351
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