Strange issue with clutch in Chevy C6500

[dieselfuelonly]

I put a new clutch in one of our C6500s. This was the one I got - https://www.phoenixfriction.com/p-4...k-topkick-66l-v8-diesel-81l-v8-gas-13-in.aspx - Worked great for just short of two months or so, then the other day one of the guys said the truck was stuck in gear when he tried to leave the lot. I managed to get it out of gear, and when I did I noticed it seemed like the clutch was not completely disengaging explaining why he was having such a hard time getting it out of gear.

This truck has a cable (no hydraulics) from the pedal linkage that pulls the lever that moves the fork to push the release bearing against the pressure plate fingers. I checked everything I can think of to make sure nothing was binding. Cable didn't seem like it was stretching. Release bearing is separated slightly off the pressure plate fingers when the pedal is out so it's not spinning all the time and wore out already.

This is where stuff gets weird - I found that if I disconnected the cable from the fork lever and moved the lever back and fourth a couple times (moving the release bearing back and fourth way further than it would normally be) , then hooked it back up, when I would push the clutch in and start the truck (and kept the clutch pushed in) I could shift it into any gear no problem.

Then, as soon as I let the clutch out in neutral, then pushed it back in to try to shift it into a gear, no dice unless I really forced it in gear. I swear you feel more pressure at the bottom of the pedal after the initial push/release.

If I started the truck up again with the clutch pushed in a second time, no luck, wouldn't go in gear. But every time I would get down under the truck and wag the release bearing around I could get it in gear no problem on that initial start.

I pulled the trans back out today separating it at the bellhousing (pulling the housing on these trucks is more involved since its used as a mount for the rear of the engine AND the transmission) and to my surprise the release bearing looks fine. Fingers on the fork look fine. I don't see anywhere there are signs of the bearing getting stuck. No broken fingers on the pressure plate.

The only thing I can figure (and this is really stretching it here) is the clutch disk can slide freely on the input shaft when the engine isn't running, but once the load on it is there as the engine spins it's getting stuck on the input shaft and is staying jammed up against the pressure plate? But that wouldn't explain why when I pull the cable and wiggle the release bearing around it works fine on the first try.

Any ideas? Really scratching my head on this one.

 

[heymccall]

What year?
What engine?
What transmission?

 

[Truck Shop]

Pressure plate not releasing equally.

 

[dieselfuelonly]

08 I believe, 8.1 Vortec, Eaton fs5406a

 

[terex herder]

The nose on the transmission may be broken.

 

[Vetech63]

Are you sure the cable mounts aren't moving? Maybe the cable is starting to break internally.

 

[56wrench]

Pilot bearing was replaced? Pressure plate release fingers were all the same height after installation. I always check the finger height after installation to make sure they are all even otherwise it may not release properly. How were the splines on the input shaft? If they are worn, the discs will hang up. Also on a dual-disc clutch, the intermediate plate could be hanging up for whatever reason.

 

[Truck Shop]

Common trait of a diaphragm clutch.

 

[56wrench]

I did not realize it was a diaphragm pressure plate. I was referring to the coil-spring type

 

[Truck Shop]

I did not realize it was a diaphragm pressure plate. I was referring to the coil-spring type

I'm just guessing, probably a stamped steel clutch cover.

 

[dieselfuelonly]

The nose on the transmission may be broken.

Front of the trans looks fine, but I was initially wondering if that could be the cause - this trans has a tube that surrounds the input shaft that bolts over the outer face of the trans over the input shaft bearing - but it looks fine and there is nothing that the release bearing could snag on.

Pilot bearing was replaced? Pressure plate release fingers were all the same height after installation. I always check the finger height after installation to make sure they are all even otherwise it may not release properly. How were the splines on the input shaft? If they are worn, the discs will hang up. Also on a dual-disc clutch, the intermediate plate could be hanging up for whatever reason.

Yep, new clutch, pressure plate, flywheel, pilot bearing, release bearing. Worked fine for around two months then this just started acting up. It's just a single disk clutch.

I'm just guessing, probably a stamped steel clutch cover.

Yeah it's a diaphragm type.

I guess I'll have to pull the bellhousing and then the pressure plate and clutch disk and see what's going on. Sure doesn't seem to be anything wrong with the trans or the release bearing.

Unfortunately this truck uses the bellhousing as mounts for the rear of the engine and the transmission, so once i pull that and support the engine there won't really be much moving the truck till I get new parts on the way.

Maybe something is jamming up the pressure plate release fingers somehow - only one way to find out I guess.

 

[dieselfuelonly]

Finally got it figured out today. Pulled the bellhousing and the rest of the clutch after crawling around in the gravel getting the engine jacked up and supported. Don't want this piece of crap in our little shop where I can't move it 'til I get all the parts. Had a real close look at everything, pressure plate looks fine, clutch looks fine. Scratching my head hard at this point. Had another look at the release bearing, looks fine. Pulled the cross shaft and the release fork out, fork was worn more than I thought from what I could see looking up through the inspection hole in the bellhousing. It had a little pocket worn in it on the bottom of the arm of one finger that was allowing the release bearing to roll in and then get stuck, and would limit how far the bearing could travel forwards. Explains why when I would remove the cable and rock the bearing back and fourth, then put it back on and crank the truck up, the first time it was no issue - the bearing would straighten out on the fork. As soon as the pressure came off the bearing and then back on when I pushed the pedal in a second time, the rotational force from the spinning pressure plate would make it rotate over a little bit into the pocket that was worn into the fork, so from that point on the clutch wouldn't completely disengage.