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Removed M-20 from my 70 Rallye 350 to replace side cover gasket and noticed severe wear on throwout bearing flange where fork contacts. The car only has 2500 miles since restoration. Will be replacing throwout for sure but what the heck is causing this. Drivability was perfect, no clutch issues at all but need to find out the cause. The throwout bearing came in a dual friction clutch kit from Centerforce (KDF717516).
Poor fork alignment. The throwout should be able to rotate, not spin, when the clutch is not pushed in. Is the pivot ball in the bellhousing worn? Maybe the wrong fork for the year. Chinesium bearing?
I'm wondering what the fork looks like. Be sure you are using all the correct parts, installed correctly. Be sure there is sufficient "free pedal". Maybe soft bearing? Try another from a different source.
All mating parts were replaced with OE style components, pivot ball, fork, etc., the fork seems to have minimal wear. The OE style bearing has a raised area to prevent rotation while in the fork? The comment about "free pedal" is something I need to look at. The throwout bearing came in a clutch kit from Centerforce, would like to replace with a different brand, what do I look for to make sure it will fit/function as intended with the Centerforce clutch? Any other thoughts would be welcomed, I really don't want to have to worry about this every 2K miles. Thanks, Curt
The only thing that comes to my mind is that you had no free play and the bearing was turning all the time creating a vibration causing the fork to dig into the collar.
As mentioned, not enough free play in the pedal. Insufficient free play causes the bearing to stay in contact with the pressure plate. The bearing was a loose fit in the fork and the entire bearing rotated in the fork. The bearing is too tight internally and wouldn't spin inside like it should so it spun at the fork.
Can you rotate the clutch face/side of the bearing while holding the part that slides into the fork?
I don't remember so someone please chime in that knows... did the '70 Cutlass use an external return spring on the clutch fork?
I don't have anything to add about the cause of wear, but I wanted to commend you on your pictures - they are excellent! I do failure analysis for a living and those look similar to pictures we would have in one of our formal FA reports.
The original release bearing actually spun on the clutch fork. Look for a BCA brand bearing as they are generally U.S made. It almost appears to be a clutch fork issue. Post pictures of your clutch fork.
Attached are fork pic's. Wear does not seem bad but one thing noticed is the spring tabs (red arrow) are fully compressed in free state (tabs do not compress when installing bearing leaving some gap). Not sure if this would contribute to the bearing wear. I have the old fork, it has significate wear on the contact side but the spring tabs are not compressed and become compressed with bearing installed. Maybe I have a fork issue also??
The fork looks fine in your pictures, however, the bearing retainer on your transmission looks scored. You may want to polish the bearing retainer where the release bearing rides or change the retainer. And get a u.s made release bearing. If you can’t one, let me know. I may have an extra bearing.
Received feedback from Centerforce, they also believe the clutch was preloaded. Will now be replacing throwout bearing, fork, and possibly ball stud and bearing retainer. Will double check to make sure there is no preload while following the Centerforce procedures Eric provided! This brings me to another question, does the Bellhousing have to be completely pulled to get replace the fork? Thank you to the group and all who took time to provide comments and suggestions! Curt H
