C2: Clutch replacement ?'s

[Dan Pepper]

This weekend my brother and I went to install a new clutch (an LuK kit) in my "66 L36. Aside from chatter, I thought I had a bad release bearing, but after inspection, I think we found another problem that was causing the noise - more on that in a minute.

Release bearing question:
The release bearing that came with the LuK kit has a funky plastic collar, so I went to the parts store and bought another with a metal collar just for piece of mind. Apparently there are "first design" and "second design" release bearing config's. The first design has a lobe in the clutch fork groove, and the bearing hole isn't concentric with the outside of the bearing housing. The "second design" which was the only all-metal bearing I could find, doesn't have the lobe and the input shaft hole is perfectly concentric.

What was the purpose of the first design's collar lobe and off-center input shaft hole? The plastic collared bearing has the lobe and isn't concentric, but the plastic makes me nervous. Should I look for another bearing with the lobe, off-center hole etc, or stick with the all-metal second design?

Could this have been the noise?
The noise I was experiencing happened when the car was in neutral, and the clutch was released. Kind of an aluminum rattling sound. It also occured when the clutch would chatter in 1st and reverse gears. Since the release and input bearings looked to be in good shape, we suspect the cause of the sound to be the broken clutch fork spring allowing the fork rattle on the ball stud. THe stud and stud socket looked pretty worn as well. It makes sense since the (first design) release bearing isn't concentric, and the off-set may/would have caused the pulsating sound as the bearing spun on the p-plate fingers, inturn rattling the fork on the ball stud. At least I think this was the problem. Sound like a possibility?

One last question:
The shop manual states that the pressure plate needs to be installed/lined up on the flywheel the same way it came off. Problem is, I didn't mark the p-plate's reletive position on the flywheel before I had the flywheel surfaced. The shop manual says to match-up the X markings on the p-plate and flywheel - but I couln't find any such markings on either peice. The flywheel is original to the car dated B256. So without seeing any markings, I just lined-up the holes and bolted the p-plate on anyway. Is this going to be a problem if the p-plate and flywheel aren't lined-up as they were at the factory? Is this a balance issue?

[Craig S.]

Re: C2: Clutch replacement ?'s

Dan - personally, I would not install a pressure plate and clutch without balancing the flywheel again if surfaced with the clutch. I did this once with new GM parts, supposedly balanced at the factory, and I had a vibration that did not exist before the replacement. I am not completely familiar with the throwout bearings other than the early and late were different lengths, and I believe the ball stud was also different and affects the geometry of the movement. Good luck!...Craig

[Joe L.]

Re: C2: Clutch replacement ?'s

Dan-----

The "eccentric" release bearings are quite common these days. In fact, they predominate. I've never learned the design rationale for these, but I'll bet it's a good one. Most of the major suppliers, including GM/Delco, use this style. I don't like the looks of them, either. However, technology tends to be progressive, and I have a sneaky suspicion that these pieces are actually better than those of days of yore. The plastic component of these units is non-structural and, given the progress in plastics technology, it might serve its purpose better than steel. I have plenty of NOS GM bearings [none for sale], but I wouldn't be afraid to use one of these new-design units. LUK/Sachs, now a unit of ZF Industries, is one of the largest clutch manufacturers in the world. I really don't think that they'd package a substandard release bearing in their kits.

As far as the noise goes, I would suspect one of the following:

1) broken or improperly installed clutch fork spring (the one on the release bearing end of the fork). This spring MUST be installed with the end tangs WITHIN the release bearing groove;

2) distorted bellhousing front cover. Even very slight distortion will cause interference and noise. Remove to test;

If you re-used the old pressure plate assembly, failure to index it to the flywheel could very well cause balance problems. Few GM flywheels or pressure plates are marked with an "X", or otherwise. YOU have to add the marks with a punch or stamping die prior to disassembly.

If you replace the pressure plate and/or surface the flywheel and/or fail to properly index the pressure plate and flywheel, then you will likely need to have the pressure plate and flywheel assembly precision balanced for smooth operation.

[Dan Pepper]

Joe & Craig...

Last thing I want to do is drop the transmition again to chase down a vibration... So do you suggest I remove the pressure plate/fly whees assy., reassemble off of the car and then have the unit balanced?

Thanks for the input. The only thing I get more satisfaction from other than tinkering on a Sting Ray is knowing I'm doing it right!

[Joe L.]

Re: Joe & Craig...

Dan-----

You don't need to re-assemble the pressure plate and flywheel off the car. Just take both components to a competent balancing shop and they'll take it from there. Usually, they'll place indexing marks on the pressure plate and flywheel so assembly can be done properly.