Slipping clutch when hot-Fixed!!! :-)

[urq]

... good to hear that was the case ... as I noted in my original response
your problem symptoms sounded like you needed to bleed the clutch.  I must
say that is the first time I've heard of the equalization port getting
plugged!  Sounds as though the clutch fluid was as old as the car too!  On
many cars it started from day one ... I don't think the dealer ever bled the
clutch unless the customer specifically asked for it.  

Hopefully you didn't cause too much extra clutch wear from the slipping ...
I've been amazed more than once to hear how long a clutch goes on the NA
cars.  I bought an '85 4kCSQ for cheap because it needed a clutch at 207K
... if the pilot bearing hadn't gummed up and worn the fingers off the
pressure plate it probably would have gone another 100K.  The QSW and 4kQs
are the closest thing I've seen to indestructible ... from any marque ...
well, except perhaps older MBz ...

Steve Buchholz

-----Original Message-----
From: quattro-bounces at audifans.com [mailto:quattro-bounces at audifans.com] On
Behalf Of L DC
Sent: Friday, April 22, 2011 7:37 PM
To: quattro at audifans.com; Tom Leppke-Hennig
Subject: Re: Slipping clutch when hot-Fixed!!! :-)

The slipping clutch problem that my 87 QSW had been having over the past
year which only got worse as time went by has been solved, and I'm glad to
report that it was not the clutch itself going south.

Clutch Master Cylinder (CMC) was the culprit!!!

Last Saturday, I spent nearly all day trying to get a possible fix on the
issue and I finally did with the install of a brand spanking-new Ate CMC and
fresh Ate Racing Blue brake fluid.

I first tried to flush, bleed the troubled CMC but could not get the fluid
to free flow even when vacuuming or pushing fluid through it using a brake
bleeder gun I rented. The CMC acted as if it were plugged.

I decided to remove the CMC from the car and diagnose why it did not allow
for fluid to be fed through it. I took the whole part apart.

There are two ports/orifices located just below the rubber grommet holding
the plastic tube through which fluid is fed from the brake master cylinder.
One of these ports, the smaller one, was completely plugged. I can see how
it can get easily plug when I learned that it has the diameter of a small
sewing needle. I actually took a need to unplugged what appeared to be
rust-like hard matter. Would this be the RETURN/Stabilization port a couple
of listers mentioned? I would imagine the fluid expanded with hot
temperatures off the engine and radiator fan causing the fluid to expand and
with the return port/ stabilization been plugged it had only one way to go
and that it the slave cylinder. I also imagine it was using the very same
fluid stagnated all this time in the line since it was not free flowing to
back to the reservoir? 

Anyway, I put the CMC together and back in the car and although I got it to
flow more fluid through than before taking it apart, I could not get it to
bleed completely, causing the clutch pedal to sink to the floor without
returning on its own to its up-resting position.

Trying to bleed the sucker for more than 30 minutes to no avail, I got
fed-up with it and removed it from the car, yet again, and replaced it with
a new one as aforementioned.

By contrast, I was able to bleed the new CMC in about 10 minutes.

Since this is my daily driver, I took it to work this past week and saw some
heavy, stop-and-go traffic with ambient temperature as high as 90*F and
high-speed fan kicking on and off quite frequently and the clutch did not
slip at all, even when putting it in 5th gear at 1K RPMS and sinking the gas
pedal to the floor.

Cody, could your car be or was suffering from the same issue?

Anyway, I'm glad it was not the clutch itself and that it still has some
life left to it.

I going to see if I could build some sort of heat-shield for the CMC and
brake master cylinder while I'm at it to prolong their usage.

Tom, it so appears that the problem is what you described initially below. 

Thanks for every ones'' input again.

-Louis

--- On Sun, 3/27/11, Tom Leppke-Hennig <printhead at usinternet.com> wrote:

> From: Tom Leppke-Hennig <printhead at usinternet.com>
> Subject: Re: Slipping clutch when hot
> To: quattro at audifans.com
> Date: Sunday, March 27, 2011, 1:06 AM

> Re: Clutch hydraulic fluid expanding due to heat, causing slippage: That
> is possible IF the return port isn't getting uncovered in the clutch
> master cylinder. This is normally due to an incorrectly adjusted push
> rod.
 
> Just as others have said, though,I don't think that is what is wrong,
> here. The way yours is acting is how they act when the friction material
> gets thin with mileage. The diaphragm spring loses preload (travels
> further), and then is aggravated when hot. The steel in the spring loses
> its ability to provide clamping pressure due to heat.

> You need a new clutch.
> 
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