Bialy concurs: "I can't speak for Jaguar, but I do know for a fact that late model Ford Escorts had different fluids for the P/S and automatic transmissions when they left the factory.  I was never able to get a technical explanation other than it affected the long term well being of the vehicle."

Jim Isbell says, "A neighbor was having trouble with a leaking power steering rack on a 1990 Continental.  He is a shrimper and on his boat he uses a power steering pump connected to the engine to drive a hydraulic motor for retrieving his nets.  In that pump he uses 30 wt motor oil.  So when his cars steering started to leak he decided to try 30wt motor oil.  It cured his leak.  I was skeptical of the life of the system with 30 wt motor oil in it but his experience with the boat made me take a "wait and see" attitude.

"Well, two months later it's still leak free and still working.

"But...something more interesting to me was that when I started reading on the fluids that were allowed in the steering and autopilot on my boat I noticed that the list, which starts with automotive power steering fluid, goes on to include motor oil of varying densities as well as almost any other semi-oil fluid you can imagine.  In other words, its not very particular what you put into it.  So maybe using motor oil to cure leaks in the power steering isn't so crazy after all."

DRAINING POWER STEERING FLUID: Craig Sawyers says, "In trying to find the source of my leak, I found if you disconnect the hoses at the rack, it just obligingly trickles out (up your arm).  I realise that is easier in the UK, where you can get easy access to the unions, than in the US where they are well inaccessible."

POWER STEERING FLUID LEAKS: If your power steering system leaks, you should fix it.  Yeah, right!  You're just gonna keep adding fluid, aren't you?  Well, there is no shortage of products that claim to stop leaks in power steering systems --but apparently there is only one product that actually will stop leaks in power steering systems.  John T. Richardson: "I've came across a product that worked well for me on stopping power steering leaks and want to share it: Lucas power steering sealer.  While the name might scare you off, their product contains no electricity so it should work.  Their product appears to be a really thick, red coloured oil.

"I recently purchased a '91 Ford Explorer w\143K miles and a massive power steering pump leak.  It had to be filled up daily and always left puddles of fluid when stopped.  I tried this "snake oil" and the second bottle did the job.  I never expected such results!  No more leaks and the outside of the pump seal is only "damp".  Since then I have been using Lucas power steering sealer to top off the Jag pumps on an as-needed basis and that frequency has gone down."

Joe Montgomery: "Having tried about every power steering sealer made, forget them all except Lucas.  I found Lucas at the local Pronto Auto Parts.  It is as thick as honey on a cold day."

George Harris: "It works! As a last resort, just until I get around to finding those d**n leaks, I thought I would try a bottle.  I had to drive my '88 XJ6 (XJ40) because the 'S' was off the road for rad R&R.  The PS reservoir was empty, so I emptied the bottle in it.  That brought it up to 'full cold'.  Since then, 2 weeks ago, I haven't had to add any PS fluid!  Normally that's at least one complete refill.  Since then I did the same to the 'S', and same story!  Now does Lucas Oil Products make a stop leak fluid for the tranny and engine?"

No, it's not the Lucas we all know and love; the company that makes this stuff is:

REAR END ALIGNMENT: There's no such thing as castor on non-steering wheels, and toe-in is not adjustable on the rear of the XJ-S; if it's off, something is bent.  The only alignment adjustment available at the rear is the camber, adjusted by replacing shims between the inner end of the axle and the brake disk.  The more shims put in, the more the top of the rear wheel tilts outward.

Note that there are usually some shims between the brake rotor and the differential unit.  These are to locate the rotor properly between the calipers, but also affect the camber as well.  If working in this area, always make sure all shims are reinstalled properly.  If your objective is to relocate the brake rotor without affecting the camber, move shims from inside the rotor to outside or vice versa, but do not add or subtract any shims to the car.  If your objective is to alter the camber without relocating the brake rotor, add or subtract shims from outside the rotor and do not disturb the shims inside the rotor.

Randy Wilson offers this advice: "Camber is not a constant.  The camber control is taken on two pivoted arms (of unequal length) so that the camber can change on a predetermined curve based on suspension position.

"It is very unlikely for the camber to change from factory specs unless one of three things happens: either something is bent, someone left some shims out during a differential or brake service, or the ride height is wrong.  The #1 cause is the last, sagged rear springs.  So, when you are told that the rear camber is off, investigate the static ride height before investing a lot of time/money in shim swapping."  Better advice: don't make any decisions about adjusting shims without ascertaining the alignment properly, which means to lock the suspension height using the specified tools; see page 356.

CLUNK - REAR: See the section on page 352.

REAR SUSPENSION SUBFRAME/DIFFERENTIAL REMOVAL: To work on the differential, as well as many tasks relating to the rear brakes, it is necessary (or merely preferable) to lower the entire rear suspension assembly out the bottom of the car.  Fortunately, this is nowhere near as difficult as it appears.  It is suggested you read through the tips on removing the inboard rear brakes starting on page 438 before starting this job.

The basic idea is to put the rear of the car on jackstands, position a floor jack under the center of the IRS, unbolt it from the car, lower it and roll it out from under the car.  The first challenge: You need to get the rear of the car high enough to get the suspension out from underneath.  To get it out the rear of the car, the lowest point of the bottom of the trunk needs to be higher than the height of your floor jack when fully collapsed plus 13".  Plus an inch for fudge, just to make sure.

As soon as you get the car propped up and the rear wheels off, the next thing you should consider doing is removing the grease fittings at the bottom of the hub carriers.  They'll get busted up sooner or later if you leave them in there.

The next challenge will be getting a jack that can get high enough to hold the subframe up while you take the mounting bolts off, and then lower it far enough to get out from under the car --which means a stroke of 13" or more.  If your jack isn't up to the task, Jan Wikström says "You'll need to shift the subframe in two lifts.  I use a 5" thick wooden block on the jack and rest the unit on two cement blocks halfway up."

"You need a friend to stabilise the subframe as you move it down and up (and help you lift it to the workbench; that sucker is heavy).  To make the job a lot easier, take the spring/shock units out first and refit them last."

When ready to lower the IRS, Jim Isbell describes locating the jack: "Make sure it is under to the point of almost being too far forward.  The cage will try to roll forward if the jack is too far back as it is front heavy."  The balance point appears to be perhaps three inches forward of the axles.

Some owners have reported good results with putting the wheels back on during removal; that way, the assembly can be rolled out from under the car.  It will require positioning the car on even taller stands, though.  Disconnecting the spring/

Note that the suspension assembly, standing on its wheels, will show a distinct tendency to roll over.  If you try to keep it from rolling over by holding onto the radius arms, you may find that the radius arms can swivel around their attachments to the lower swingarms without warning and the assembly rolls over anyway, probably onto your toe or some such.  John Napoli suggests "let it flip upside-down.  Now you can wheel it anywhere you like, wheelbarrow-style, using the trailing arms as handles."

If you're going to position the suspension assembly upside down --either during this rolling or later when working on it -- you might consider capping the vent on the final drive unit so you won't leak oil everywhere.

If you can't get the car very high, the suspension assembly may need to come out the side rather than the rear.  If you position something with wheels under each hub carrier and lower the suspension onto them, you can then pull your floor jack out the rear and roll the suspension out the side.  Bob Gallivan says, "I dropped it onto my creeper on one side of the center of the diff & a moving dolly on the other side.  Worked like a champ.  Rolling it out the side is the way to go."

Craig Sawyers suggests you don't use the kids' skateboards, though.  "My thought exactly the first time I tried this.  Miserable failure; totally unmanoeverable -works like two independent bogies.  Impossible for one person to handle, and requires an act of coordination beyond anything mere mortals can achieve if two try it.  Complicated by the fact that the top of the board is resiliently mounted to the wheels, so it tilts in wierd and unpredictable ways."

Of course, just using the floor jack from the side instead of the rear might work.  Sawyers: "I found just balancing it on the head of a trolley jack and rolling it under the car worked just great."

When several members of the online discussion lists tackled IRS removal, there was a lot of discussion of details.  When the smoke cleared, it turned out that several of the problems discussed were related to the XJ saloons rather than the XJ-S; the IRS is identical, but a couple of detail differences apparently cause consternation when removing the IRS as a unit.

The first issue discussed was the need to remove the stainless steel exhaust tips, apparently because they protrude through holes in the bodywork on the saloon.  Removal is one of the steps listed in the Haynes manual as a precursor to removing the rear mufflers themselves.  On the XJ-S, there is no problem here; you can leave the tips on if you want and remove the rear mufflers with them attached.  In terms of repair manual correction, this means that Section 28 of Chapter 11 in the Haynes manual should include a note that Step 2 of Section 27 can be omitted in XJ-S work.

The next item was what to do when the rear mufflers won't come off!  If the pipes won't come apart at the forward end of the rear mufflers, the obvious solution is to remove the rear mufflers with the IRS.  Again, removal of exhaust tips is necessary on the saloon and not necessary on the XJ-S --but you might choose to remove them anyway to keep them from getting dinged up.  Jim Isbell explains this procedure with the saloon: "It is complicated greatly if, like me, you're not able to remove the tail pipes because it's then necessary to slide the cage forward as it drops so that the tail pipes will drop free in the rear.  As the cage goes forward it hits the front exhaust pipes and the drive shaft so those have to be kept out of the way."  David Littlefield points out that none of this is a problem with the XJ-S: "The cage will just drop straight down, the muffler/pipe/tailpipe combination won't hang up on anything."

"This combination is best left in the cage until it is on the bench.  Then disconnect the lower fulcrum pin from the shocks and push down the axles.  This will allow removal of the pipes without too many contortions.  Replacement is reverse of removal.  I put the whole rear muffler/pipe/tailpipe assembly back into the cage before refitting to the car.  The mufflers actually provided some leverage to wrestle the whole thing around.  It helped to temporarily hang the over-the-axle pipe on its rubber mounts to keep the mufflers from dragging around and from accidently falling out."

The next issue involved exactly how to disconnect the mounts holding the subframe to the car along the upper edge of the wheel well.  There are four mounts, two on each side, and the questions involve whether to unbolt the mounts from the subframe so they stay on the car or to unbolt the mounts from the car so they come away with the subframe.  Littlefield explains: "In my correspondence with Jim Isbell, we determined that it is difficult to get at the rear mounting bracket to chassis bolts (two in each bracket) on the XJ6 and that the Haynes manual recommends removing the suspension cage to mount bolts (three on each bracket) instead --but just on the rear.  On the XJ-S, I had no problem getting to the bracket to chassis bolts on all the brackets.  Not a big deal, but I think it might be a bit easier moving

Franck Guilloteau says, "I believe that there is one important step that need to be added before dropping the cage.  Loosen the nuts that hold the half shafts to the differential.  If yours are as tough as mine were when I did the camber change (first time), removing them with the cage off is no fun exercise.  I forgot to do it the second time when I dropped the cage.  Fortunately I hadn't removed the hand brake calipers and was able to use a long pipe clamp to compress the calipers and stop the shafts from rotating.  Even with anti-seize compound it was no picnic (air tools did help though).  If you have removed the brakes....well good luck!!

"Using a 20" extension and 11/16" deep socket (not to forget the long pipe to use as leverage at the end of the ratchet) you can remove/loosen up 3 of the bolts that hold each half shaft (remove the u-joint cover and rotate shaft until you can get to the nut -use the hand brake to stop rotation).  The 4th bolt which has a zerk fitting in the way so you need a shallower socket.  It should come last in the removal sequence." Of course, you might opt to temporarily remove the zerk fitting to get the socket on the nut.

Littlefield: "Or, you can put an open-end wrench on the nut, turn the drive shaft until the end of the wrench contacts the cage and stops the drive shaft from turning.  Then take a breaker bar or other long lever and turn the hub by using the lugs.  With that kind of leverage, the nuts should break away pretty easily.  It is a good idea to put the lug nuts on to prevent damaging the threads.  I own an impact wrench and an air compressor, which helped, but there is one nut that is under a zerk fitting and I used the above method for it."

GETTING THE RADIUS ARMS OFF: The ©1975 ROM, section 64.35.28, step 4, describes disconnecting the rear anti-sway bar link from the radius arm.  Most XJ-S's don't have a rear anti-sway bar, so you can skip this step.

The point where the front end of the radius arm attaches to the lug on the bottom of the car is a notorious spot for difficulty of removal.  There's usually a goodly amount of rust involved.  Mike Morrin describes his preferred method of removal: "I have found that the "no muss, no fuss" way to break the bushes from the body involve the use of a lever or pry-bar with the end shaped so that it will go through the hole in the bush, allowing a lot of leverage between the inside of the bush and the mounting thingy on the bottom of the car.  I tried most of my (extensive) collection of C spanners in this role, and found a BSW spanner which looks about 60 years old, and has just the right curve on the outside of the C that when one jaw is poked in through the hole in the bush, the outside of the C makes contact with the thingy.  The spanner handle is pushed upward (maybe encouraged with a BFH), and the bush just pops off.  Because the joint is tapered, it seems you need to apply enough pressure to start to deform the inner ring of the bush before it will move."

Miles Milbank offers an alternative method: "Remove all the pertinent fasteners.  Place a small hydraulic bottle jack on top of the radius arm and unscrew the jack's adjuster to contact the underside of the subframe mount and jack it up until the large rubber mount is well stretched.  Spray liberally with Liquid Wrench or other penetrating oil from all sides, including inside from underneath where the main bolt was extracted.  Walk away and do something else for awhile until you hear the assembly pop apart, and the bottle jack crash to the floor.  Repeat for other side.  If it doesn't work within an hour or so, one can come back every so often and apply a bit more: 1) penetrating oil 2) jack pressure and, finally, 3) a few helpful taps at the fitting to encourage it to give way.  One time I have hooked a slide hammer to the lip inside the fitting where the main bolt had lived, and the most stubborn radius arm immediately came off."

John Napoli describes a method that works for him, but note that it involves removing the entire rear subframe: "The car should be supported by 2 jackstands at the rear lifting points.  Get the cage ready for removal: brake lines, emergency brake cable, exhaust pipes opened (exhaust pipe(s) in front and the resonators in back --the over-the-axle pipes can stay in place).  You don't have to remove the driveshaft --it will pop at its slip-joint.  If your car has a two-piece shaft, remove the plate holding the carrier to the unibody.

"Place your floor jack under the cage.  Remove the safety brackets and main bolts holding the trailing arms to the unibody.  Don't try to remove the trailing arms, though.  Remove the bolts holding the cage to the unibody (the four rubber mounts).  The mounts will stay on the unibody for removal/replacement later if needed.  Lower the cage so the weight is on the trailing arms.  You want 'a lot' of the weight of the cage on the trailing arms, but not all of it.

"Take your air hammer, and put a blunt chisel in it.  Place the tip of the chisel between the trailing arm and the body (you and the air hammer are standing perpendicular to the car --you do this from the side, not underneath!).  Let the air hammer rip, not enough to cut the metal, just enough to vibrate things a bit.  The trailing arms will pop off as nice as you'd please."

If you intend to remove only the radius arms and leave the rest of the subframe attached to the car, you might be able to modify this procedure and make it work.  If you disconnect the radius arm at the swingarm first and find a way to pry it downward, you'd be applying essentially the same loading to the attachment.

Obviously, during reassembly it'd be a good idea to use anti-seize compound on this connection to make it easier to get apart next time.

REAR SPRING/DAMPER DISASSEMBLY: The obvious way to disassemble the springs from the dampers on the rear end is to remove the damper with the spring installed, then use a spring compressor on the bench to separate them.  However, Ian Macfarlane provides an alternative procedure: "To change the rear shock absorbers without using a spring compressor, the springs can be held in the compressed state by fitting four elongated "C" shaped brackets (two per spring) over the centre 80% of the spring with the car jacked up under the suspension (preferably with a load in the rear of the car to maximize spring compression).  Then, when the car is jacked up under the body, the springs will remain partly compressed and the shock absorbers can be replaced relatively easily."

REAR WHEEL BEARINGS: Justin Pashley says, "A couple of weeks ago I posted a message asking for opinions for what could be causing the rumbling noise coming from the rear of my car.  Initially I thought it was a wheel bearing but after jacking up all the wheels none had any excessive play.  Well, everyone who responded said it most probably was still a wheel bearing, even though there was no play.  I have now had the rear wheel bearing changed and yes, the noise has gone!  So, to anyone else that has a rumbling rear end with no play in the wheels, it is probably a wheel bearing."

Martin Lappin agrees: "I've had cars that sounded like the diff was toast, no play at the wheels, but change the bearings and everything was quiet!"

Tom Bernett concurs: "Several years ago I had a rear wheel bearing go on my '87 XJ6 SIII.  I didn't feel any extra play in the wheel.  But, if I remember correctly, I was able to determine it was the wheel bearing by spinning the wheel while listening with a stethescope on the hub.  Compare sides and I think you'll be able to tell if one's bad."

Jerry Holloway reports, "When I disassembled the drive shafts from the diff and could turn them, it became obvious the outer wheel bearing on the left side carrier was down.  Interesting that it didn't show itself until I was able to turn it freely parted from the diff.  Showed no extra end-play or anything (couldn't feel it with it turning the diff. either) but man was it starting to grind."

Interestingly, if you do have play in the wheels, it might not be the bearings!  See below.

According to Chad Bolles, the bearings in the rear wheel carriers are a Bower/BCA part number 18590-18520 for the inner, and 18690-18620 for the outer; available in any auto parts store.

Getting the old bearings out is always fun.  Jim Schultetus says, "A neat way to remove the bearing cups is to weld a bead around them with an arc welder or a mig welder.  Let it cool down a bit and they will fall out as the weld bead will shrink the cup as it cools.  Freeze the new cups and tap in." Not sure I'd go this way in aluminum housings; use at your own risk.

REAR WHEEL BEARING SLOP: I was thinking of adding an illustration here, but cannot think of how to draw this so it'll make sense.  There is an exploded view in the Parts Catalogue and there are a couple of cross section views in the ROM but neither makes it too clear how the stack goes together with shims to establish the proper end play in the bearings.  I have decided that a wordy description is probably best.

The stub axle, which is the section of the rear axle from the outer U-joint outward, has threads on the end where a

Note that the inboard oil seal track actually serves more purposes than simply as a seal track.  It has a large chamfer on the ID on one side to clear the radius on the stub axle between the shaft part and the yoke part.  And it also provides a flat surface that the shim is tightened against.  The shim is tightened against the innermost portion of this flat surface, while the outer portion has the inner race of the inboard bearing butted up against it.

All of which led to the problem that Sean McKee ran into.  Since the inner race of the inboard bearing is not securely clamped, it was apparently free to rotate in his car.  As it rotated around the hub, it wore away the surface of the inboard oil seal track.  The flat face of the seal track was no longer flat; it was unaffected at the innermost area where the shim was tightened against it, but the outer area was worn back several thousandths creating a circular step in the surface.

That isn't all it created; it created a quarter inch of play at the top edge of his rear tire!  Having the step in the face of the seal track loosened up the end play adjustment, allowing gobs of slop.  The protruding unworn inner portion on that face is just like having a shim that's too thick.  He found the same problem on both sides of his car, so it probably wasn't a fluke.

The fix is obvious: replace the inboard oil seal track.  Perhaps less obviously, you can fix the problem by simply grinding the face of the old inboard oil seal track flat again.  McKee reports that the seal track didn't seem especially hard, as though Jaguar didn't expect that inner race to rotate.

Less obviously still, you could grind the old inboard oil seal track flat and then install an arbor shim in front of it.  The ID and OD of the arbor shim would need to be the same as the seal track itself.  The whole point of doing this is that, hopefully, the arbor seal will be made of something much harder than the seal track and hence won't wear as quickly.  It doesn't really matter how thick the arbor shim is; it won't affect the bearing adjustment.  However, any such playing in here -- replacing the inboard oil seal track, grinding on it, adding an arbor shim -- should be followed by an alignment job on the rear end of the car, as this all may affect the camber.

The part number for the inboard oil seal track in the 1987 Parts Catalogue is C.15232, but McKee says there's apparently a later part number CCC6807.  Perhaps Jaguar made the part harder to resist wear!

By the way: if you actually expect that oil seal to seal against oil leakage, you'll want to apply sealant between the inboard oil seal track and the stub axle at assembly.  Otherwise oil could sneak out along the surface of the stub axle itself, bypassing the oil seal entirely.  Of course, what's in here is grease, not oil, but it still makes a mess when it gets out.

Regarding selecting the shim: The ROM describes trial-assembling the hub with tool JD.15 and carefully measuring the end play and subtracting to determine the shim you need for final assembly.  The tool is effectively a fat shim, which means you can skip buying the tool and just buy a fat shim.  Using the stub axle for this trial assembly may be inconvenient, but you can just use a section of threaded rod with some nuts and washers.

So, after all that fiddling, you finally get to put the shim on order!  If you don't want to wait on shipping, you can either order an assortment of shims before starting or you could just order one really fat shim (you may have already!) and take it to a machine shop and have it milled to final size when you determine what size you need.  Mike Morrin says, "I was unable (despite repeated attempts) to buy spacers from the local dealer, so got some sent out from the UK."

Craig Sawyers says, "The shims (they look like either brass or bronze) are stock items.  Part number CAC3818/xx, where xx is the number of thou plus 0.1 inch (so if xx was 14, the shim thickness would be 0.114 inch).  Price in the UK is £3.70 each plus tax off the shelf.  They are available in 2 thou increments (ie xx is always even), consistent with setting

Apparently there's an easier way: just reuse the shim that came out.  Everyone who's done this job confirms that apparently the companies that make the bearings maintain excellent control of their tolerances so you just take the old bearings out and install the new bearings and the same shim is the one you need.  Jerry Holloway says, "I spent hours (ok, too much time anyhow) dial indicating the new bearings on the hubs in.  After just a few miles of operation I could clearly see that the original spacer would have been fine.  After consulting a couple of sage Jag people (who weren't in it for the hourly base rate) I found that using the original spacer is exactly what they had done for years, with no problems."

REAR AXLE FAILURE: Jan Wikström reports on his problem and solution: "The stub axle in the hub carrier (the bit that turns in the rear wheel bearings) is splined for the hub and has a large thread and castellated nut on its outer end.  This thread comes right down to the splined part with no fillet whatever and creates a horrendous stress concentration at the end of the thread.  Mine suffered a fatigue fracture in consequence; my local parts pusher tells me this is not uncommon, as one would expect from such an elementary error, especially if the nut is overtightened.  Accordingly, I ground and polished a shallow rounded groove at the base of the thread of the new part... (see Figure 19 and Figure 20, illustrations graciously provided by Wikström).

Figure 19 -Rear Stub Axle Failure Location

Figure 20 -Rear Stub Axle Modification
"The next time you do the rear wheel bearings or U-joints, I strongly recommend having the stub axles checked and modified; any competent engineering shop will know about stress relief.  Modifying parts of the Jaguar may be sacrilege to some of us, but fine as the design is, it isn't perfect..."

If the stub axle has already broken, it is possible to fix it by drilling and tapping a hole in the end and using a bolt and washer instead of the nut.  GT Jaguar (now defunct) offered a grade 8 bolt and a specially designed washer for this purpose, and you could easily come up with suitable parts from local sources.  This fix may also be used as a preventative measure, since cutting off the stub and drilling for the bolt eliminates the stress concentration in the original part as well as the shallow groove does.

Perhaps one thing to note is that GTJ offered these parts at all; that would seem a serious indicator of just how common this problem is, and how important it is to address it.

Sean McKee reports that the stub axles in his 1990 XJ-S already had a suitable radius in this corner when he got there.  Apparently Jaguar addressed this problem somewhere between Wikström's mid-70's XJ12C and McKee's 1990.

The design of this pivot joint allows the bearings to be adjusted with shims to be tight.  When correctly assembled, they roll firmly; there should be no slop or rattling whatsoever.  This pivot joint holds the alignment of the rear wheel; any slop means that the wheel is sloppy in which direction it aims.

REAR SWINGARM OUTER PIVOT -GREASING: The grease fitting is obvious, dead center bottom on the hub carrier.  But just what good does it do?  Patrick MacNamara says, "the relief port for the grease pressure is only about 1" away from the nipple (center of swing arm about 90° around the fulcrum from the nipple facing inboard) adjacent to the hollow end pipe of the lower arm.  When cavity is full, it just vents out of the hole and fills the hollow longitudinal portion of the swing arm and no old grease will be pumped out.  The only way to get rid of the old grease is disassembly."

On the author's '83, MacNamara is incorrect.  There is a cast-in boss facing inboard, but the hole in it has a bottom; it does not open into the pivot joint area.  There is a grease relief, though, just above this cast-in boss.  It points upward and inboard at about a 45° angle.  It's a 3/32" hole, completely obscured by all the dirt and grime that has accumulated on that surface of the hub carrier.  In other words, MacNamara was in error regarding the location of the grease relief, but he was correct that it was there -- and in its effects.

You might consider plugging the grease pressure relief port.  A 1/4" long #4 self-tapping screw will work nicely --two per car.  This will at least help keep dirt and water out.

If you plug the relief port and then use a grease gun to force grease in there under pressure, it'll push against the felt seal.  Will it ooze through the felt seal?  Maybe; at least, any air in the area will push through the felt.  Hence, you might actually achieve some beneficial lubrication with the grease gun.  I wouldn't count on it, though; you're still not likely to improve the lubrication in there without disassembly.

If you install oil seals as suggested below and plug the grease vent and then force grease in there with a grease gun, you'll probably destroy the oil seals.  Your chances are a little better that the grease will just push past the seals if you install them backwards as Ron Moore suggests, but not much better.  If you feel compelled to use the grease gun, you might be best advised to remove the vent plug first, then put it back in when done.

Better idea: Richard Dowling reports, "Of all the 24 bearings in the IRS and diff I only had 4 bad ones, namely the outer fulcrum tapered rollers.  There was plenty of grease in the bearing cavity, but that around the bearings themselves was pretty old since the new grease goes in the zerk and out the vent next to it.

"In my stripdown I put 2 zerks in for each wheel hub to force grease through the bearings, and a vent hole on the outer side of the fulcrum bearings to ensure grease from the central zerk can exit only after going through those bearings.  All this is dead easy when the whole shooting match is cleaned up and on the bench.  What about the fulcrum area on your car which is probably like my XJ6, not giving any trouble, but a future concern?

"When I had my XJ-S fulcrum stripped I measured all the items accurately and made an Autocad file (see Figure 21) of the bearing area.  From that I could see a possibility of drilling a small hole through the standard assortment of spacers and felt seals into the area next to the bearing race to make a vent, all without stripping the assembly.  This morning I tried it on my XJ6 and it works.

Figure 21 -Rear Outer Pivot Grease Vent

"You take the wheel off, and drill a hole about 2.5mm diameter starting at 3mm from the machined end of the alloy casting.  The drill must be at an angle of 65deg to the centreline of the 5/8" shaft running through the bearings.  The 3mm and 65deg are moderately critical.  I drew an angle of 65deg on a piece of paper and put it under the hub to give me a guide as I drilled.

"On the first one I broke the drill because I was in a hurry.  You drill about 5mm though alloy then you hit the mild steel cup that backs the felt seal.  You go through the first face of that cup which is parallel with the shaft since it fits the bearing bore, then you hit the felt seal and a little further on you hit the return face of the cup which is at 90deg to the shaft centreline.  This latter face is hit at an acute angle of 25deg which is where I broke the tip off my drill.  If you exercise patience and take about 5 or 6 minutes to drill each hole, backing off as you break into the felt seal, then going carefully for that return face, it is no problem.  Total drill depth is around 12mm.

"As soon as I thought I had broken through I put my grease gun on the zerk and tried it.  That also pumps out the swarf.  In any event, looking at the pounding on my XJ-S bearing, a small piece of swarf most likely would make no difference.

However, if you grease the thing every 6 months you are pumping grease in a direction that takes the swarf out of the bearing - that will be the least of your worries.

"Small self tappers were used to seal off the vents.  I found on my XJ6 that as I pumped, no grease came out of the Jag supplied vent next to the zerk; it must be well and truly blocked.  I got plenty of grease out my new vent holes.  At first very old and stiff grease, then newer grease sitting in the centre of the cavity, then new moly grease.  I also loosed off the 5/8" shaft nuts and rotated the shaft to rotate the bearings which spreads grease and spreads the wear pattern.

"Now I know how it should be done, I guess an hour would cover the job for both wheels.  You might want a spare drill, it is not too hard to break one.  That is no tragedy, it just means you have an extra hole which may or may not penetrate the bore."

Since lubrication is a challenge, it might help to use the most suitable grease rather than simply whatever's on hand.  Richard Griffiths says, "EP should be fine; in my view grease for this application requires:

High viscosity base oil at operating temp.
Water resistant filler
Oxidation inhibitor additive
Corrosion inhibitor additive

"Other additives such as Moly are of no significance for this application.  In my experience Moly was usually specified for sliding applications; in this case the trick is to keep the rollers actually "rolling" under high oscillating loads while maintaining the oil film.  EP should do better here."

REAR SWINGARM OUTER PIVOT -OIL BATH LUBRICATION: Getting grease right into the contact points between rollers and races is an iffy proposition at best, especially the rollers that happen to be at the top.  Unlike wheel bearings or other applications, the motion of the bearings themselves cannot be expected to help move the grease around to where it's needed; these rollers don't move as far as the spacing between rollers.

Richard Griffiths proposes a novel solution: "Two things we know for sure; EP additives work and channeling can occur in "thick" greases leading to lube starvation failures.  So if I had your set up with the better seals, I would consider using a hi visc EP oil instead of grease.  Highest stuff that will still pour at say -10°F."

Obviously, having the oil seals installed on the pivot joint as described on page 396 is essential for this idea; the OEM felt seals will simply allow oil to ooze out, and the last thing a Jaguar needs is another oil leak.  The oil seals should be installed flat side out, since they will used to hold oil in -- exactly what they were designed to do!

Also, you need to use sealant when assembling.  Apply sealant to both sides of everything in the stack along the fulcrum shaft to make sure oil can't leak along the shaft to get out.  And before the oil seal is pressed into the hub carrier, some sealant should be applied in the recess.

Having an oil-filled assembly sealed airtight would not be good, so using a screw to plug the grease vent as described above is not recommended.  As with other containers holding oil such as the GM 400 transmission or the differential, the ideal arrangement would be for the joint to be fitted with a breather that allows the chamber to be vented while keeping oil in and water and dirt out.  There are a couple of ideas here.  One is to drill the existing grease vent hole out to a larger size and then thread it to hold a fitting of some sort --possibly the same fitting as the one used on the differential.  Another is to press in a small tube and connect a hose to a remote breather, similar to that used on the GM 400; such a remote breather would need to be secured to the hub carrier so it doesn't flap around too much when the wheel bounces over bumps in the road.  Remember to make sure the breather connection doesn't interfere with the axle U-joint or its cover; an elbow fitting may be in order.  The simplest idea is probably to simply drill the existing grease vent hole bigger but only part way down, not all the way through, and then jam a piece of felt or a cotton ball in the hole.

Richard Griffiths says, "One of those breather plugs with the sintered "filter" center piece would be neat also.  See the stuff from the Stewart Warner or Tedeco companies for example."

When devising a breather, remember that you will also need to be able to put oil into this compartment.  If a really small (1/8" or so) breather is devised, you'll probably need to make a second hole so you can add oil to one hole while air comes out the other.  If you make the breather hole large enough, you may be able to feed a tube down through it so you can feed oil in through the tube while air escapes around it; a capillary tube on a syringe would work well.  If you can figure out how to get the oil in via the zerk fitting, great, but otherwise you might want to remove the zerk fitting and plug that hole with a screw.  Again, the enlarged hole with felt or cotton jammed in it provides the simplest solution: remove the felt or cotton, fill up the chamber with oil, and jam the felt or cotton back in.

When set up this way, you want the assembly full of oil; that's the only way oil will get to the rollers at the top of each bearing, since they don't spin.  Griffiths points out you want to keep the seal lips wet, too.  So, add oil until it appears at the breather.  This will still leave some air pockets, but driving uphill or downhill will help make sure those upper rollers get oiled every now and then.  Driving over bumps may splash some oil around in there.

Tom Wilson says, "Thoughts on oil filled hubs bring back a time when Bell Helicopters figured out that the oscillating movement of the pitch change on the rotor blades would tend to work the lube out of the needle bearings and would allow metal to metal contact.  They went to great lengths to seal the blade grip to yoke contact point, and even supplied a clear reservoir so one could easily check the oil level in the grips.  It was for the most part a failure and you will usually only see a UH-1 with an oiled head in a museum.  The point of this tirade is simply that on a worst case, that being an oscillating load the oiled bearing was replaced by greasing.  Replacing the felt wiper with a rubber lipped seal and using a synthetic grease like Mobil (that horrible red stuff you always see being slung out of the heads of Bell helicopters) will almost guarantee that the wheel bearings will outlast the rest of the car."

REAR SWINGARM OUTER PIVOT -SERVICING: Do your pivot joints need attention?  Probably.  Patrick MacNamara's did: "Old bearings were completely shot.  The worst were the ends closest to the front of the car.  The starboard side inner race was almost a rusted solid mass and the outer race was pitted and dented.  There had been so much movement that it had chewed and straightened one of the annular spacers.  The yaw I used to experience when letting off the gas at speed is now gone as well as a little rear end steer/swaying when changing lanes at speed.  I think these things should be disassembled and regreased as well as rotated a few degrees every few years."

Greg Meboe had sloppy bearings. "This can be noticed as a light to medium growling vibration as you're driving on the freeway.  This occurs only during the transition as you gently press and release the throttle.  This can be misdiagnosed as a differential problem.  To test, jack up one side of the car under the steel lower suspension arm, then remove the wheel.  Pry a flat-blade screwdriver between the aluminum hub carrier and the steel lower suspension arm.  Try to wiggle the carrier forward and backward, while the suspension is at ride height.  Otherwise, you can look for evidence of scraping between the carrier and the lower arm."

If you only need to rebuild the outer pivot joint, here are some things you don't need to do: You don't need to drop the rear suspension cage.  You don't need to fiddle with the shocks and springs.  You don't need to fiddle with the radius arm.  You don't need to mess with the rear anti-sway bar, if you have one.

The fact is, working on the outer pivot is pretty easy; just slide the axle out of the hub and remove the fulcrum shaft from the pivot, and you can work on the hub carrier on the bench while leaving the swingarm in the car.  This hub carrier removal is clearly described in Section 64.15.01of the ROM, but is not as clear in the Haynes where the section on rebuilding the outer pivot itself follows a section on removing the entire swingarm from the car.  This seems to imply that outer pivot work requires removing the swingarm from the car first, and that would involve some serious work.  Removing the swingarm is totally unnecessary; if you're using the Haynes, just follow steps 1, 2, 5, 6, 7, and 8 of Chapter 8, Section 4.  Then you can begin taking the pivot apart according to Chapter 11, Section 22, and as soon as the fulcrum shaft comes out you can relocate the hub carrier to the bench.

The hub carrier removal procedures call for removing the cotter pin and the castellated "Jesus nut" holding the axle in the hub.  If you just happen to have wheels that permit access to this nut, it's easier to break it loose first while the car is still sitting on the wheels.

The procedures also call for a special Jaguar tool JD.1D to get the axle out of the hub.  A generic hub puller will do - but you might not even need a puller at all, it might just slide out.  If you can get the Jesus nut off while the wheel is still

Still sounds like too much effort?  Then forget removing the hub carrier; rebuild the outer swingarm pivot right there on the car!  Patrick MacNamara says, "Very simple job to replace the fulcrum bearings without disconnecting the hub from the splined axle.  I just laid an 18" 2x4 across the lower arm fork and rested the hub carrier on its side on the 2x4 for the pounding out of the old bearing cones."

Section 64.15.07 of the ROM and Chapter 11, Section 22 of the Haynes manual provide step-by-step procedures for rebuilding this pivot.  However, many owners have expressed confusion; in fact, apparently Jaguar was confused, because there are different procedures described in the manuals for different cars that all use the same rear suspension assembly.  John Napoli says, "I have opened up three fulcrum assemblies on three different Jags (my XJ6, my XJ-S and another) and each had the parts in a different sequence, none of them matching the various and sometimes ambiguous manuals."

The confusion is also partly because you need something more than step-by-step procedures --you need to know what the hell you're doing!  There are two separate shimming procedures involved.  Both are described in the following pages; once the objectives are understood, the step-by-step instructions should begin to make more sense.  Figure 22 shows the assembly, assembled at the right and the individual parts to the left indicating the order of installation.  The fulcrum shaft has been omitted, since it makes the diagram clearer and you know where the fulcrum shaft goes.

Section 64.15.07 of the ROM includes instructions for rebuilding the outer pivot and for rebuilding the wheel bearings, all in the same sequence.  That only causes more confusion; although both bearing assemblies are within the same hub carrier, they are unrelated operations and should have been described separately.  If you are only rebuilding the pivot joint, you only need concern yourself with steps 1-3 and 18-31.  The Haynes manual does describe them separately --in fact, in separate chapters, as the wheel bearings are covered in Chapter 8.

Disassembly is fairly straightforward until right after you remove the felt seal ring itself.  There is a metal ring with an L-shaped cross section (looks like an oil seal with the rubber part missing) that the felt seal ring sits in, and this ring is pressed into the hub carrier.  There doesn't seem to be any non-destructive way to get it out; you just have to put a screwdriver in there and pry, which will usually mangle it beyond reusability.  So, if you plan to rebuild using the OEM felt seal scheme, you probably should order four new rings C20179 in advance; Craig Sawyers says, "this is an expensive part -the price I have is £7 (about $10) each, and there are four on the car."  Better idea: rebuild using the oil seal scheme described below, which doesn't require these rings.

While you have it apart, take a flat file and file a small bevel on the inside corner of the outboard ends of the swingarm fork.  Don't make it at 45°; rather, make it nearer to parallel to the flat inside surface of the fork tine, perhaps a 10° angle.  These bevels will make it easier to get the hub carrier back into place in the fork.

The outer pivot reassembly calls for a "dummy shaft", JD.14.  John Robison suggests you use a 5/8" wooden dowel.

Cut it to exactly 6" long.  Note that a 5/8" wooden dowel may not be machined all that precisely, so trial fit it through a new bearing before you get started.  If it fits snugly at all, spend a few seconds with some sandpaper on it.  It needs to be a slip fit, so it's easy to slide in and out of the bearing assembly.  If it's humid out, you may need to sand it some more.

Richard Dowling had another idea: "In my collection of rubber items I had some 5/16" ID rubber fuel hose that was near as dammit 5/8" OD.  This made excellent dummy shafts, especially for the inner fulcrum shaft that needs a real belting to get back into position.  With hard dummy shafts that belting can easily propel the dummy out and drop a big collection of seals and spacers all over the bench.  The rubber dummy is much less likely to be inadvertently propelled and thereby helps keep your blood pressure low."

The fulcrum shafts in the author's '83 have a little dowel tip on one end.  Purpose unknown.  If installed pointing to the rear, it may permit the use of a simpler ride height setting tool than the one shown in Figure 17 on page 358.  Other than that, the fulcrum shafts can be installed with this tip pointing forwards or rearwards, it won't make any different to the pivot joint itself.

REAR SWINGARM OUTER PIVOT -BEARINGS: Craig Sawyers says, "Jag supplied a couple of cut-outs on the inside of the hub so you can get a brass drift in to knock them out.  Of course, that will be buried in grease, so you have to go by feel, but it is not a difficult job."  It helps somewhat to have a drift that's shaped just right at the tip, so you might consider grinding the tip a bit -- flatten one side, etc.  Also, it doesn't need to be brass unless you plan to reuse the bearing; a steel rod will do.  And make sure to switch back and forth between sides with every whack; you don't want to get that race cocked sideways.

Generic bearings can be used, of course.  Gregory Wells says, "Inner cone and bearing is Timken 03062, outer race is Timken 03162, for Jaguar p/n C-16029."  Duncan Williamson indicates that NSK bearings use the same numbers.  Ron Moore says "These are the same bearing and cap as those fitted to the Triumph Herald front wheel bearing outer."  Moore is in New Zealand; if you're in the US, it might be more useful to know that it's also the same bearing as the outer front wheel bearing on the Triumph Spitfire and TR6 which were actually imported to this country.

Wells, a Jaguar parts vendor, adds, "Don't assume that because these bearings can be ordered by numbers from a bearing house that they will automatically be cheaper than from the parts peddlers like ourselves.  Jag vendors will be cheaper than bearing houses on the Jag-specific bearings a goodly percentage of the time."

Sawyers: "Replacing is easy.  Stick the hub in the oven (I waited until my dearly beloved was out) at 100°C.  Put the bearing track in the freezer.  The two parts just drop together, and then tighten up as the assembly cools down.  When it is cool, give the track a knock or two with a drift just to confirm it is completely seated in the recess."

Conversely, Patrick MacNamara --who didn't remove the hub carrier from the car so it couldn't very well go in the oven -- used a length of threaded rod with nuts and washers to pull the bearing races into place.

The author used a similar method, except using the fulcrum shaft and nuts themselves.  You will need two 5/8" flat washers with a 1-1/2" OD, and it's nice to also have two 5/8" flat washers with a 1-3/4" OD.  Use the 1-3/4" OD washers to pull the races in until they are flush with the ends of the hub carrier, then switch to the 1-1/2" OD washers for the rest of the way.  The threads on the fulcrum shaft aren't very long, so you have to stop a few times and add more spacers.  The old bearing inner races make fine spacers.

REAR SWINGARM OUTER PIVOT -REPLACING BEARINGS WITH BUSHINGS: Tapered roller bearings work best when rolling continuously; the motion helps feed grease in between the contact areas, and the continuous motion ensures a uniform wear track.  But the bearings in this pivot don't roll far enough.  Hence, the wear is not uniform, but rather in local spots on the race.  And the grease can get pushed out from between the contact points, piled up between rollers, and the contact points actually run dry.  The result is a pattern of dimples on the bearing races.

Greg Meboe agrees: "As a mechanical engineer, I must say that the choice to use tapered roller bearings in the hub pivot area is poor, really poor.  A roller bearing is designed to roll continuously, not sit in a static position.  This pivot has a high amount of stress on it during acceleration, braking and cornering, yet never turns more than one or two degrees

Gran Turismo Jaguar (now defunct) offered a kit to replace the tapered roller bearing idea entirely with brass bushings.  Concours West (page 708) offers urethane bushings.  Either of these has the considerable benefit of being an order of magnitude easier to install, since there is no need for adjustment and fiddling with shims.

However, whether or not going to bushings is actually an improvement is far from clear.  First, note that the entire point of renewing these bearings is to eliminate sources of slop in this joint, but you cannot adjust the slop out of bushings.  If the bushings don't fit very snugly on the fulcrum shaft, the slop may get worse rather than better.  And even if the bushings are really snug, of course, any wear in those bushings would cause slop --if you're unlucky, more slop than would be caused by the wear rate of the OEM tapered roller bearings.

ALLOY WHEEL SEIZING: Believe it or not, one of the places where Jaguars are known to have seizing problems is between the alloy wheel and the hub.  Robert Woodling suggests use of anti-seize compound on the mating surfaces, especially at the hole in the center of the wheel.

If your wheel is already stuck, you might as well try loosening all the lugs about two full turns, take the car down off the jack and drive it up and down the street.  Swerve left and right a couple of times.  Of course, if the tire is flat you won't want to do this --so you might want to check if your wheels are stuck now and take corrective measures before you're stuck on the side of the road with a flat tire.

XJR-S WHEELS: John Goodman reports that the XJR-S uses "8" wide special alloys (the front and back wheels are not interchangeable because of different offsets)."

SPOKE WHEELS: Yes, a Jaguar with real wire wheels really looks good.  Unfortunately, it generally doesn't drive worth a hoot.  The spoke wheels available have a reputation for trouble.  Spoke wheels were a good idea in the ‘50s when Jaguars needed to maximize air flow to cool their brakes.  Since that time, two changes have conspired against spoke wheels:

1. The advent of tubeless tires.  Many spoke wheels won't work with tubeless tires, so you must install a tube.  A tube installed in a speed-rated tire (the XJ-S should be fitted with V-rated tires) completely negates the rating, and renders the tire unsafe at speed.  Don't drive fast with inner tubes in your tires!
2. The advent of low, wide tires.  A spoke wheel is a reasonable structure when it's tall and skinny, like a bicycle wheel or the automobile wheels of the ‘50s.  But it is a structurally poor design for modern low, wide wheels.
Furthermore, Jaguar XJ wheels need an offset (distance from mounting surface to centerline of wheel) of around 1¼", which is not conducive to spoke wheel strength.  It requires all the spokes to be crammed together near the outer edge of the wheel rather than centered and optimally oriented for strength.

Spoke wheels tend to need truing on a regular basis.  This is not a job for the home mechanic, and finding someone who can do it right is a challenge.  Often the wheels must be returned to the manufacturer for truing.  Truing will obviously require removing the tire, remounting the tire afterward, and rebalancing --so it probably would make sense to plan on a wheel truing whenever new tires are fitted.

Modern spoke wheels normally have stainless steel spokes, which is a big improvement over earlier designs.  However, spoke wheels generally still have chrome-plated steel rims and centers, leading to rust problems, flaking chrome, and

By the way, if it's a weight reduction you expect, forget it.  There is nothing lightweight about spoke wheels.

It should also be noted that since the spoke wheels are more flexible than alloy, the handling will suffer somewhat.  With a car this heavy, the difference in the way the car corners is noticeable.  You may even get sounds, as the spokes strain and creak with the load.

Note that older Dayton wire wheels had 60 spokes while later designs have 70 spokes, with the 70-spoke versions reportedly better.  John Tompane says, "The 70-spoke wheels weren't available until I think '89.  I have 70-spoke Daytons on my wife's XJ6 and they have been trouble-free for years.  When I got the new XJS it came with the same wires already on the car.  Since I sometimes drive harder than my bride, I had planned to replace them with sport lattice wheels like I had my '88.  But frankly, so far they have been great.  I've pushed them pretty hard and they have stayed in balance.  I think I'm going to keep them at this point.  If I were going to race, autocross or really push the car hard for long periods it would be stupid to use them.  They aren't designed for that.  But for everyday driving and little spirited driving they're pretty damn good.  Not great, but not nearly as bad as advertised.  The 60-spokes were true nightmares (or is it untrue nightmares?) and should be avoided at all cost."

Peyton Gill counters: "The Daytons which failed on my '86 XJ-S were 70-spoke.  The point of failure was the wheel. Cracks formed between the spokes.  In some cases the cracks meet from one spoke to another.  The car had not been subjected to any abusive or aggressive driving."

"I bought my XJ-S from my sister who bought it new.  She had one wheel self-destruct when a car pulled in front of her.  She did not hit the car but the action of hard braking caused one wheel to collapse."

There are (or were at one time) also 50-spoke wire wheels made by TrueSpoke.  Brett Kelien says, "I have had enough problems out of 60-spoke Daytons and TrueSpokes to say they will never be on a car of mine.  I have broken them going down the highway.  On the good side Dayton did make me a good deal on the 70-spoke wheels which I really like."

Actually, it appears that Dayton will make anyone with their 60-spoke wheels a good deal.  Steve Gallant says, "I called Dayton Wire Wheels and found that they would not repair the wheels under any circumstances.  However, they would replace them with new ones for a very low price.  And these new ones had both a larger spoke diameter and more spokes.  Dayton was trying to get these wheels out of circulation by offering good replacement deals.  I'm sure they could see the liability issue coming to bite them in the ass sooner or later with wheels not sufficently strong for the intended application."

DOT 5 BRAKE FLUID: Many people swear by "Dot 5" silicone-based brake fluid, and others swear at it.  Silicone brake fluid does not absorb moisture, does not harm paint when spilled, and has a very high boiling point.  It is also nontoxic.

Some of the arguments are based on it not absorbing moisture.  If there is no water in your brake system to begin with, theoretically none will get in by being absorbed by the fluid in the reservoir.  But if there is water in the system to begin with, the silicone fluid will not absorb it, and it may puddle in local spots and cause corrosion.

Silicon fluid absorbs more air than conventional fluid, meaning that the brake pedal will feel spongier, even when fully bled.  Of course, this will not be apparent at first, since it takes some time to absorb air within the reservoir and for the air to diffuse throughout the system.

It is important that the two types of fluid not be mixed.  Silicon fluid is less dense than normal fluid and won't mix with it, so it is theoretically feasible to fill the reservoir with silicon fluid while bleeding the conventional fluid out at the wheels.  If you've had the calipers apart, you probably don't believe this; maybe it'd be better to only change fluid types in the midst of a full caliper rebuild.

The name is a deliberate misleader.  DOT 3 and DOT 4 brake fluids are referred to as such because they conform to Department Of Transportation standards.  "Dot 5" silicon-based fluid, however, is a trade name, not a DOT standard.  There are even reports that DOT has now issued a standard #5, and it is not for silicone-based fluid but for something else.

Older (pre-XJ-S, actually) Girling systems require DOT 4 fluid to keep the natural rubber seals pliable to seal properly.  Some components are reported to get hard when exposed to silicone fluid; others are reported to absorb too much silicone and swell so much as to jam the works.

According to Jim Beckmeyer, who had a master cylinder resleeved: "White Post (page 703) said that the warranty would be voided if I used DOT 5".  Draw your own conclusions.

WHEN TO BLEED BRAKES: Bleeding the brakes is essential after disconnecting brake lines in order to get air out of the system and ensure a "hard" pedal.  Bleeding is also a periodic maintenance action, sorta like changing the oil; brake fluid absorbs moisture, either that was already within the system or from the air in the reservoir, and this moisture is not good for the insides of the brake cylinders.  Moisture also lowers the boiling point of the fluid.  Also, the fluid eventually becomes contaminated with tiny particles of metal from wear within the cylinders, and the particles only serve to accelerate the wear.  So it is beneficial to occasionally bleed the brakes even if there is no air in them, and to bleed them enough that the entire system is filled with fresh fluid.

Steve S says, "In Delphi-AP Lockheed tech notes I came across the following quote:

In addition to regulations that define performance hydraulic brake fluids are required to meet international standards with regards to their colour.  The following classifications have been established:

. less then 0.006 Abs Colourless
. 0.006-0.100 very pale straw
. 0.101-0.197 pale straw
. 0.198-0.296 straw

This means that the color of the brake fluid indicates how much moisture it has in it.  So, it needs to be close to "colourless"; if it's closer to "amber", it's time to bleed that stuff out and get new, dry stuff in.  Of course, you can't see the color of the fluid anywhere except in the reservoir, but that's where moisture typically gets into the system in the first place.

Modern brake fluid reservoirs are translucent white plastic.  This is so that you can see not only the level but also the color of the fluid without removing the cap, since removing the cap introduces more air and moisture into the system.  Of course, with the OEM reservoir on the pre-ABS XJ-S, the reservoir is vented anyway so it will gradually gain air and moisture even if you don't ever remove the cap; see the idea for replacing the reservoir on page 596 if you'd like to correct this shortcoming.

BRAKE BLEEDING: Before beginning the bleeding procedure, remove all of the old fluid from the reservoir using a turkey baster or something.  And, of course, get any dirt or crud out that you can.  It simply doesn't make sense to try to pump that crap through the system to get it out; get it out the easy way, and fill the reservoir with fresh, clean fluid before starting.

Bleeding the old-fashioned way requires two people.  One person sits in the car and "pumps" the pedal to get the pedal up where it belongs, and then holds pressure on the system while the other person opens one of the bleed screws to allow the fluid to squirt out.  A small piece of hose routed into a container helps reduce the mess.  When the bleed screw is opened, the pedal will go to the floor, and the person in the car must keep it there until the bleed screw is closed once again; if the pedal is allowed to rise, it will draw air back in through the bleed screw.  After the bleed screw is closed, the pedal is pumped back up and the cycle is repeated.  If a clear hose is used on the bleed screw, it is easy to see when the crud is gone and clear fluid is coming through.  You must pause every now and then to top up the reservoir with fresh fluid.

If you want to make things easier or require only one person, there are numerous gadgets available to help.  Dan Welchman suggests the "Eazi-bleed" kit: "I think they're made by Gunsons but I'm not sure.  This device uses your spare tyre as a compressed air reservoir which pressurizes a large plastic brake fluid reservoir via a hose and footpumpstyle valve connector.  A tube dips into the bottom of this reservoir and feeds fluid up to an air-tight cap that screws onto your brake fluid reservoir on the car (the kit comes with a wide range of different caps and rubber gaskets to fit most cars).

"Once you've fitted this and got it air-tight you can bleed the brakes by just opening each of the nipples and letting the fluid flow out until it's bubble free (or longer if you're changing the fluid).  No pumping, no assistant needed, and no worrying about having to top up the reservoir for fear of running out of fluid and pumping air through the system.  They're extremely cheap and work pretty well."

Many owners install Speed Bleeders, not only because it makes bleeding brakes quicker and easier but it also makes it a one-man job.  It's just a bleed nipple with a check valve in it.

Speed Bleeder Products, Inc
13140 Apakesha Rd.  Newark, IL 60541 USA
Tel: 815 736 6296 Fax: 815 736 6297

BRAKE FLUID RESERVOIR CONNECTION HOSE: To make the brake fluid reservoir fit under the hood, Jaguar uses a remote reservoir connected with metal lines and short pieces of flexible hose.  If these hoses need replacing, do not use conventional fuel line; the brake fluid attacks the fuel line material, and the result will be darkened fluid with lots of crud in it.

The fact is, none of the hose commonly sold at an auto parts store will serve.  Also, nylon tubing is unsuitable; the brake fluid soaks right through it, and then it hardens and shrinks.

Of course, using Jaguar original hose is not recommended, as it is a British non-metallic product.  After all, you are now having to replace it.  But there are other cars that also use hose to connect a remote reservoir to the master cylinder, including Mercedes, BMW and Fiat, so you can check other dealers for suitable hose.  Andrew Weinberg says, "Volkswagen Beetles also use a remote reservoir, and the hose stocked for that application works perfectly...  The hose is available from any VW supply shop.  The only hitch is it's a (nice?) blue color."

Non-automotive hose is also a possibility.  You can visit an industrial supply store and attempt to find a clerk who knows his stuff, or a reference manual that lists acceptable applications for different hose materials.  Commercially available air hose works well in this application; it is red with a black inner lining, and is sold in many hardware stores.  It's so cheap that many Jaguar owners can't believe it could ever work.  The inner lining is EPDM, which is compatible with brake fluid.  Note that this hose will not withstand the pressures seen in other parts of a brake system, such as the

Keep in mind that this application sees no pressure, so high-pressure brake or hydraulic hose is unnecessary and will only make it very difficult to install over the plastic fittings.  Some suggest that you use lines that will hold perhaps 30 psi in case you ever want to "pressure bleed" the system, but just about any hose will handle 30 psi.

While you're replacing the hoses, you might consider tossing the original metal tubes and simply run the new hoses all the way from the reservoir to the master cylinder.  This makes for a cleaner appearance under the hood.  You need to take care, however, that the engine shaking on its mounts doesn't cause the corner of the air filter housing to rub on the hoses and eventually cut a hole in them.  If it did, the reservoir would drain and the warning light would come on in the dash before there were any operational problems with the brakes, but you still wouldn't be happy with brake fluid all over the engine compartment peeling all the paint off the chassis.

BRAKE FLUID RESERVOIR LOCATION: A brake fluid reservoir must be located above the master cylinder so that fluid will gravity-feed into the master cylinder and air bubbles in the master cylinder will rise into the reservoir.  Unfortunately, the remote reservoir location on the pre-ABS XJ-S is stretching the definition of "above".  It works OK when kept topped up, but if you ever have air in the hoses or master cylinder for whatever reason it is suggested that you unbolt the reservoir from its support bracket and position it about six inches higher, merely allowing the hoses connecting it to the master cylinder to flex.  With it in this position, operate the brake pedal a few times.  You might also just wiggle it a little.  With any luck at all, any air in the hoses or in the master cylinder will bubble up into the reservoir.  Once all the air is cleared, you can bolt the reservoir back onto its bracket.

BRAKE FLUID LEVEL SWITCH: Hey, it's electrical, so it's discussed on page 596.

BRAKE FLUID RESERVOIR CAP FAILURES: Apparently the cap occasionally breaks into a center portion and an outer portion.  According to Michael Neal, "This is a problem and tends to reoccur if you don't modify the reservoir.  This is on the pre-abs XJ-S brake reservoirs.  Usually just flattening the sharp vertical ridge on the reservoir with a file will do it."

Better fix: replace the entire reservoir with one from a Mitsubishi.  See page 596.

MASTER CYLINDER REBUILDING: There was an "early" type master cylinder used before 1977½, and a "later" type used up until the advent of ABS brakes.  However, apparently not all of those "later" types were the same.  In the Jaguar manual section 70.30.09, step 14, a seal is installed on the secondary piston with the lip facing forward.  In step 15, a second seal is installed in a second groove facing rearward.  Chapter 9, section 7, steps 13 and 14 in the Haynes manual say essentially the same thing.  However, some master cylinders only have one seal on the rear end of the secondary piston rather than two.  The one in the first step is the one that was omitted; if only a single seal groove is available, the lip on the seal should be installed facing rearwards.  Of course, if you have purchased overhaul kit #M7673, you will have one seal left over.

POWER BRAKE SERVO: The (non-ABS) servo assembly comes apart in the center, by twisting one half until the retaining tangs line up with the cutouts.  There is a special tool for this job, but Bruce Hayes reports the tool can be improvised.  He carefully mounted the master cylinder in a vice, and fashioned a tool to attach to the studs on the housing to turn it.

FRONT BRAKE PAD GROOVES: Some of the pads offered for the front of the XJ/XJ-S have grooves across them.  Ferodo pads, for example, have two parallel grooves across the face of each pad the short way; each groove is about 1/8" wide, and they are about 1-1/16" apart.  These grooves might help with cooling, or getting dust out from between the pads and the rotor, or letting water get out on rainy days, but Chuck Sparks says the primary objective is to prevent squealing; the grooves break up the long, solid surface of the pad into three separate shorter panels.

If you get pads without grooves, you might opt to cut your own grooves.  Brake pad facing material is not difficult to cut; a hacksaw will do it.  The Ferodo pads are not grooved all the way to the backing plate; the grooves stop about 1/16" short of the base plate.

FRONT CALIPER REMOVAL: The front brake caliper is attached to the hub carrier with two bolts.  The steering lever is likewise attached to the hub carrier with two bolts.  And, just to make things interesting, one of those bolts is shared; there are a total of three bolts, two short and one long.  Some of these parts are clearly illustrated in the ROM: the hub carrier (also called a stub axle carrier) is shown at the beginning of Section 60 under "Accidental Damage".  The steering lever is shown in Section 57.65.01.  The way the three components come together is shown as clearly as can be expected in Section 70.55.02 or Section 57.55.29.

When removing the long bolt, don't lose the shim that falls out.  See below.

The two short bolts are the same length.  However, the short bolt holding the upper end of the caliper to the upright has a smooth shank and safety wire holes in the head.  The short bolt holding the forward end of the steering arm to the upright looks like a regular high-strength bolt, threaded to the head and no wire holes.  I guess brakes are considered critical and steering isn't.

Removing two bolts will get the caliper loose --but won't get it off.  There is also a hard brake line wrapped in a semicircle between the outer end of the brake hose and the port on the lower end of the caliper, and this line is firmly attached to a bracket that is attached with the two bolts holding the steering arm.  Hence, if your objective in being in here is not to rebuild or replace the caliper you will want to remove all three bolts in order to get the caliper to come off with its hard brake line attached.  Otherwise, you'd need to disconnect the line and get involved in brake fluid.  By unbolting the bracket you can hang the caliper by a wire to avoid stressing the hose and just bolt it back on when done.

Remember to turn the steering back and forth while trying to remove and reinstall the forward steering arm bolt.  Otherwise, the shock absorber is in the way.

FRONT BRAKE CALIPER SHIMMING: As mentioned above, there is a shim (or a couple of shims) between the steering arm and the brake caliper at the long bolt.  The objective of this shim is to compensate for variations in the thickness of the caliper mounting lug to avoid stressing the steering lever as the bolts are tightened.  If your plan is to take things apart and put them back together with the same hub carrier, caliper, and steering lever, you need to take care not to drop or lose those shims when you take the long bolt out.  If you put it back together with the same shims in place, you should be OK.

If you do plan to replace something --exchanging the caliper for a rebuilt, for example --you will need to measure for the correct shim thickness.  Mount the steering lever with its short bolt tight and the long bolt threaded in but not tightened; you may want to fit a flat washer on the short bolt between the dust shield and the steering arm to make up for a bracket attached to the caliper being omitted here.  Measure between steering arm and upright at the long bolt, and subtract the thickness of the caliper mount lug to determine the shims needed.

New shims are available from Jaguar in two thicknesses: C44146/1 is 0.004" thick and C44146/2 is 0.010" thick.  It's really nothing more than a thin flat washer, so you could just buy arbor shims locally or cut washers out of shim stock.

Whenever changing shims or anything else involved in this steering arm attachment, the car will need a new alignment

It is apparent that the shimming between the caliper and steering lever was originally the only place shims were intended to be used here.  Step 4 of Section 70.10.10 and step 3 of Section 70.55.02 in the ROM clearly indicate this is the only place to be looking for shims upon disassembly.  However, apparently Jaguar decided that shims might also be needed between the caliper and the upright, either to center the caliper or to align it properly.  There's no excuse for the machining incompetence that would require shims here for either reason, but Craig Sawyers and others report that their cars came with shims in these locations.  Steps 10-14 of Section 70.10.10 and step 5 of section 70.55.02 discuss shims between caliper and upright for centering and aligning the caliper.

The Parts Catalogue doesn't list any shims for between caliper and upright, but obviously the shims intended for between caliper and steering lever will serve.

It's pretty easy to get shims in between the caliper and steering lever.  Getting shims between caliper and upright is nowhere near as easy.

If you add shims between the caliper and the upright, you need to be removing the same thickness of shims between the caliper and the steering lever!

FRONT BRAKE ROTOR REPLACEMENT: Jaguar chose to bolt the rotor to the inside of the hub flange, rather than the outside like some cars.  As a result, the hub must be removed to get the rotor off.

The various manuals suggest unbolting the rotor from the hub during this process by inserting a tool through the opening in the dust shield.  However, Nance O'Neil points out that there is no need to unbolt the rotor before removal, and instead the hub/rotor assembly can be removed as a unit and then disassembled on the bench.  Either way, the brake caliper must be unbolted from the upright.

John Himes adds a tip: "The 5 bolts that hold the rotor to the hub assembly can be very stubborn, especially when working alone.  If you place the wheel face down, then place the lug nuts through the holes, now you've got a nice big vice to hold it in place without buggering up anything."

Matthias Fouquet-Lapar has an alternative suggestion: "I actually took the hub out and put the disk in a large bench vice.  When I mounted the new disk, I simply used the old brake pads to protect the disk from the vice."

If you intend to have the rotor turned, don't separate the rotor from the hub.  Leave them together; you get a more accurate turning job by allowing the machine shop to mount the assembly by the hub.

FRONT BRAKE CALIPER SEPARATION: On the front calipers, fluid communicates between the two sides via drilled passages through the caliper halves themselves.  Hence, there are seals between the two halves to prevent leakage.  If you separate the caliper halves, you'll want to put it back together with new seals.  Note, however, that the square-section O-ring seals used between the halves may be difficult to find, and the Lucas caliper overhaul kit SP2887 does not include them.  A normal nitrile O-ring --square-section or not ---won't work; if you don't believe me, put one in a jar with some brake fluid and watch it for a few weeks.

Chuck Sparks says the seals are Lucas part number 67320782.  The package these seals come in says they are .325ID, .495OD x .070, but measuring one found it to be .079" thick.  Basically, they are 1/2" OD, 1/16" thick (the ID doesn't really matter as long as there's a hole).  Each front caliper needs two, so you need four per car.  The burgerflippers in the local auto parts store are likely to give you a blank stare when you ask about such seals, but according to Rob Reilly you can get them from John Farrell (page 710).  John Robison says, "XK's unlimited sells the caliper seals separately."

It's also been suggested that you can find suitable seals at a Chevy dealer.

Coventry West (page 693) sells an O-ring, 1/2" OD and 1/16" thick and made of EPR.  Apparently this works OK; according to their rep, "The o-ring will seal better on uneven surfaces than the square seal.  We've never had a problem with the o-rings sealing.  Not a single warranty or return."  Nevertheless, most mechanics would probably agree that the original Lucas square-section seal is preferred.  It does provide an idea for buying seals locally, since any industrial O

Brian Schreurs found that Motorcars Ltd. (page 695) lists a "caliper half O-ring" part number IN101648.

Joe Bialy says, "If you want to cut your own gaskets, McMaster Carr sells EPDM rubber sheeting, a 12" X 12" piece 1/16" thick is $3.78.  Part #8609k31.  I'm sure they'd have the cutters too.  I don't know if it's applicable for this, but they also sell 1/2" OD X 1/16" width EPDM O-rings."  See page 711 for McMaster-Carr.

On the rear calipers, the fluid communicates between the two halves via an external hard tube so there are no issues with seals.

FRONT BRAKE HOSES: The front brake hoses have coils around them to prevent kinking and to protect the hose in case of a tire rubbing against it or debris flying around in the wheel well.  On the '83, the coil around the original hose is plastic about 1/8" thick.  Replacement hoses, however, as well as the originals on some other year cars, come with a steel coil around the hose.  Obviously, the plastic coil won't rust --but if your steel coil is rusty enough to be a concern, it's probably time to replace your brake hoses anyway.

Ed Sowell says, "The new hoses I got came w/o coils.  I reused my original plastic ones." This is a workable plan, since it is a simple matter to wind the plastic coil off the old hose.  If your old hoses have steel coils, though, they apparently cannot be removed without destroying them or the hose itself.  Since it probably would not be a good idea to operate the vehicle without coils at all, if you don't have the plastic coils you should either make sure your new hoses come with coils or try to get some plastic coils from a junkyard.  And if you're replacing hoses with plastic coils with new hoses with steel coils, you may want to wind the plastic coils off the old hoses and store them away in case you need them next time you replace hoses.

FRONT BRAKE COOLING --'92-ON: The 1992-on XJS comes from the factory with air scoops for the front brakes built into the front spoiler.  According to David Buchner, it also comes with an inlet built into the dust shields on the front brakes themselves.  To obtain the same sort of ducted cooling that race cars have, all you need to do is connect flex ducts from the back side of the spoiler to the dust shields on the brakes, and tie them up so the front tires won't rub them when turned full lock.  Simple.  The opening at the back side of the spoiler is a rectangle, but you might actually be able to find a section of flex duct sold in auto parts stores for engine intake ducts that has a rectangular end on it.  Otherwise, any place that sells air conditioning supplies can provide a small sheet metal transition piece for connecting a round duct to a rectangular opening.

TWR FRONT BRAKES: Alan Heartfield owns an '85 TWR, and relates the following info from a TWR brochure: "This document states that the front rotors are 295mm X 35mm.  The calipers are AP Racing 4 pot solid calipers."  Obviously, this may provide some guidance to anyone looking to upgrade the front brakes on a non-TWR XJ-S.

REAR BRAKE HOSE: There is a single hose on the driver's side connecting the line from the car to the line on the subframe.  This hose, CBC1393 or CAC6143 or GHP65, is unique to the XJ-S; the saloons use a different hose.

INBOARD REAR BRAKE ROTORS: The OEM rear brake rotors are described as "externally damped".  This means they have an iron ring around the circumference that actually fits rather loosely.  If the disk tries to "ring", this ring will rattle, and the rattling will absorb the energy trying to cause the disk to ring.  IOW, the iron ring is to help keep the

Michael Neal pointed out that the OEM rear brake rotors are a "sandwich" construction.  This probably has something to do with fabricating a disk with the external iron ring.  "The stock rear rotors have the actual thin outer rotor surface attached to a solid core.  These thin outer surfaces are very brittle and break easily."

There are also reports of the ring breaking and coming out and jamming things up.

When rebuilding, Neal recommends the use of aftermarket rotors made from a single chunk of iron.  Often, when you order new disks, suppliers will send you these aftermarket rotors without even asking; the aftermarket parts are what they stock.  The aftermarket rotors don't have the iron ring, but nobody seems to have noise problems with them.  The aftermarket rotors are arguably quieter, since the loose rings on the OEM rotors sometimes jingle when you close the car door or the like.

"Never turn the rear rotors, the oem style rotors are sandwiched construction and would probably self destruct when you put a bit to them.  The aftermarket style could probably take one light surfacing but it just isn't worth it, price them sometime, they aren't that much."

Randy K. Wilson concurs: "Don't bother turning the rear rotors.  It's around eight hours of labor to get the things out.  If they are bad enough to require turning, the labor involved warrants replacing them with new ones.  Besides, it's rare for those rotors to be torn up and still be turned down and remain in spec."

INBOARD REAR BRAKE ROTOR REMOVAL: The instructions in the manuals are for removing and replacing the rotors with the rear suspension subframe in place.  However, many suggest dropping the entire subframe to make the job easier --and dropping the subframe is really easy, much easier than most people expect; see page 384.  Note that, regardless of whether the subframe is in the car or not, the lower swingarms will either have to swing down a long ways or be removed altogether to get the rotors out.  This means that the shock absorbers will have to be disconnected from the lower swingarms, so you might as well get to it.  It also means that the tie plate on the bottom center of the subframe will have to come off, because the swingarms hit it before they swing down far enough.  All in all, a case could be made for leaving the subframe in place if you're not doing other work that requires dropping it; at least, with it attached to the car, you don't have to worry about how to support it while working on it!

If you have the cage out, swinging the swingarms down far enough to get the rotors out means you have to get the cage a couple of feet off the ground --and supported in such a way as to allow the swingarms to swing down.  Peter Cohen suggests, "since the cage is out, just tilt the cage backward so that the input shaft is facing up, and then swing the swingarms to your heart's content."  Note, however, that before doing this you will need to either cap the differential vent or drain the differential, or it's gonna drain itself!

The ROM, Section 70.10.11, Step 8, says that after you remove the nuts holding the axle inner U-joints to the brake disc and output shafts, you are supposed to "Tap disc mounting bolts towards final drive unit."  Those bolts are welded to the output shafts; if you manage to tap them towards the final drive unit, you have screwed up big time!  The Haynes manual, Chapter 9, Section 12, Step 8, contains similarly erroneous instructions.

The rotors will not come out without removing the calipers.  Hence, before tackling the job of rotor replacement, read on about two different methods for disassembly of brakes mounted on a Salisbury final drive unit as well as the disassembly of brakes mounted on a Dana final drive unit.

DANA VS. SALISBURY: Much of the work on the inboard rear brakes is dependent on which type differential you have; see page 349.  If your car is in the 1985-88 range, check your differential before ordering parts or planning your work.  It's fairly easy to check: if the differential has a drain plug, it's a Salisbury; if not, it's a Dana.  If it's '84 or earlier or '89 or later, you can safely presume it's a Salisbury.  You have to check in the '85-88 vintage because the official Jaguar repair for a Dana is to replace it with a Salisbury.

INBOARD REAR BRAKE CALIPER REMOVAL (SALISBURY): Removal of the left inboard rear brake caliper is straightforward using the steps described in the manuals.  However, removal of the right inboard rear brake caliper might be considerably more tricky due to the proximity of the pinion shaft of the differential.  The pinion is located to the right of center so there's lots of room on the left side, but the right side is tight.  Specifically, the lower bolt holding the caliper to the output bearing flange is trapped and won't come out other than with the caliper itself, and it just barely comes out with the caliper!  If the bolt was a quarter inch shorter this job would be a snap --but you don't wanna shorten the bolt!

The particulars here vary from car to car, so some people won't even understand what the problem is while others will have trouble.  This author couldn't get that caliper out for two days --and then it finally came right out without doing anything noticeably different!  Peter Cohen says, "Correct!  I have had experience with that bolt.  There is a single caliper position and bolt angle at which it will come out, and when it does, it happens so unexpectedly that you will not remember what you did."

Here are some tips that might help.  When trying to get the caliper out, hold the upper end of the caliper rearward - toward the disc.  Once you've moved the bottom of the caliper forward and upward and reached the point where it doesn't want to move any more, twist the forward edge of the caliper (the edge where the pad retention pins go) in the outboard direction, away from the differential pinion.  If you can't twist it far enough to get it to come loose, you may need to remove the nuts holding the axle and rotor to the output shaft to allow the rotor to wobble a little.

INBOARD REAR BRAKE CALIPER REMOVAL (SALISBURY W/ BREMBO ROTORS): If you obtain Brembo replacement brake rotors for a Salisbury, they come with a pair of large access holes drilled in the mounting flange -- and no explanation.  Tim Dapper figured out what they were for: Using the access holes, you can remove the five bolts holding the output shaft bearing assembly onto the differential.  Remove the exhaust pipe hanger attached to the top of the cage with two bolts.  Then slide the output shaft bearing assembly out of the car with the rotor and caliper still attached!  The caliper mounting bolts can then be dealt with on the workbench.

The shims between the rotor and the output shaft obstruct the access holes a bit.  Before installing the shims, cut suitable notches in them.  Dapper suggests that if you find your car already has rotors with access holes but they are obstructed with the shims, it's easier to break out the Dremel and trim those shims in situ than it is to remove the brakes using the method described in the ROM.

When working on the handbrake caliper, you'll want to have the new rotor securely bolted to the output shaft.  Since the axle isn't in place, the nuts won't thread down far enough to seat on the rotor; you'll need to provide some washers or spacers.

Obviously you need new O-rings for reinstalling the output shaft bearing assembly.  This should be considered a benefit of using this method; any opportunity to seal that thing up better is good.

"But what good does this do me?  The old rotors on my car don't have the access holes."  Dapper nevertheless suggests you get Brembo replacement rotors with access holes.  That way, you can sweat and cuss and skin knuckles getting the calipers and rotors off, then take the output shaft assemblies out, then assemble them all together with the new rotors on the bench and reinstall them as a unit.  "I must admit I was quite surprised when the whole thing just slid into place.  A little jiggling is needed to get the splines to align.  This is so much easier than dealing with the caliper bolts and no clearance!"

When installing the five bolts in the output shaft bearing assembly, you must screw each one all the way down before turning the rotor to install the next.  There is precious little room between the heads of these bolts and the heads of the axle bolts on the back side of the output shaft flange.  If you start turning the rotor around with the bolts only part way in, you can get it jammed and have to struggle with an open-end wrench to get moving again.

INBOARD REAR BRAKE CALIPER REMOVAL (DANA): If you have a Dana final drive unit, trying to make sense of the disassembly procedures in the ROM will only cause confusion.  The manuals describe the Salisbury attachment in which the brake calipers are bolted to the inside of the flange holding the output shaft bearings in the final drive unit, and

There apparently are no Jaguar publications describing the removal of the brake calipers from the Dana differential.  Fortunately, it's not difficult to figure out once you're in there; in fact, it's easier than working on the Salisbury.  Jim Moore says, "Bolt access holes exist in the rotors and you can see them if you slide back the dust covers on the axles.  Not mentioned in Haynes, not obvious whilst on your back with halogen lamp heating up the back of your head."  Use these access holes to remove the two bolts holding the caliper in place.  Once the caliper is off, you can then remove the rotor.

If you're ordering parts beforehand, make sure you get rotors with the access holes if you have the Dana final drive.  Such rotors are usable on the non-Dana cars as well, although the access holes won't serve any purpose.

If you've ordered the wrong rotors and don't have time to exchange them, Tony Bryant says, "you can use the non- holed rotors on the Dana diff.  It's just a royal PITA to juggle the caliper bolts into place, and then do them up with a open ended spanner.  But it can be and has been done..."  Really, if you have the non-holed rotors you might be better advised to take them to a local machine shop and pay them to put holes in them while you wait.  There are dimensions in Figure 24 that will help, even though the two-piece rotor hub looks different.

DANA VS. SALISBURY/BREMBO ACCESS HOLES: With OEM rotors, the difference between Dana and Salisbury rotors is obvious: the Dana has access holes.  With the aftermarket Brembo rotors, the difference is no longer so obvious.  John Wynne says, "I purchased both sets of rotors.  Both sets had the access holes in them.  The only difference was the location of these holes."

Charlie Welkie says, "Guess which (Brembo) rotors I got first!  Yes, the ones with holes that didn't work --they were too close to the center of the rotor.  They were completely on the flange surface.  Try as I might I just couldn't get the caliper bolts in.  By now I had determined that I had a Dana and the rotors went back for exchange.  The replacements went in very smoothly (perhaps due to all the practice I had by now).  They have access holes out further that are partly on the flange and partly in the stepped portion of the rotor.

"The Altrom number for Brembo rotors for the Dana diff (hole spacing further apart) is 094-1106.  The other -smaller spacing - number is 094-1104."

Both sets of access holes are shown in Figure 24; the holes closer to the center are for Salisbury diffs, and the holes closer to the outer edge are for Dana.  You can check the dimensions to determine which access holes you have --or you can just lay the rotor on the paper and see which holes line up.

5/8" SOCKET: Whether you are using the access holes to get at the caliper mounting bolts on a Dana final drive or to get at the output shaft bearing bolts on a Salisbury, the tool is the same: a 5/8" socket.  Various reports, probably reflecting variations in hardware, describe the access holes as being anywhere from 7/8" to 1".  If they happen to be 7/8", you will need the right socket to fit.  A high-quality six-point socket will usually fit through a 7/8" hole with a bit of wiggle room, but a clunky 12-point from Taiwan hasn't got a chance.  If the access hole happens to be located a hair off so the bolt head isn't perfectly centered under it, well, things just get harder.

I'd suggest you buy a thinwall socket, except that thinwall sockets are also usually deep sockets --and you'd be better off with a short socket here.  It's best to just shop around with a dial caliper in your hand and buy the smallest OD short 5/8" socket you can find.

Remember: 5/8" is functionally the same size as 16mm.  So, check the other drawer in the toolbox for sockets that might work before heading for the tool store.  And while you're at the tool store, that gives you more sockets to check for a small OD.

Of course, you could just make sure that the access holes on your rotors are large enough --by boring them out, if necessary.  Going to 23mm, 15/16" or even all the way to 1" will provide enough clearance for the bulkiest of 5/8" sockets.

ONE MORE DISASSEMBLY METHOD: In addition to the two disassembly methods for the Salisbury and one for the Dana described above, there is one other method that should work for either: splitting the caliper.  Remove the bridge tube connecting the two halves of the caliper, and remove the pivot pin for the outboard handbrake caliper. Remove the four large bolts holding the halves of the caliper together, which allows you to remove the outboard half of the caliper from the car.  Then you can remove the rotor, which will permit better access to the bolts holding the inner half of the caliper in place -- whether Dana or Salisbury.

BRAKE COOLING: If you regularly drive your car hard enough to get the brakes hot, you would be well advised to improve the cooling air flow to the final drive area.  A scoop on the bottom of the car directing air up into this space might help; the Series Three E-Type came with such scoops, and it was a lighter car.

UPGRADING TO VENTED ROTORS: Jeffrey Gram installed vented rear brake rotors in his car.  The interesting thing was his reason for doing so: to reduce the tendency for the brakes to cook the final drive seals.  He expects that the use of vented rotors, even if braking performance is insignificantly improved, will extend the life of his final drive unit.  Jan Wikström --who drives a long, twisty mountain road to work --also installed vented rotors: "They worked well.  The old brakes worked pretty well too, and I certainly never got them hot enough to induce fade, but the oil seals didn't last, and they seem to last well with the ventilated disks."

There is yet another possible reason for upgrading to vented rotors.  The author noticed that the outboard pads were much more worn than the inboard pads, and Andreas Boedenauer explained: "I owned a couple (about 15) of Citroens with inboard front brakes.  All of them had almost unworn inboard pads (lubed with oil from the diff) even when the outboard pads where completely gone.  You only had some wear on the inboard pads on a brand-new car (the first 2 years).  I doubt that the differential --especially the output shaft --on a Jaguar is 100% dry and without any greasy surface.  Maybe I am wrong and there are Jags with immaculate bone-dry new or rebuilt differentials on the road --if yes, I want to see them."

What does this oily brake situation have to do with vented rotors?  Because vented rotors may avoid the problem.  When oil comes out of the differential output shaft seal, some of it runs along the shaft to the disc and ends up running down the inboard disc surface.  But with vented rotors, it will come to the inner end of the air passages through the rotor before it gets to the inboard friction surface.  The oil will then pass through the air passages all the way to the outside edge of the disk, completely bypassing the friction surfaces.  Hence, if your diff output seals leak, having vented rotors can improve your braking considerably, even when cold.

If you're interested in upgrading to vented rotors, there are kits available.  See XK's Unlimited (page 697), Terry's Jaguar (page 696), or Bob Greene Developments (page 716).  All of these kits provide ventilated rotors (which inherently must be thicker than the OEM solid rotors), spacers to put between the halves of each caliper to provide clearance for the thicker rotors, and several small parts that are necessary as a result of the caliper widening.

Brian Schreurs says, "I talked to Terry's about their kit two days ago.  According to them, their kit makes no accommodation for the handbrake whatsoever; they assume you're not going to be using it."  So, if you'd like a working handbrake, you might want to consider other kits --or consider the possibilities described below for obtaining the handbrake parts you need.

If you ask around, you may find negative reports on vented rear brake kits for Jaguars.  This is because GT Jaguar (now defunct) offered vented rear brake kits that were garbage --they didn't fit right, you had to grind on your final drive output shafts to bolt them in, they came with distorted hubs that caused runout in new rotors, etc., etc.  Perhaps this helps explain why they are now defunct.  Whatever, note that these problems have only been reported with the GTJ kits; the kits from all other vendors reportedly fit and work well.

If you wish, you can upgrade to vented rotors without a kit.  All you really need are the rotors themselves and a few minor knickknacks.  This has the potential of saving a little money or a lot of money, depending on your abilities to fabricate parts yourself as opposed to employing a machine shop to do the fabrication work.

This author has installed such a do-it-yourself rear brake upgrade (making small parts but hiring a machine shop for the hubs), and will provide considerable detail here; if you're not interested, skip the rest of this section.

The rotors described here are two-piece style --as are the rotors in most (not all) of the kits mentioned above.  Two-piece rotors are largely unknown in production automobiles where obviously it is cheaper to set up a casting process to create the entire rotor as a single part.  However, two-piece rotors are very common in the performance and competition arenas, where they are well proven.  In their simplest incarnation, they provide a simple benefit: the outer portion of the rotor, the part that has the cast-in ventilation passages, can be machined from a standardized casting (or even from brake rotors designed for other cars) rather than requiring a custom casting for each application.  The center hub portion of the two-piece rotor assembly, commonly called a "hat" because that's sorta what it looks like in most applications, is a non-wear item that sports most of the unique features --bolt patterns, offsets, pilot diameters, etc. --that make a rotor assembly a custom fit to one car or another.  Not only does using a two-piece rotor make it cheaper to obtain the custom rotor design needed, it also makes it considerably cheaper to maintain: when the rotors get worn, only the standardized outer portion needs to be replaced.

There are other features often incorporated into two-piece brake rotor designs including aluminum hats to save weight, "floating" attachment schemes to better deal with thermal expansion issues, carbon outer discs to save weight and work at higher temperatures, etc.  For our purposes, we'll be sticking with a basic design to keep the costs within reason; the ventilation is the feature we're looking for here.

Alan Heartfield found a company that'll provide special-order outer discs:

In the ROM, under "General Specification Data", page 04-2, the handbrake is described as "Mechanical, operating on rear disc pads".  Technically correct, but perhaps misleading; they operate on their own rear disc pads, not on the main pads that are operated by the footbrake.

CABLE ADJUSTING: In short, don't.  The cable adjuster is right behind the lever under the carpet on the XJ-S (different location on the XJ12, which has a pull handle under the dash), but is not intended to need adjusting as the pads wear.  The handbrake calipers have a self-adjusting feature and should maintain proper operation of the handbrake throughout the life of the handbrake pads.  If the handbrake seems to need adjustment, the self-adjuster has probably seized.  You should address this; don't try to get by with adjusting the cable.

Gregory Wells of Coventry West concurs: "The vast majority of handbrake calipers we see in our shop on inboard rear brake cars are seized and/or frozen up.  The things rust up badly in service and whatever grease Jag used on the handbrake calipers on the assembly line does a wonderful imitation of glue after a few years.  I would suggest pretty strongly that the handbrake calipers be inspected first before performing the cable adjustment."

Of course, if the calipers have been out for service or some nimnul has been fiddling with the adjustment, the cable may very well need adjustment.  Section 70.35.10 of the ROM stipulates that the handbrake lever should be released and the cable adjusted so there is some detectable slack.  This is misleading.  There are two different situations possible, and I shall explain how to adjust the cable under both conditions.

If the calipers have just been serviced and reinstalled, the self-adjusters within the handbrake calipers are presumably adjusted fully out and a new bronze fork has been installed in each side to hold the new handbrake pads well away from the rotor.  With the cable not yet in place, the handbrake caliper levers will be pulled outward against their stops by the spring on each side.  Note their position; in fact, you might simply measure the distance between the two cable clevises.  Install the cable, and then adjust the cable to just pull these levers off their stops.  The tension of those two springs should be applied entirely on the cable, not against the stops within the calipers.  If the springs are permitted to pull the levers against their stops, it tends to rock the caliper and pads such that one pad rests against the rotor, which can cause squeaks as well as premature handbrake pad wear.  And, of course, since the caliper will adjust to compensate for that wear, it will continue to wear until it's metal-to-metal.

Adjusting the cable this tight will not cause the handbrakes to bind if they aren't binding to begin with.  The self-adjusters work when the travel of each lever exceeds a certain amount; it doesn't matter if they start at their stops or a little off their stops.  If the levers never release past a given point, they will never adjust to be binding at that point.

If the system is together and operating but you just read that description above and now realize that your handbrake cable is adjusted too loosely --the levers are sitting against their stops when released and the cable is slack --you'd like to adjust the cable tighter.  Unfortunately, presumably by now the handbrake adjusters have worked, so tightening the cable adjuster now may cause the pads to drag -- and this is what the instructions in the ROM are warning against.

You have two options.  One is to take the handbrake calipers back out and reset the adjusters back to fully out and start over.  Presuming you don't wanna do that, your most viable option is to adjust the cable tighter gradually, making sure not to cause the pads to drag.

If the cable is really sloppy, you can take all the slop out of it right away.  As long as you're not pulling the levers off of their stops, you're not really making the handbrakes any tighter, you're just taking slop out of the cable.  Once you have the cable tightened to the point where the levers are beginning to come off their stops, then you must be careful.  Tighten the cable adjuster only a little bit farther, and check that the wheels still turn freely.  Then leave it alone for a while, allowing the pads to wear a little; you might even opt to make some of your stops while driving by using the handbrake to help it wear a bit faster.  Try not to ever pull the handbrake handle hard enough to cause the adjusters to tighten up.  Then, when you can get the handle up to the first click without any noticeable drag, go back in and adjust it a bit tighter.  Repeat until the levers are just off their stops with the handbrake released.

By the way, the ROM fails to mention that the way to get at that adjuster is to unbolt the seat belt from the floor on the driver's side.

DISCONNECTING THE HANDBRAKE CABLE: In the Haynes manual, Chapter 9, Section 18, step 5 describes disconnecting the handbrake cable from a caliper operating lever by extracting a split pin and a clevis pin.  The arrangement they are describing is illustrated in Fig. 9.18.  Must be an XJ12 thing, because the handbrake cable on the XJ-S isn't attached that way.  The ROM shows the connection correctly.

In the ROM, Section 70.55.04, steps 1 and 2 describe peeling back the carpet near the handbrake handle and backing off the cable adjusting nuts.  This is totally unnecessary; just make sure the handbrake is in the completely released position.  If the cable is adjusted properly, it should not require loosening in order to disengage or reengage the cable at the levers on the brake.  It should be possible to pull the levers together enough to pop the cable off or to pop it back on.  Note that it will require moving both levers, however; one is operated by the cable itself and the other by the housing moving the opposite direction, but both movements will be needed to disengage the cable.

Step 4 in the ROM starts with "Using suitable lever..." in describing how to disconnect the handbrake cable from the caliper arm.  Any sort of lever is unnecessary; the cable is easily disconnected by hand without tools.  Merely pull the two levers towards each other and pop the cable tip out of the block at the end of the caliper arm on the passenger's side.  Then pry the little rubber boot off the end of the cable housing at the block at the end of the caliper arm on the driver's side (as mentioned in step 5), and slide the cable housing back and out.

HANDBRAKE LEVER DAMAGE: As mentioned above, the cable attachments on the XJ-S don't require the removal of a split pin to remove; they can be engaged and disengaged by hand, slipping the cable into each clevis through a slot in one side.  The author found those clevises to be damaged, though.  They get spread a little bit, which just makes the ends of the cable fit loosely in the holes.  But the clevis no longer pivots; it gets jammed, since it is spread wider within the side plates of the arm.  It actually spreads the ends of the levers themselves a little bit.  This might not be a huge deal, since they seem to get jammed in nearly the correct position.

This whole situation didn't seem cause for major concerns; there are no known reports of the thing actually coming apart in service.  Just the same, though, while in there, I made two changes.  First, I carefully squeezed the clevises back to their original shape so that they would spin freely in the lever arms.  Second, when refitting the cable, I turned the clevises around so that the slot faced towards the lever rather than away.  This makes cable attachment far more fiddly since you must feed the end through the tiny gap between the clevis and the lever before sliding it through the slot.  The opening is so tight that it actually wouldn't fit; I ground three flats on the sides of the cable tip to help get it to fit through the levers.  Once the cable is in place, those flats have no effect.  With the clevises turned around this way, it seems far less likely that they will spread open because the lever itself will prevent them from spreading.

Another option, of course, might be to convert to the other design attachment using the split pin --but that would probably require buying new handbrake calipers, and that would require finding them.  Perhaps an easier fix would be to simply cut the weak clevises out and fabricate some replacements with more meat to them.

DUMB MISTAKES WHEN CONNECTING THE HANDBRAKE CABLE: You got the cable off, but now you can't get it back on!  It turns out that if you're fiddling with the cable end underneath the car and push the cable into the

You can go into the car, pull up the handbrake, push the button, and lower it back down, and you'll put it back into released position --but it's hard to tell you've done anything until you get back under the car and find you have more slack!  And good luck getting the cable latched onto the ends of the levers without accidentally pushing the cable in a little bit again, and have to get back out from under the car and manipulate the handle again.

HANDBRAKE CALIPER REMOVAL: Both the ROM and the Haynes describe how to remove the handbrake calipers without dropping the rear subframe from the car.  Jan Wikström describes the work: "It's a fairly tinkery job, and definitely easier the second time...  If you have a reasonable manual with a good picture of the system, patience is really all you need (you'll be working by feel as you can't see the upper side of the handbrake bits)."

Note that the reinstallation is considerably trickier than the removal.  The pivot pins in the main caliper that the handbrake caliper attaches to also hold a bronze fork with tines that insert into holes in the top of each caliper half.  The purpose of this bronze fork is to act as a spring to pull the pads back off the disk a little bit --but just a little bit.  As the handbrake pads wear and the caliper moves closer to the rotor, it pulls the bronze fork far enough to deform it --which leaves it just the right shape to pull the pads back just a little bit again.

So, to ensure proper operation, this means that prior to assembly the tines on the bronze fork should be positioned to hold the handbrake calipers away from the rotor a little bit.  Simultaneously, the caliper adjuster itself should be adjusted to hold the pads away from the rotor a little bit.  So, after the calipers are in with the fork properly installed, the lever on each handbrake caliper can be manually actuated a few times to allow the self-adjusters to bring the calipers back up near the rotor --and properly "set" the bronze fork to be applying the correct amount of retraction.  Manually operating the levers also serves to confirm that both adjusters are working prior to connecting the cable.

Several owners have reported errors in installing the pivot pins --missing the entire inner boss on the main caliper, apparently.  Bob Gallivan says, "Not only will they thread in but they look to be correct while missing the lower hole completely.  Been there & have the crick in my neck to prove it..."  After Carlos Artal was told this might explain the problems he was having, he reported: "I put the car on ramps again, and proceed to take the h/b calipers off.  Well, not 1 or 2 of the fixing bolts were out of place, but 3 of them were, with just one poor guy left there to do all the work!"

Another common problem is that the tines of the bronze fork end up on the disc side of the caliper --against the disc side of the pad backing plate -- instead of in the holes in the caliper where they belong.

Tip: Use a pair of 1/4" rods about 3" long to assemble the calipers instead of the pivot pins.  This allows you to install the calipers with these substitute pivots first, then finagle the bronze fork into place (since there are no heads on the substitute pins), and finally to carefully remove the substitute pins one at a time and replace them with the actual pins.  You can grind a tapered end on the substitute pins to make insertion easier; in fact, you could use 3/16" or 6mm rods just to make insertion really easy.

If you have the main caliper out, by all means take advantage of the situation and trial-assemble the handbrake calipers on it before putting it in the car.

HANDBRAKE PAD CHANGE: Since the handbrake calipers on Jaguars with inboard rear brakes are separate from the main calipers, they also use dedicated pads.  Really, these pads should never need replacement -- what are you doing, using them to slow going downhill or something?

The lining on new handbrake pads is about 7/16" thick, all the way across.  However, since the calipers pivot around the attachments on the main caliper, as they wear they become tapered.  This is normal, don't panic.  If they get worn too far, though, the rear end of the caliper will hit the rotor.  The service limit of 1/8" on the main pads is probably a good number for these pads as well, but you need to be measuring the lining thickness at the thin end.

Technically, the handbrake pads could be removed and reinstalled without taking the handbrake calipers out of the car.

Unfortunately, that won't do any good, because to install new (thicker) pads you will need to readjust the self-adjuster and install a new bronze fork.  In other words, the handbrake calipers have to come out.

Do you really need a new bronze fork, or can you just rebend the old one?  Well, if the handbrake pads are not being replaced, you only need to spread the bronze fork a little bit prior to reinstalling, and you will probably get away with it.  If you're replacing the handbrake pads, though, you will have to spread the bronze fork all the way back to its as-new shape.  Mike Morrin says, "Really bad idea.  I have seen a couple of cases where the fork has broken due to metal fatigue.  In itself not a big problem, but both times the rotor was destroyed before the fault was noticed.  Always replace the forks when you have the hand brake calipers off.  They are cheap."

When you go to removing the pads from the handbrake calipers, the ROM, Section 70.40.04, says "remove nut and spring washer securing pads to brake pad carriers, remove pads."  The Haynes says the same thing in Chapter 9, Section 18, step 10.  Removing that nut and spring washer is unnecessary; merely loosen it two full turns and the pad will slide right out, leaving the bolt, nut and washer loosely in place.  They even provided a little hole at the top center of each pad to make it easier to grab and pull out.  Of course, the new pads come with new screws in case you want to replace them, but there's really no need unless you strip them or something.

Just getting the nuts loose may be a challenge, though: The nut is 0.325" (8.25mm) across the flats.  This isn't even a standard Whitworth size!  Craig Sawyers says, "The nuts that secure the handbrake pads to the arms are 2BA.  And only a 2BA socket will get in there to remove the nuts."  Paul Burke says, "BA stands for British Association - believe it or not.  BA threads start at size 0 (zero) which is the biggest, and the bolts and nuts get smaller as the number gets bigger."

Well, at least you know what to look for.  This author used an 11/32" socket which worked but didn't fit too well; a 21/64" would have been better, if such a thing exists.

The bolt that this nut threads onto has an unusual head, but the threads are standard 10-28 fine thread.  So once you get those weird nuts off, you could put normal-sized nuts on to replace them --but that might not work well, either.  The nut on the outboard side fits down into a well, and installing a nut with a larger 3/8" hex will probably mean you can't get a socket or wrench on it.  This author found an excellent solution: the nuts used on military jet aircraft are extremely high strength and high temperature, yet they are very tiny and require a 12-point box end wrench or socket to install.  If you can find a source for such nuts, they are highly recommended for this application.  And you can leave the spring washer out, since the military nuts are self-locking.  You will need to find 12-point sockets or box-end wrenches in 1/4" or 5/16" sizes; Snap-On makes them.  I can guarantee they'll be easier to find than 2BA -- at least here in the US.

The facing of the handbrake pads is a rectangular shape with a corner cut off diagonally.  The end with the corner cut off diagonally must go towards the rear of the car, or away from the pivots on the main caliper.

All agree on one important point: make very sure the fingers on the bronze fork are correctly in place in the little holes when it's all together.  If one has slipped out, the handbrake pad will ride against the rotor, and this will damage the rotor itself in only a few hundred miles.

HANDBRAKE CALIPER REBUILDING: Jan Wikström says, "The self-adjusting ratchet mechanisms in the pad holders are quite likely to be clogged with semi-carbonized grease and dysfunctional; open the pad holders up, clean out the ratchet mechanism and grease very lightly with high-temp grease or MoS2 (molybdenum disulfide).  Drowning them in grease as the factory did is just silly; the ratchets may rotate one turn every few months and don't really need lubrication."

Mack Kamna describes rebuilding the handbrake calipers on Jaguar inboard rear brakes: "In the past my parking brake lever had to be pulled quite a ways to be effective.  I found the self-adjusting nuts to be galled up with dry grease and very tight on adjuster bolt threads.  I cleaned them up and dressed the gear teeth with a small file, then greased both the adjuster bolt threads (using C5A, anti seize), and the adjuster nut gear teeth (Hi-temp brake grease).  I then installed the handbrake mechanism assembly with new retraction plates, and adjusted the handbrake "system" per the manual.  When I pulled the handbrake lever, you could hear the adjusters smoothly clicking, and the pad assemblies tightened right up.  I make no claims on my choice of lubricants; none of my 3 reference books on this maintenance task mention lubrication,

"...With the lever released there is no drag on the rotors, yet it only takes three clicks to make the wheels unmoveable by hand.  I hope this can be of help to those of you who like myself have long suffered anemic handbrakes."

This author went a different way with lubricants, and lubricated everything in the handbrake caliper self-adjusting mechanism with graphite only.  Graphite is good to extreme temperatures, won't ever dry out (it's dry already!), and won't collect dust and grit.  The only concern is that it might not protect ferrous parts from rusting, and then the rusting could cause the adjuster to seize up.

HANDBRAKE ADJUSTER LUBRICATION: It is possible to lubricate the adjuster too well.  Peter Cohen: "Upon refitting each handbrake assembly, it is an easy matter to operate the arm to check that the adjustment mechanism is clicking, and, in fact, to adjust them up.  The first one I fitted worked fine.  The second one refused to click.  I removed the cover and refitted the mechanism to watch it in action.  When the lever arm moves, it moves the piece of spring steel that has a pawl that is supposed to catch the toothed wheel and drag the toothed wheel back a notch, if necessary.  What was happening on this one was that, when the spring steel moved, it was moving the toothed wheel in both directions, accomplishing nothing.  I couldn't figure out what is supposed to put drag on the toothed wheel to prevent this from happening.  Cleaning all lubricant off the threads wasn't sufficient.  I finally applied a bit of dirt to the threads to add more resistance, and now the adjuster works fine.  I'm sure it is not what the designer had in mind, but it worked."

THE ULTIMATE SOLUTION TO HANDBRAKE PROBLEMS: Some so-called "Jaguar experts" actually recommend removing the handbrake calipers from the inboard brakes entirely and throwing them away.  This is probably because they can't figure out how to assemble them correctly.  Obviously, it is irresponsible to recommend that an automobile owner simply remove a piece of safety equipment, but it is interesting to note that the handbrake calipers can be removed without adversely affecting the operation of the foot brake.  The Jaguar is a rare example of a car on which this is possible.

SCRAPE, SCRAPE, SCRAPE: Ron Ickse describes the cause of a scrape, scrape, scrape sound that seems more pronounced when turning one direction and goes away when turning the other direction: "I've had this now three times on Jaguars over 20 years.  In each case, it turned out that the retracting spring on the handbrake mechanism on one side or the other had failed, allowing the handbrake pad to remain in contact with the disk.  Eventually, the pad wears down to the metal, so then you hear metal-to-metal contact.  If the disk isn't quite true, you'll get the characteristic intermittent scraping noise.  Fiddly but not particularly expensive to mend, if you (or your mechanic) knows what's what with Jaguar brakes."

The rear brakes on a TWR are essentially the same idea as the do-it-yourself mod described starting on page 441; in fact, the www site listed includes a page of pictures of the rear brakes on Alan Heartfield's TWR.

Heartfield used Essex (see page 442) just to get replacement disks for his TWR since it proved easier and cheaper than trying to find genuine TWR parts.  There are other companies that can provide such discs, including Wilwood.

Ordering discs through Essex involves filling out a "Custom Brake Disc Order Form" which they can fax to you.  In the middle of the form there is a chart where you must fill in "Nominal Dimensions" of the discs you need.  Fill the form in as follows:

ØA B ØC ØD E MOUNTING HOLES APPROX.
WEIGHT
OUTSIDE
DIAMETER
THICKNESS EYE
DIAMETER
FLANGE
INSIDE
OFFSET NO. DIAMETER ØM

The rest of the form is self-explanatory --name, address, credit card number, etc.  You can opt for tricky stuff like cross drilling or face grooves if you want.  Essex will quote you a price once they get the form.

Note: the design shown starting on page 441 is not exactly the same as that used in the TWR --8 mounting holes vs. 6 -- so don't use the Essex order form shown there for getting replacement discs for your TWR.

Heartfield's TWR happens to have a Dana final drive unit.  With the TWR vented rear brake design, it appears that the calipers were offset inboard by about 1/8".  This may have been accomplished by milling 1/8" off the calipers themselves or off the mounting bosses on the Dana final drive unit.  If you need to replace either the calipers or the final drive unit on a TWR, you should check these parts carefully to see if the replacements will need to be modified accordingly.  If the Dana final drive is replaced with a Salisbury (the standard repair procedure) it would appear that 1/8" spacers would be required between the calipers and the output shaft mount flanges --spacers that would probably be lots of fun installing.  If you run into stuff like this, you might opt to rebuild the calipers or final drive unit rather than replace them --or you might opt to machine a 1/8" step in the inner hubs of your rotors like the ones shown on page 443, since the purpose of that step is to provide an assembly that doesn't require offsetting the calipers.

Chad Bolles says the outboard brakes used on the later XJS are exactly the same as those used on the XJ40.  Stephen Gibson says, "Outboard brakes on the XJS started at VIN 188105 with the solid rear disc for the 4.0 and 6.0 litre.  The vented rear discs came in at VIN 198335."

The handbrake used with the outboard brakes on the later XJS is actually a drum brake within the center portion of the disk rotor.  Stephen Gibson says, "The outboard handbrake mechanism and shoes are identical for the XJ40 and XJS installation.  When the vented rear discs came in the same handbrake mechanism and shoes were retained.  They naturally have the same part numbers."

HANDBRAKE LEVER JAMMING: This has only been reported on the cars with outboard rear brakes.  The handbrake will not release, no matter what.  Gary Penovich says, "One thing to try before you go through all this is to make sure the hand grip is back as far as it will go on the lever, before pushing the button.  It has a habit of moving forward, and blocking one's thumb from pushing the button in far enough to release the brake."  Of course, you might just opt to take the grip off and throw it away.

The problem probably isn't the grip, though.  "It can be fixed.  But, unfortunately, to really get good access to the lever assembly, you need to remove the four bolts holding the drivers seat to the floor, and tilting the seat up and away from the lever.

"Once you have good access to the lever assembly, remove the plastic cover.  I believe it is held on with only one screw.  Once off, you will see that the lever terminates at a flat, round metal plate.  In the inner area of this plate is a slot.  In the slot is a relatively thin, curved, metal rod.  That rod is supposed to move with the lever/plate, when you press the thumb button and move the lever.  Unfortunately, it appears that the lever can be over-tightened, causing the rod not to be able to engage properly in the slot.

"Take a large, flat-head screwdriver, and jam it into the slot, so that when you move the lever, the rod will move with it.  That will force the rod to disengage the brake.  Once disengaged, spray some WD-40 around the whole mechanism, and up inside the underside of the lever in the channel where the rod travels.  Also, check the mechanism a number of times before putting the cover and seat back."

Brian Jamieson had the same problem: "I was able to remove the cover on the handbrake lever without removing the seat."  He used a Pozidriv tip for an interchangeable-tip screwdriver.  "It is only one inch long and with the seat moved forward and the back tilted forward I could get this on the screw and turn it with a small quarter inch wrench.  When I got the cover off I pushed/levered the small rod that is connected to the button and then pushed down on the handbrake cable which dropped down and released.  I think the cable was binding where it goes into the outer cover.  Anyway, problem solved for the time being."

Antilock Braking System (ABS) brakes have gotten a lot of press.  Essentially, the system involves sensors in the wheels that sense when a wheel has stopped turning and releases the brake on that wheel.  When the wheel resumes turning, the brake is reapplied.  If the brakes are applied forcefully enough, this results in a "pulsing" as the brakes to each wheel are cyclically applied and released.

When initially developed, ABS was expected to provide a considerable safety benefit; in fact, many auto manufacturers pursued development of ABS in expectation that it would later be required on US cars.  After a few years of voluntary application (typically on higher-end cars such as the XJ-S), accident statistics failed to confirm any safety benefit, so proposals to require ABS have been stifled.

In a straight line on dry pavement, ABS brakes do little good; a car with comparable conventional brakes can stop in essentially the same distance.  However, the application is different; on the car with conventional brakes, the driver can achieve the best stopping distance by applying the brakes as hard as possible without locking the wheels, and many skilled drivers are very adept at doing so.  On the car with ABS brakes, the driver might as well simply jam the pedal as hard as possible and let the ABS work.  While this was originally expected to be one of the safety benefits --the driver no longer needs to be skilled at braking --it is theorized that this is in fact one of the reasons the statistics haven't panned out; the driver is still trying to modulate the brakes carefully as before, and he and the ABS system don't work together well and result in longer stopping distances.

In a straight line on wet pavement, ABS has little benefit as well.  Since the car does not stop as quickly, there is less weight shift from rear to front, and a set of conventional brakes with fixed proportions between rear and front may lock the front wheels.  However, the vast majority of conventional braking systems had addressed this problem decades ago, providing more rear braking at light pedal pressures with the emphasis shifting forward as the pressure increased.  Perhaps the biggest benefit of ABS here is control, since a car with the wheels locked may turn sideways on slick pavement.

In a straight line with water or oil only on one side of the car, ABS offers a major benefit.  If the conventional brakes are applied hard, one side of the car will slide and the car will turn violently.  Alternatively, if the brakes are not applied that hard, it takes a long distance to stop.  ABS allows the brakes on the dry side to be applied hard while the brakes on the wet side are kept from sliding, and the car can be brought to a rapid halt in controlled fashion.

In a curve, ABS provides perhaps its greatest benefit.  If conventional brakes are locked in a curve, the car will slide in a straight line, which runs it off the side of the curve and into a tree or over a cliff.  Skilled drivers know this and never apply the brakes hard in a curve; they will aim the car straight, even if it's aimed off the road, before applying the brakes hard.  With ABS, however, it is perfectly workable to apply the brakes hard in a curve, since the wheels won't lock and control will be maintained.  Since the curve causes a weight shift to the outside, the outside brakes can be applied forcefully without locking the lightly-loaded inside wheels.  However, this is yet another possible reason that ABS hasn't lived up to its promise of increased safety; drivers may still refuse to apply the brakes hard in a curve.

Loose-packed snow, gravel, or the like, may be one of ABS's most notorious shortcomings.  On such surfaces, the quickest way to stop a car is often to lock up the wheels and let them dig in.  However, ABS prevents this from happening, so the car seemed to roll along forever, pulsing all the way.  If the car ahead doesn't have ABS and has dug its wheels in and stopped in short order, this can be a real problem.

Richard Drozdowski says, "Shifting to neutral is almost a must for an XJ-S in the snow or ice.  Leaving it in drive tends to push the car ahead and plays havoc with the ABS.  The immediate ABS chatter greatly increases stopping distances."

Of course, stunt drivers don't care for ABS.  When you see those guys in the movies spin the car around backwards and take off in the other direction, rest assured they do not have ABS; that 180º spin requires that the steering wheel be turned first one way, then the other way hard and the brakes locked.  With ABS, they'd probably just drive off the side of the road.

ABS SYSTEM TYPES: ABS brakes were introduced on the XJ-S in March of 1988 (midst of 1988 MY) with the Teves Mk III system, and this system was used until early 1995.  The Mk III system can be distinguished by having an electric pump and an accumulator ball; they're on the right side under the hood on LHD cars.  It also has no vacuum-operated power brake booster; the master cylinder, which is a long, convoluted assembly, is bolted directly to the pedal housing.  The air filter housings on the V12 engine were shifted forwards to accommodate this master cylinder.

From 1995.25 on, Jaguar switched to the simpler Teves Mk IV ABS system for the XJ-S.  There is no accumulator ball, and there is a vacuum power brake booster.  In fact, the power brake booster as well as the master cylinder look remarkably like the pre-ABS components.

ALWAYS USE DOT 4 FLUID: Greg Meboe clarifies: "ABS systems call for (and need) DOT 4 fluid.  Not DOT 3, not "DOT 5" (silicone).  This is not the same thing as the early British systems.  The fluid required in the 50/60's cars must be compatable with the rubber used.  The fluid readily available in the US for this just so happens to be DOT 4 spec.  ABS systems require the boiling point (wet) of DOT 4 fluid, and don't care about being compatable with old British rubber."

Reportedly, Pat Goss, the host of the TV show Motor Week, said the following: "Never use silicon brake fluid in an ABS system!  [Silicon] brake fluid doesn't like the pumping action of the ABS pump.  The pistons move so rapidly that it causes the silicon to foam and all of a sudden you have aerated fluid and you have a pedal that's on the floor."

PAD CHANGE: If the car has ABS brakes and the calipers are pressed back, fluid within the calipers is forced back up the lines and into the master control system.  Since the fluid that has been within the calipers for some time often has a high degree of contamination (wear particles from the cylinder walls, etc.), when this fluid is backed into the controls it tends to cause problems --and very expensive problems at that.  It is suggested that when pressing the calipers back (like when installing new pads) to open the bleed port and allow the fluid to drain rather than pushing it back up the lines.

Perhaps this isn't a bad idea with any brakes.

Pat Goss, the host of the TV show Motor Week, reportedly advised to "exercise" the ABS at least once a month on a gravel road or in a wet parking lot -- meaning, jam the brakes and let the ABS kick in.

TEVES Mk III ABS OPERATION: Here's a brief synopsis of how the Teves Mk III ABS brakes work: There is an electric pump and a pressure accumulator that provide pressurized fluid.  When the brake pedal is depressed, the pedal linkage moves a piston within a chamber in the ABS master cylinder.  This piston directly applies pressure to the fluid leading to the front brakes, which means the front brakes will work even if the pump stops working.

This leads some to conclude that the front brakes are not assisted, but they are mistaken.  The force applied to this piston also actuates a valve that allows pressurized fluid to enter the chamber behind this piston, helping push it forward and applying the front brakes.  The result is a 4:1 power assist on the front brakes when the system is working properly.

The pressurized fluid applied behind that piston to assist the front brakes is also ported directly to the rear brakes.  The rear brakes are therefore actuated entirely by the power assist to the front brakes.  If the pump fails you will have no rear brakes whatsoever, save for the handbrake.  Combined with the loss of power assist on the front brakes, the fact that something is very wrong with your brakes will be apparent immediately --even without all those warning lights lit up on the dashboard. Now to the ABS operation.  There are three systems here: the LF, the RF, and the rear.  Each of these has two solenoid valves within the valve block.  If a wheel sensor detects that a wheel has stopped rotating, the first solenoid valve closes off the line from the master cylinder so no further pressure can be applied to that caliper.  Then the next solenoid valve opens, relieving some of the pressure within that caliper back to the brake fluid reservoir.  As soon as the wheel sensor detects that the wheel has begun rotating again, the second valve closes and then the first valve opens, applying more pressure to the caliper.  In practice this all happens over and over very quickly, leading to the characteristic pulsing of the pedal.

With the rear brakes that are fed entirely by the pump, that's all there is to it.  With the pedal-operated fronts, however, this alternate relieving and repressurizing would quickly allow the brake pedal to fall to the floor.  So there is one more valve involved that applies pressurized fluid directly to the front brake circuits during ABS operation to keep the pedal up.

ERRORS IN THE MANUALS: Page 70-4 of Volume 4 of the 1987-on Service Manuals (JJM 10 04 06/20) includes diagrams of the ABS booster unit and a description of how it works.  At one point it says "The control valve (3 Fig. 2) opens the unpressurized booster chamber to the reservoir (9 Fig. 2);"  The sentence is correct, but the reference to item 9 in Figure 2 is not.  Item 9 is the master cylinder piston.  There is no item number marking the booster chamber, but it's the chamber surrounding items 2 and 4 in Figure 2.

Item 1 on Figure 2 is called an actuator piston several times, but farther down on the same page they call it an "actuator plate".  That's just to confuse you.

Later in that same sentence, the term "preset pedal force" is used.  The word "preset" is there just to confuse you.  Just leave that word out and you'll understand the sentence better.

On page 70-9, the text says that item 2 in Figure 2 is the connection to the reservoir.  This is incorrect; item 2 is the connection to the booster circuit.  The connection to the reservoir is unlabelled but it is to the left of item 2.  I think.  I think Figure 2 is somewhat incorrect as well, showing the valve in energized position.

Mike McGaw and Brian Rice add another glitch: "The document in question is March 1991 XJS Service Manual Volume 5 Section 90, page 90.5.10-1.  This schematic clearly shows the switch states on the pressure switch as normally closed (whether under pressure or at no pressure is not clear from the drawing).  Furthermore, although the document is dated 1991, the schematic does not show the presence of the Brake Inverter Relay, which is clearly on 1990 and later cars."  You can read about that Brake Warning Inverter Relay below under the Blue Top Combination Switch.

As mentioned earlier, the Teves Mk IV ABS system has no pump and no accumulator ball but does have a vacuum booster just like the pre-ABS brake systems.  The ECU for the Mk IV system is in the engine compartment, in the right rear corner.  The ECU part number is JLM12004.

FAULT CODES: George Balthrop says, "The Teves IV (vacuum boost) brake system introduced during the 1995 model year no longer has the "blink codes" capability that existed on the earlier Teves (hydraulic boost) systems.  The ABS CM is linked to communicate with the Portable Diagnostic Unit (PDU)."

ABS SYSTEM REMOVAL: Some people, faced with the prospect of paying serious dollars to repair an ABS system, opt instead to simply remove it and convert the braking system to the far more reliable and easily repairable non-ABS power brake system used on the pre-ABS cars.  Sean McKee did this job on his '90, which came with the Teves Mk III system:

"Parts list:
. Complete master cylinder/ vacuum booster/ pedal assembly
. Check valve and vacuum adapter for RH intake manifold.
. front steel brake lines

"There are really no tricks in the installation.  The rear brake line screws into the master cylinder.  The steel lines for the front simply replace the existing lines.  I used the fluid supply line from reservoir to pump to be used as a vacuum line RH manifold to booster.  A tab needs to be welded to the pedal to push on the brake light switch.

"Note: the ABS/brake light will remain illuminated, less a rewire, the bulb needs to be pulled.

"Pedal feel is identical to the ABS unit with the free play distance maybe slightly shorter."

Why would you need to weld a tab onto the earlier design pedal?  Surely it operated the brake lights, too?  True enough, but the pre-ABS brake light switch had a long lever on it that the arm of the pedal itself contacted.  Perhaps, instead of welding on the tab, you could retrofit the earlier brake light switch as well --or just utilize a generic microswitch with a long springy arm over the button.  Paul Hanson says you can alternatively "use the cruise control switch up top of the pedal box along with a relay to reverse polarity so the brake lights come on when brake is applied."

Hansen adds: "New non-kinking steel brake lines are available at NAPA, which are a joy to use!  Connect the front port of the Master Cylinder to the two front brake lines using a "T" connector and doing some flaring of the ends.  The rear port of the MC connects with the rear brake line at the Pressure Delay hexagonal unit on the drivers side inner wing."

Tom Hollingsworth did the same job: "The swap was not difficult.  You do need to replace the entire unit, pedal to master cylinder (the pedal/box is slightly different) you'll need a few metric pieces, and a small piece of bubble, not doubled flared, brake line."

Obviously, you'll want to remove much of the ABS equipment such as the pump.  Maybe you can get a good price on EBay.  The wheel sensors and associated wiring can be abandoned in place.

It might be considerably easier to remove the Mk IV system, since the vacuum booster and master cylinder appear "normal".  I have no reports of this having been done, though.

Really, you should inform your auto insurance carrier so they can delete any credit you may be getting for having ABS.  This author tried that once with no luck; the insurance company's database showed that that particular model automobile has ABS and there's no way to change that in their computers.

If you decide you want to keep the existing braking system but just disable the ABS function, well, be careful.  You can't just pull a fuse and be done with it.  You must keep the pump, accumulator, and combination switch working --and those are perhaps the most failure-prone components!  But if the pump and accumulator on the Teves Mk III are not functioning, you have no rear brakes at all, and the front brakes require excessive pedal pressure to stop the car.

It might be more viable to disable the Mk IV ABS system in place since it has vacuum assist and a conventional-looking master cylinder, but details are unknown at this time.

1991: For the 1991 model year, the body of the XJ-S was significantly altered.  The most obvious differences were the totally different taillight arrangement with new "neutral color" taillights that don't look red until they come on, and rocker panels that flared toward the wheel wells rather than being perfectly straight.  But despite the outwardly similar appearance of the rest of the car, supposedly almost every panel was altered, so purchasing any replacement body panels will probably require specifying pre- or post-1991.

The more significant change, as far as buyers of used cars are concerned, is that beginning with the 1991 body style revisions the entire body was supposedly made from galvanized steel.

RUST: The following is a description of where to keep an eye out for rust on an XJ-S, courtesy of John Butler, Mike Morrin and others:

John Nuttall adds, "I found two places where rust, if left untreated, could cause serious damage:

1. Chassis rail/tunnel area.  By the chassis rails I mean two heavy gauge steel members that run from near the back of the floor right to the front of the engine compartment.  These rails from the backbone of the body.  The floor and tunnel are made from two separate pieces, one for each side, joined at the top of the tunnel.  There is a step in the lower part of the tunnel.  The chassis rail is welded to three faces of this step.  The lowest part of the rail is horizontal and extends under the floor about two inches.  The two are spot welded together.  On my 1987 shell the rail was not formed properly so that the part of the rail under the floor slopes downwards to the outside.  Looking under the car I can see a gap between floor and rail that was not filled by sealer.  Looking at the floor from above I can see depressions in the floor at each spot weld where the tongs of the welder forced the thinner floor metal down to meet the rail.

The consequence of all this is that rust has started in the space between rail and floor and has spread to the vertical part of the step in the tunnel to such an extent that rust is visible on this part of the step when viewed from inside the car.  The rust is eating away this part of the floor/tunnel stamping.

The serious implications to the structural integrity of the body are obvious.  This fault appears to be caused by improper manufacturing of the rail and lack of quality control, and it probably occurred on other vehicles.

2. Front lower outer seat belt anchorage.  On the '77 and '79 cars this anchorage is a nut welded inside the vertical face of the inner sill.  Presumably it was thought that this was not strong enough, and at some point before '87 the anchorage was moved to the sloping part of the floor adjacent to the sill.  A thick plate was welded and bolted to the underneath of the floor to reinforce the area.  Unfortunately, the floor has a ridge in at this point and there is a gap between the floor and the plate here.  The undercoating has proven inadequate to stop rust between plate and floor.  This rust has spread between undercoating and floor.  Rust is visible from the inside on parts of the floor, which means that rust has eaten through the floor.  The strength of the anchorage is clearly at risk.  This fault is mainly due to poor design, I would think, and it is certain to be present on many other vehicles.  "I urge owners of cars that might be affected by these problems to inspect their vehicles.  Inspection from the inside requires that carpet and insulation be removed."

RUST AVOIDANCE -TRUNK LID: Julian Mullaney sends this tip: "Beginnings of rust under the lowermost lip of the trunk (boot) lid.  There are not enough drain holes here where the two sheets of steel are spot welded.  I will drill a couple more drain holes."

RUST AVOIDANCE -TAILLIGHT AREA: Julian Mullaney points out that water may collect behind the taillight fixtures, since there is no drain from this area.  If it appears to be a concern, perhaps the best solution is to merely coat the metal with something to prevent rust, since it doesn't show.

The gaskets around lenses on cars generally follow one of two schools of design: they either attempt to totally seal thereby not allowing water in, or they include a notch at the bottom to allow water to drain out.  This author's observations and experience indicate that the second idea is more often successful.  Jaguar, of course, uses the first.  To drain the water from the area behind the taillights, the gasket between the fixture and the body can be cut prior to installation to form a drain channel.  If done at the bottom corner near the boot lid, it will scarcely be noticeable.

RUST AVOIDANCE -GENERAL: Car enthusiasts generally recommend a product called Waxoyl (see Brit-tec, page 701) for treating the areas of bodywork prone to rust.  According to Frans Hoekemeijer, "It can be painted or sprayed.  It can be thinned with "white spirit", which evaporates rather quickly.  Only a very thin layer is sufficient to protect metals against corrosion as the molecules are polarized and cling to the surface through electrostatic action, in the same way water molecules do unfortunately.  It sets to a waxy substance.  If used on the outside of the underbody of the car it has to be renewed every so often."

In the UK, Waxoyl sells a "pump kit" which screws onto to can of Waxoyl and you manually pump it and it becomes a spray gun.  It comes with a thin lance so you can poke it into various holes and get good coverage.  Pete Hamel says "It's quite thick at normal temperatures so you can either thin it with white spirit or immerse the can in a bucket of hot water to make it more sprayable.

"The beauty of it is that you do not have to completely clean all dirt off the surfaces you apply it to as it creeps into small crevices and through dirt.  It's good for hard to reach areas.  You can also apply it over surface corrosion (remove any flaking rust).  It does leave a slightly waxy/sticky surface though so you don't want to use it anywhere that appearance matters."

There are some people advertising in Jaguar World who come to your house and treat the car for you.

Another product favored for protection is called P.O.R. 15.  According to Vince Chrzanowski, "A customer once painted the exterior of a car radio with POR (don't ask me why).  When we tried to remove the stuff, we found it was nearly like porcelain in hardness and durability.  We had to change to a more aggressive abrasive in the bead blast cabinet.  I hope never to see POR on a radio again, but wouldn't mind it on the frame of my Mark IX."

PAINT: Jeffrey Gram reports: "Here in Europe many cars imported from the US are eventually repainted, and even many professionals are not aware of a pitfall in this area.  According to a local "spritzer" the paint used on US cars are of a different and higher elasticity than Europe paint to be able to cope with extreme temperature variations causing expansion and contraction of the body sheet metal.  If a US paintwork is spraypainted with EU paint, cracks will appear since the EU paint cannot cope with the expansion and contraction of the US paint layer.  The solution is to either repaint from bare metal, or to spraypaint the US paint with a couple of layers of "bridging paint" before the new paint layer."

FASTENERS: All fasteners on the exterior of a car need to be stainless steel.  On the XJ-S, it appears that most of them are --if nobody's been working on your car.  If there's a chance that some of yours have been replaced by some repairman or PO that didn't know any better, check all of them with a magnet (a magnet won't attract stainless steel) and replace any that are not stainless.  This includes all the screws holding lamp lenses on.  Here in the US, another good indicator is to carefully inspect the cross drive head; if it's Phillips, it is not the original screw --the original screws were Pozidriv.

This author was unfortunate in that the turn signal bulbs in my front bumper had not burnt out in a long time.  I say unfortunate because the screws that hold the lenses on had corroded and seized so badly they had to be drilled out - four out of four, 100%.  These screws were plain steel; since it is probable that Jaguar originally fitted stainless steel screws to these lenses, I may have been a victim of a previous repair.  If your screws are still removable, I highly recommend you check to make sure they are stainless, and if not to purchase four 10-32 x 1-¼" Phillips drive oval head stainless steel screws to replace them with.  Even with stainless steel screws, be sure to apply some anti-seize compound when reinstalling -- the clip nuts are not stainless.

Here in Bubbaland, 10-32 stainless steel screws are difficult to find, so I replaced the elaborate clip nuts on the bumper with conventional #10 clip nuts (available at auto parts stores) and bought some #10 x 1¼" stainless steel Phillips drive oval head sheet metal screws at a marine supply store.  I never have to worry again about getting them out.

Stainless steel fasteners can be found at most marine supply stores and many better hardware stores, although fine thread or metric sizes are often a challenge.

ADHESIVES: According to Charles Daly, "A call to 3M produced the following info: If it's neoprene, as in a fitting, washer, etc., then 3M-8001 (Neoprene) is best.  If it's weatherstripping type application and the rubber is EPDM (Ethylene Propylene Dieme Monomer) (which is what most auto weatherstrip is) then use 3M-80119 (which is called weatherstrip adhesive)."

WATER LEAKS -A/C SYSTEM: Bob Tilley investigated the cause of water leaking from his air conditioning system during rainy weather.  It turned out that the plastic cover over the windscreen wiper motor had deteriorated and started breaking apart --a common problem discussed on page 618.  In Tilley's case, the various parts of the cover found their way into the drain pipes that feed from the wiper area through the engine compartment and out through the wheel wells.  The drains end with a rubber elbow, and the plastic parts got lodged in it and plugged it, causing the wiper compartment to fill with rainwater and start draining into the air conditioner.  Tilley recommends that the drains be fully disassembled to ensure that all plastic scraps (as well as leaves and other debris) have been cleared.

WATER LEAKS -DOORS: Ian Finlay suggests applying talcum powder to the seals, then closing the door and applying a hose.  The talcum should make the location of the leak obvious.

WATER LEAKS -A-PILLAR DRAIN: At the corners where the rain gutters meet the windshield, the seal appears to have a gap underneath the chrome trim.  This is deliberate, providing a drain for this area of the roof down the inside of the A pillar.  It'd be a bad idea to try to seal it up.

Pat Johnson was getting rainwater on the floor, and finally figured out it was coming from these drains at the top front corners of the roof.  Water that finds its way into these drains -- a goodly amount, to be sure -- is supposed to run down the pillar between the chrome trim piece and the structure and through the bodywork in front of the door.  Somehow, it was being diverted inside the structure, and ended up in the carpet instead.  The solution involved removing the chrome trim piece covering the A-pillar.  "Being a novice at this, I was a little (a lot) scared to start removing rivets.  They look so permanent!  But I bit the bullet and started drilling.  It was easy!  I found gaps between the body and the molding.  After calling a glass repair shop and getting some silicone, I went to work.  I filled all the crevices and opened the drain hole.  I then refit the chrome and put my first rivets in.  I must say, I think I did a pretty good job.  It looks just like new and the lake is gone.

"It is supposed to drain in front of the door.  Leaves and some other unidentifiable gunk were plugging it.  The channel was also narrower than I think it was supposed to be due to the black rubber material under the chrome spreading toward the center."

Harry Trafford elaborates: "After drilling out the little pop rivets, carefully pry the chrome off.  It will come off.  I used a small stiff detailing brush to clean it all up under there.  I took a very small screwdriver and ran the blade under the gasket edges to clean them out.  A lot of dirt was removed.  I purchased a tube of Permatex Auto Glass Sealer, then using the screwdriver end, I gently lifted the gasket edges, sliding the tip down the glass and followed right behind it with the sealer.  The sealer is thin and is supposed to run into the crevice.  If you get the sealer smeared all over, use acetone or nail polish remover to clean it up.  Do not get acetone or nail polish remover on the car's paint!

"I used small 1/4" to 3/8" sheet metal screws to reattach the chrome strips on the "A" pillar.  Works fine." Stainless steel is recommended.

WATER LEAKS – FRONT WING ATTACHMENT: In the December 1996 issue of Jaguar Enthusiast magazine, John Wood describes tracking down and correcting a leak from the "wing rail", which made it into the area beside the footwell and managed to soak the carpets.  This particular problem was apparently aggravated by body work done on the sill.

WATER LEAKS --MIRRORS: Emile A. Des Roches says, "My wife's XJS had a seemingly "irremovable" white mineral dripline under the outside mirrors --the only blemish on her 16,000 original mile '95 XJS coupe.  After many experiments with paint rejuvenation problems the blemish was removed --until the next rainstorm.  It seems that water builds under the mirror, minerals gather from the various metals involved in the plating process, screws and blind nuts holding the mirror to the body and the oxidized product finds its way out under the black plastic piece separating the mirror from the door.

"The fix is to disassemble & clean the back side of the door mirror/plastic escutcheon assembly, then to put RTV or similar sealant around the inside of the black plastic escutcheon.  After a couple of months, it worked so well that I tried it on my car too.  Incidentally, the excess H2O will drain into the door and out the bottom drain holes harmlessly."

This author has never had this problem; when I first got the '83, the black plastic gaskets were so badly deteriorated that they were immediately replaced with pieces of rubber cut from an old inner tube.  Since the rubber is more pliable than the plastic ever was, it apparently sealed effectively without the addition of sealant.

Des Roches responds: "OK, I admit to cheating and using "black again" on the crappy-looking grey plastic escutcheon.  As I recall from my friend's mid-'80's S, the newer cars have a thicker (about .4") escutcheon around the outside mirror.  Wish I had thought of the rubber however."

SUNROOF --FACTORY OR DEALER ADD-ON?  The question of whether the XJ-S ever actually was fitted with a sunroof from the factory always seems to generate more argument than definitive answers.  Whether or not any sunroofs were actually built into the car at Coventry, it is apparent that many of the sunroofs that came on new cars were installed by dealers to boost sales.  In this case, each one may be different.  Steve Draper, who owns an '88, says, "I note that in my XJ-S manual, the sunroof switch is located on the center panel between the window switches, on the same plastic panel.  In my car, the switch is under the steering wheel, and when viewed closely has the aftermarket name on it.  An easy indicator of factory installation may be the switch (which I wish was on the center panel)."

"I, Chad Bolles, do hereby state for the record once and for all that Jaguar did offer a sunroof in the XJ-S and I do not care what anybody else says.  Quoting from Jaguar XJ-S Drivers Handbook publication part no. JJM 18 02 03/85, in the index section 5: "Fittings -Sunroof-Coupe: page 71" and on page 71 we see how to operate same and on page 72 we see how to operate in the manual operation mode.  If those who know everything had taken the time to look in the parts book, part no. RTC9888CE dated August 1987 on page 2J 11L you would see part no. BBC2682 and I will be damned if it doesn't look like a sunroof and even has the title "Sunroof" and uses part no. JLM440/ND Headlining Cloth.  Then try page 2J 11R and what do you know all the pieces for the roof are listed.  Next try page 2J 12L and I will be darned all the elec pieces are listed there.

"The roof was offered as an option in 86 and from then on as a kit."

WATER LEAKS -SUNROOF: At least some of the sunroofs installed, as well as the ones fitted to the XJ6 at the factory, use drains on the front corners to route water down the A-pillars and out the bottom of the car.  These drains are thin and easily plugged with debris.  If a wire is used occasionally to keep them clear, the tendency of the sunroof to leak water to the interior is greatly reduced.

There also may be some problem with the connection between the sunroof and the drain tube.  It may be helpful to inspect the connection and, if necessary, apply some sealant.

SUNROOF REMOVAL: Since sunroofs for XJ-S's don't exist, your ROM may not tell you how to remove it; so, here are instructions provided by Murray Trotter.  Note that these instructions actually apply to the XJ6, but apparently the sunroofs are similar.  Also note that when he says "hood lining", he means the headlining.  "To remove the metal outside skin of the sunroof, slide back, undo the phillips head screws along the front edge, slide roof forward, on switch until almost closed, lift up front of roof and pull forward, back edge is clipped in.  Take care not to lift roof too high otherwise you will mark it on the outside edge of the roof.  Quite simple to remove with a bit of care.

"The actual body of the roof is a little bit more difficult, removal of the hood lining is required.  First remove the outside rim around the hood lining; this requires removal of the sunvisors, etc.  Then prise all the covered mouldings off carefully.  This is hard to do and I always seem to end up breaking a clip or two.  The actual lining can then be dropped.  It is glued around the outside edge.  Careful with this one, it is easy to rip the lining.  You will then see the the actual sunroof is all one unit which has four metal brackets, like legs coming off it.  These are pop-riveted to the inside edge of the roof; drill these out, and you can drop the whole thing out as unit.  Don't forget to unplug the wiring."

WATER LEAKS -CONVERTIBLE TOP: Julian Mullaney says, "I've never had a single drop come in my 1991 XJ-S Convertible, but I did adjust the top to fit tighter.  This is simple, just screw in the hooks a turn or two on each side of

WATER LEAKS -WINDSHIELD: Most modern automobiles glue the windshield to the structure and then attach a piece of trim over top to conceal the joint.  You can tell such arrangements because the glass itself has a black pattern printed on it; the black is to keep the sunlight off the glue, which would cause it to deteriorate.  Supposedly the Jaguar XJ-S went to this sort of attachment scheme in the 90's.

On the earlier cars, Jaguar actually used a real rubber gasket that fits around a lip on the car and fits around the edge of the glass, holding it in.  The seal is called a Clayton-Wright type seal, meaning that it involves a locking strip; the seal and glass are installed, and then a hard plastic strip is pressed into a groove in the seal which jams it firmly against the glass.  If you remove the four stainless steel trim pieces, the locking strip is hidden underneath.  Once you remove the locking strip, the glass can be removed and reinstalled fairly easily.

In an article in the February 2002 issue of Classic Jaguar World, Ray Storer of National Windscreens Romford points out that water can get in between the laminates of a windshield and cause whitening of the glass.  To prevent this --or prevent it from getting any worse once it's already begun -- Storer applies liquid rubber to the edge of the glass itself.

If you're lucky, you may be able to stop your leaks without removing the glass.  Remove the stainless steel trim remove the locking strip, and then it's a simple matter to pry the edge of the seal away from the glass.  Clean all the crud out, clean it all really well with alcohol or some such, then apply some clear flowable windshield sealant and jam the plastic strip back in.  As the strip presses the seal hard against the glass, the flowable sealant will ooze out.  Wipe off the excess, reinstall the stainless trim strips, and you should be leak-free.

You're supposed to use a small loop of metal wire to reinstall the locking strip.  The loop fits into the slot and the strip passes through the opening, so just sliding the loop along the slot puts the strip in place.  You can buy a special tool, but you can also just make one from a coat hanger.

WINDSHIELD SCRATCHES: Chip Lamb suggests: "I was told Bon-Ami household cleaner works great.  Removes pits and scratches.  Removed the scratches made by my windshield wiper ends on my Saab 1991 900 2 or so winters ago.  Worked like a charm."

Somebody else suggested toothpaste -- the abrasive kind, not the gel kind.

WINDSHIELD REPLACEMENT: Chad Bolles says, "What you really need is a glass shop that knows what it is doing.  The seal will not fit if you install it on the glass out of the car, it will be loose, but once installed will be tight.  The seal must be sealed to the body and to the glass itself, if the glass shop says anything different, then take your car elsewhere, they do not know what they are doing.  The factory manual says to seal it that way."

Mark West concurs: "My experience with a new windshield in my '89 XJ-S, installed by the dealer, was enough to convince me that a broken windshield is equivalent to a blown engine in terms of severity.  Three tries, two new seals, a glass shop that claimed to know what they were doing but installed it with the seal in upside down once (gave the car a sort of "Mickey Mouse" ears), and gallons of antacid later, I finally had a windshield that didn't leak, seemed to fit okay, didn't make too much noise going around corners, and was generally 80% acceptable.

"Don't think that Joe's Local House of Glass can do the work.  You'll hate yourself in the morning."

HOOD GAS STRUTS: If you're tired of your XJ-S hood falling on your head, but don't want to pay the $$ for new Jaguar struts, Herbert Sodher provides a suggestion.  There is a device made by Pylon called Lift Lock, and it is sold at auto parts stores as well as Wal-Mart and Kmart for about $8.  It is a device which is clamped onto the plunger of the strut, and has an arm that slides along the outside of the strut housing as the hood is opened.  When fully open, the arm clears the end of the strut housing, falls against the plunger, and jams against the end of the strut housing to hold the

Peyton Gill came up with another idea: buy a "split bolt connector" of a suitable size and install it on the strut plunger.  A split bolt connector is a device used to connect two copper electrical cables.  They are made of solid copper or bronze, so it probably won't even scratch the strut plunger.  Just raise the hood, slide the connector down, and tighten the nut.  When you want to lower the hood, just loosen the nut, slide the connector back to the far end and tighten it down there.

If you want to replace your struts, you can use a reasonably-priced aftermarket strut intended for another type car that will work on the XJ-S.  Aftermarket struts such as Motormite's "MIGHTY LIFT!" (lifetime warranty!) are available in discount auto stores for about $20 each.  Of course, you can have a discussion with your local junkyard as well.  For the late 1976-on XJ-S, the gas struts for a Chrysler LeBaron Hatchback (MIGHTY LIFT! no. 95018) are close to the original length and can be made to work with a few 3/8" washers.  Larry Barnes adds that the struts he fitted to his wife's ‘92 "are mfg. by "STEDY LIFT", PN# D072-157, $19.99 and they come with a Life Time Warranty."

Note that aftermarket struts are a good deal more powerful than stock struts.  This is OK for most cars; customers are happy when the hatchback on their LeBaron opens more forcefully than it ever has.  However, it may cause minor problems on the XJ-S.  While you no longer will have problems with the hood closing on your head, you may have trouble closing the hood; you probably will have to hold the hood down against the latches while operating the lever under the dash, and in the worst case you may require an assistant on the other side of the car to get the hood closed.

You should always replace both struts together; one strut stronger than the other distorts the hood, and it bangs the fender on one side when closing.

Note that the pre-late 1976 XJ-S used a different strut.

Michael Neal says that Jaguar is now making struts with a built-in locking device to hold the bonnet open even if the gas pressure is gone.  Your only remaining problem will be getting your fingernails under the edge of the bonnet to lift it up.

LONGER HOOD GAS STRUTS: With the stock struts, the bonnet doesn't open very far, making it a pain to work in the engine compartment.  Jaguar apparently limited the range of opening because the bottom center of the grille contacts the top of the front bumper.  However, Michael Neal points out that the contact doesn't appear to do any harm!

John Napoli figured out how to replace the stock struts with longer ones so that the bonnet opens a reasonable amount without having to disconnect the struts.  The first step in replacing the struts is to make sure your bonnet will open far enough to use them; the alignment of the bodywork varies slightly from car to car, and breaking the front grille will not make you very happy.  So, with the aid of an assistant, disconnect the struts and gradually tilt the bonnet farther and farther toward vertical, keeping an eye on the grille/bumper contact.  See if you can open the bonnet enough that the mounts for the struts are separated by 22-1/4".

Note that there may also be a minor interference between the hinges and the plastic filler piece between the bumper and the car.  If there is a problem here, the openings in the plastic for the hinges can be enlarged slightly.

If this much opening presents no problems, go to your local auto parts store and purchase a pair of aftermarket struts intended for a 1984-85 Honda Accord 3-door.  They are made by Pro Lift, part number 92307, or by Motormite, part number 95038.  The ends of these struts are thinner than the stock Jaguar struts, so you should add some spacers to the mounts to make sure the body of the strut doesn't contact the mounting brackets.  Actually, suitable spacers may come in the package!

The XJ-S requires a strut that will collapse to 13-1/4" or shorter, and the application catalog lists the Honda struts as having a minimum length of 13.4" --too long.  However, measuring the struts themselves indicates they will compress as far as 13", perhaps even a hair under.  Therefore, they work fine, and hold the bonnet a lot farther open than the stock struts.  If yours end up not quite short enough, you should be able to make them work by elongating the holes in the

Note that the OEM Honda struts will not work.  The struts needed are those sold as aftermarket replacements for the Honda, not the original struts.

Here's the measurement from the corner of the opening for the hood to the corner of the hood when fully open with these new struts: 46.5"  Go measure yours!

PROTECTING THE HOOD STRUTS FROM HEAT: Michael Neal claims that heat in the engine compartment will toast most aftermarket struts, and that only the Jaguar originals will do.  Of course, the aftermarket struts have a lifetime warranty and the Jaguar struts don't.  And the Jaguar struts seem to fail as quickly as any, while several owners have reported long-term success with the aftermarket struts.  However, heat probably is a serious concern here, and it's easy to provide any strut with a measure of protection by merely wrapping it with some aluminum foil.  In this case, it is very convenient, since the width of aluminum foil matches the length of the strut nicely; just tear off about six inches from the roll, and wrap it around the strut, crimping it a little near the bolted end to keep it in place.

GETTING THE HOOD OUTTA YOUR WAY: On most cars, if the hood is in your way when working, the option is to remove it.  With the XJ-S, however, there are several options in between.  Michael Neal found that if the gas struts are disconnected, the hood can be opened to a nearly vertical position, greatly improving conditions for the mechanic.  The plastic grille contacts the front bumper, but that doesn't appear to hurt anything; the grille simply flexes.

Neal commonly disconnects the struts when working on customers' cars, holding the hood in a wide-open position by removing a rubber plug forward of the strut mount and propping the bottom end of the strut, with the bolt, in this large opening.

Jim Isbell points out that another option is to remove the grille first.  Then, with the struts disconnected, the hood can be opened to vertical, and the front edge rests on a rubber portion of the front bumper.  Putting a cloth in between may be wise, and providing a prop so the wind doesn't blow it down on your head would be nice.

When using any of the above methods, keep an eye on the plastic filler panel just under the grille.  It has openings for the hood hinges, but the openings may not be large enough for the wider opening and the plastic may crack.  It may be helpful to remove this piece, or to enlarge the openings in it.

HOOD POP: John Napoli says: "Here's a cool mod for your XJ-S.  It works best if you have good hood (bonnet) gas struts, and really well with the generic (Honda) replacement listed in Kirby's book.

"Remove the hood safety latch.  Just pull the pin and it comes off.  There are not many failure modes on an XJ-S where you need this feature anyway, so I wouldn't worry about it being gone.

"Now, when you want to show off your V12, just pop the release handle from within.  The hood rises silently and majestically.  Everyone is impressed.  Men stand in awe.  Women weep.  Children cheer.  Way cool."

HOOD LATCH: Up until at least 1993, the XJ-S was fitted with a hood latch that is closed from the inside; set the hood down on the latches, and operate the lever on the inside to pull it shut.  Starting in '94 or '95, the XJ-S was fitted with a hood latch that works more like a typical American car, you slam it to shut it.

Of course, anyone familiar with the newer cars will now join the list of boneheads that will be slamming the hoods on the older cars.  Anyone meeting the engineer responsible for this revision, please give him a thump on the head for the rest of us.

HOOD ORNAMENT: The flat disk emblem on the hood with the puddy-tat face (commonly referred to as a "growler") apparently may be either blackened silver or blackened bronze in color, but it is supposed to be blackened.  The one on the author's '83 is metal so polishing may be possible, but Stefan Schulz reports that his is plastic and therefore should not be polished lest the plating be removed to expose the bare plastic.

LEAPER: Most Jaguar owners feel that the "leaping cat" hood ornament looks really bad on the XJ-S.  If you just gotta have one, note that it would be wise to remove the disk emblem and install the leaper in its place, keeping any additional drilling located so that reinstallation of the disk would cover it up.  Also note that the leaper is available in a couple of sizes, and the smaller ones will be less obnoxious in this application.

Finally, note that hood ornaments are regulated as safety hazards in some areas.  In order to minimize harm to pedestrians you run over, they may be required to be mounted on springs or some such.  This not only makes installation more complex, but it also makes it easier for a thief to steal the ornament.

Most leapers are made to be mounted on a nearly level surface, so on the XJ-S they appear to be leaping downhill.  However, Michael Kenrick reports on one made specifically for the XJ-S: "It's modeled on the early MkV (?) version and sits on a round base that is directly interchangeable with the authentic OEM bonnet badge, bolted from underneath.  And the plinth is beveled to take account of the sloping bonnet.  Contact:

Bill Tracy
4050 Red Rock Lane
Sarasota, FL 34231 US
+1 (941) 924-9523

"I have one mounted on the hood: it certainly looks very good, and adds a subtly different character to the car."

UPPER RADIATOR GRILLE: If you have a pre-1992 car, face it: your old grille looks pretty bad.  The chrome is flaking off, and it's cracked in several places.  And a new one is expensive.  The solution: install the 1992-on grille.

The newer grille makes a substantial difference in the appearance of the car.  Where the earlier cars had the all-chrome plastic grille with chrome frame, three horizontal chrome ribs, two vertical chrome struts on each side, and the V12 badge in the center, the '92-on grille is all black with a single chrome strip across the top edge.  There is no V12 badge.  The chrome strip makes a match with the narrow chrome strip across the top of the bumper, surrounding the grille top and bottom.

Another difference is the profile.  The earlier grille forms a distinct angle from the nose of the bonnet downward and rearward.  The '92-on grille is more "bulged" giving a rounded profile.

The ‘92-on car also came with oblong composite headlights that bulged, so the front of the headlights forms a continuous surface with the front outline of the grille.  How well the bulge of the new grille matches the non-bulged four-lamp headlight bezel is therefore a point of concern.  The bulge of the '92-on grille results in the ends of the grille protruding farther forward than the headlight bezel, so the edges of the grille are clearly visible.  These edges of the grille were presumably never intended to be visible, since they would be covered by the bulging composite headlamps.  However, the appearance of the ends of the grille are quite acceptable indeed, since the chrome strip continues around the corner and the black plastic surface is still black there.  The only problem --and it's a minor one indeed --is that the black plastic ends just a hair short of where you'd like it to, leaving a triangular opening at the bottom rear edge of the end of the grille.  You've gotta be looking for a problem to notice it.  But having compared this configuration against what the factory-designed earlier grille did here, I can't say it appears any less deliberate or properly fitting.

BREAKING IN: If you get locked out, Victor Naumann provides this tip: "you can unscrew the outside mirror, and carefully reach through with a long blade and flip the lock handle to unlock."  This works entirely too well.  If you happen to have a Slim Jim (the long blade that is inserted between the glass and the seal --standard car thief's tool), it works just fine too.

If it's the boot you're locked out of, Cliff Sadler says "The latch is held in by two sheet metal screws.  If you ever need to get into a locked XJS trunk, simply grab the handle, and pull straight up with a snap; then, replace the screws with

WINDOW GLASS: Reportedly, some XJ-S windows have the metal "runner" riveted to the glass through two small holes about 1/4 inch from the bottom; in this setup, pulling on the window is a very bad idea --it will break easily, since the rivet holes form a starting place for cracks.  Later ones are glued, making the glass itself much less likely to fracture.

If you have to replace a window, make sure the correct one is ordered -- with or without rivet holes.

REAR QUARTERLIGHT REMOVAL: Both the Haynes manual and the Jaguar repair manual describe removing this glass, but the descriptions vary.  Both start by removing interior trim panels, but then the Jaguar manual says "Using suitable tool prise rear quarter glass and rubber from body."  The Haynes manual says "With an assistant pressing the glass outward, peel back the rubber weatherseal from the body at one corner until the glass can be pushed out of its frame."  The Haynes method works fine, no "suitable tool" required.

SIDE VENTS: The vents on either side of the C-pillars (the "buttresses" on the XJ-S) are functional.  When the A/C system is blowing outdoor air into the interior, these vents are allowing air back out.  They also allow air out when a door is being shut, preventing that obnoxious problem of doors that won't shut unless a window is rolled down.  The actual route the air takes begins with mesh grilles in the top of the cubby holes above the rear armrests.  From there it goes through the bodywork, through a set of three flaps on each side of the car, and then out the slot on the outside.

The repair manuals provide no information on how to get these vents apart.  So, the following is from Mike Morrin:

1. Remove the quarter side window glass and rubber (see above).
2. Remove the little chrome corner corner piece at the bottom rear of the vent cover (nut reached from inside boot).
3. Pry off the chrome strip at the rear edge of the vent cover.
4. Drill out the rivets which held the chrome strip and rivets which are behind window rubber.
5. Remove the cover piece.
6. Remove another 6 rivets holding the vent assembly into the car.
7. Lift out assembly and wonder why you went to so much trouble.
Note that the rivets under the chrome strip not only go through the center of the retaining snaps themselves, but also through three tiny washers behind each one of them.  Don't lose the washers; they are there to keep the rubber seal from being crushed by installation of the rivet.

Despite Morrin's skepticism about the value of this job, the flap assembly within this vent may actually need attention.  Each of the three flaps consists of a metal plate with a layer of foam on the face, suspended from a piece of cloth.  There is a foam bumper on the back side to keep it from making noise when it opens forcefully enough to bang the housing.  All of this is British non-metallics, so the foam face has long since rotted away and the metal plate itself is closing over the opening.  This makes a quite distinctive racket, especially when closing a door.

The flaps themselves are also installed with pop rivets.  It is a fairly simple matter to drill them out and rebuild each flap, using materials that hopefully will be more durable and quieter.  You might wanna have some headliner material handy; it might make a suitable face material.  The type of nylon fabric used to make backpacks and light jackets might work well as the "hinge", but I simply used vinyl upholstery material; make sure that whatever you use doesn't crinkle or otherwise make noise as it flexes.  A can of 3M's "Super Trim Adhesive" #08090 will also be helpful.  For the bumpers on the back side, some 1/8" thick 1/4" wide foam tape weatherstripping will do nicely, sold in building supply stores for sealing windows and doors.  Get the heavy-duty high density closed cell stuff, this is no place for the flimsy foam.

You might find it helpful or necessary to remove a cover from the flap assembly that is held on with staples.  Therefore,

There are (or were) a couple of strips of foam seal along the back side of the cover, but they have dried up and fallen off.  They can easily be replaced with some 1/4" thick 1/2" wide weatherstripping, similar to that described above except the next size thicker.

To reassemble, you're gonna need a lot of 1/8" pop rivets (1/4" grip length) --at least 24 per side of the car.  The original rivets are a special type with a closed end, intended to prevent leaks.  These type rivets are very expensive and difficult to find, and it's not like anything here is truly airtight.  The only conceivable reason for using these rivets is to avoid a whistle, but if you're concerned you can accomplish the same thing by covering each rivet with a piece of aluminum tape or some silicone sealant.

The four rivets underneath the rearmost chrome strip must fit inside the snaps for the strip, and chances are the rivets you have won't fit.  It is a fairly simple matter, however, to chuck the rivets up in your drill and file the head diameter down a little bit.

These same four rivets end up recessed within these snaps.  This presents another problem, since the "anvil" of the rivet gun must sit squarely on the head of the rivet when installing, and of course that anvil isn't small enough to fit within the snap.  So, you will need a little sleeve to fit around the nail of the pop rivet when riveting, or a few very tiny washers will serve.  You must be careful not to lose them after each rivet pops.

TAILLIGHT REFLECTORS: Many people fail to realize the importance of the reflectors to the appearance of taillights, turn signals, etc.  Jaguar XJ-S reflectors are mostly chrome-plated plastic, which is fairly durable; but the chrome sometimes deteriorates, and the neutral plastic color is only a fair reflector.  Also, the metal panel that separates the taillights from the brake lights can get pretty dull.

To make your taillights look good, you should restore the effectiveness of the reflectors.  You can cover them with aluminum foil or aluminum tape.  The best method, however, is to mask the bulb sockets and paint the reflectors with flat white spray paint.  Flat white gives a more diffuse appearance to the light, which is prettier than the bright center appearance of the original.  If you want to make the light even more diffuse, you can paint a white spot on the bulb to prevent a direct view of the filament.

BRAKE LIGHT LENSES: There's a little panel with a chrome frame along the inside edge of each pre-1991 taillight lens that may or may not have paint on it.  David Cleary explains, "The center section of the boot lid was painted black up to about 1977, at the same time the B posts were chrome, and the lenses were also black."  Mike Morrin says, "I think that they only had the black paint on the boot lid between the tail lights for 1975 and 76.  I presume the paint on the lenses was deleted at the same time.  The parts book shows that the part number changed at 2W4023(RHD) and 2W54660(LHD).  I presume that this is the same change."

What it changed to is not as clear.  This author's '83 had silver paint, while later cars just left the underlying chrome uncovered.  Cleary says, "Both my 79 and 82 cars came with silver finish on the rear lenses.  I have only ever seen the silver finish lenses available from the factory.  No spares or autojumble retailer has them, only the black or chrome.

"At a recent autojumble I wanted a pair of rear lamp lenses.  I noticed that the early ones with a black finisher were much cheaper than the ones with the chrome (£15 a pair rather than £25).  With 10 minutes work and some careful application of thinners you can save yourself £10 by removing the black paint to reveal the chrome - simple eh?"

The silver paint comes off just as easily.  I said this author's lenses had silver paint.  They don't any more --one look at someone else's car with the bare chrome, and that silver paint was outta here.

The panel in question is actually a separate piece from the lens itself.  The chrome plating is applied to a metal panel, and then the panel is attached to the plastic lens assembly with press-on clips.  If the nonremovable clips are removed (!), it's a lot easier to work on getting the paint off -- you can dunk the whole thing in a can of solvent.  Or, Cleary says you can "Use masking tape to protect the chrome when using thinners.  That way you don't have to remove the bit from the lens

If you're having the car painted, you might consider something really radical: mask off the chrome rim and the rest of the lens and have them prime and paint those panels the same color as the car.  This will give a unique look, since none of the XJ-S's apparently came from the factory with this panel painted body color.

THIRD BRAKE LIGHT CUTENESS: John Himes sends this tip: "If you wanted to get creative, remove the entire housing and place a piece of custom cut metal or cardboard or something with the leaper cut out, paint black and place against the window.  Now when you brake, instead of just a light there, you will be showing a glowing red leaper to all that you leave behind."

LICENSE PLATE LIGHT LENSES --PRE-1992: This lens is actually an assembly of two parts: the lens itself, and an opaque white plastic hinge that the lens attaches to.  The hinge is provided to facilitate bulb replacement, since it's not all that easy to get a screwdriver into this area.  Both the lens and the hinge are often problem areas.  Patrick MacNamara says, "British/Auto USA flyer has an XJ-S license plate light repair kit which includes the flexible plastic hinge piece, lens and bulb."  See page 692.  Chuck Sparks points out that the lens is the same item as used for license tag light lenses on the ‘74-76 MGB and the ‘75-76 Midget; it is offered by Victoria British (1-800-255-0088) as part number 0-6912 for less than ten bucks.

The bulb holder is integrated into the lens, which is unfortunate; otherwise, it would be a simple matter to replace the lens with any flat piece of transparent plastic.  As it is, such a replacement of the lens requires figuring out some other way to hold a bulb.

One repair possibility is to simply buy a suitable automotive light fixture, throw the original hinge and lens away and mount the entire fixture within the space.  The space is shallow, but the sheer variety of aftermarket light fixtures available means that something can usually be found to fit.  Be sure to check truck stops, which sell a wide variety of "marker lights" for the corners of tractor trailers.

Alternatively, you can make something to hold the bulbs; this author simply made some connectors that clip onto both ends of the bulbs the way a fuse is held in a fusebox and mounted them with suitable plastic cut to serve as insulators.  Remember, whether you buy or make, there's no good reason to stick with the original style bulbs; any 12V bulbs of comparable wattage that can be made to fit in the space should work.

Once you've fabbed bulb holders, you will need to provide lenses.  This author purchased a small piece of plexiglass (Lucite) at the local building supply store, 8" x 10" x 0.093", for less than $2.  It comes with either thin plastic or paper on both sides to protect the finish (paper is better); leave the stuff on until after you have finished cutting and drilling.  It's really easy to cut and drill.  Trapezoidal pieces were cut with two holes each to replace the hinge and the lens with a single piece.  When done, one side was sanded with 320-grit sandpaper to provide a "frosted" appearance; the other side could be done to make it even more frosted, but going to a coarser grit makes the individual scratches too prominent and a finer grit seems to not do enough.  Finally, the edges of this lens could be wrapped with strips of aluminum tape or (better) stainless steel tape to make it look more professional, but in this author's opinion the finished product already looked neater and more esthetically pleasing than the original cobbled-looking assembly.  These lenses are not all that prominent, although they are plainly visible when the trunk is open and are apparent in the reflection in a well-cleaned rear bumper as well.

Julian Mullaney: "I also made replacement lenses for my old XJS.  It is better if you use polycarbonate (Lexan) instead of acrylic (Plexiglass).  Unlike acrylic, polycarbonate can easily be cut with scissors (or metal snips) without cracking.  It can also be folded along a straight line without heating."

If your lenses are not that far gone, Ed Avis provides a fix for the hinge itself: "I removed the old flaps and used them to trace the pattern onto a plastic VCR tape case and simply cut out new flaps.  The nice hinged cover on the tape case served the same purpose as the hinge on the original flaps.  Total cost of the repair was about $1 for the tape case.

Mullaney has his own ideas for that hinge, too: "PET (polyethylene terepthialate sp??) is very good for this application

CHROME-PLATED PLASTIC: If you ever find yourself needing to remove chrome plating from plastic, John Goodman suggests: "You can probably remove the chrome by removing the paint underneath, with oven cleaner, or any of those concentrated cleaners containing sodium hydroxide.  Wear eye protection and rubber gloves.  Liberally spray the part with the goop, seal it in a plastic bag, and wait.

"I haven't tried oven cleaner to remove chrome from plastic, but I have used it to remove paint from plastic.  Works like a charm, doesn't harm the plastic.  Model railroaders use it on their delicate miniatures"

See COTECH, page 702.

BUMPER VARIATIONS: In some countries that don't require high-impact bumpers, the XJ-S has been fitted with lighter, less obtrusive bumpers.  The front bumper is fairly thin, and the turn signals mount on the bodywork rather than in the bumper.  The locations for the turn signals are clearly evident on US-issue vehicles, hidden underneath the heavy bumper.

Scott Horner says, "if they are UK based, then the difference in Pre-'82 to post-'82 is in the bumpers...Pre-'82 (Pre- HE's) used the impact absorbing bumpers without chrome tops...the same for all markets; but at the H.E. for all markets (except the USA) Jaguar fitted slimline bumpers without the impact absorbers.

"This means that most trim kits like the TWR & XJR-S packages sit very close to the body and don't use the rubber bumper beam cover - which I've seen on some US kits...."

For the US, the bumpers changed in 1982 as well --but both pre-82 and 82-on ere impact-absorbing type.  Section 76.22 of the ©1975 ROM obviously applies only to the pre-82 bumper design, but the ©1982 Supplement covers the revised design.  Note that the 1982 bumper change also entailed a change in the front turn signal assemblies.

LICENSE PLATE FASTENERS: No matter how pretty your Jag is, having streaks of rust on the tag streaming downward from the attachment bolts doesn't help.  There is apparently no consistency in attachment schemes here, it looks like each dealer fastened the tags whatever way he saw fit --and rare indeed is the dealer that springs for proper stainless steel fasteners.  It shouldn't be too hard to find some stainless steel fasteners that will serve.  On the author's '83, the tag was held on with chincy sheet metal screws directly into the metal of the trunk lid, so a nice chrome license plate frame was added with four stainless steel screws.

REMOTE TRUNK RELEASE: Bob Whiles says: "There are several "Trunk Release Module" kits on the market.  All you get is the actuator (solenoid), a button, fuse holder and wire.  But Chevy has a pretty nice -heavy duty -one in some of their "upper" models.  Just look for a Monte Carlo or above in the junkyard.  All you will need then is a momentary button, wire and fuse/holder.  Cheaper and better than the kits."

REAR SPOILER: Welsh Enterprises (page 697) offers a rear deck spoiler for the XJ-S.  JaguarSport does too, and John Goodman reports: "There are actually two types of (JaguarSport) deck spoilers available.  The post-'92 deck spoiler has more "sweeping ends" to compliment the revised tail lights and I'm not sure, but maybe an integrated brake light."  Several of the vendors listed starting on page 713 also offer spoilers, some with slightly different styles, so hopefully you can find one that suits you.

Note that rear deck spoilers have a hole for the antenna to poke through.  Also note that rear deck spoilers are attached to the trunk lid while the antenna is attached to the fender, so opening the trunk with the antenna up won't work.  If you

Now, if you have the earlier XJ-S, you know those springs that hold the trunk lid up when open?  Do you think they will still hold the trunk lid up with the additional weight of the new spoiler on it?  Not likely!  Reportedly, the fix is to fit the earlier cars with gas struts, just like the later trunk lids have.  Goodman again: "The struts and the relay with harness come with the spoiler if you buy them from a Jag dealer."

STYLING KITS: Several outfits, including Welsh Enterprises (page 697), JaguarSport (page 8), and several other vendors in the listing starting on page 713, have developed styling kits with components to add all around the bottom edge of the bodywork --from the bumpers downward at both ends, and along the rocker panels under the doors.  Some kits cover the bumpers, while others mount underneath the bumpers with the bumpers protruding through.

The Welsh kit supposedly fits any XJ-S 1982-on, apparently due to some problem with bumpers on earlier cars.  John Goodman says (regarding the JaguarSport versions), "There are three different body kits, pre-'92 and post-'93 US with rubber bumpers and '93 UK."

Michael Minglin reports: "I have installed a ground effects kit (body styling kit) that I purchased from the dealer.  From the pictures it appears to be the same kit Welsh is offering.  The kit installs over the shock absorbing beams on my '84 XJ-S.  The chrome top trim and the black rubber end pieces are removed.  I find this preferable to the newer kits that do not have the shock absorbing beams protruding through the spoiler.  It may not look as nice, but it provides excellent protection in the event of slight bumps, like backing into a post I didn't see.  The kit is fiberglass and would easily crack if it was not for the shock absorbing beams.

"The negatives on this kit are: You have to be very careful when pulling straight into a curb, or one of the concrete parking curbs in parking lots.  The front spoiler is so low it will hit the curb and break.  This point must be stressed when leaving the car at a shop or using valet parking.  In addition I have noticed that the engine runs a little warmer on the open road since I installed the kit.  It seems to restrict the airflow somewhat.  But, it sure makes the car look great.

"FYI, this kit is manufactured by Arden, a German company."  Arden is listed on page 713.

LUGGAGE RACKS: Herbert Sodher wanted to make his car look different, and found that a luggage rack designed for a 1968-75 Corvette will fit on the XJ-S trunk lid nicely.  He chose a really nice stainless steel model rather than the basic chrome.  He opted not to use the mounting scheme included, since it was intended for fiberglass; instead, he visited a good hardware store and purchased some stainless steel flush head sheet metal screws.  He carefully measured locations and drilled some small pilot holes, and with very little effort was receiving complements on the appearance of the installation.

MUD FLAPS: If you drive in mud, snow, slush, etc., you probably are sick and tired of cleaning the slop off the car.  The place to get mud flaps for your Jaguar is at the Jaguar dealer.  In fact, the panel behind the front wheels already has a set of square holes for mounting the flaps.

H.E. VS. V12 EMBLEM: If you feel that "V12" is a more descriptive emblem than "H.E.", you may be happy to learn that the V12 emblem is available as a stick-on item, and will perfectly cover the holes used to mount the original H.E. emblem.  If you purchase the V12 emblem (part number BEC4717 -don't get the earlier 4-piece emblem), merely pry the H.E. emblem out, clean the surface, and stick the V12 emblem on.

COLOR COORDINATION OF WHEELS: Coordinating the color of the wheels with the body color of the car --via some accents in the pattern or the like --can make a dramatic improvement in the appearance of any car.  This is almost never done at the factory, presumably because tracking different colored wheels to make sure they end up on the correct

If your car happens to be red, green, black, or grey, this color coordination of the wheels might be easy! &nbp;Just replace the little growler emblems with ones that match!  Richard Mansell points out that Jaguar offers wheel emblems "in the following 5 colours: Silver/Green, Gold/Ruby, Silver/Ruby, Black/Gold, Grey/Silver (Jaguar), Gold/Ruby, Grey/Silver, Black/Gold (Daimler)."  Available at the dealer.  The Silver/Ruby part number is MNA 6249EA.

Apparently Jaguar's intent was not color coordination, which may explain the imited selection of colors.  David Buchner says, "each year model has its own color.  '94 uses red..."  Maybe more colors will be available in future years!  The early H.E. domed starfish wheels came with a two-piece emblem (growler and retainer) while the 90's Jaguars use a single-piece emblem, but the single-piece item fits the domed starfish wheels just fine.

WHEEL ARCHES: These are bright metal trim pieces that fit around the edges of the wheel wells; they are available in either chrome or gold.  They are another item about which opinions vary, with many owners finding them gaudy and tasteless while others love them.  Of course, if the edges of the wheel wells are where your car is rusting, you might suddenly decide they look good!

John Dyson says, "I have the chrome wheel arches on my '91 "Classic Collection."  It is my impression that they are part of the limited edition trim which includes chrome wheels, gold bonnet badge, leather interior with contrasting piping, and "Classic Collection" badge on right rear."

CONVERTIBLE RIGIDITY: In the old days, cars had a rigid frame and the body merely went along for the ride; chopping, removing, or otherwise screwing around with the bodywork did not functionally affect the car.  However, a frame is now considered a waste of steel, space, and money, and the body of the car is usually the stress-carrying structure.

About the same time this change was taking place --early 70's or so --convertibles also disappeared, largely in anticipation of safety regulations that never actually materialized.

In the 90's, the convertible made a comeback --including the lovely XJ-S version.  Unfortunately, the stressed-body concept doesn't take well to a convertible; removing the roof removes a great deal of the structural rigidity, and such cars often end up weighing considerably more than the hardtop versions due to added structural reinforcement needed elsewhere to compensate.

Early XJ-S convertibles were structurally good but not great.  With the bodywork revisions in mid-1991, mounting points were added under the car for a system of front and rear cross-bracing to add rigidity.  This renders the structure truly excellent.  Unfortunately, the 1988-1991 convertibles lack the mounts for installing the bracing.

The cross-bracing can be added to earlier cars.  A kit including all the parts is available from Classic Engineering (see page 715), but installation involves some welding.  They are reportedly working on a similar kit for the rear bracing, but the front is the more important.

According to Julian Mullaney, the rear brace is very similar to the front, but fashioning mounting points is harder.  "This brace mounts on the chassis in front of each rear wheel and crosses to attach on the opposite side, behind the rear end cage on the bottom of the trunk (boot).  This is where the problem is.  In the new cars, the trunk well is stamped with two downward pointing depressions to which a brace can be bolted.  In the early convertibles some sort of stand-off (about 2-1/2 inches deep) must be mounted to the bottom of the trunk-well in order to attach the brace."

Meanwhile, similar cross-brace kits are available from Harvey Bailey Engineering, page 714, but theirs apparently require no welding.  Chris Carley installed both front and rear cross-bracing: "Heck knows why it works but it really does make the car feel so much more solid.  When you hit a bump you just get a normal tire thump -no rattles or shakes.  It also improves the handling, which surprised me; feels like much less roll and more firmly planted.  Fitting: front was dead easy; need 1-1/8" socket for subframe mounts.  The rear fitting is just fiddly to get the thread started in a blind hole (took hours and lots of 4-letter words)."

MAKING YOUR OWN CONVERTIBLE: Discussing chopping the top off a coupe, Scot D. Abbott says "I've seen several XJ-S coupes made into convertibles.  I also saw several XJ-S bodies cut apart just for examination and have experience evaluating convertible conversions.  IMHO, changing the XJ-S unibody to open configuration must be done with some care to minimize strength loss, and reasonable stiffening elements can be added back to make a sound car.  This must be done properly and can be done in many ways.

"Roof removal is not necessarily the main thing that can take away body integrity/strength in a conversion.  I cut the roof off an XJ-S, towed it on a dolly 2000 miles, and still the door gaps remained the same.  I could raise the car with a jack and not twist or deform it significantly differently from an XJ-S with its roof intact.  Please note that I kept the sundeck/rearward bulkhead intact.

"Compromise of the rear sundeck/rear bulkhead system or removal of the rearward bulkhead (i.e. the sheetmetal wall behind the rear seats and between the rear wheel wells) from the XJ-S makes the car very flimsy, especially to torsion stress, and it permits undue flexure during motoring which will likely fatigue the sill/floor joints with time.

"Removing the rearward bulkhead is done to make room for a large power top to fold down.  An alternative to this is to use a compact folding top and thus avoid creating the basic problem.

"A commercial version of this conversion design strategy is available locally (Driver's Seat of Delaware, Inc., Box 542, Montchannin, DE 19710, 302-998-7889)."

STATION WAGON: See Lynx Motors International Ltd., page 719.

XJSS: A radical kit car based on the XJ-S offered by Autostyle (page 714).  Pat O'Keeffe got the literature, and reports that the blurb says:

PREPARATION: The bonnet (hood), boot (trunk), bumpers, lights, front wings and doors are unbolted.  The rear wings and roof are removed.  Note that the windscreen pillars and glass are not disturbed.  The tubular sill reinforcer, which is supplied, is fitted.  The fuel tank is adapted.  The rear boot lid support assembly, which we supply, is fitted.

ASSEMBLY: The one-piece front body section is fitted.  The bonnet is fitted.  The one-piece rear body section and sill covers are fitted.  The boot lid is fitted.  The XJSS door skins are fitted and the doors returned to their original locations.  The lights and number plates are fitted.

PAW PRINTS: Cats love cats; those flea-bitten varmits just love to stroll around on your freshly-washed Jaguar with their filthy paws and leave little prints all over it.  Aside from solutions involving firearms, the following suggestions have been made:

Peter Cohen says, "There is a product called a ScatMat.  You place it on the car, plug it into the mains and it administers (chuckle) a mild electric shock to the little bugger.  I actually own one of these devices.  The bad news is: 1. The cat figured it out and just doesn't step on it. 2. My wife drove off with it still on the car.  I found it 2 weeks later in the bushes, 3 streets away.  My only workable solution is: the Jag goes in the garage, the cats may not go in the garage."

Chuck Wood says, "I know some of you will laugh, but it really works if you have cats that know they should not be on the car and get off when you come out or you yell at them.  I took a motion detector which had two lights.  I took one light out and put a receptacle in it.  I then recorded my voice on tape very sternly telling the cats to get down using the word No and whatever other words that they are used to hearing when they are doing something they should not be doing.  The recording was about 5 minutes long.  Set the motion detector for about the shortest time on and position the sensor to pick up anything moving on top of the car.  It should not go off when the cat walks on the floor any where.  When this is set correctly, the cat gets on the car which activates the sensor which turns on the light and activates the recording telling the cat to get down or off..  It shuts off in about 5 seconds.  The recorder is in the play mode all of the time.  It really works well if the cat is conditioned to knowing it should not be up on the car."

David Danvers says, "I have sprinkled red cayenne pepper around my carport to keep them away...it is a great deterrent and cheap...go lightly so you don't track it in the house or car and re-apply after it rains....they'll get the point pretty quick..."  Apparently, the reason this works is because the first thing the cats do when they get settled on the car is to start licking their paws.

Stefan Schulz suggests, "Dihydrogen Monoxide, the colder the better, and lots of it.  Apply by slinging it with a bucket.  They will get the message.  It also goes some way to remove the paw prints."

VIBRATION: The Hess & Eisenhardt convertibles have chunks of lead mounted behind the headlights, probably to address a resonance problem.  Julian Mullaney says, "Actually, one of them had come loose and was rattling around in the headlight cavity.  This is a problem with a ~15 lb. lump of lead.  It beat the sheetmetal in the cavity until it cracked open, and the lead almost dropped out into the wheel well.  I patched it up and bolted it back in place.  I think the vibration may have been slightly less afterwards, but not a huge difference."

CONVERTIBLE TOP REPAIR: Steve Wilke reports: "Had problems when one of the hydraulic lines chafed its way to oblivion.  Resulted in a good bit of hydraulic fluid in the boot.  I found that our local auto parts store carries a hard black emissions control tubing, which looked very much like the original tubing.  A couple of trips to Home Depot's plumbing department got me the fittings I needed to splice the tube, and Home Depot also had hydraulic jack oil in gallon jugs.  After splicing the tube and purging the lines by raising/lowering the top several times, each time refilling the pump with hydraulic oil utilizing a turkey baster, the top worked better than ever."

Note: The instrument panel is discussed on page 590.

CHANGES FOR 1988: The interior was significantly changed for the 1988 model year.  Changes included:

Chincy plastic door sills replaced with beautiful chrome-plated steel sills with "Jaguar" written in them.
Painted metal "ski slope" (panel surrounding the shifter) replaced with wood burl version.  The cruise control switch was relocated from the shifter pedestal down to the ski slope itself.
New seats with heaters and electrically-adjustable lumbar support.  Switches are on the sides of the console.
New steering wheel.

LEGROOM: If you are tall, you may be pleased to know that the front seats in the pre-'88 XJ-S's have two sets of mounting holes.  The cars came from the factory with the seats mounted on the forward holes.  Simply unbolt the seat rails from the floor, turn the seat over and unbolt the rails from the seat.  Remount the rails to the seat using the alternate set of holes, and the seat will adjust farther rearward.

Note that the '88-on seats don't have the second set of holes and are bulkier to boot, making it much more difficult for the larger driver to fit.  When Jaguar incorporated electric motors in the seat adjustments in the early 90's, they got bulkier still.

Tall people should also avoid the H&E convertible.  Relocating the seat mounts rearward will do no good, because the housing for the convertible mechanism limits rearward motion of the front seats.

SEAT RAIL SPACING: John Nuttall notes that the seat rail spacing on pre-'88 cars was 17½" while on later cars it was 16½".  Obviously, the seats will not be interchangeable.

SEAT MOUNTING BOLTS: On the early cars such as the author's '83, the four bolts that hold the front seat rails to the floor tend to be aggravating.  The front two bolts go into rectangular block nuts that do not hold themselves in place, although it usually isn't too difficult to hold them in place with a large screwdriver until you get the threads started.  The rear bolt near the door threads into a trapped nut that can move around for alignment.  The rear bolt adjacent to the console is threaded directly into a boss welded to the floor; since this is the only corner that cannot be moved for alignment, this is the one that locates the seat.  When putting the seat in, it is a good idea to get all four bolts started before tightening any, and then tighten the rear one near the console first.

Mike Wilson reports that both rear nuts are firmly attached on the 1990 model, neither one can move around for alignment.  Still, it would probably be better to have all four bolts started before tightening any, and tighten the rear two first.

To make the job a little easier, you can replace the two rectangular block nuts at the front with clip nuts that will hold themselves in place.  The clip nuts are described as an "extruded U nut, 5/16 Regular" or "Long".  The "regular" means that the clip part is 5/8" deep, while the "long" has a clip about 7/8" deep.  Suitable U-nuts were bought at Lowe's and made by Curtis Industries, Inc., Eastlake, OH 44095.  The Curtis part number is 838758 for the regular and 838759 for the long.  Similar U-nuts are also sold by auto body parts shops, with the regular having a part number 4016.

The best course of action seems to be to have a selection of regular and long U-nuts on hand to do this job.  On the author's car, the regular fit the locations near the doors while the locations near the console required the long.  You

Of course, strength here is of some importance; you don't want that seat coming loose in an accident.  However, even though the U-nuts are extruded from sheet metal, they are probably stronger than the original rectangular block nuts - which are made of something related to silly putty.  Since the U-nut is a clip, it is made of spring steel and therefore quite strong.  And the extruded threads are perhaps twice as long as the threads on the rectangular block.

Since U-nuts seem to only come in coarse thread and the original mounting bolts are fine thread, you will have to replace the front two bolts as well to get the U-nuts to work.  The shape of the head of the bolt is crucial, since the wrong shape may obstruct the adjustment of the seat.  The bolt to use with it is a "socket head cap screw, 5/16-18 x 1".  Curtis part number 835558, but this is a fairly common critter and can be found most anywhere.  This is driven by a 1/4" Allen wrench.  The original lock washer may be used with this bolt.

On the earlier cars, these bolts were Pozidriv #3 head.  This makes them quite difficult to get really tight, especially the rear ones since it may be difficult to get a screwdriver to engage the bolt head straight on; if you have Pozidriv bits for a changeable-tip screwdriver, you might try using one with a 1/4" box-end wrench or a 1/4" socket with a ratchet here.  Later cars use Torx T-40 bolts instead, a big improvement.  The Allen drive cap screws also work quite well; if you have the Pozidriv, you might consider picking up some 3/4" long fine 5/16" fine thread cap screws for the rear locations, making all four removable with an Allen wrench.

SEAT DIAPHRAGM: If you take the seat out and turn it over, you will find that the bottom cushion is supported by a rubber diaphragm stretched across the frame and hooked on with hog rings.  This diaphragm is classic British non-metal stuff and is rotten and torn, and that's why you seem to sink farther into the seats than you did when you were younger.  Ron White says, "They are available for the Jag from BAS Ltd."  See page 699.  Note that this is valuable information; apparently many Jaguar suppliers (including the dealers) will not sell you the diaphragm, they want you to buy the entire seat cushion assembly.

Still, installation is no picnic.  The foam of the cushion is glued to the diaphragm, so replacing the diaphragm will entail carefully cutting the foam away and gluing it to the new diaphragm.  You'll need good glue, like 3M Super Trim Adhesive #08090.

Note also the above comment about the seat rail spacing change.  It is unknown whether a different diaphragm is called for between the two types of seat, but some owners have commented that the diaphragm was really tough to install, requiring serious pulling --but maybe it's supposed to.  Also, there are reports that the replacement diaphragm required a somewhat different mounting hole pattern in the frame, so a few new holes had to be drilled.

This author took a different route and left the old tired diaphragm in place and reinforced it with a piece of plastic sheet above it (between it and the foam) and a webbing woven of curtain rod cord underneath it.  The webbing is remarkably easy to do, just loop back and forth between the same hog rings that hold the diaphragm itself, stretch it tight, and tie it; it might be advisable to do this while the diaphragm is still in good shape, thereby postponing the cushion regluing considerably.

COMFORT: Some of us prefer the bottom portion of the front seat to be inclined somewhat; this helps hold the occupant in position with less effort on his part, as opposed to having to brace one's feet against the floorboard to keep from constantly sliding forward.  This is especially a problem if you like the seat back reclined somewhat.

The seats in the '83 XJ-S have no angle adjustment on the bottom.  However, a small amount of incline can be permanently added by inserting a few 5/16" washers under the front end of the seat rails, around the front mounting bolts.  It wouldn't be a good idea to add more than 1/4" or so since you may start distorting the rails, but 1/4" can make a dramatic difference.  If you need more, you can also insert washers between the upper rails and the seat itself.  Beyond that, you need to make some tapered washers to be able to bolt the rails to the floor without distorting them.

LEATHER: Robert Olman of New York sends this tip.  If your leather interior has areas where the dye has worn through and the color of bare leather is showing, it can be re-dyed.  The original leather, by Connolly Leathers, is painted with dye rather than vat dyed like other cars --if you look at the back side of the leather, you see the undyed color.  Connolly uses a lacquer-based dye; you'll need 2-3 pints for the entire interior.  Before using, you must determine which pieces are leather and which are vinyl, as the lacquer-based dye will destroy vinyl (Some XJ-S's are all leather, others have vinyl in areas that don't contact humans such as the sides of the seats).  Or, you can use a non-original non-lacquerbased dye.

You might want to remove seats, console, etc. from the car to make the job easier.  Clean the leather with lacquer thinner, sand it lightly with fine sandpaper to remove the shine, then clean again with lacquer thinner.  Then apply the dye evenly, perhaps in two coats.

If it is humid, it will take a long time to dry.  Heavy coats will also require a long time.  Heavy coats in damp weather may require a week to dry.

If you would rather spray the dye, you will have to remove all items from the car, thin the dye with 5-7 parts thinner to 1 part dye, and apply many thin coats.  It will require more dye due to waste.  Many marine supply shops sell disposable aerosol sprayers (about $6) with replaceable aerosols (about $3).  You'll need about three aerosols.

A complete restoration kit is available directly from Connolly (see page 699), with instructions.

Note that Jaguar has used at least three different colors called "biscuit".  To get the correct one, you must specify model and year.

FOOT ROOM: The footwells are tight enough; does the brake pedal have to be so big?  Of course not!  It doesn't have to be any bigger than a brake pedal in a manual transmission car.  John Ashcroft says, "Just a small mod: cut 20mm off each side of the brake pedal to gain much needed foot room.  What a difference it made!"  Note that you don't even have to cut equally off each side: you can cut entirely off one side if you'd like.

Tip: Go to the auto parts store first and check out the sizes of replacement brake pedal pads available.  Choose the size you want, take it home, and then trim your pedal to match.

You can take the brake pedal out fairly easily, if it will make it easier for you to trim.

INTERIOR WOOD: There are two different types of wood commonly used in the XJ-S interior, elm burl and walnut burl.  The elm burl is a light honey color, while the walnut is dark.  Neither type holds up well in direct sunlight, so it is recommended that all XJ-S owners purchase sunshades to put in the windows when parking ina sunny parking lot - especially if you have a later car with the wood ski slope, which is positioned to get more direct sunlight than any wood trim in the earlier cars.

INTERIOR WOOD WORK: Gene Halaburt says, "An excellent article on wood finishing for Jaguars appeared in the October 1996 issue of "Jaguar Enthusiast" Magazine.  Written by John Sundberg dba "A&B Leather & Wood Renovation." (see page 698).

INTERIOR WOOD TRIM REFINISHING: Rick Lindsay provides this suggested procedure for refinishing the wood trim: Sand the veneered wood very carefully with 200 or 400 grit paper removing only enough wood to freshen the surface.  Even with 200 grit sandpaper it is easy to cut through the thin veneers used in britcars -especially on edges.  I've found it better to leave a bit of the ‘old finish' than to sand thru the veneer and have to stain the substrate.  Pay particular attention to edges that should be left crisp -not rounded.  It adds a professional look.  Always sand linearly, not in circles.

Alastair Lauener provides an alternative method of stripping the wood: "I used a chemical called Nitromors, a paint stripper, water soluble, to strip off all the old varnish, and washed under cold water.  I tested on an old spare dash first.  Careful not to let the wood get too wet.  Allow to dry out for a few days.  Be careful not to scratch it."

‘88-ON SKI SLOPE: Removal of the earlier metal ski slope was obvious, three screws.  With the wooden ski slope, however, the screws are hidden.  Matt Dillon reports: "In order to remove it, you need to take out the lighter and cruise switch.  This gives you access to the bolt on each side that hold the ski slope in place."

John Keppler: "I would like to suggest an alternative approach.  The cruise control switch and the cigar lighter are held in place with plastic tabs that are bevelled to snap on, but not to snap off.  I don't believe you can reasonable expect to pry these fixtures off without breaking at least one of the four tabs on each (as I ended up breaking one of mine).  I would suggest instead the the ashtrays be removed first.  The bolts that secure the console lid are mounted horizontally with their heads pointed toward the car's center immediately next to the electrical fixtures.  They hold the console with a vertical tab which has a slot that slips down over the bolt.  The bolts only need to be loosened to remove the lid.  Reach back through the ash tray openings in the lid with a 5/16" wrench to loosen the bolts.  Once the lid is removed, you have a much better chance of removing the CC switch and cigar lighter without damage.  Reinstall the ash trays, remove the electrical items, and reinstall the lid.  Then the bolts are easily accessible for tightening, and the wiring is easy to reattach."

The wooden ski slope is notorious for cracking and peeling, perhaps because it gets more direct sunlight than the other wood in the interior.  Dillon suggests a repair: "The ski slope is a piece of metal that has the wood veneer glued to it.  I took a belt sander to it to remove the old veneer.  I ordered the veneer from Constantines and re-applied it as per their instructions.  The veneer was a little lighter than the rest of the wood, so I used a little stain to darken it up a little.  I

"I did go to the dealer to price a new one.  They told me somewhere around $250 and couldn't guarantee that it would come even close to matching the rest of the wood.  The wood veneer from Constantines cost me about $25 with the can of veneer glue to go with it.  The epoxy coating was about $10 more.  Aside from being a whole lot cheaper, it allowed me to get the color very close." Constantines is on page 699.

"I called them and just asked them for a piece of their "premium" burl walnut veneer and gave them the measurements.  I specified a piece much larger than what I actually needed just in case the edges were a little rough.  They sent me 3 pieces.  In order to make it fit, I used 2 of the pieces with the seam running straight down the middle.  It wasn't obvious to me, but the original Jag piece also had a seam in the middle.  The pieces are matched, so it looks really nice.  The left side is a mirror image of the right side.  There were a couple of knots in the veneer, but I liked that.  They're very helpful, and I'm sure that if you send them a piece, they'll try to match it."

CONSOLE PANEL: For those of us who own an '83 XJ-S, removing the panel from the top of the console is easy and obvious --there are three clearly visible screws.  However, John S. Whitford has an '89 with one of those newfangled wood veneer panels, and apparently somebody decided that visible screws would be passé.  "The cruise control switch and the cigar lighter can be pried out and that exposes a sheet metal bolt into the console wall locking down the lid on each side.  Getting those out allowed me to raise the lid and slide it back some and there are two pegs on the front edge of the cover that fit under the radio-A/C cover."

ADHESIVES: If you're doing interior work, you need to know about adhesives.  The following is from Timothy J. Hesse; "I am the product marketeer for the ITSD Industrial Aerosol Adhesives and I formerly was the product marketeer for Auto Trades Aerosol Adhesives."

"74 Foam Fast Adhesive is an excellent foam bonding adhesive which performs well up to about 120°F.  Above that temp, the adhesive will soften, and with sufficient stress, you can pull the foam apart.  It is possible to experience up to 150+ degrees in a closed car, and the seat part does see a fair amount of stress when a person is sitting on it.

"Another 3M product which is a good foam bonder and has 160° temp resistance is General Trim Adhesive, pn 08080, which is sold by the Automotive Trades Division.  This would be a better product to try for seat bottoms.

"76 is a good product---but does not have very good plasticizer resistance.  Vinyl material is typically loaded with plasticizing oils, and in time these plasticizers migrate from the vinyl to the adhesive, and they soften the adhesive to the point the adhesive becomes very soft and gummy and "lets go".  76 has 160°F temp resistance and would work on foam bonding, but vinyl bonding would not be a long term success.

"A better product for bonding vinyl is Super Trim Adhesive, pn 08090, also sold by Automotive Trades Division.  Super Trim is a neoprene-based contact adhesive in an aerosol can.  It has 200°F temp resistance, and is plasticizer resistant.  In fact, Super Trim is very good for reattaching vinyl tops, vinyl trim, etc. in auto restoration projects."

HEADLINER: Apparently, if you don't want to have headliner trouble with an XJ-S, you'd better get a convertible!  They all seem to fall down sooner or later, and the roof light is poorly placed to help keep the headliner off your head when it does.

The material used in a headliner is a fabric bonded to a thin layer of foam.  The failure mode of headliners (not just Jaguar) is that the foam rots and falls apart.  While it appears tempting to just find some way to glue it back up (and there are people who are willing to sell you products to "inject" glue in there with), the fix will not last; once the foam is shot, gluing it back together only makes it fall apart again above or below the glue layer.

The only real solution is a new headliner.  Fortunately, this problem affects cars other than Jags, and a competent

You will be given the choice of insisting on genuine Jaguar headliner fabric or just installing a generic material.  You should have learned about British non-metallic materials by now; if not, let me point out that you are replacing a genuine Jaguar headliner!  True, it appears that American headliners fall too, but it isn't any sooner than Jaguar ones.  The only reason to get the original material is to match the color perfectly, but most of us aren't that picky about headliner colors.

While this is a good example of work best left to professionals, there are those who want to try doing it themselves.  Frank Perrick says, "The trick is to buy only 3M spray adhesive and read the can.  There is only one 3M adhesive recommended for this job.  The wrong can will say ‘not for head liners', and the first hot day you will be wearing your headliner.  Headliner kits including fabric and clips are available at local auto parts stores."  The correct stuff is Super Trim Adhesive #08090.

By the way, the headliner fabric in the XJ-S is bonded to a piece of stiff cardboard or fiberglass.  It is somewhat of a challenge to get this thing out of the car; the Jaguar manual specifies removing the windshield! Apparently, that isn't really necessary; Rob Ward reports: "You need to get someone to support the other side while you turn it through 90 degrees.  Moved the seats back and lowered the headrests, moved steering wheel fully in.  Mine came out through passenger door no problems. (RHD)"  Regardless of the methods attempted, everyone who's tried it agrees you will need at least two people.

Richard Dowling offers some guidance for fiberglass repair of that headliner structure: "I pulled the old headlining and used a fibreglass repair kit to beef up the crumbling edges of the moulded roof panel.  That was a big mistake, because the rear edge of the moulded panel fits into a slit in the rear window seal.  Now my panel is a bit thicker around the edges and perhaps 5mm longer.  It pushes the new and pliable rear seal outwards even with the window in place.  This has distorted the seal, although it does not leak.  The problem is the distortion does not allow me to put the bright trim pieces back in."

FACIA: On the dashboard, just below the speedometer and tachometer on either side of the steering column, there is a panel covered with a fuzzy black fabric intended to be nonreflective to prevent glare on the gauges.  This fabric tends to come apart after a few years' exposure to sunlight.  To replace it, visit any shop that installs automobile headliners.  These two pieces would qualify as scrap to them, you might even get it for free.  Take the panels out, remove the old fabric and install the new with contact cement.

GLOVEBOX: The lining on the inside of the glovebox is -- you guessed it -- headliner material.

MOTORMOUSE SEAT BELTS: John S. Whitford relates his experience: "The passive restraint shoulder belt (that I hate), got stuck in the engaged position.  I just unsnapped the belt and forgot about it.  But it kept trying to return to the disengaged position and that eventually ran down the battery.  When I connected the recharged battery back up, I heard it straining, and a little fiddling got it unstuck."

Sean Straw's motormouse seat belts went nuts.  "I've noticed on more than one occasion the passenger side passive seatbelt decide that it wants to freak out as it is closing -it reaches the (upper) stop point, then backs off as much as a couple of inches, then reactivates to the stop point again.  Back and forth.  It'll do this as much as a dozen times (usually less) then stop and act normal.  The same thing has occurred on the driver side perhaps twice.  Less occasionally, the passenger seatbelt will not actuate until the driver side door has been closed.  I can count the number of times this has happened in the past five months on two hands.  This seatbelt weirdness only occurs when the vehicle is at a stand still, and just after I've inserted the key into the ignition -- it isn't as if I'm driving along and it freaks out."

Bob Morazes says, "I have a 92 VDP with the same bizzare seat belts."

John Wynne says, "I had a similar situation with my seat belts.  Only the driver's side was affected, but not only did it joggle the belt back and forth, it would also trigger the door open buzzer and activate the interior lights.  The first time it happened was late at night during a heavy rain storm and it scared the hell out of me.  Lights coming on and buzzers

"It was only occurring during and after heavy rains so I unwisely ignored it for a while, until the day the belt started to move into its open door position and suddenly changed directions pinning me so hard into my seat that I thought it was going to dislocate my shoulder.  The retractable portion of the seat belt located to the rear and right of the drivers seat had finally siezed from all the erratic passive belt movement.  I was surprised to find that the belt motor had that much force to pin me into the set like that.  To top it off I was going about 45 mph into a pretty sharp turn.  Talk about panic!

"Basically, what I'm trying to say is don't be dumb like me and let it act weird until a mishap like mine.  I was really upset with myself when I found that the cause of all the mayhem was the driver's side door plunger.  You know, the one that activates the open door buzzer, turns on interior lights and causes the seat belt to retract.  I can't believe the symptoms were so obvious and I ignored it for almost a month.

"It might be one location for you to check out before digging under the dash or inside the track mechanism.  The way I tested mine since things seemed fine with a multimeter, was to tape a quarter to the metal plate on the door which contacts the door plunger.  This forced the plunger to seat a little further and eliminated the problems.  A local parts store had a suitable replacement for about $2."

The good news: According to John Alexander, since the motormouse seat belts are supposed to be a substitute for air bags, they are "warranted for life in US -- had mouse motor repaired and car washed gratis by my dealer."

Morazes agreed.  "My Jag dealer replaced them for free.  Yes, I said free.  Its not every day that you get a free trip through the dealership."

Charles Maraia wasn't happy with the warranty: "I took my '88 to the dealer and they said the motor is warranteed, but nbo the other parts.  Well, guess what?  They found fault with all the switches and on.  Cost me over $100 to fix a warranteed item.  And I still pull the fuse!  That won't happen again."

Maraia may have been ripped off, but it doesn't always happen.  Ned Wesley says, "I took my '88 in to purchase the seat belt assemblies and was told move the car in line for service.  The service manager attempted to operate the belts.  When they would not operate, the entire system was replaced at no cost to me.  The right and left side seat belts had an invoice of $1,900 for parts and labor.  I believe that the motors are invoiced at $500 U.S. each."

REAR SEAT SHOULDER HARNESSES: The 1983 XJ-S doesn't have rear seat shoulder harnesses, it has lap belts only.  However, it has the mounts for shoulder harnesses, hidden behind the rear quarter upper trim pad.  Since studies have indicated that wearing a lap belt only in a rear seat is more dangerous than using no restraint at all, those who actually have occupants in the back seat might want to consider adding shoulder straps.

MORE WOOD: Since more is obviously better, the tasteful touches of burl wood in the interior of the XJ-S can be supplemented with other panels ad nauseum.  The ‘88-on wood veneer ski slope reportedly will not fit the earlier cars - the console itself was changed at the same time; however, Autostyle Ltd (page 714) can provide wood veneer ski slopes to fit any XJ-S.  They also offer burl wood panels to replace the radio facia, the little panels around the headlight switch and ignition switch, and the panel surrounding the gauges within the dash, as well as burl wood shifter knobs.

DOOR SILLS: The ‘88-on metal door sills are a lot more impressive than the earlier plastic items.  As soon as you see one, you're going to want to retrofit a pair into your earlier car.  Patrick MacNamara says, "I had to machine about 1/2" off a center ridge the entire length of the underside of the plate to adapt it to my '82.  It was either that, or cut out/remove part of the carpeting and underlay where the sill plate sits.  The center ridge does not allow for the plate to sit flat and down tightly on the older cars."

While the plastic sills were one-piece, the metal sills have separate finishing caps at both ends and a series of clips underneath.  Richard Mansell provides a parts list: "The part numbers for the coupe are:

Tread plate RH BDC 4642

Note that the sills for the convertibles are different.  On the other hand, one might presume that the H&E convertible probably uses the same sills as the coupe.

Mansell also reports that there are aftermarket firms in the UK offering metal sills.

CUP HOLDERS: The XJ-S doesn't have one!  What a cheap car.  Gary Penovich says, "I definitely needed a cupholder in NYC.  How else was I gonna drink, drive, and give somebody the finger at the same time?"

There are lots of cheapie drink holders available; a visit to any truck stop or auto parts store should reveal a wide selection.  One place to consider installing a foldable drink holder might be the inside surface of the glovebox door.  On the '83, the glovebox door has a pop-up mirror on one side and nothing on the other, so you could install a drink holder on -- or in -- that other side.  But if it's a surface-mount, you might even mount it on the pop-up mirror.

PERFORMANCE CHECK: On max cool, this system should provide air at the center vent in the dash in the upper 30's F.  Steve S says, "My '85 XJ-S with R12 achieved 35°F at the vents, at idle, doors open, fan auto, max cool on a UK 70°F day after I'd topped if off in July of this year."  If your car ain't getting that cold, it ain't working right.  There are a few things to check.  First and foremost, while the system is trying as hard as it can to cool, check the sight glass at the receiver/dryer along the front edge of the radiator upper support rail.  There should be no bubbles visible in the glass --zero, zip, nada.  If there are any bubbles, the freon circuit is undercharged.  See page 514.

If the charge is OK, other things to look at include the adjustment of the linkages on the Delanair MkII system (see page 535) and checking for leakage through the heater valve when closed (see page 495).

SYSTEM TYPES: From the inception of the Jaguar XJ-S until 1987, a climate control system known as the Delanair MkII was used.  In 1987, the Delanair MkIII was introduced, and continued in use until the XJ-S ceased production.  The housing within the dash was a sheet metal assembly painted gloss black in the MkII, while the MkIII is largely plastic.  The MkII is controlled by a single servo assembly via a conglomeration of linkages within the right side of the console, while the MkIII uses multiple local servos and controls.  Both systems underwent several detail changes over their production lives.

The compressor and freon circuit is essentially common to both systems, as are a few other things.  Within the dash, however, the two systems are totally different.  So, the climate control tips are divided into three sections: Things that are common to all systems, things that pertain to the MkII only, and things that pertain to the MkIII only.

Was there a MkI?  Yes, but it was used in SI XJ6 and XJ12 saloons only; it had been superceded by the MkII prior to the introduction of the XJ-S.  Hence, it will not be addressed in this book.  Mike Morrin says, "The Mk1 system did not have an electronic amplifier and servo, and relied on a thermostatic bellows controlling a set of vacuum valves for temperature and air flow control." It also had considerably less cooling capacity.

The 1995-on XJ12's, which are based on the X300 body, use the climate control system that was introduced with that body.  It's not Delanair.  Obviously, it likewise is not covered in this book.  It has an electrically-operated heater control valve, as opposed to the vacuum-operated valve used in the XJ-S.  It also features an electric pump in the heater line.

POLLEN FILTERS: Richard Mansell reports: "If you are interested you can get pollen filters for the ventilation system.  I have no idea how or where you fit them but according to a Jaguar accessories brochure from 1997 three are available:

93.5-96 JLM11696
92-93 JLM11355
Pre-92 JLM11108
One might expect that these pollen filters would only fit the Delanair MkIII system, so that "Pre-92" probably really means 87-92.  If you have an older car, at least ask first before spending the money.

WINDSHIELD FOGGING: If your windshield fogs up more than it should, the first thing to do is determine if the