Jaguar XJ-S. Manual - part 89

 
 

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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 edge.” 

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 (see page 689) offers a differential cover gasket (part number 3931) 
that is supposed to be better than the original -- thicker and better material. 

 

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 sleeve. 

 

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.” 

The output shaft assembly for the Salisbury differential is available as a pre-assembled unit under a single part number: 
AEU1802 for the right side, AEU1803 for the left.  This simplifies repair considerably; by getting this assembly pre-
made, the mechanic doesn’t have to fiddle with bearing preload, crush sleeves, etc., he just removes the old assembly 
and bolts in the new.  Obviously, there is a core charge on the old assembly, so it can be rebuilt with new bearings and 
seals. 

 

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 

 
 

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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 loose. 

“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.” 

 

FINAL DRIVE RATIO CHANGE:  There are many ratios available to fit the Salisbury final drive.  However, be aware 
that if the ratio is changed significantly, the differential carrier will also have to be replaced.  Since the lower ratios 
(higher numbers) require a smaller pinion, the ring gear needs to move closer to center to mesh properly.  This could be 
accomplished by making the ring gear thicker or adding a spacer, but instead a replacement carrier is used with the 
mounting flange in a slightly different position.  Unfortunately, the carrier costs more than the gears. 

If you have the Dana final drive unit, Greg Wells of Coventry West reports that he can only get one set of gears to fit: 
2.88:1.  So, step #1 for changing the final drive ratio is to replace the Dana unit with a Salisbury.  Wells adds that, 
thanks to the popularity of that change, Coventry West can no longer offer core credit on Dana final drive units -- they 
have more on hand than they can use.  So, changing the final drive ratio on a Dana-equipped car means buying an 
entire new Salisbury final drive unit outright and simply discarding the Dana -- an expensive proposition indeed. 

 
 

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SUSPENSION & STEERING 

 

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 373. 

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 365; 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. 

 
 

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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 371. 

 

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