Re: driveshaft question (kinda longish)

["Fred Munro" <munrof@isys.ca>]

-----Original Message-----
From: Thomas Turse <tturse@ps-b.com>
To: quattro list <quattro@coimbra.ans.net>
Date: Sunday, April 19, 1998 7:15 PM
Subject: driveshaft question (kinda longish)


>Hi all.  Well, I was going to get new tires this weekend, but as fate would
>have it something else is wrong w/ my car.  Shocker huh.  O.K., here's the
>problem- I had the center support bearing replaced about three months ago
>(the BMW part conversion).  This included checking the driveshaft out,
>servicing and re-packing the drive universal and replacing the very worn
>center support bearing.  Prior to this service the car had a slight
steering
>wheel and dash shake at a very small speed rage- about 70-75 mph and
usually
>under throttle.  I assumed it was an out of balance tire or ball joint
>etc...  I had the front tires balanced and the whole front end checked out
>and all was good and in spec's.  I then concluded that the shake was
>probably due to the play in the worn center support- which a knowledgeable
>mechanic said was very plausible.   After some time the bearing started to
>deteriorate very quickly, so I had it replaced.  Needles to say the slight
>shimmy didn't go away nor did it get any worse for that matter.  I was
>somewhat perplexed at this but because it was very minor, it didn't warrant
>immediate attention.
>    I did notice however, that the shake got much worse- wheel and dash
>shaking became more severe and the speed range became wider- about 65-85
>mph, when the temperature warmed up above sixty degrees.  When it got cold
>again, the symptoms returned to their minimal characteristics.  This lead
me
>to consider rubber mounts- either sub-frame, tranny or A-frame mounts that
>would be affected by temperature.  Well, in the past few weeks the shaking
>has gotten very severe at certain speeds.  It is fine up to 65 mph and
>begins to shake from there to about 85 mph.  When I say severe I mean the
>whole car shakes- from the dash to the hood to the seats etc...  It's bad.
>    So I took the car to my mechanic who said it was probably bad/worn
>sub-frame/transmission mounts.  He replaced those @ $140 but it had no
>effect on the problem.  He put the car on a lift and  had someone drive and
>accelerate through the gears and he notified the driveshaft started to
>wobble at certain rpm's.  He said this is what is causing the shaking and
>the driveshaft needs to be taken out and sent off to be balanced.  At this
>point I'm about ready to lose it.  Anyway, I was just wondering if this
>balance procedure is the solution or if it could be the center support
>conversion that is causing the problem- bad part, not done correctly,
etc...
>It still is affected by temperature which leads me to think that it could
be
>something else.  The guy who did the conversion said he matched the front
>and back when doing the bearing and he has done many of these and said he's
>never seen one come out of balance after the installation of the bearing.
I
>would very much appreciate any suggestions or input about similar
>experiences with driveshaft problems.  Sorry about the length.
>
>Sincerely,
>Thomas C.  Turse
>85 4ksq
>Evergreen, CO


Hi Thomas;

    I did have a problem with an out-of-balance driveshaft on a '79 Chev
van. A strong vibration was present at 60-80 kph, particularily under
acceleration. After trying (and only partially succeeding) in re-balancing
it myself using gear clamps, I surrendered to the inevitable and took it to
a good automotive machine shop. They cut off the u-joint flanges, trued the
shaft, welded it back together, and balanced it. Problem solved.
    Driveshafts are balanced units and they should be index marked before
removal from the vehicle and before disassembly so they can be re-assembled
and re-installed in the original postion.

HTH

Fred Munro
'91 200q  250k km