Clutch fork
 

Anyone able to comment on a source for a correctly designed clutch release fork for a 77 T/A? I’m having issues with my T/O bearing making contact with the PP unless I adjust a lot of slack into the linkage and I think part of my issue is a worn out fork (namely the pivot spring clip and the spring clips where the bearing rides).

Thanks!

You probably just need to use a longer adjustable pivot ball.. The Lakewood ones are good #15500. and #15501 pivot ball. What bellhousing are you running?

It’s a stock bell. I’m not sure if an adjustable pivot ball will help my situation. At rest, with the pedal out, the return spring tends to want to pull the whole fork forward. The fork seems to come off the pivot ball leading me to believe the spring clip is a little weak. Unless I’m missing something else

Also, it's critical to install the throwout bearing correctly in the fork. Very easy to install it the wrong way and it will eat up the bearing flange in a hurry.

Are you referring to this? If so, I do have it installed correctly. Unfortunately this trans has been out enough times I’ve become aware of the proper installation. I don’t have a picture handy but oddly enough, the portion where the fork presses against the bearing when disengaging the clutch does seem to wear rather quickly. Not sure if that’s normal or a result of poor geometry for some reason.

Full disclosure, I swapped a 76 ST-10 into my 77 T/A, which was an automatic, 8 or so years ago so this isn’t a factory setup though the fork was supposed to be the original fork from the 76 the trans came out of.

Never had issues till I was recently chasing a clutch chatter issue and replaced my flywheel, clutch, PP and T/O bearing. Haven’t gotten many miles on it but I may have had the linkage too tight as the T/O bearing started making noise. Replaced it yesterday which fixed the noise but I decided to investigate the bearing clearance further which led me to discover it spins with the PP even though I can’t see any diaphragm fingers touching it by looking through the inspection hole in the bell. They must be touching on the “top” but that’s even with quite a bit of slack adjusted into the linkage.

I was able to snap a few pictures of the noisy bearing a pulled out. Every time I’ve pulled one it had wear marks similar to these. The fork has always been installed in the manner described it the picture above.

I can't even imagine how that witness mark is possible on your TO. That would take a lot of force from a hardened fork. Definitely, the pressure is not applied evenly (flat against the TO), it's digging at an angle.

Maybe from the pedal to the TO, go all stock? Your bell housing is already stock, so not too bad.

That’s two marks actually. I didn’t make that clear. I attached another pic showing both.

Everything is stock replacement. Pedals are donors from another car, zbar and linkage are factory replacements but not original parts, fork is allegedly original to the 76 the trans comes out of.

I don't think I've ever had witness marks like that on any throw out bearing. Hmmm.. What are you using for a return spring, and how strong is it? Also wondering about you adjustment rod that sits in the clutch fork. Is it a stock one? Also, try to minimize grease on the bearing. There is a channel inside the bearing that holds grease for sliding on the input shaft and a tiny dab on the points when the clutch fork pivots. Reason is the bearing spinning will fling excessive grease all over.
There is also 2 divots on these throw out bearings that prevent the throw out bearings from spinning when installed into the clutch fork. I'm thinking those divots on your throw out bearing are just that.
Check out this video, You can see the bump out on the bearing that I'm referring too. https://www.youtube.com/watch?v=owcUNZmP8zI good video. He talks about the clutch fork worn out where it contact the throw out bearing.

Those anit-rotation things are bumps, not divots. When I looked at the photos the OP uploaded, I thought they were divot witness marks, but that could be an optical illusion.

OP - are the bump outs or divots (witness marks).

If divots (witness marks), I think it doesn't have anything to do with the return spring. It think it is to much force being applied at a weird angle when the clutch pedal is pressed.

Return spring is a factory replacement for what it’s worth. I don’t know how else to describe it or its tension. It’s strong but can be removed with two hands.

The adjustment rod is stock style.

The grease has me a little puzzled also. Not sure if the bearings have grease in them that may have escaped the seal but I didn’t put that much grease on it. Just a small amount of graphite lube on the trans bearing retainer and inside of the T/O bearing where it rides the retainer. I don’t believe I put any grease where the fork contacts the T/O bearing. Maybe I should’ve.

The marks are divots. I’d guess from something going on with the fork maybe since they always seem to appear on any bearing I’ve ever installed. Pedal always felt smooth and not a lot of pedal force required.

Brian. The bearings do have grease in them. They are also self centering. Some grease must have escaped the seal. Bearing should be replaced. As for grease on the bearing where it touches the pressure plate forks is a No. I think you should also replace your clutch release fork.

I did replace that bearing I posted the photo of as it began making noise. It’s literally got less than a thousand miles on it. Maybe a few hundred actually. I assumed I’d had the linkage too tight which led me to check the newly installed bearing with the engine running. Even though the diaphragm fingers don’t appear to be touching, they must be at the top where I can’t see. That’s what’s led me to wonder about the spring clips on the fork and why I may seek a replacement.

As it happens, I have another throwout bearing that was in the car though I can’t recall for sure how long it was in there but it’s the one pictured below. It was definitely longer than the one pictured above with the orange seal. This one was replaced with the orange seal one as I was chasing some chatter issues. I just noticed it doesn’t have the same witness marks on it. Maybe slightly so perhaps it’s possible the orange seal one is just a victim of chineseium. I do recall seeing marks on older bearings in the past but I don’t recall the circumstances.

Having pulled the trans so many times recently I think my approach is to wait and see if/when the new T/O bearing makes noise again at which point I’ll pull the trans again and investigate. I just read about some of the replacement forks not being the proper geometry so I wondered who had info on correct forks should the need arise in the future.

Try going back to the taller bearing, new.

They’ve all been the same size

Double check the part number of the clutch fork, I did have an issue with the wrong one causing issues. Just an idea.

Must have misinterpreted this.
If you a going to replace fork, try to find a GM piece. The replacement I bought that was supposed to be the best wasn't as hard as my original.

Yea I’m sorry, that was my fault. I meant installed longer than the other. Not longer length wise.

I got a little time to climb under and play with things. I feel like the majority of my issue is with weak spring clips attaching to the pivot ball. At rest, the return spring tends to pull the entire fork forward rather than just the clutch rod side. I feel like if the springs were holding the fork against the pivot ball the fork would pull the bearing away from the diaphragm more efficiently. Next time the T/O bearing goes, I’ll install a new fork as well.

Just to say, without the linkage or return spring in place, if you hold the end of the clutch fork where TO bearing is just touching the PP, the end of the clutch fork (where the rod sits in pocket) should be at a 90 degree angle to the centerline of the drivetrain.

If it's past that 90 degrees, the TO is too tall, if it's before that 90 degrees the TO is too short.

There is a limited range of motion of the fork, it has to be at rest at that 90 degree angle to the drivetrain centerline.

Think about it, if you're holding the clutch fork in your hand, with the TO installed, the fork ends will contact the retainer area and be forced into the opposite side of where it rides. That's how you get those divots/marks, it's binding from over/under range of motion.

To me, it appears the TO is too short, or the bellhousing ball is too short. Or possibly both

Take pics and post, include shots of the Z bar and spring.


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I’ll snap a few pics next time I have it in the air. Probably won’t be till next week though