C3..Pilot bearing problem.....

[Michael H.]

Re: C3..Pilot bearing problem.....

That's a really good question Mike. I wish I had a really good answer. I've gotten involved in quite a few of these in the 60's and early 70's but they were all near new cars under warranty so we never got to see what happened as mileage increased. If I remember correctly, the problem seemed to start just a few weeks after delivery. Some lasted longer, probably several months.

Another part of this that was strange was the fact that some customers would report this problem but by the time they came into their dealer for service, the noise was gone and there was no record of it ever being a complaint again. Othere would report that the noise would come and go.

I would have to think that if this continued for several thousand miles, it would eventually damage the transmission front brng retainer but I don't remember ever seeing one, from a low mileage warranty car, that was excessively worn. Just lightly polished. A lot of the dealer mechanics were replacing the T/O bearing and the front brng retainer which almost always corrected the problem.

It just occured to me that, if I remember correctly, this problem was almost unique to high perf cars with the raised finger diaphragm pressure plate, not cars with the flat diaphragm. Corvettes, big block Chevelles and Camaros etc. I don't remember typical "mom & pop" 307 Chevelles having this but that could be wrong.

[Michael H.]

Re: C3..Pilot bearing problem.....

The original T/O bearings that were supplied to GM in the 60's and early 70's came from BCA, if I remember correctly. I don't have any information on the current source though.

Also, I can't help on the new design bearing that you describe with the keyways/flat spots. I'm not sure what that would be.

I agree, we would think that a pilot bushing would require extra lubrication. However, if it did, that small amount of lube could never be expected to last for the life of car, yet, a pilot bushing can and does last for several hundred thousand miles without frequent relubrication. That's why the lube is in in the material. There really isn't any heavy side loading on this bushing. (unless the clutch disk is out of balance) It can't hurt to add a thin film of lube thought.

If your bushing and the tip of the input shaft are shinny and smooth, I would say that this is a normal condition. If it looks burned or scared, that would most likely indicate a transmission alignment condition but since the car never had that problem before, it can't have it now if all the same components are reinstalled.

I've never actually measured the clearance dimensions for the input shaft to pilot bushing but I would guess it's at least .005 and probably more. That would make the fit seem loose but it's not necessary that it be a close fit. If you still have the used one that you removed, it would be interesting to measure the ID and compare to a new bushing.

[Clem Z.]

make sure the pilot bushing is "oilite"

there are some out there that are not and will not lube correctly.

[John H.]

Re: make sure the pilot bushing is "oilite"

The commercial parts system was flooded with Chinese counterfeit knockoffs of pilot bushings about eight years ago that were more cast iron than Oilite bronze, and some may still be out there. Don't buy a pilot bushing anywhere without taking a magnet to it - the Chinese ones with all the iron in them will attract a magnet, genuine Oilite bronze will not. The Chinese ones will eventually score the hardened surface of the input shaft.

[Page C.]

Re: C3..Pilot bearing problem.....

Hi All,
This was probably a post I made a couple of weeks ago. I think it must be beyond the 5 days and not yet in the archives. The new GM#15680264 is made by BCA(the BCA# is in the original post that I can't locate and the bearing is installed}. It is designed to prevent the inter part of the bearing from rotating on the trans input bearing retainer. The inter part that fits inside the clutch forks is not round. It has a peaked shaped side that will not let it rotate inside the clutch forks.
Page Campbell

[John H.]

Re: C3..Pilot bearing problem.....

I've been buying throwout bearings for decades, and have never seen one that didn't have the anti-rotation design; the bearing has always been designed such that the inner collar only slides fore-aft on the bearing retainer and does not rotate - the only part of the TO bearing assembly that rotates is the face of the bearing itself that contacts the clutch fingers.

[Page C.]

Re: C3..Pilot bearing problem.....

Hi John,
The decades from 1955 to at least 1982 used a GM#908244 (NDH #24AG) It had no anti-rotation protection in it. Thats why the chutch forks on so many cars have grooves in them where they contact the bearing. The only anti-rotation on this style throw out bearing is the pressure from the clutch forks on the inter bearing. Once the bearing starts to dry out the fiction from the outer part of the bearing that contacts the chutch fingers rotates the whole thing.
Page Campbell