[urq] Diff Noises

[Johnny]

The prop shaft center bearing could be causing all of the clunking. By
having play, when the diff engages it would send a bit of movement
through the shaft. With the bearing allowing it to move it can cause
the "clunk" your referring to on the bottom of the car just as you
have described. I ran in to this issue on a past 4000 quattro of mine.
As for the shaft hitting the exhaust anything is possible with a worn
bearing, but I would tend to believe the shaft bearing itself is the
root of the problem.

On Tue, Jun 1, 2010 at 7:56 AM, Maurits Jonkergouw
<urquattro at moregraphics.nl> wrote:
> Now the check valve behind the rotary switch is fixed, I'm noticing a loud 'booming' or 'thumping' noise if the center diff is getting engaged. Sometimes it silently locks up straight away  but usually it takes some seconds (light goes on and off briefly, then on again and stays on). I can't really say where the noise is coming from but it seems from in the middle or rear of the car.
>
> Prior my own repair of the check valve, my mechanic told me he had to manually 'secure' the rear diff actuator because it locked itself up occasionally, just like the center diff actuator did with me a few months later. He would not have secured the rear actuator if it didn't lock in the first place, i.e. it already locked once already and that's why he secured it for that reason.
> Now I think about it: because of the 5 months delay during the rebuilt-project, the shop compensated me with some credit and a spare gearbox which I believed because they damaged the gearbox housing outer shell and I heavily complaned about that...
>
> My new theory is that during his first test drives with the new engine, the rear diff locked up at high speed/acceleration (because of the bad check valve) and this might have damaged the rear diff and is the main reason why I now hear these noises best described as "something hitting the bottom of the car with a very large rubber hammer".
>
>
> PS the center bearing holding the prop shaft does have a fair amount of play. Could it hit the exhaust pipe by any chance?
>
> Any thoughts? Thanks in advance.
>
> Regards,
> Maurits
>
> 1986 quattro GV (rebuilt)
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