Jaguar XJ-S. Service manual - part 86

 
 

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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 715) provides the adapter hardware necessary to fit the TH700R4 to the Jaguar V12 5.3.  Scott 
Horner says that Dellow (page 713) does as well, and Chad Bolles of Jaguar South (page 714) 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 694) 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 693) and 
Vicarage (page 702). 

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 693) 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 

 
 

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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 715) offers a kit using the Tremec TKO, and Conversion 
Components Ltd. (page 712) 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 713), 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 712), 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 718):  “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.” 

 
 

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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 
only work on an XJ-S with ABS, and I have found no way to make it work on a non-ABS car.”  Aaargh!  Note that that 
AJ6-powered XJ-S existed in Europe before the advent of ABS brakes, so perhaps there is still a possibility there. 

Vintage Jaguar Works (page 694) offers a pedal box with clutch pedal and master cylinder. 

AJ6 Engineering (page 710) 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. 

 

 

TRANSMISSION MOUNT 

 

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 

 
 

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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 715) 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 694) 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.