Rally Guy

I recently had my slave cylinder replaced and the tech noted that my clutch effort was way too high. I drive the car regularly and hadn't really noticed. So I tried to push the clutch pedal with my right foot and holy moly did that take effort!

I know my clutch is wearing out - and I've always understood that in our cars a wearing clutch creatses this heavy pedal effort. But, while I'm pretty technically inclined (and if not injured would have done the SC my self) I don't understand the mechanics behind heavy pedal pressure just because a clutch disc is getting thin.

Why is this?

RK

tbennett017

IT has to do with the wearing of the clutch disk changing the tolerances. The clutch fork ands up working on a different point of leverage, thus increasing the required pressure. IMHO, it is engineered into the process so we have a live indicator of the wear...

My knowledge isn't perfect on this, but if you look at a slice/cutaway drawing of the clutch mechanism the intent becomes clear eventually.

Grazie

I've wondered the same thing - hope to get some insights here. I do know that this phenomenon is not limited to 964s or pcars....the same was true on my '95 Toyota 4Runner (which has about nothing in common with the 964).
Cheers,
ATC

Rally Guy

I know tragically little about geometry - but I wonder how the change in tolerances of a mere mm or two at the clutch disk thickness level can so dramitcally increase pedal effort.

I'm not doubting your logic - in fact its the first time I've heard any reasoning behind this and I would give it a mythbusters' "plausible". ; )

Can anyone dive deeper?

RK

The Stig

Some interesting information here.

http://auto.howstuffworks.com/clutch1.htm

Makmov

The diaphram gets work hardened.