The GMC CCKW

My 1942 Chevy has developed a weird problem. Actually, it has had this problem for a while but it has always gone away.

The clutch will sometimes get "stiff" and not disengage. Giving it gas and strssing it with the brake too will break it free and then it is fine and pedal pressure goes back to normal.

The other day, when I needed to plow with it, it did it again but would not break free. I finally took it to the barn (outside) and crawled under it. This is quite a feat as it has push bars on it for the plow that are mounted behind the cab. With a coat on, I cannot get under them and have to come in from back by the rear end.

The fingers looked twisted from what I could see with my new glasses and water dripping on my face. I have seen GMC clutches do this. This is the famous "GMC clutch" failure. The diaphram twists and then some fingers are up against the throwout bearing all the time.

This time too, with the pedal out, there is a noise of something hitting something about once per rev.

Now as I was positioning the truck under Annie the CCKW-Schield-Bantam crane so that I could take the wing plow off, all of sudden, the clutch started working again. It had the new noise, once per rev of something hitting in the bellhousing and there was no play in the pedal which would go along with a twisted diaphram.

Soooo.... I will take it apart this weekend

Ideas....?

Doc I had a similar problem some time back, had the unit been stood for any length of time ?

In my case the clutch plate had frozen to the flywheel face. That bent the petals on the pressure plate an made a few funny noises.

Some newer pressure plates have a less or no asbestos friction lining, they soak up damp from standing, not being used they dont dry out....and bond to a pressure surface.

Could it be ?

Mine had set for a week so it was not stuck to the flywheel.

The other possibility is that the nose of the transmission that the throwout bearing rides on broke and that the throwout bearing is/was not free to not press evenly on the fingers

I had one friend with a CMP chevy who had a little vermen get into the clutch and build a nest. When he started the engine with his foot on the clutch, the centrifical force threw all the material out into the pivot area for the diaphram and effectively jammed the clutch! Clutch removal time.....

Mystery sort of solved....

I got ever every thing out anf found nothing initially. WTF over? Fingers were even, no marks on the flywheel, disc, disc springs, pressure plate etc. OK, what gives? The pilot bushing could have looked a bit better, but it was OK. The whole assy was rather new from the lack of wear on the disc to the minimal rust on the pressure plate housing.

As I was taking out the final screws that held the plate to the flywheel, I heard something loose and metalic roll around inside the pressure plate but did not see or hear anything initially when I pulled it out while under the truck.

When I got out from under the truck, and into the light and reall examined the pressure plate, a large object fell out. It was a whole, or large portion of a pilot bushing! There is a pilot bushing in the crank, but this is an additional one or piece of one and it is all chewed up. How it got in there, I have no idea. I can only speculate that it fell out during installation but that begs the question, why 2? Did the previous installer think the crank was drilled too deep? I have a front shaft with nothing on it, so I can try it to see if it is supported though I would think that if it were not supported with a pilot bushing, you would have transmission problems as the front shaft would be cantilever off of the front bearing and not supported with the weight of the clutch disc tending to make it wobble.

I will probably install the new clutch because I have no idea what damage the "extra bushing" did and the last time it was working, I had no free play like the disc was worn out even though the clutch was adjusted correctly and there was plenty of meat on it.