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

[L DC]

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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