The XJ-S was originally
fitted with a Borg Warner Model 12
automatic transmission, but in 1979 this was replaced with the
GM 400 automatic. The following section is
divided into the two transmission types.
Borg Warner Model 12
Bolt Patterns
The bolt pattern for the transmission/engine attachment is the
same for the B-W and the pre-1993 GM 400, and apparently was the same
for the Series III E-type with manual transmission. However, when the
GM 400 was incorporated, the dowel pin arrangement was changed. The
GM 400 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 B-W automatic
with the later GM, the bolt holes will line up but the dowel pin
holes won't.
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.
If you need to know more about this dowel situation, call
Chad Bolles.
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.
Faulty Torque Converter Valve
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.
Transmission Fluid
Please see the comments on fluids in the section on
Drivetrain
Modofications.
GM 400 Transmission
Interchangability
It is well known that the later XJ-S's are fitted with the GM 400
automatic transmission. What is less known is that this transmission
has a housing designed specifically to mate with the Jaguar V-12.
Because the GM 400 has an integral bell housing, a GM 400 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.
High Performance Sprags
If the tranny is apart, it is recommended that the sprags be
replaced with high-performance aftermarket models. The Jaguar is hard
on even the trusty GM 400, and has a tendency to tear it up.
As a result of a complete revamp, the 1993-on 6.0 liter V-12 has a
standard GM engine/transmission bolt pattern. Cars with this engine
come with a 4-speed version of the GM 400.
Soft Shifts
Yes, those gentle shifts are suitable for the Jaguar image of
luxury. Unfortunately, they are apparently to blame for the GM 400'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.
Slipping
It is occasionally reported that the GM 400 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 to 60 seconds. It still moves since it's actually
pumping oil. It's just sucking in air from the orings 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 flowing.
Since the GM 400 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 fluid.
Wilson added that slipping is not good on the transmission, and
the sooner it is corrected the less damage will be done.
GM 400 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 together. Figure 2 is a
section drawing of the assembly, in hopes that it will be of some
help.
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 3.925 inches.
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 clunk.
GM 400 Fluid and Filter Replacement
Since the GM 400 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 GM
400 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 GM 400 transmission may be the best course of action.
It should also be noted that J.C.
Whitney offers a replacement oil pan for the GM 400 that has a
drain plug. It's also chrome plated, and costs only twenty bucks. If
you're more worried about fresh fluid than filter blockage, this
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 K. 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 intact.
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 end coils.
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 backserviceable 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 mineralbased
ATFs. Synthetic transmission fluids basically share all the same
advantages that synthetic motor oils enjoy over conventional
mineralbased oils. These include improved lowtemperature 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 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.
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 without kickdown.
GM 400 Kickdown
In the case of the Jaguar with the GM 400 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 scream.
Diagnosing Problems
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.
Repairing
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 on.
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 the solenoid.
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.
Replacements
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.
Greasing
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, 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.
Spring Cleaning
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 properly. The transmission must be jacked all the way up
into the tunnel before the spring support is installed.
Center Post Assembly
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.
GM 400 Transmission
When 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 the nut.
Borg Warner Transmission
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 GM 400 assembly. If they are
missing, 3/8" washers totaling 1/4" in thickness may be used.
Checking Movement
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 V-12
powered cars with the GM T400 'box...
On to the Final
Drive
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