Jaguar XJ-S. Manual - part 87

 
 

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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. 

 

Borg-Warner Transmission Mount 

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. 

 

GM400 Transmission Mount 

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 

 
 

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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. 

 
 

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W

A

S

H

E

R

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Figure 16 - Assembly of Transmission Mount (GM400) 

 
 

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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 715) 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