Hey, maybe someone can tell me what kind of diff (Code, model etc.) goes to 1994 XJS v12 6.0 Facelift?
Is it the same as older jags? Did other models used it?
Mine is broke and before even taking it out i would like to source used one in order to save time while car is handing in the air.
By saying broke - then turning in to the corner on low speeds loud "clunk" comes from the rear of the car.

Thank you in advance,

 

It is a Salisbury/GKN limited slip differential and is (basically) the same type as in all V12s (with the exception of a few mid 1980s models that were fitted with DANA differentials of the DANA 44 type as used in Jeeps of that era). Only the final drive ratio changed with the adoption in the facelifts of the 4 speed gearbox, the rest is the same.
(As ICS America corrected me below, there are differences in internal construction between earler and later models, but all types will fit into your car. ICSA mentions the speedo signal which is taken from the diff, which your car's speedo will need, is only fittable to the later versions of the diff with the requisite cover-type to accept the sensor).

 

Dear Greg, am i right that drive ration should be 3.54 for 6.0L cars?

 

I think so, but someone knowledgeable on the facelifts will confirm.

 

Finding a 3,54 may be a challenge. Might be better off rebuilding existing. Id be interested in buying the broken one if shipping isnt too horrendous to Canada.

 

I don't want to be disagreeable but they are not the same. There are many internal differences but externally they are still a bolt in many cases. Below are some key differences.

1. The stub axle and bearings are a different design and use a crush washer, the whole side bearing assembly has proven to be less robust and more complicated that the earlier design. Every facelift diff I've come across needed at least 1 stub axle repaired due to noise and lash.

2. The power-lok function is low bias, it basically acts like an open diff. There is very little limited slip function compared to the early diffs. So much so Jag issued a TSB becasue customers were showing up at the dealer's service departments and complaining their new XJS has a broken limited slip since it didn't work as they were accustomed to from the prior models.

3. U-Joints are smaller and un-greasable. They are the same as those Ford used in Volvo's and other makes of the day. Not really part of the diff though.

4. Input and output seals are different.

5. All the 4 speed 3.54 diffs have a boss to mount a speed sensor in the diff cover with a matching tone wheel on the ring gear in order to generate a wheel speed signal.

That's all I can recall at the moment. The hot setup is to find an open 3:31 and add an Dana 44 center section of your choosing. It's far less dear becasue you can use the low cost dana 44 side bearings in leu of the expensive Jag side bearings and in the end you'll have a modern limited slip. The stub axle bearings are also easier and less expensive to rebuild on the earlier diff's. The stub axles on the facelift diffs are extremely difficult to mend becasue of the skill and force necessary to cinch the crush washers. I suspect this is why so many of them fail, they were probably not setup right at the factory due to the complexity and speed of production. The 3.31 is also a great ratio for many custom configurations. Just barely tall enough to be used with a 3 speed Auto and low enough to work with retrofit 4 speeds like the 700R4 (4l60e). This wont be an option on a facelift car unless the speed sensor is relocated or reengineered.

 

Not disagreeable at all ICSA! Great to have your detailed knowledge.

 

I believe the 3:54 power lock came in all the XJS '94 up 6 and 12 cylinders but you should identify the problem first. The low speed clunk could be a loose stub shaft, hub bearings, brakes, lugs or even u-joints and not the differential. A quick inspection of each side should locate the source of the clunk.

 

Good advise and the lower fulcrum shaft bushes are also a common source of rear clunks. Certainty a good going over before throwing parts at it would be salient considering the time, labor and costs involved.

 

And, come to think of it, the two bolts attaching the lower fulcrum casting to the side of the diff each side. The alignment shims can fall out and the casting is then immediately loose.