Zphere

Hello everybody,

My A4 Quattro Avant with 215k miles has suffered a catastrophic failure somewhere in the rear end and I am not certain as to whether is in in the drive-train or the suspension.


The rear suspension has been slowing deteriorating over the month month to the point that the rear right side bushings will creak/squeak with an loading/unloading. Last night as I was heading home I was decelerating to a stop sign when the car starting humming/vibrating loudly from the rear as I was coasting to a stop. Very noticeable. I slowly picked up speed to about 30mph were the vibration grew in intensity until the point where I knew something was tragically wrong.


The best way I can describe the vibration is a pulsating wobble that feels like a horribly out of round tire.

Thankfully I was 1/2 mile from home so I was able to limp back. I was able to drive the car up to 5mph with no ill effects. As soon as I breached that 5 mph limit the vibration would begin and climb with speed. Anything over 10mph and the rear end would begin bouncing.

Since I was planning a suspension rebuild soon anyway I have the vehicle up in the air now.

I have looked over the rear suspension and nothing appears drastically out of place. I pushed on the wheels before I took them off and they didn't give an inch..

Another note on the suspension, it is riding on Bilstein struts and H&R springs which have at least 40k miles (time since I bought the car with them installed) on them if not more. I have noticed a slow decrease in damping in the past 10k miles.

So, what in god's name is going on here?

Did the rear end diff fail?

Perhaps a CV joint failed?

Since the control arms are still intact perhaps the strut failed?

Tomorrow I am going to begin breaking everything apart so maybe I'll find something while I'm doing that.

So far my plan of attack:

- Remove rear spindles

- Remove rear axles

- Slowly disassemble the entire rear suspension (control arms/struts/springs)

- Remove rear diff and carrier

- Remove rear sub frame

- Replace all related bushings

- Replace struts/springs with coil overs

- Possibly replace both rear axles?

I'm not a fan of blindly throwing parts at a problem but this is all work I've been planning anyways however I still am not certain what is causing the issue here.

Any thoughts?

Thanks in advance!