rphillips

Symptoms: Clutch pedal will not return to home position after shift made during heavy braking (Mosport corner 5 for example) and requires a light tap from behind with foot for pedal to return to home position.

Other info: Clutch pedal ALWAYS behaves normally during upshifts. The clutch system has been bled three times (including once by Porsche mechanic) without any signs of air. This (obviously) hasn't addressed the problem. There is no loss of brake fluid at either cylinder. When the clutch is released and the pedal stays close to the floor, power flows through the clutch. The clutch feels progressive during engagement beginning within a small handful of mm’s of travel (perhaps just the elongation of the return spring but you can feel slight vibration of the release bearing at this point).

Suspected stuff:
1. Flexing of the firewall during application of the brakes is distorting the master cylinder of the clutch and causing its piston to bind.
2. There is something else binding as clutch "system" passes through the firewall.
3. Binding of the clutch release fork or release bearing.
4. Leaking master/slave.

Anyone else ever had this problem and can offer a solution? I see some similar postings in the archives but usually the default recommendation is replacing the master and slave cylinders but I'm not convinced I am seeing the same thing.

While I have the winter to fix this, I’d rather not go to the trouble of pulling the clutch apart if it turns out that all I had to do was click my heels and chant "I want it to work" three times...

Cheers,
Rob

Luis de Prat

Time for a new hydraulic clutch master cylinder, I believe. Replace the slave too, because it will fail shortly afterwards. YMMV.

Kevin M

I am going through the exact same scenario right now. I have been advised to replace the clutch slave. It is going in this week. Let's see if it does the job.
Kevin

944V8inDFW

rob and kevin you both may want to check the return helper spring adustment before throwing money at a new MC. On the late cars the best way to get to it i have found is pulling the fuse panel back. the adjustment was set VERY light at the factory and once you get a little wear or in need of lube they tend to stick or return slow. oh yeah so you wont relive christmas tree lights all over again unhook your battery before pulling backe the fuse / relay panel. It is reachable from under the dash but it is a major PITA to do from there. i knew of a 944 that was once sold over this problem as the owner replaced the slave and MC and was convinced it was the pressureplate. new owner had a 30 minute no cost fix that turned a $3500 project needing a new clutch into a $8500 cream puff.

rphillips

944V8inDFW,
Thanks for the heads-up. I'll be sure to check this out. A preliminary glance didn't suggest any problem with the pedal itself but I'll re-check. As the cylinders are original, I'm inclined to replace them anyways and this has been suggested to me by a mechanic too.

However, I still don't understand what is going on if it is in fact the cylinders. Does anyone have an explanation for this behaviour given that the system has no air in it nor does it leak? Can a non-leaking master/slave cause this? How?

Luis de Prat

Contamination. The clutch cylinders and the brake system share the same reservoir and hydraulic circuit. Over time, debris in the brake fluid scores the cylinders causing them to bind.

They can be rebuilt as per the Haynes manual, but most people just bite the bullet and replace them. Good luck with it.