Persistent vibration, 87 5KQT

[john at westcoastgarage.net]

The problem appears to have been solved!  Bad CVs at both ends of the driveshaft.  I've not seen that before, but this a business (and hobby) where you learn something every day!  Thanks to those of you who replied with good ideas.  Too many to reply to each of you individually.  I suppose this is gonna show up more as time passes and the cars approach 300 or 400K miles.  BTW, I have a good, but wholesale only, place to get Audi driveshafts reconditioned.  Not particularly cheap, but significantly lower than dealer prices.

John



From: John Larson<john at westcoastgarage.net>
Sender:quattro-bounces at audifans.com
Date: Sat, 30 Oct 2010 18:41:13
To:<quattro at audifans.com>
Subject: Persistent vibration, 87 5KQT

I'm about at the end of my rope.  I have a customer's well worn, high
mileage, 5KTQ here that has developed a low pitched humming vibration at
freeway speeds, although the noise persists as low as 30MPH, maybe even
lower.  I've checked the axle shafts for bends, replaced a bent RR
wheel, and aligned the driveshaft with a cool home made fixture.  I
spoke with a chassis and alignment guy this afternoon (he's gonna drive
it Monday) and he asked about the wheel bearings.  I've done probably
500 double row wheel bearings in my career, and I've never had one sound
like this.  They mostly howl or make a low frequency rumble, and usually
(but not always) change tone or volume when side loaded by turning the
car one direction or the other.  This noise comes on as you build speed
on the freeway, and is there whether you're going straight or turning.
The volume, tone, and frequency appear to remain pretty constant.  As
always, any and all constructive input would be sincerely appreciated!

TIA!  John