New clutch slipping in 5000 turbo quattro

[Ben Swann]

Based on what the owner told me about the car's service, I think the clutch master
cylinder had already had the rod extended to its full length to compensate for failing
slave and/or air in the system.  I really don't know, but think he had been nursing the
car along until he could find someone to do the clutch - he said his "mechanic friend"
could not get to the slave to replace it.  

I have the feeling that since I bled the circuit prior to re-installing the engine, the
full force of the fluid was on the slave when I put the engine in.  When clamping the
engine and bell-housing back together, I suspect the rod only retracted partially, but
since the rod is adjusted to its full length there is enough pressure on the plate that
the clutch is partially disengaged and slipping under full load.

So although I didn't do any work on the Master Cylinder, I think it had been adjusted to
full length. I'm hoping that all that needs to be done is to re-adjust the rod on the
master to a shorter length.  If it is putting pressure on the system, this should reduce
it. It doesn't fully make sense to me, as I'd expect the pressure to equalize.  Maybe it
is the check valve is not allowing the pressure to release.  I really hope that is all
it is and I just don't see how anything was messed up with the clutch job.  I am slow
and methodical doing these, so it is not a backwards disk or something installed wrong.

All I can do at this point is to pass information and things to try along to the owner.
I didn't think about re-adjusting the master at the time as he needed to get back and
we'll I wasn't thinking straight - just spent two weeks doing the job and this happens.

As Ado suggests it would not be advisable to have the car driven back to me and I'm not
going to do another clutch job anyway - that was a favor and I now regret it.

Ben

-----Original Message-----
From: Ado Sigal [mailto:a.sigal at bluewin.ch] 
Sent: Monday, October 15, 2007 3:12 PM
To: Ben Swann
Cc: urq at pacbell.net; quattro at audifans.com; auditony at gmail.com
Subject: Re: New clutch slipping in 5000 turbo quattro

Ben, Steve,

- I am sure Ben knows that any car can be easily driven without the use 
of clutch just on revs. Stops and starts are particular. Warmed up car 
must be started in first gear (and clear road in front), and then 
accelerated and shifted up and down regarding engine revs, rather than 
syncros'. Braking and stop should be done in neutral, but no big deal 
since the engine would stall at stop, and then it needs to be started in 
gear anyway. In traffic its a pain but doable. On clear road and for 
testing, quite easy.

- The E/port problem can be ruled out by three facts:

1) The piston movement is on the MC is not adjustable.
2) No work was done on MC.
3) Been able to insert SC (with the rod fully extended) into its 
position in the bellhousing, and bench bleed it doing same rod and SC 
piston movement. If anything was blocking the the line on SC, MC or 
line, that would not been possible.

- The rod didn't change in length, but something inside changed the 
travelling distance. One can be reversed fork, which I don't think is 
possible, the other the thickness of the f/wheel (confirmed this isn't 
the case), pressure plate height (that was confirmed to be slightly 
bigger than on the old PP, which when assembled would give more distance 
from the SC, not less, as the case is), and the disc thickness (which 
was established to be thicker), and the third is the rod been outside 
its location, which I don't think is the case, because the rod would 
slip in or out of the fork location within first few operations. 
- Another possibility that can keep the p/plate at constant pressure is 
the thrust bearing resting on the guide sleeve, but that can only happen 
on cars with plastic sleeve that has deformed from the heat, like on Urq 
(on 5000 I believe this sleeve guide is metal), and in this case the 
problem would manifest itself differently.

- Further possibility that could manifest itself with same result is if 
the SC was pushed to far in and pin locked after its groove. (can't 
remember if is physically possible to push the pin through in any other 
location but in the groove)

Anyway, the only way to establish where the problem lies is to take out 
SC and test the car without it in place. Unfortunately for Ben, the car 
is far away, and that must be done at the owners location. That however 
is more viable than risking to burn the clutch on the trip back to Ben. 
Audi Gods never seize to surprise, don't they.

HTH,

Ado

Ben Swann wrote:

>Steve, Ado,
>
>It must be something to do with too much pressure to the slave from the master circuit.
>Unfortunately the car is not here and he may have problem finding competent mechanic up
>there, but at least there are some things to try.  Most probably the master may be
>adjusted out too far to compensate for need of proper bleeding - who knows what was
done
>before.
>
>Basically all parts replaced were either new, or nearly new - flywheel was simply
>cleaned up - really not much taken off, just enough to make a shiny surface.  Pressure
>plate was like new, but that would make the problem more likely to happen since the
>tines were sitting ever so slightly higher than the ones on the used disk - but part
>numbers matched.  Disk had like 5000 miles on it and basically like new spec and
thicker
>than the glazed greaser I took out.  I tried to get a new disk, but dealer informed me
>they are NLA.  The slave and release bearing are new - I did bench bleed the slave, so
>it was chock full upon installation.  Then I repetitively forced any air out of the
line
>up to the MC reservoir - so I essentially bled the system prior to putting the engine
>back in.  I did nothing to the master side, so that was however it was.  
>
>Before the work commenced, the clutch would slip in 5th gear under full load.  I
>attributed slippage then to the oil components I found when I took apart and so
replaced
>the real main seal in the engine.  I'm now wondering if part of the slippage before was
>related to what is going on - I have removed far worse clutches that weren't slipping.
>
>When I put the engine back in, things mated fairly easily compared to many of the swaps
>I did.  I needed to compress the assembly a little, but basically seemed no different
>than others I've done. Sometimes after this sort of work I have had to re-bleed the
>master circuit to get air out because the clutch won't disengage - this is the opposite
>of that problem. 
>
>Since I had to redo my UrQ clutch several months back when I installed 5000 turbo quat
>trans along with the new engine,  I always check engine and trans are mating and wheels
>turning, and I did not detect slippage in this case.  That problem I had with the UrQ
>was the slave cyl. Stuck open - basically the rod had jammed in the extended position
>and would not retract.  In that case, the clutch was completely disengaged.  Turned out
>some water got in as the trans was outside for awhile - the slave was almost new, but I
>found a rust ridge on the slave cyl. Rod - Ouch!
>
>Thanks for the tips - anything that can be done to keep from pulling the engine out.  I
>don't think I'll ever do another clutch job for anyone but myself, because if something
>goes wrong, you need to pull it all apart again just to see what is happening.  This is
>so Sick!
>
>Ben
>
>p.s. what is with all the substitution of ?'s (question marks) in posts to this list
for
>special characters commas, tildes, apostrophes, punctuation, etc.???
>
>[Date: Mon, 15 Oct 2007 00:28:33 -0700
>From: "urq" <urq at pacbell.net>
>Subject: RE: New clutch slipping in 5000 turbo quattro
>To: <quattro at audifans.com>
>Message-ID: <000401c80efd$00891e00$019b5a00$@net>
>Content-Type: text/plain;	charset="iso-8859-1"
>
>Ado's recommendation is a good one in that it allows you to know if the problem is
>inside or outside the bellhousing ... although it might be a bit difficult to test as
>you can't use the clutch if the slave cylinder is not staked into the tranny ... but
you
>could do the first part, to loosen the bleeder to relieve any excess fluid between the
>master and slave.
>
>Equalization port ... it's the mechanism that allows more (or less) fluid into the
>hydraulic circuit as the parts wear.  The clutch and brake M/Cs each have an
>equalization port, it's a little hole in the master cylinder's piston that runs from
the supply side of the cylinder to the part of the circuit that is conveying the force.
If the equalization port were always open the brakes or clutch wouldn't work as any
attempt to compress the fluid would get bled out the hole ... but the supply side port
is strategically placed so that once the piston starts moving into the cylinder bore the
port gets blocked.  
>
>What can happen is that the adjustable rod that connects the pedal to the master
>cylinder can be set too long ... which means that the clutch pedal stops before the
>piston has come far enough out of the bore to open the equalization port.  If this is
>the case and you happen to have excess fluid in the line the slave will never fully
>disengage the clutch.  If you fix that problem by opening the bleed port on the slave,
>eventually the clutch hydraulic system will not have enough fluid to fully disengage
the clutch and it will be difficult to get the car into 1st or reverse at a stop and you
might see grinding during shifts.  
>
>HTH!
>Steve B
>San Jos?, CA (USA)