in a Book
The XJ-S was originally fitted with a Borg-Warner Model
12 automatic transmission, but in 1979 this was replaced
with the GM400 automatic. In the mid-70's exactly 273 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.
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. I figured that there had to be some major
electrical fault that toasted most, if not all, of the
wiring in the console.
"We took part of the console apart and immediately 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 that links the gearbox to the body. The current
chose the next best available route, which was through the
shifter cable to the body. Had it been a beefier shifter
cable without all sorts of plastic sleeves, it might have
worked fine and I'd never known there was a problem, but
such was not the case."
"I called Special Interest Car Parts to order the part,
but before I said what I wanted, I told the guy what the
symptoms were and that I had a loose ground strap. He
immediately said that I had fried my shifter cable and that
he moved a lot of those parts."
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. The GM400 alignment relies on a pair of 1/2"
dowels located the same way as on GM vehicles; the earlier
arrangements used a smaller diameter dowel. All of this
means that if you replace your early BW12 automatic with the
later GM400, the bolt holes will line up but the dowel pins
will fit loosely in the holes and won't serve their intended
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
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: Please see the comments
on fluids in the section on Drivetrain
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
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 - 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
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."
SOFT SHIFTS: Yes, those
gentle shifts are suitable for the Jaguar image of luxury.
Unfortunately, they are apparently to blame for the GM400's
poor durability record in this application. Per Jim
Cantrell: "Old transmission types know this phenomenon well.
Take a cadillac with the same transmission as a truck and
the cadillac will last half as long. You can tell when you
pull the pans on those bux luxury cars - lots of
transmission dust in the bottom (clutch wear). Seems that
grandma and grandpa would rather have to replace the
transmission every now and then than to have their tushes
bumped during shifts. I guess that this allows them to have
a deeper sleep while careening down the highway."
If durability is more important to an XJ-S owner than the
gentle shifts, use of alternative
fluids or installation of a "shift
kit" may be in order.
GM400 SLIPPING: It is occasionally reported that
the GM400 transmission slips; sometimes when cold, in first
gear, or under other specific circumstances. Leonard Berk
reported that his slipped until he deliberately overfilled
the transmission fluid, then it worked fine. Randy Wilson
provided this explanation:
"On GM vehicles, a loose/fallen filter is a normal
occurrence, and is known for causing weird problems. The
most common problem is the transmission briefly finding
neutral right after a hard turn. Most THM transmissions, the
400 included, hang the filter low in the pan. The filter is
supported by the o-ring on the pickup pipe (pipe from filter
to valve body), which snaps into a machined groove at one
end and a steel clip at the other end. If the o-ring is bad,
or the filter has fallen, the fluid pickup point is
effectively raised to the bottom of the valve body, about an
inch up from the filter."
Jim Cantrell provides more elaboration: "The o-rings on
the filter an at the pump inlet are known to leak in cold
weather which results in pump cavitation. Pump cavitation
can usually be heard - a whining sound of the pump. On the
400 in the cold (talking 40 degrees F and below), it will
usually last about 30-60 seconds. It still moves since it's
actually pumping oil. It's just sucking in air from the
o-rings and this gives the cavitation.
"Second hypothesis is that once cold, the o-rings leak
and air leaks into the oil pickup tube and drains the oil.
The result is the pump runs dry until oil starts
Since the GM400 dipstick has warnings not to overfill,
perhaps overfilling should be done only as a diagnostic
measure. If it fixes the problem, suspect a dropped filter.
Just go ahead and change the filter (and O-ring!) and
Wilson added that slipping is not good on the
transmission, and the sooner it is corrected the less damage
will be done.
CHEAP GM ACCUMULATOR: Sandy Gibbs reports, "My
tranny (GM400, 1987 XJ-S) went belly up. I took it to the
shop for a rebuild. The mechanic showed me a small plastic
cuplike looking thing which he said had caused my
transmission to burn up. He claimed this piece (called the
accumulator) was usually the problem when a GM400 dies. This
information was confirmed by the owner of the parts place
(which deals exclusively in transmission parts) where I
bought all my parts for the rebuild. GM knows about the
problem and now supplies an aluminum accumulator which won't
break. It seems to me that anyone who plans to have some
transmission work done anyway might want to invest in a new
Thomas Alberts adds, "You are talking about an
accumulator piston. One of the two accumulators has a
plastic piston that can fracture with fatigue after high
miles. It is a common failure mode. The piston breaks
leaving a 1/2" hole that hydraulically "shorts out" parts of
the transmission logic and leads to clutch packs burning up.
It prevents kickdown and can cause second and (I think)
first gear to engage simultaneously forcing one of the
clutches to slip in second. It is pretty easy to replace the
piston with the transmission in the car. It involves removal
of the oil pan and valve body. I wouldn't advise everyone to
rush out and do this, but if you are ready to replace filter
and fluid it would be worth the extra effort to put in the
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
"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
fluidity of DEXRON-IIE fluids and incorporated major
improvements to the frictional stability, high temperature
oxidation stability and material compatibility.
"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: http://www.mobil.com/lubes/atfpds.html
"I think most of the other synthetic providers also have
DRAIN & REFILL CAPACITY: The repair manuals
seem to agree that a drain and refill of the GM 400
transmission will require 9.6 US quarts or
19-point-something US pints. However, Larry Barnes reports
that it only took about 6 US quarts on his car. Reason
KICKDOWN: Since there seems to be a lot of
confusion about this term, I will first endeavor to define
it. Kickdown does not refer to the normal
downshifting of the transmission due to increased throttle
(reduced vacuum) at low speeds. Kickdown refers to the
forced downshifting of the transmission by a very
definite pressing of the accelerator pedal all the way to
the floor, and pushing it hard enough to operate a separate
"snap" that the driver can feel when the pedal is moved the
last quarter inch or so. It is intended to be a distinct
enough feel that the driver can easily choose whether or not
he desires kickdown operation, or merely full throttle
In the case of the pre-1992 Jaguar with the GM400
transmission, kickdown is accomplished via a microswitch
mounted on the throttle cable attachment at the bellcrank.
After the throttle is wide open and the bellcrank is against
the stop, further pressing of the pedal can move the
bellcrank no more. Instead, the cable housing moves in the
opposite direction against a very strong spring, strong
enough to ensure that the driver must really want it to
move. When the cable housing moves against this spring, a
microswitch closes a contact sending current to a solenoid
within the GM 400. This solenoid causes the transmission to
downshift now. At any reasonable speed, it will
downshift to at least 2nd; below 30 mph or so, it'll
downshift all the way to 1st, and the engine will
The results should be obvious and dramatic.
Unfortunately, all too often this system doesn't work, and
the owner doesn't even know it; since the transmission will
downshift normally under heavy throttle, they presume that
everything is OK. It is easy enough to test, though; with
the car shut off, make sure pressing the accelerator hard
operates the microswitch on the throttle cable as it should.
Make sure you know what it feels like to press the
accelerator all the way without kickdown as opposed
to with kickdown. Then, take the car for a drive. If
there is an eye-popping difference between full acceleration
with kickdown and no kickdown, it's working as it should; if
you have a hard time telling the difference, it ain't
working. If you're not sure you can distinguish the feel of
the pedal, simply disconnect a wire from the microswitch on
the throttle cable housing and go for a spirited drive; if
you can't tell the difference, it ain't working.
If it doesn't work, check fuse #5; there should be power
to the kickdown switch on the LG/W wire when the ignition is
If that's OK, check that the kickdown switch itself makes
good contact. Physical adjustment may be necessary, since
problems may be caused by the switch not positioned
correctly or the roller arm bent.
Next, check the inhibit switch on the shifter. One of the
microswitches (hey, the car is covered with them) within the
console and operated by the cams on the shifter is a
microswitch that closes only if the shifter is in D. This
prevents the operation of the kickdown solenoid in any gear
other than D. Note that this same switch also prevents
operation of the cruise control in any gear other than D,
and it does so by grounding a signal line from the cruise
control through the solenoid in the transmission!
Problems with this inhibit switch may be mechanical in
nature as well; it might not be positioned properly for the
cam to operate it reliably.
The next possibility, as Greg Meboe points out, may be
that the wire at the transmission isn't connected right.
"The kickdown connector on the outside of the transmission
case had two separate connection points on it, in the shape
of a "T". The vertical connector which "bisected" the
horizontal connector was the kickdown one. I had been
explicitly told that the horizontal connector was the proper
one to connect the kickdown wire to, so that's what I did.
When I took apart the tranny, I saw that the horizontal
connector went to what looked like some type of sender on
the valve body, whereas the vertical connector (which I
hadn't used), went to the kickdown solenoid."
For the final test, it helps to be under the car with
your ear near the transmission and all quiet in the area.
Have an assistant turn on the ignition, put the shifter in
D, and operate the kickdown switch, and you should be able
to hear the solenoid within the transmission click. If
there's no click, make sure you are getting 12V at the wire
to the connector; if so, time to drop the pan and replace
Richard Mansell quotes from a Jaguar publication on the
changes for the 1992 model year:
The kickdown switch
is no longer located in the underbonnet area but is
changed to the XJ6 type and is positioned under the
TRANSMISSION MOUNT: The
transmission mount in the XJ-S 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. Jaguar 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.
A picture is worth a thousand words here. Exploded views
abound, although many seem to be missing a few parts, which
doesn't help someone trying to figure out how it goes
8 is a section drawing of the assembly, in hopes
that it will be of some help.
Note: If you lower the transmission significantly, Thomas
E. Alberts suggests you take care that the top of the engine
does not damage the heater valve.
The following sections describe several reasons for
disassembling the transmission mount, followed by a section
on proper assembly.
SPRING: Michael Neal reports that the tranny
support spring (CAC 2327) 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 sags as it gets older.
To check the old one, the unloaded length of a new one is
GOT A COUPLE EXTRA WASHERS? There have been
several reports of washers being found between the vertical
post and the housing of the transmission. 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
GM400 FLUID AND FILTER REPLACEMENT: Since the
GM400 has no drain plug, draining the fluid requires
removing the pan. To remove the pan, the forward mounting
bracket must be removed. Therefore, changing the fluid and
filter in the GM400 transmission requires complete removal
of the transmission support. The correct reassembly of this
system is not obvious, and non-Jaguar (Aamco?) mechanics
will often reassemble it incorrectly, and perhaps even omit
some of the parts. Taking this book along to the shop may be
helpful; having an experienced Jaguar mechanic service your
GM400 transmission may be the best course of action.
Alan Jenks reports that B&M Racing offers a drain
plug kit (B&M #80250) which can be fitted while the pan
is off. Also, J. C. Whitney offers two replacement oil pans
for the GM400 with drain plugs, one "original capacity" and
one that's 1º" deeper for "extra capacity". They're
both chrome plated, and cost only about twenty bucks. Note
that Larry Barnes reports that "...I purchased a J.C.
Whitney chrome transmission oil pan (standard size) with a
drain plug ("GM TH400 Original capacity"). It did not
fit. Bolt pattern was correct, but the pan was not deep
enough for the filter. So, if you are thinking of getting
the same pan, get the 1.25" deeper than original "extra
capacity" oil pan."
If you're more worried about fresh fluid than filter
blockage, one of these changes might be a worthwhile
investment. If you do your own work it might still be a
worthwhile investment even if you pull the pan every time,
since you can drain it first and then remove an empty pan
rather than a full one.
John Himes adds a note: "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."
The filter is held in place by the O-ring on the suction
tube on one end, and a bolt at the other. This bolt is
shouldered so it cannot be tightened down on the filter, so
the filter is free to rattle around a little. This is
apparently deliberate; there are no parts missing. Randy
Wilson says "That bolt is shouldered for a reason, though I
can not tell you exactly why. All GM trannys of that
general era use a floating filter that sort of lays in the
bottom of the pan. At least the 400 has a positive bolt.
Others use a cheesy spring clip."
RUBBER BUSHING & SPRING CUP REPLACEMENT:
Finding the rubber bushing (CAC3227) or the rubber spring
cups (CBC2517) intact appears to be a rare occurrence; they
are often missing, damaged or mislocated. Reportedly, the
bushing utilized on earlier cars was made of foam rather
than solid rubber, and was even less likely to be found
To properly install a new rubber bushing requires removal
of the spring support; you cannot simply slip 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
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
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.
There is a philosophy 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.
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.
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 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
Once the spring support is supporting the tranny, 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
If the car is fitted with the BW automatic, the post
assembly is the same except for an additional sleeve that is
installed first. So, the order is sleeve-special
washer-sleeve-double washer-tie plate-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 -- at least on the GM400
assembly. 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.
SPEED SELECTOR CABLE TRUNNION MOUNT: This is the
little bracket that holds the shift cable housing to the
transmission housing. The bolt that holds the trunnion mount
to the tranny housing goes in from above, and cannot be
removed from underneath the car. The only way to remove it
is to remove the console, shifter mechanism, and a panel
underneath to get at the bolt.
It is suggested that if you ever have an opportunity, cut
a hole in the panel inside the console and fit it with a
rubber plug or cover, so the trunnion mount bolt can be
removed by simply lifting the console cover (three screws)
and removing the rubber plug.
If you are trying to remove the engine/transmission
assembly and must disconnect the speed selector cable, the
above trunnion mount problem may appear to be a real holdup.
It is not, however. The attachment of the swivel joint to
the end of the cable is a removable clamped-on device.
Simply loosen the two hexes from each other, and the entire
joint slides off the end of the cable. Then the cable can be
slid through the trunnion, allowing the removal of the
engine/transmission from the car.
ADDING A TRANSMISSION COOLER: In the May 1995
issue of Australian Jaguar Magazine, John Pearson says "Most
Jaguar engines run fairly warm...and transmissions prefer
cool running, so you may consider incorporating a neatly
positioned transmission oil cooler...This is especially
recommended on V12 powered cars with the GM T400
REAR SUSPENSION/DIFFERENTIAL REMOVAL: It's
discussed in the section on Steering
DIFFERENTIAL: The XJ-S has
apparently been fitted with at least three 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
From 1985-1987, a 2.88:1 DANA unit was used. This unit
can be distinguished in that the bearings on the output
shafts are held in place with three bolts; the differentials
both before and after these years have five bolts. It also
has no drain plug.
When working on a DANA unit, you can get the seals from
Jaguar, bearings from a local bearing house, and the
clutches, shims, and those silly little clutch retainers
from any performance shop that has access to Dana rear end
parts. When ordering, they will usually ask for a ring gear
diameter and an "axle" spline count.
Jaguar does not want to admit to the Dana as having ever
existed. The problem is those "silly little clutch
retainers". The Jag, with it's high weight and sticky tires,
really hammers on the clutches, which eventually chew
through the retainer. By design, the half retainer can't get
out into the gears where they would do major damage. But it
does get pushed out the end of its access hole, mucking up
the carrier bearings.
From 1987 to 1993, there was a differential referred to
as the GKN Power Lock with a 2.88:1 ratio.
Reportedly, the official Jaguar repair procedure for
final drive units is to replace them as a whole.
All XJ-S differentials are limited slip, and all the
systems operate using essentially the same principle (a
series of friction discs, with the compressive load
increasing through increased drive torque) although the
feature has often been given different names.
The gears for the DANA Type 44 limited slip differential
will fit in the Jaguar unit. This includes gears from many
larger American cars and small trucks. However, there are
problems that must be overcome. First, the DANA ring gear
will be threaded for smaller bolts than the Jaguar
originals, so bushings will have to be fabricated to make
the smaller bolts fit snugly in the holes.
Second, the replacement pinion will not mate with the
Jaguar input flange, so a Chevy input yoke will have to be
used. The Chevy yoke is the type with U-bolts that retain
the U-joint bearing caps directly, so the flange on the rear
end of the drive shaft will need to be removed. Since the
Jaguar driveshaft uses standard Chevy U-joints, they will
match up fine.
The salesman at Quality Jaguar reports that while the
DANA gears will work, they are considered inferior to the
Jaguar parts. Specifically, they tend to whine more, and of
course the smaller mounting bolts are not as sturdy.
From 1993 on, the entire rear end of the XJ-S changed. A
suspension similar to that on the XJ40 was used, with
outboard brakes rather than inboard. Along with the engine
being enlarged to 6.0 litre and the fitting of the 4-speed
GM 400, a 3.54:1 final drive was used.
Apparently the AJ6-powered XJ-S's, 3.6 or 4.0 litre, all
have 3.54:1 final drives.
DIFFERENTIAL BREATHER: John Goodman reports on
special parts for the XJR-S: "Looking through the parts list
I notice that there is a revised diff cover with additional
baffles. <Quote manual> ..."the diff rear cover is
redesigned to improve breathing at high road speeds. The
altered baffle plates direct oil flow so that turbulence is
kept away from the oil breather.""
DIFFERENTIAL OIL CHANGE: Getting the fill plug out
is no picnic. It has been suggested that removing the center
reinforcing plate under the final drive unit (14 bolts, 6
with nuts) may be worthwhile. Don't worry, the whole car
won't fall apart while the plate is out.
Many Jag owners suggest a length of plastic hose and a
squeeze bottle for topping up or filling up the final drive
unit. The hose should be long enough to feed out the right
side wheel well so the oil can flow downhill.
Brian Sherwood points out that if you open the boot,
remove the spare tire, and peel back the matting forward of
the fuel pump, there is a round metal plug; removal of this
plug provides access to the fill plug on the differential.
"I just popped it out with a screwdriver, did my lube thing,
then pressed the plug back in with some RTV around the
Note that while the diff can be topped up with
conventional gear oil, a drain and refill requires an
additive for limited-slip units.
According to a salesman at Quality Jaguar, the XJ-S final
drive unit uses both natural leather and natural rubber
seals. Therefore, synthetic lubricants are not
recommended. It is recommended that synthetics be avoided in
the special additive as well.
DIFFERENTIAL GASKET: British Auto USA offers a
differential cover gasket (part number 3931) that is
supposed to be better than the original -- thicker and
better material. Of course, the Jag differential is a common
Dana design used in lots of cars and trucks, so gaskets
should be available at any parts store.
TEFLON: Dennis Hurvitz reports: "While having a
quickie lube joint change the oil in my wife's car (ok, i
was pressed for time), a guy pulled up in an older Mercedes
to thank the manager. Seems the Mercedes guy had a
differential whine and the manager recommended replacing the
differential fluid with some new mixture containing teflon.
The owner made a point of thanking the manager, because the
problem (sound) mostly went away!!"
Unfortunately, lubricants containing teflon are not
recommended for limited-slip differentials, and all XJ-S's
have limited-slip differentials. Still, if you're facing a
diff rebuild anyway, perhaps you can add the teflon to quiet
the whine and do without the positraction until you get
around to having the diff rebuilt.
INPUT FLANGE RETAINING NUT: It's a really big nut,
obviously it should be tightened down really tight, right?
Wrong. This nut is used to set the preload on the input
shaft bearings. Between the bearings is a "crush sleeve",
and during assembly this nut is tightened just enough to
provide the proper bearing preload while compressing this
sleeve. If the nut is overtorqued, the entire final drive
assembly must be torn down to install a new crush
DIFFERENTIAL OUTPUT BEARING FAILURE: One of the
common failure modes of the Jaguar differential unit is the
failure of the bearings in the output shafts, possibly
because these bearings take lateral loads imposed by the
working of the suspension. Whatever, the failure is usually
indicated by clunks from the rear when driving or the tire
rubbing the wheel well where it formerly had clearance.
Checking by grabbing the top of each rear wheel and shaking
vigorously in and out clearly indicates a problem. Closer
inspection shows that the output shaft is free to move in
and out, and the only thing limiting movement is the brake
disk banging back and forth within the caliper!
According to Jan Wikström, "it's very likely that
all you need to do is replace the bearings and seals. This
is not difficult, but you'll need to take the rear subframe
off your car. You can do it from underneath, but that
probably takes longer because of the difficulty in getting
the brake calipers off and back on. Besides, taking out and
dismantling the complete rear suspension gives you a great
opportunity to check everything."
CLUNK: Julian Mullaney shares an
unpleasant experience: "I had a clunk on my '87 XJ-S from
the rear end. My clunk was because the diff itself was loose
in the mounts. The mounts in this case were 4 cone-shaped
bolts which attach the inner lower wishbone mounts to the
diff casting. The bolts screw right into the diff, and are
wired in place. These bolts had just become a bit loose even
though they were still wired together from the factory. The
constant rocking with power on/off had worn the fit between
bolts and casting. You can easily check for this by jacking
the car up high, putting the trans in P, crawl under and
look for movement in the joint while violently rotating the
rear tires back and forth." This is reportedly a fairly
common problem; it should be noted that proper torquing and
lockwiring of these bolts is very important. Many owners use
Loctite on the threads as well.
Jan Wikström adds, "If the PO has omitted the
security wires on the bolts, they come loose - and then the
U-shaped shims fall out and the diff is really
"The inner pivot bracket is shimmed to the diff to line
up with the pivot mounting holes in the cage; with the bolts
tight, the pivot spindles should slide in and out easily. If
those inner pivot carriers aren't correctly shimmed, it's
jolly well impossible to get the trunnion bolts out without
slackening the diff bolts -- which is very hard to do
because the trunnion bolts block access to the bolt heads.
You need a very thin open-ended spanner."
"My second XJ had pivot spindles that couldn't be moved;
somebody had botched the assembly and just forced the whole
thing together without shims. I had the devil's own time
finding a thin enough spanner to loosen the mounting bolts
enough to slide the spindles out."
"To get this right requires an extra step in the assembly
procedure: you measure the space between brackets and diff
(bracket mounting bolts finger-tight, bottom plate out) and
get spacers to that thickness. Now, there's not a hell of a
lot of space between the suspension arms and the
bracket-to-diff bolts; unless you have some extremely thin
spanners (and thin fingers to get the locking wire on), you
now need to pull the inner pivot spindles. Put the spindles
back in without the suspension arms and tighten the bejasus
out of those bolts (the torque is in the book); now try the
inner pivot spindles. If they don't slide out easily, you
need to tinker with those shims. Apply lock wires and
assemble the inner pivots.
"Now bolt on the bottom plate; you'll find that the
complete assembly is rigid.
"Another thing I noted on that car was that the final
drive had been flopping around to such an extent that the
rear sub-frame was fractured on top, where the four top
final drive mounting bolts are (invisible without taking it
out). There's a (1/4 in? 5mm?) steel plate inside the
double-walled top of the sub-frame (as I found when I welded
fatigue cracks in my first one); the retaining bolt heads
have an underside taper matching a taper in this plate. With
your diff slopping back and forth, there is good reason to
suspect fatigue cracks in the top."
On to the