Delrin drive shaft support

[Kaklikian, Gary]

	My point was that with all the rubber mounts in the drivetrain and
subframes, there are plenty of flexible points, including the driveshaft
center support, where vibration is absorbed and excessive play can be
introduced.  I would think a failure at one mount point would increase
stress at the other mount points.    
	 
	There's no denying that the rigid driveshaft support will reduce
driveshaft movement and misalignment and transmit the engine rotational
torque more efficiently to the (rubber-mounted) final drive.   And the
delrin has to be more durable than the rubber it replaces .  

	The center u-joint is not commonly replaced; the center bearing
support is.  But, it sure would be nice to find a replacement u-joint.  When
this was discussed on the list last year,   I don't remember seeing a p/n
for a u-joint, although several shops were reputed to include a new u-joint
in their driveshaft rebuild.

	  Thanks for the tips on driveshaft rebuilding and alignment.  

        btdt with the rear wheel bearings too. Rumbling sound when turning
right; culprit - left rear wheel bearing. 

Gary Kaklikian

> ----------
> From: 	S. Jaworski[SMTP:syljay at optonline.net]
> Sent: 	Friday, February 16, 2001 3:50 PM
> To: 	quattro at audifans.com
> Subject: 	Fw: Delrin drive shaft support
> 
> 
> > ----- Original Message -----
> > From: Kaklikian, Gary <Gary.Kaklikian at compaq.com>
> > To: <quattro at audifans.com>; 'S. Jaworski' <syljay at optonline.net>
> > Cc: <JShadzi at aol.com>
> > Sent: Friday, February 16, 2001 2:19 PM
> > Subject: RE: Delrin drive shaft support
> >
> >
> > > Even with the delrin driveshaft center  mount, won't enough flex be
> > retained
> > > in the drivetrain due to the rubber motor,  transmission and rear diff
> > > mounts?  I had a problem with failing motor & transmission mounts on
> my
> > 4000
> > > turbo ( the motor mounts  are the oil-filled variety), which was
> resolved
> > by
> > > building a very stiff front motor mount attached to a large steel
> plate
> > > welded across the bumper support crossmember.  Less flex under power,
> no
> > > more broken motor mounts, and no noticeable increase in body
> vibration.
>  ****I think you misunderstand the problem. The Delrin center bearing
> mount
>  does not restrain flex in the engine, trans, etc. The part is just too
> small
>  to restrain anything. The problem as I see it is that the engine and all
>  associated components will stress the Delrin support . . .. and not the
>  other way around as you describe it. The dog wags the tail, as opposed to
>  the tail wagging the dog.
> 
> > > I've also had a rear diff mount fail. And, although a new driveshaft
> > center
> > > bearing assembly was fitted about 15k miles ago, the drivetrain seems
> to
> > > have developed excessive play which is noticeable in on/off throttle
> > > transitions.  (Yes, I drive the car on the track frequently, with the
> > center
> > > diff locked, which  puts more stress on the drivetrain components than
> > your
> > > typical daily driver.)
> > >
> > > So,  my concern is "Will the delrin driveshaft support minimize stress
> on
> > > and movement of the motor/tranny/rear diff rubber mounts  and reduce
> > > driveshaft wind-up and overall driveline flex without putting undue
> stress
> > > on the driveshaft CV's, u-joint, etc?"  If I read your post correctly,
> > Syl,
> > > your answer is "yes",  but at the expense of short-term failure of the
> > > delrin.
>  *****As I stated above, the delrin support minimizes nothing. Its just
> there
>  to support the center of the drive shaft. But, since this delrin support
> is
>  immobile(has no flex) as opposed to the original part which is rubber and
>  flexes, any movement of the shaft in up/down or side/side direction will
>  result in stress at the Delrin support as it has NO FLEX in it.
> 
>  To demonstrate what is happening: secure the tip of a long pencil in a
> set
> of pliers. Then move the eraser end with the other hand. Easy to move it,
> no? The pliers are the Delrin support, the other hand is the engine. No
> matter how hard you grip the tip with the pliers and try to keep it
> immobile, your other hand has no trouble moving that pencil up and down.
> In
> the car, that Delrin support is rigidly fixed to the chassis . . it cannot
> move. The bearing in this support cannot move either. Yet the drive shaft
> will move up and down or sideways a bit due to engine torque. Something
> has
> to give, and it wont be the driveshaft . . it will be the Delrin support
> because it cannot flex to accomodate the drive shaft movements.
> 
> > > I'm curious Syl, when you say you've rebuilt several driveshafts,
> which
> > > components have you replaced? Anyone ever have to replace the center
> > > u-joint?
>  ****On the 90 100q, I had a vibration which I thought was due to a worn
> out
>  bearing in the driveshaft. I took it apart and replaced the center
> bearing
>  with a Blau replacement. There was nothing wrong with the original
> bearing
> .
>  . .maybe just a little play in it.
>  I took apart the U-joint. The U-joint insides looked fine . . no wear. So
> I
>  cleaned the parts, packed them in grease, and reassembled the U-joint.
>  I took apart the CV joints at each end of the driveshaft and cleaned
> them.
>  Repacked them in new cv joint lubricant and installed new boots. I also
>  replaced the end gaskets as they are inexpensive. I cleaned out and
> checked
>  the grease nipple for proper operation.
>  After I re-assembled the drive shaft, I adjusted the grease nipple so it
>  could be accessed with a grease gun. The original mounting is square to
> the
>  center line of the driveshaft and cannot be reached with a grease gun. I
>  added grease until I saw grease coming out of all the U-joint boots . .
> all
>  four of them. Wipe off the excess grease.
>  Install the drive shaft.
> 
>  To align the drive shaft, use a string. Tie one end of the string to
> front
>  cv joint, the other end to rear cv joint. Make it snug. The string will
> lie
>  along the drive shaft.
> 
>  Make some "guages". Get a wood square molding, 1"X1". Cut off 3 pieces
> about
> an 1.5" long. Place the three pieces next to each other on a flat surface
> and make sure the tops are all even with each other. If not, grab all
> three
> pieces together as one unit, flip them and sand other side till all are
> even. Now you have 3 identical measurement blocks.
> 
> Slip one block under string at the front cv joint. Slip second block under
> string at rear cv joint. Use the third block as feeler guage under the
> string at the center support.
> Adjust center support up or down till that third block just kisses the
> string.
> Do the same for side to side alignment.
> 
> This is a lot simpler and cheaper than trying to make/use the alignment
> tool
> that the Bentley shows. And if you use a smooth string, you can set the
> driveshaft straight to + - .020"   . . . . good enough for me.
> 
> 
> > > Also, regarding vibration transmitted to the body. I think as long as
> you
> > > retain the stock rubber motor,tranny and diff mounts and the rubber
> > > front/rear subframe bushings, vibration levels should be accepable. I
> know
> > > delrin subframe bushings are available, and race cars use aluminum
> ones,
> > but
> > > I don't think either would be desirable on a street car.
> > >
> > > I'm definitely going to try Javad's delrin driveshaft support.
> > >
> > > Gary Kaklikian
> > > 86 4ktq
> > > 92 S4
>   **** I've been talking to Jarad about this. I'll forward to you our
> emails.
>  I think that our conclusion is that the engine will torque rotate about
> its
> crankshaft/transmission output shaft. Therefore there should be none or
> very
> little lateral(up/down or side/side) motion in the forward end of the
> driveshaft. That being the case, there is no stress imparted to the rigid
> Delrin support at the center of the driveshaft.
> 
> I'm forwarding to you my chats with Jarad regarding this topic.
> 
> Oh, by the way, the vibration problem on the 90 100Q turned out to be a
> bad
> rear wheel bearing.
> And, the problem on the 88 5kq turned out to be seperated treads on one
> tire.
> SH_T!    SH_T!    SH_T!!!!!!!
> 
> Ahh, what the heck, I did all the work myself. Just had to pay for the
> parts. Parts were pretty inexpensive . . I get them at a good discount
> from
> a small local shop that specializes in Audi and VW parts.
> 
> It was a "learning" experience. Have to do something to get away from the
> wife. Neither car talks back. I hope the wife dont read this, otherwise
> I'm
> in a world of hurt.
> 
> Syl
>