Annoying situation developing. S3 4.2, 300K Km, Final drive ratio 3.058.
Recently, upon taking off from a standstill, whether on a straight line or out of a corner, if I apply quasi-heavy throttle, the rear end of the car will knock with clunking noise and accompanying vibration. I've checked the rear wheel bearings and axle u-joints, no significant play whichever directions, so they should be fine(?) I figure it must be the propshaft center bearing so I changed that with a new OE unit, Symptom went away 60-70%, but is still there. I do suspect final drive internal wear, given its high mileage, but I have no replacement unit to do an A-B test. I do also suspect those three u-joints of the propshaft going bad, but again, no replacement unit at hand. Your assessment greatly appreciated!! By the way, car vibrates and shakes at 110-120 km/hr, but the tires are all new..

 

What condition are the rear suspension mounting rubbers in? Try jacking up the body and see if you can see any separation in each of the V mounts at each corner of the IRS cage. I have had one separate, causing the whole IRS to "squirm" and move under power. I would also look at the gearbox mount, the rear of the engine/transmission could be moving as well.

When you replaced the centre bearing did you align the driveshaft?

 

Check the tightness of the dog bone castings that anchor the bottom wishbone to the base of the diff. The shocks need to be removed to test this easily. These are the most likely cause, after the centre bearing.
I have just replaced my rear axle UJs, I had no symptoms but when they came apart they were 100% shot.

 

Hi Jagboi64:

Much appreciated!! I've just replaced all 4 rear V mounts, as well as the transmission mount. However I do not know the procedure of aligning the propshaft. Can you share this knowledge?

 

Hi Greg:

Great information! I shall look into that!!

 

There is an alignment jig/fixture shown in the service manual to align the shaft; even instructions on how to make one. However, I've not heard of anyone actually doing so.

In my own experience over the years the center bearing adjustment is always set to 'full right' so if yours isn't set there, that's where I'd begin. Then, if vibration continues, start adjusting it to the left in 3mm increments. A bit tedious but probably easier, all considered, than making and using the jig.

As for the clunking, also check that the exhaust isn't banging against the undersides of the car

Trans mount: correctly assembled? It is possible to assemble that crazy thing upside down...which naturally bollixes everything up although it will still function in a sense. A person would have to be as addlepated as me to do such a thing but, well, I just thought I'd toss it out there as something to check

Cheers
DD

 

Just in case you get to the worst case scenario, when you have an hour or so (!) read this thread:
https://www.jaguarforums.com/forum/x...3/#post2177390

I thought all this had completely cured the problem, but it had not quite. My latest effort has been to put in my spare differential, and I have just tested it today for the first time. I am, at last, VERY cautiously optimistic that the problem has been solved; but I will not be sure until a few more trips have been completed.

 

How difficult was it to change out the center bearing. I think that job is ahead of me.

Bill