JustinL

The symptoms go as follows:

1. Normal clutch operation for 1.5 years of hard track driving.
2. Poor disengagement over a race weekend that ends in total inability to release the clutch.
3. During that weekend there was a rattle at idle that would go away with pushing the clutch down.
4. Replace throw out bearing and all hydraulics.
5. Clutch works again, but again gets progressively worse through the weekend and again ends the weekend totally locked. Rattle persists.
6. reroute hydraulics, bleed the system, verify fork movement is good.
7. Clutch still locked.
8. Pull clutch and everything comes apart nicely, fork looks good, release bearing spins, but is banged up on the inside. Disc looks perfect. Splines slide nicely on the driveshaft to clutch disc.
9. Photograph everything and post on rennlist.
10. I'm wondering if what I'm seeing is a broken pressure plate drive strap, and would this cause the symptoms I've been having? Are the finger springs also worn out and letting the throw out bearing rattle around?

Tiger03447

Pressure plate looks good.check the springs in the disc. they can rattle around if they are broken.

JustinL

Clutch disc looks perfect. Some wear, but otherwise no problems.

Van

Looks like there's some galling on the inside of the throwout bearing? Perhaps your throwout bearing guide tube is causing the pressure plate to hang up.

JustinL

Agreed. That bearing is one race weekend old, as is the guide tube. My current theory is that the drive strap is broken and causing the pressure plate to disengage asymmetrically which then pushes the bearing on to the guide tube crooked while not releasing a couple pucks of the clutch disc. Is this a reasonable hypothesis?

StoogeMoe

I would check your pilot bearing.

JustinL

Feels good to my finger, and looks good visually. Can you elaborate?

StoogeMoe

You didn't mention it, so I wanted to make sure you checked it! Either the shaft is moving or the releasing bearing is moving to cause wear on the inside of the release bearing. That doesn't look good.

What's the drive strap? But yeah, if the release isn't symmetrical, the fork could push the bearing to one side. Are the fork and fork bearings ok?

JustinL

The drive straps are the 3 leaf springs around the outer edge of the pressure plate. They're also called tangential springs. I've been reading about other cars where these fail more frequently (lotus Elise). It's caused by rough and high rpm downshifts as well as clutch chatter. I'll use my spare pressure plate with a new release bearing and cross my fingers that it fixes it.

FRporscheman

I had a failure of one of those "drive straps" on my 951 when I bought it. The broken spring would swing out and destroy the speed sensor.

But I was able to disengage the clutch and drive it fine(after cutting out the broken spring through the starter hole). Clutch felt like it dragged a bit but it wasn't too bad.

JustinL

I should update this thread seeing as how the problem is fixed. Swapping in the spare pressure plate solved the problem. Made it through the race weekend with the clutch pedal coming up fast again. Also less clutch chatter on engagement. Lesson learned: inspect the pressure plate carefully before installing.