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:
http://i407.photobucket.com/albums/pp152/QB93Z/Flywheelm%20wear%20pattern/DSC04709.jpg

Here is the flywheel surface:
http://i407.photobucket.com/albums/pp152/QB93Z/Flywheelm%20wear%20pattern/DSC04714.jpg

Here is the clutch disc:
http://i407.photobucket.com/albums/pp152/QB93Z/Flywheelm%20wear%20pattern/DSC04721.jpg

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:
http://i407.photobucket.com/albums/pp152/QB93Z/Flywheelm%20wear%20pattern/DSC04710.jpg

Flywheel:
http://i407.photobucket.com/albums/pp152/QB93Z/Flywheelm%20wear%20pattern/DSC04720.jpg

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:
http://i407.photobucket.com/albums/pp152/QB93Z/Flywheelm%20wear%20pattern/DSC04735.jpg

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

[Paul Workman]

Ya know...Looking at the pilot bearing, it looks to have been cast with the hole centerline off-set, based on the three little satellite dimples surrounding the hole. Installing the transmission might have been interesting - especially getting the trans bolts to line up with the bell housing. I would think there would be some serious tweaking to the input bearing at the very least!

Wow!... That's pretty amazing!

P.

[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

[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.

[Paul Workman]

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!:dancing

P.

[gbrtng]

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?

[efnfast]

Just an obervation, Jim, is it the hole that is out of center, or is the bevel cut off center making the hole look out of line. Maybe it's just the camera angle, but when I hold my precision pen held up to the screen it makes it look like it may be an optical dilution.

[QB93Z]

I have done a more detailed inspection of the pilot bushing.

The picture I posted was the end of the bushing facing the block. On the end of the bushing facing the transmission, the misalignment is less noticable.

I measured the wall thickness of the bushing with a caliber:

From the transmission end: Thin side is 6.26mm, wide side is 6.35mm

I tried measuring the thicknesses on the engine end of the bushing (the end in the picture), but there is a raised rim/edge on that end which made the mesaurements suspect.

The pilot bushing was tight in the crankshaft. We removed it using a blind hole bearing puller. The bit end of the puller made the axial marks on the inner surface of the bushing.

Visul inspection of the crank shaft while we had it apart showed no abnormalities.

So my conclusion is that the hole in the bushing is slightly off center and angled slightly to one side.

I appreciate all of your comments. It is a good discussion.

Jim

[rhipsher]

Ah! Hello. Machinist speaking here. I know that my 23 years of machining experience doesn't hold much weight. But that hole was manufactured off center. Aint no optical illusion or chamfer. Even the I.D grooves are symmetrically off with the whole. These are my old pilot bushings from two of my trans pulls and they are clearly on center front and back.
http://i301.photobucket.com/albums/nn63/keeno1970/2012-06-11_19-43-48_480.jpg
http://i301.photobucket.com/albums/nn63/keeno1970/2012-06-11_19-43-07_588.jpg

[GOLDCYLON]

Im not machinst but wow Jim that is WAY off center just look at the offset surface area on one side vs the other. I think the bearing grease failing and going into the surface area and scoring are also strong on what happend list.

[rhipsher]

That pilot bushing hole being that far off center is going to cause your whole drive train to sit cockeyed. Transmission will be off to one side. Uneven contact between plates. That bushings is your entire problem. Must have been slipping like a mofo.

[mike100]

According to Bill Boudreau, you do NOT add any grease to those bronze bushings. The grooves and the impregnated material provide lubrication.

If you do lube it, once the grease dries out, the bushing will spin in the back of the crank and generally get worn out much faster. Mine was spinning and the car only had 28k miles on it...the clutch even less because it had been replaced once already.

I'm sure that clutch will feel 100x better with all new parts and a propely installed pilot bushing. I used the same disc and flywheel and I could tell a big difference upon reinstall of just the bushing change.

[scottfab]

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.