clutch wont release
 

Have an '81 Firebird that was a factory sbc 305 car with 4 speed BW ST10 trans. Bought it with a '76 350 sbc swapped in at some point.
Engine was wiped out so I put in an '87 350 sbc......... One piece RMS engine.

So the issue is the clutch will not release. Pedal feels perfect and everything is adjusted properly. The first clutch I used was from LUK but it had a grinding noise coming from it when depressing the clutch pedal with the engine not even running. It wouldn't go into gear when I had it running so I thought the pressure plate was bad. Swapped in the new RAM clutch, same problem.


I used a new ATP 168 tooth flywheel for the '87 350 engine that accepts the bigger 11" clutch. (RAM 88764 with short TO bearing.) Same size flywheel that was on the '76 engine I pulled out.
I transferred everything else from the old engine to the new one, all OEM stock parts..........bell housing with the short pivot ball (PN 3729000). Also used a new NOS fork PN 14066235. It's a replacement for the original fork. It's beefier but the geometry is the same looks to me. TO bearing is installed on the fork correctly with the clips inside the collar.
Correct short head flywheel bolts from ARP also used.

I double and triple checked everything before I installed the new RAM clutch and everything seemed in order. All linkage good, no binding or hanging up. Pedal is smooth as butter and I can feel it depressing the PP properly..........but it wont' release the disc.

I wouldn't think so but does the newer sbc 350 engine with the one piece RMS need the longer pivot ball for the fork? Is the bigger flywheel an issue? I measured the height of the flywheel from the back of the block to the face of the flywheel on the old '76 engine I took out and it was 2 5/8", same measurement on the new 350 with the new 168 tooth ATP flywheel.

I am open to any suggestions as what to do next because this doesn't make sense unless I am missing something obvious. I have done many clutch jobs before but I am a bit stumped. The Chevy bell housing is all enclosed, no inspection hole/opening in the bottom to at least see the disc and try to turn it. Makes this prob tougher to figure out.

Not sure that flywheel will work on that engine? 1 piece rear main seal engine uses different flywheel. Info from another site.
In 1986 a crankshaft and flywheel change was made to the improved, once-piece seal design. 1986 and newer Chevy engines will not accept older flywheels due to the different crank flange and bolt pattern. Older bellhousings, however, will work on 1986 and newer engines.

It's a correct flywheel for the one piece RMS engine. The older sbc flywheel won't even fit the hub of the crankshaft of the '87-up engine.

disc springs hitting flywheel bolt heads ???

Sorry read post wrong. Disc in backwards? Most have the spring stepped portion to the trans.

Did you test fit the clutch disc on the input shaft? Maybe it's getting hung on the shaft. Was it difficult to mate the trans to the bell?

You mentioned 11" setup, did you hold the disc up to the plate to make sure it fit? Possible stuff got mixed up from another box.

And just to ask, the 'flat' side of the disc is towards the flywheel?

You can drill an inspection hole in the bell too, if you need to.

If there's too much pedal throw, fingers/To might be able to hit the disc.

It's rare, but possible, the TO isn't centered on the fingers, or one side of the TO is under the fingers. You can try to peek in the hole the arm passes thru and make sure it's flat on the fingers.

Can't always trust the TO part listings either.

Just throwing stuff out there...


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Pretty sure the flat side of the disc usually goes towards the engine/flywheel.

EDIT: Ok, my turn to read post wrong!


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Short head ARP bolts were used. No witness marks on anything. I test fit the disc to the flywheel beforehand and it fit flat no touching.

Definitely in correctly. If it was backwards it wouldn't sit flat and flush I tried it.

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Just another thought, are you putting throw out bearing on fork correctly, the spring on fork goes on the groove with fork, not behind bearing?
Sorry not trying to say you did it wrong, just throwing out idea's.

Well, guess it could be a defective plate, but not sure that would give the same results.

So when the fork is in the 'relaxed' position, with the fork free play slack taken up (just resting the TO on PP fingers), is the rod pad 90 degrees to the centerline of the drivetrain?

If it's not, and the pad is more towards the rear of the car, that could mean you're not getting enough pedal/linkage throw. To correct, it would require a different or adjustable pivot ball in the bell.


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Rod pad, correct, the pocket where the push rod meets the fork. It's 'flat' there where the divot is, and that flat spot angle should be 90 degrees to the centerline of the driveline.



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I will check that out.
Also found this at the RAM website:

CHECKING CLUTCH FORK ANGLE AND MAKING APPROPRIATE ADJUSTMENTS
1960’s-70’s GM applications used several different fork pivot ball lengths and release
bearing lengths. Understanding fork angle will help you achieve the best release position for
the fork to minimize pedal effort and maximize bearing travel. For optimum operation, the
fork should have an angle to the front of the bellhousing exit window when the bearing is
just touching the fingers. If the fork is positioned in the middle or to the rear of the window,
travel and leverage is lost. To compensate for this, RAM offers two longer release bearings -
pn 488L is 1.560” overall and pn 495 is 1.810” overall.
You can pre-check the need for a longer bearing by sliding the transmission in and, before
proceeding with completion of the install, pulling the fork up manually to check and make
sure the fork is angled to the front of the exit window in the bellhousing when the bearing is
just touching the clutch finger

First pic is clutch pedal at rest all the way up. Fork is at about mid window. According to the RAM instructions it should be more towards the front of the window opening.

Second pic if fully depressed.

Impossible to see inside the window without a bore scope to see how far fingers are down. But without a bottom inspection hole to see what the disc is doing looking in with a bore scope may not say much.

Old clutch with the flatter diaphragm fingers with same short TO bearing worked fine.......new PP with more raised fingers same short TO won't release disc. Makes no sense.

Ok, have to admit, not too familiar with the chebbie stuff, I can see the angle of the bell, and the bend on the fork, so maybe it needs to be at rest further forward, not sure.

It kinda looks like theres a witness mark on the bell fork opening, maybe it's reaching max travel?

It does look like you have more room to maybe go to the next height TO though, that might do it.


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I take that back, think the pivot ball needs to be longer, or an adjustable one so you can move it taller. That would make the fork go forward without it going at an angle, which would be the case if you went to the next height TO.

Is that bell cast aluminum? If it's steel or else, you can cut into it and not worry about it failing.

Think you're on the right track.

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That pic of the fork I posted has less of an arch to it, maybe because it's a Pontiac one.


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Yeah, more I look at that pic at-rest, more I think the next size up TO isn't going to help, it will probably put the fork at more of an angle and create an 'arch' path of travel, making it hard to initially push the pedal in.

Difference between the 2 TOs that the RAM website lists is a touch over a 1/4", that may make the end of the fork too close to the bell.

It's a toss up, you could try the next taller TO, but I think if you ever have to replace it again, the adjustable ball would be a better option.


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So after pulling the trans for the third time I was able to take a look at the PP in action.

Had someone push down on the clutch pedal and the disc dropped. It is releasing as it should be. But with the trans installed and engine running it will not go into gear. As soon as I shut the engine down I can shift into any gear.

When I had the trans out on the bench a while back I took the shift cover off to change the gasket. Reinstalled the shift cover and bench shifted it thru all gears. Also had the tail shaft housing off too to change the rear bushing. Nothing in the main case was taken apart.

I'm ruling out a trans issue because it shifts fine when engine is off and when I had it on the bench.

Trans was not hard to install either. Went right in practically by hand. Didn't draw it into the bell with bolts.

Still searching for an answer.

Any chance the splines on the pilot shaft are bottoming out against the pilot bushing?

Clay

Thats the same symptom's i had in a 69 c10. It was 3 speed in the floor and didn't want to go into first with the engine running. You could put pressure on the shifter and at the same time turn off the ignition off and it would drop right into first gear. Had ran the tranny a little low on lube at one time, but before that it always shifted fine. I always blamed it on synchronizers after that. Later i bought a Muncie m20 4 speed and swapped it out and left the same clutch, pressure plate and throwout bearing in place untouched. Solved the problem.

That's a good thought! I was focused on the clutch setup!


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You stated that the flywheel was brand new. Don't assume that it was surfaced correctly from the factory.

Several years ago I had a similar issue, difficult to place the trans into first gear, grinding going to reverse. Everything was Brand New, Autogear M22, Hurst shifter, fork, throw-out bearing, clutch disc/PP, and Hays flywheel, all new.

Tried everything I could think of to the fix the issue, adjustable throw-out bearing, adjustable pivot, different clutch linkage, nothing worked.

Finally, after a couple thousand miles of putting up with the gear grinding, I decided to change the clutch and pp to a different manufacturer. I doing so I also figured that I would take the NEW Hays flywheel to the local machinist and have it resurfaced, for the hell of it. Turns out the flywheel surface was WAY off, not close to being true. That was my issue the whole time, even with the clutch depressed, the high point of the flywheel was touching the clutch disc at every revolution, just enough to keep the input shaft slowly spinning causing the gear grinding in reverse and the difficulty going into 1st gear.

So don't assume the new flywheel is true.

Very true on the surface, and to add to that, balance too.

I've never seen one so far out on surface runout to cause dis/engagement issues, but it could happen.



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[QUOTE="QUICK-SILVER";6457711]Any chance the splines on the pilot shaft are bottoming out against the pilot bushing?

I considered this too. I put grease on the nose of the input before installing the trans as always. It was dark moly lube type. When I took the trans out yesterday I looked at it and there was a "ring" of grease about midway or maybe a little further up towards the trans on the nose which told me it was not jammed all the way into the pilot bushing. I also test fit the bushing on the input nose to make sure it was not tight and when I drove it in I made sure it was in as far as it could go. It was flush with the hole in the crank.



Could it be so uneven that it won't allow gear engagement? I guess anything is possible because it is an offshore made part. Do you think your issue could have been the first clutch you were using and went away with the replacement and not really a flywheel prob?
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[QUOTE=abefromen;6457741]
With mine, I could put the trans in 1st gear, but had to be VERY forceful with it. With engine not running it went to 1st easily. Reverse grinded everytime.

The machinist said that the flywheel was one of the worst he ever saw, and it was a brand name Hays, so yes, an offshore flywheel could be an issue. For nearly two years I tried everything to fix the issue. Had the trans out several times, different height throw-out bearings, forks, linkage, etc. Tried anything to get more of a disengagement, and I did get more, but it was never enough to fully cure the problem. I did use a different clutch/pp, but the issue was the flywheel. The original clutch/pp went into a different car soon after and had no issues.

Now I'm not going to say that the flywheel is definitely your problem, but just pointing out that you shouldn't overlook it.

Since it's all apart and staring me in the face I'll take it off and have it checked. Thanx for that suggestion.

pull the pressure plate off and inspect the disc and parts

You can lay a straight edge across the face of the flywheel at different points, use a feeler gauge to check runout.


EDIT: Same with the pressure plate too
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[QUOTE=Singleton;6457747]Just to say it out loud, you should always shift into 1st before you go into reverse, reverse is not synchronized.

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[QUOTE=HWYSTR455;6457786]Definitely, but if the input shaft starts turning again after going to 1st because of a partially engaged clutch disc, it's still going to grind in rev.

[QUOTE=HWYSTR455;6457786]I remember a service bulletin regarding the grinding going into reverse. GM pretty much said it was normal and the trans needed "spin down time" after going from a forward gear to reverse to avoid gear clash.

My reverse gear and reverse idler were in surprisingly good shape. Trans is original to the car with 104K on it. I've seen some on Muncies ans ST10's that were really chewed.

UPDATE:

Took the flywheel into a shop Friday and explained the situation. He checked it out and said it was a little wavy but nothing that would cause a clutch to hang up. I had it resurfaced anyway.

The problem turned out to be pilot error. Literally.

The pilot needed to be driven in a bit more than it was because it was contacting the input and turning it when the engine was running. I was more diligent when shoving the trans in this time and noticed it wasn't quite flush with the bell. Removed the bell & clutch and tried putting trans in with just the bell. No go...........took my bearing driver and hammer and banged the bushing in past flush. Test fit again and trans was flush with bell this time. I was surprised how close the tolerance was with this sbc.

Kinda odd because it felt solid to me when I hammered it in originally. I thought I hit bottom and that was it. It was also flush with the hole in the crank which is as far as I ever put a pilot bearing/bushing in any Pontiac engine I ever did before.

Thanks for all the help. :beerchug: