Clutch and Flywheel Wear Pattern

[QB93Z]

Last weekend we removed the clutch and flywheel from a low milage, 1991 ZR1 to correct a noise problem from the throwout bearing and/or the pilot bearing.

Upon removal of the clutch, I noticed an interesting wear pattern on the flywheel, the clutch and the clutch disc:

Here is the clutch pressure plate face:


Here is the flywheel surface:


Here is the clutch disc:


Notice that the inner third of the friction surrface shows a different pattern that the rest of the surface. There seems to be significant material transfer to the pressure plate and flywheel:

Clutch:


Flywheel:


The dual-mass flywheel internal dampers have failed and the relative motion of the parts is about 25 degrees with a "hard" stop at each end of travel.

The only other unusual thing we found was that the pilot bearing inside diameter is off center:


We replaced the flywheel, clutch, disc, throwout bearing, and the pilot bearing.

Any thoughts of the cause of the wear patterns?

Jim

[VetteMed]

That off-center pilot bushing is a little worrisome, basically causes the input shaft to be subjected to some side-loading all the time. May not be significant, but a small angle on the input shaft might magnify to a larger angle at the periphery of the clutch disc which is riding on the input shaft?

Just thinking out loud...

[scottfab]

Was there by chance some fluid leakage by the slave cylinder?
Most eventually do.
Sure looks like fluid burns on the surfaces on about 120 deg of the circumference. But then maybe the effect of that bizarre pilot bearing let the ZF6 leak onto the clutch? dunno

[QB93Z]

There was no evidence of clutch fluid leakage. I wonder if the throwout bearing spun out some grease as it failed. Maybe that is what caused the build up on the inner part of the surface.

Jim

[gbrtng]

You're seeing a combination of a driver who slips the clutch a lot, and maybe some related misalignment due to the pilot bushing being out of alignment. What shape is the ZF-6 input shaft bearing in? It was taking a pretty good beating from the misalignment. Not to mention the rear main bearing of the LT5. I'll bet the out-of-balance made the car shake like a dog p00ping pineapples ...

And looking at the wear of the clutch facing, the clutch disc does not have many miles on it.

[QB93Z]

The car is low milage. The owner reported that he could balance a nickle on the plenum at idle, so I guess the vibration was not as bad as the picture would predict.

Jim

[Paul Workman]

Originally Posted by QB93Z

The car is low milage. The owner reported that he could balance a nickle on the plenum at idle, so I guess the vibration was not as bad as the picture would predict.

Jim

Let Pete or Marc put an FBI timing on the cams, and that nickle will dance a Texas Two Step!

P.

[gbrtng]

Originally Posted by QB93Z

The car is low milage. The owner reported that he could balance a nickle on the plenum at idle, so I guess the vibration was not as bad as the picture would predict.

Jim

Amazing - It looks like the bushing is a replacement and was damaged by the input shaft clanking into it when the ZF was being reinstalled. Equally hard to believe that the bushing didn't knock out the crankshaft plug.
How did you remove the bushing without damaging it?

[scottfab]

Originally Posted by gbrtng

Amazing - It looks like the bushing is a replacement and was damaged by the input shaft clanking into it when the ZF was being reinstalled. Equally hard to believe that the bushing didn't knock out the crankshaft plug.
How did you remove the bushing without damaging it?

Removing a pilot bearing without so much as a scratch is not hard.
I've done it twice.

[rhipsher]

That pilot bushing is the problem. That's way off center. Who ever made that and let it get passed inspection should have been fired. That is worse than Chinese made off.