Re: Evil Quattro Driveline Noises...HELP!

[Audial <Audial@aol.com>]

Thanks for the checklist...

Now it's time to inspect everything.  The exhaust hangers are in good shape
and the exhaust is aligned properly and, at rest, clears the driveline along
its length by what should be more than enough. The differential was
_definitely_ locked when these problems occured.  Rear diff locks immediately
and very noticeably while driving.  I am somewhat suspect of the tranny
mounts...the little thin films of rubber that normally web between the little
rubber protrusions on the mount are completely missing and, at least on the
driver's side, the trans. mount looks deteriorated with a crumbling of the
rubber.  The motor mounts _look_ OK, but I haven't tried putting them under
stress yet. 

I am betting that perhaps I have a bad engine and transmission mount that is
causing the driveshaft to have to assume an unnatural angle and then bang
against the floorpan in some way.  

If this turns out to be correct, I think it will be a good diagnosis procedure
for anyone buying a similar car...lock the center diff on dry ground and try
some moderate turns...if you feel vibration, it's normal, but banging/clanging
noises signal that a mount is broken somewhere. The U-joint in the driveshaft
must be there because Audi expects some misalignment of the pieces of the
driveshaft due to compliance in the engine/tranny mounts when the center diff.
is locked.  And it should, when those mounts are OK, cause a vibration twice
per revolution.  But I am getting a loud bang at each of those events instead
of a dampened vibration.

Thanks again for the advice,
I'll be in touch

Alex