Sounds like throw out bearing but is not

[Jeffrey B.]

I thought my throw out bearing was bad because when I pressed the clutch peddle I heard this intermitent screeching noise. I pulled the M20 tranny and rebuilt it, then replaced the throw out bearing when reinstalling the tranny. Well, when I push the clutch peddle in I still get the intermittent screech just like before. The old bearing was in the car for several years and looked fine. Any thoughts would be greatly appreciated.

[Paul D.]

Re: Sounds like throw out bearing but is not

Probably NOT what you want to hear, and I HOPE your answer is YES, but did you closely examine your release bearing fork when you were in there? The area that comes in contact with the bearing could be worn enough to allow it to come in contact with the spinning part of the bearing. This area would not "catch your eye" as it faces the pressure plate / flywheel. A worn one will feel as if it is grooved or stepped. The contact "pad" should be completely flat or smooth. The only way I know of to check it is to R&R the tranny again. Chip.

[Jim D.]

Re: Sounds like throw out bearing but is not

Did you replace the pilot bushing?????????

[Jeffrey B.]

Re: Sounds like throw out bearing but is not

The clutch fork was replaced about 4 years ago when I installed a new clutch kit. It probably has been driven less than 2000 miles in that time.

[Jeffrey B.]

Re: Sounds like throw out bearing but is not

I replaced the pilot shaft bushing back when I installed a new clutch kit as I had stated in a prior reply. This sounds like steel on steel. I'm not sure what a brass pilot bushing would sound like if it goes bad.

[Jim T.]

Re: Sounds like throw out bearing but is not

Are you sure you installed the throw-out bearing correctly on the clutch fork?

[Jeffrey B.]

Re: Sounds like throw out bearing but is not

I was careful and even pulled the boot off of the bell housing to check with a bright flash light. I have heard that a harmonic balancer might make a similar noise, and I'm not sure how depressing the clutch would play into a situation like that.

[Edward J.]

Re: Sounds like throw out bearing but is not

Jeff, Just think about about whats happening when you depress the clutch, You are disengaging the the transmisson and clutch disc from the spinning engine.It does not leave much thats spinning other than the throw out brg. and the surface it rides on (presure plate). Are you are fully depressing the clutch when this noise is evident.If you are just touching the pedal or slightly depressing and the noise is there, this maybe something that was missed.


Jeff, I added this, sometimes I have seen the metal cover on the bell housing cause a problem, If they get bent it will cause the flywheel to hit the shield. and since its bolted to the bell housing if there was any flexing of the bell housing when depressing the clutch it could cause a noise of metal contact. This is just a possibilty.

[Erich C.]

Re: Sounds like throw out bearing but is not

When you installed the pilot bushing did you check to see if a magnet stuck to it. The original GM bushings were made of oilite bronze. That material is semi-porous and lubricant was drawn into the bushing by vacuum. I'm not sure of exactly when
but some of the replacements are made of "contaminated" bronze ( = cheaper to manufacture ). That bronze has a higher iron content and a magnet will stick to it. It is also not porous = no lubricant. When you push the clutch pedal in there is a difference in rotational speed between the crankshaft and the trans. input shaft. So there is some rotation of the pilot bushing on the pilot end of the input shaft. If you decide to replace the bushing and can't find a "real" oilite bronze bushing I have the name of a company that sells it.
Erich

[Jeffrey B.]

Re: Sounds like throw out bearing but is not

It seems to happen when the clutch is fully depressed or when I just begin to let off of the peddle. I checked the dust cover on the bell housing and there is no evidence of rubbing on the inside. The odd thing about this is it does this very intermittently.

[Jim D.]

Re: Sounds like throw out bearing but is not

I replaced the pilot shaft bushing back when I installed a new clutch kit as I had stated in a prior reply.[/B] This sounds like steel on steel. I'm not sure what a brass pilot bushing would sound like if it goes bad.

Nowhere is this thread did you state you replaced it. I agree with Erich, sounds like it could be the pilot bushing. Yes, the cheap ones will "screech".

[Jeffrey B.]

Re: Sounds like throw out bearing but is not

I did not check the pilot shaft bushing with a magnet when I did the installation. I'm not sure why it would have been quiet for a few year then get noisy just before I stored the car for the winter last fall. A guy told me the screeching might be from springs in the clutch disc if the car is not driven often. Not sure if that makes any sense.