[s-cars] S6 driveshaft R&R question

Mon Apr 12 10:36:40 EDT 2004

Rokas,

$405 to replace the center bearing?  I'm in the wrong line of work.

The wobble is likely caused by the failed support, not the bearing.  In
either case, both can be replaced without removing the center u-joint.  If
the center u-joint has failed, then your best bet is to find a used shaft
that needs CV's, etc., but has a good center u-joint (more common than you
think).

I think you are confusing the bearing from the support.  The "support" is
the rubber bushing and metal bracket that supports the bearing, and you can
modify a MBz or  BMW part.  You can replace the bearing with any number of
configurations, but I decided to talk to the horse itself - FAG Bearings.

The OE FAG bearing is p/n 639850.R20.28, and is made in Germany, but is NLA.

I tore down my prop shaft last summer, the night before a track event.  I
replaced the center bearing with a FAG unit from New Hampshire Ball Bearings
( Tel: 603-924-4100).  The OE bearing uses a polyamide cage, which is NLA -
FAG presently only makes a bearing for this application with a steel cage.
The bearing cost me no more than $14-18.  FAG p/n 6006.2RSR.C3.  This
replacement bearing is made in Korea.

You'll need a 12-point torx socket to yank the prop shaft (T-55?)  I can't
remember the exact size, but I bought a cheap 8-piece set at Autozone, and
it had the correct size.

AFAIK, the u-joint is specific to Audi.  On the cars with carbon fibre
shafts, this non-serviceable joint was "staked" into the cradle - there is
no bolt-on "strap" or cir-clip to center and lock the u-joint into the
cradle.  A former lister mfg'd a jig to cut out the stake marks, remove the
joint, replace and restake, all the while ensuring that the joint was
properly aligned in the cradle, but he is no longer doing work on Audi's.

Also, Trevor Frank has a polyurethane center support that he purchased and
modified for his S4.  My discussions with Trevor led me to believe that this
center support was a one-off for rallye use and is NLA, and was made by the
same gentleman that mfg'd the jig to R&R the OE joint.

Your best bet is to find a used prop shaft - ask around on the list, or try
the usual suspects.

Ray

-----Original Message-----
From: Rokas Reipa [mailto:rokas at umd.edu]
Sent: Monday, April 12, 2004 1:00 AM
To: ray at s-cars.org; s-car-list at audifans.com
Cc: quattro at audifans.com
Subject: Re: [s-cars] S6 driveshaft R&R question

Thanks for the reply, Ray. I have been researching this endeavor for a while
and have so far come to the following conclusions:
1) the center carrier bearing can be replaced with a BMW part, various
numbers of which are floating around. The bolt pattern for the support is
different and needs to be drilled out accordingly.
2) The front and rear CV joints are to be repacked but nobody really
replaces them. If they run dry for a long time, they need to be replaced. I
have read somewhere that CV joints off of a Porsche 911 turbo shaft fit
fine.
3) Very vaguely, I recall reading somewhere that the u-joint is the same as
on some old mercedes model(gullwing?). The replacement procedure is still a
mystery to me. I believe it needs to be repaired/fixed. Is there NO WAY of
doing that?

One thing I am not doing is spending $1100 for a new driveshaft from Audi.
I'd also rather not spend the $405 quoted me by a few driveshaft rebuild
places. The center bearing can be picked up for around $35 and this R&R
sounds like a weekend's project, if that. Has anybody actually done this?
I'd really like to hear some BTDT's...I absolutely hate the fact that Audi
made this driveshaft 'non-serviceable'. Thanks so much for all your help.
Its wobbling up a storm now and I'd really like to get this done, if at all
possible.

Rokas
95.5 S6
----- Original Message -----
From: "Ray Tomlinson" <ray at s-cars.org>
To: "Rokas Reipa" <rokas at umd.edu>; <s-car-list at audifans.com>
Sent: Sunday, April 11, 2004 11:10 PM
Subject: RE: [s-cars] S6 driveshaft R&R question

Rokas,

The center u-joint is non-serviceable on the UrS4/6 - it is staked in.  You
can, however, remove the front portion of the shaft from the u-joint and
replace the bearing, but you will need a MAPP torch to separate the splined
gear from the u-joint.

List wisdom dictates that the center rubber carrier may be replaced with a
unit from a MBZ, but that you need to fabricate/modify the bracket.  I
purchased the MBZ unit, but found that the rubber surround was of a lesser
durometer than the OE Audi unit, and did not want the added play, despite
the fact that my center rubber surround had some miles on it.

If you do not have the Audi alignment tool to remove, be sure to index the
joints on both diffs, and mark carefully the position of the center carrier
bearing, otherwise, an out-of-alignment center prop shaft will vibrate and
without a doubt will shorten the service life of both end CV's, the center
u-joint, and possibly more.

Be sure to repack completely your driveshaft CV joints, and clean up any
mess.

Ray

-----Original Message-----
From: s-car-list-bounces at audifans.com
[mailto:s-car-list-bounces at audifans.com]On Behalf Of Rokas Reipa
Sent: Sunday, April 11, 2004 10:14 PM
To: s-car-list at audifans.com
Subject: [s-cars] S6 driveshaft R&R question

Hey everyone. Can anybody who has ever r&r'ed an S4/S6 center driveshaft
chime in on this question: I am almost ready to begin r&r'ing mine and I
need to know what to do about a loose u-joint. I gather the one in my car is
replaceable but with what? If not, what did you guys do to it? Thanks a
bunch,

Rokas
95.5 S6

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