[urq] Diff Noises

Keith Lloyd spotatashleys at hotmail.com
Tue Jun 1 10:55:36 PDT 2010


Maurits
This could be the centre bearing or it could be the exhaust being fitted too 
close to the body. I had a scorpion exhaust on my car when I bought it and 
it was fitted rather too close such that when I drove it in the wet the cold 
water hitting the underside of the hot exhaust caused it to warp and hit the 
bottom of the car.  It would return to normal once it had cooled again on 
the top.I reckon the centre bearing might be your problem. I replaced mine 
with the much documented "BMW" part and made my own alignment tool using a 
long spirit level which I drilled and tapped on the top surface and fitted 
long bolts (setting two within about a foot of each other and the other at 
the far end) which I locked in position with lock nuts. I set them all to 
the same height using a caliper gauge.I used this to make sure it was all in 
alignment from each side and the bottom (you can't do the top for obvious 
reasons). It did the trick.
A knocking noise does not sound like a diff issue to me other than perhaps 
diff mounts worn but others may have more experience and have a different 
view.

Re: diff usage - I only ever lock the centre diff when driving in the wet 
with standing water. I never lock the rear diff other than occasionally to 
make sure it still works.
I hope this helps
All the best

Keith
'87 WR

----- Original Message ----- 
From: "Maurits Jonkergouw" <urquattro at moregraphics.nl>
To: "Audifans" <urq at audifans.com>
Sent: Tuesday, June 01, 2010 3:56 PM
Subject: [urq] Diff Noises


> 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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