[urq] New to list - Scary noise

[Morin, Jean-Léon]

Hello everyone. 

I hope I am on the right list. I don't drive an URQ but a 4000SQ, which is similar in some respects. If I'm not in the right place, please don't hesitate to let me know. 

My new-to-me 1986 4000S quattro has been phenomenal for the past six months. With studded Hakkas, it's a true traction machine.

However, lately, when driving at low speeds and coasting (not braking on compression, not accelerating), a really substantial vibration, somewhat irregular in nature and alarming, can be felt and heard. it can also be felt at other times when braking on compression at higher speeds. It seems to be coming from the rear differential. I suspect that I have a serious issue back there, shredded ring and pinion. It might be an axle problem but it really sounds like a ring and pinion problem. I am considering draining the oil to confirm my suspicions. 

I have been told that these cars are completely bulletproof in the drivetrain department, which I don't doubt - a diff failure at 400 000 kms is not exactly premature - but I am wondering if this is a somewhat rare or common failure. I'm wondering if I could find a used diff and swap it over, or if anyone has any recommendations, or would like to take a guess at what happened. 

Thanks for reading this, I welcome all opinions. 

J-L
Ottawa Ontario

Change is inevitable, except from a vending machine.