[s-cars] Re: Noises after replaced 5-Speed

[Paul Gailus]

A possible source of confusion about the alignment of the
driveshaft is that unlike the traditional RWD designs of yore,
the Audi design has only one "single Cardan" U-joint (at the center)
and has CV joints at both ends. At least that's what I remember.

On one-piece driveshafts with U-joints at each end that are shifted
90 degrees from eachother, the angle at both joints needs to be the
same to get a first order cancellation of the velocity changes.
However, because Audi uses CV joints at both ends of the
driveshaft, they cause very little variation in angular velocity and
no such cancellation is required (or desired).
So the U-joint in the center of the Audi driveshaft needs to be
aligned in both planes so it doesn't mess up the nice constant
velocity of the CV joints.

All that being said, I seem to remember that operating a U-joint
at _exactly_ zero angle all of the time is not good, because then
the needle bearings won't move and the joint is prone to freezing up.
I guess with the soft OEM center bearing mount, that's probably
never a problem.

 Paul


----- Original Message -----
From: Fred Munro <munrof at sympatico.ca>
To: <bob.rossato at att.net>; Adrian Hart <mail at red-wing.co.uk>
Cc: <s-car-list at audifans.com>
Sent: Monday, August 11, 2003 4:23 PM
Subject: RE: [s-cars] Re: Noises after replaced 5-Speed


> I have the tool and it is as Bob describes. When clamped to the
driveshaft,
> it holds it straight in two planes.
>
> Fred Munro
> '94 S4
>
>
> -----Original Message-----
> From: s-car-list-admin at audifans.com
> [mailto:s-car-list-admin at audifans.com]On Behalf Of bob.rossato at att.net
> Sent: August 11, 2003 3:03 PM
> To: Adrian Hart
> Cc: s-car-list at audifans.com
> Subject: Re: [s-cars] Re: Noises after replaced 5-Speed
>
>
> Well I'll have to qualify my statement that the alignment tool keeps both
> halves of the prop shaft in the same plane (not two planes) is based on
the
> drawing in the Bentley/factory repair manual.  It shows the tool as being
a
> straight bar with four blocks attached that have a semi-circular cut at
the
> top to pick up on the diameter of the prop shaft.  If that is an accurate
> depiction of the real tool then you could easily make up your own with a
> section of square tubing and some appropriately sized U-bolt exhaust
clamps.
>
> I can't imagine why you would want to introduce an angle but anything is
> possible.
>
> The prop shaft is also supposed to be centered within the front to back
> movement allowed by the system.  There are also alignment marks on the CV
> joints at either end of the propshaft as well as the mating flanges.  If
the
> alignment marks aren't present you are supposed to mark both halves before
> removing the prop shaft.  How much that matters, I don't really know.  I
> would imagine that proper centering and shimming of the bearing mount is
the
> most important.
>
> When we did the clutch on Mike P.'s avant we didn't have the tool but we
> marked everything before hand and made sure that the shims were
maintained.
> I don't believe he's had a problem from vibration.
>
> Bob
>
> > I've just had my prop shaft in and out by an expert, and have the exact
> > symptoms described. I would have sworn something was rubbing, but it
> wasn't.
> > Fiddling with the centre bearing certainly helped but it's still not
quite
> > right. Now, could anybody confirm that the propshaft alignment tool
keeps
> it
> > (the propshaft) straight in two planes, as somebody wrote earlier, or
does
> > it introduce any angle at the centre joint (as I have just been reliably
> > informed). If the former I'm going to make one up, if the latter it's a
> > different proposition and it's off to the stealer (or more time on my
back
> > fiddling).
> >
> > Adrian Hart
> >
> > UK
> >
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