Thanks for the replies.
We've built a few rally car diffs and it doesn't look like back lash in the diff or shafts.
There seems to be a 'two stage' rotation, with the first step taking up the slight 'slack' and then when more torque is applied there's a significant second rotation that leads up to the clunk. It's as if there's some type of 'cush drive' inside the diff, which seems extremely unlikely.
When on the level I can change F/R direction and creep the car on tickover without causing the clunk, but as soon as any further torque is applied it takes up the movement and clunks.
No we aren't 100% sure that it isn't a mounting and that's what I'd expected to find (propshaft centre bearing carrier was prime suspect), but the visible rotation in the rear coupling/joint really does point the finger.
If I can't find any specific info I'll take the coupling off and investigate it, I was hoping to line up a replacement source or firm up a plan to use the one off the A4 beforehand tho.
Any in depth technical info available for Audi transmissions?
I don't mind buying some if it's available commercially at a sensible price, as we're also considering an S3/A3 Quattro rally car.
Last edited by M3 Compact; 30th January 2015 at 02:04 PM.
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