Throw out bearing problem?

SmokinBBC

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Mar 25, 2008
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Oak Ridge, NC
I am getting a vibration in the clutch pedal when I start to push it in. Goes away when slightly depressed. Freeplay is currently 1/2 inch. I tried adjusting to less than 1/2 inch and the vibration is constant. More than 1/2 inch and the vibration is very similar to when freeplay is at 1/2.

Clutch has about 7k on it. Problem started about 500 miles ago. Zoom clutch with stock fork.

I am guessing that it is the throwout bearing is not going into the pressure plate smoothly. So how do I know for sure what the problem is. How long can it go this way?
 
Sounds like you found the solution. Found this of the net:



This description is from a 1969 Chassis Service Manual, that covers Chevrolet,Chevelle,Camaro,ChevyII/Nova and Corvette.

CLUTCH LINKAGE ADJUSTMENT
There is one linkage adjustment (clutch fork push rod or pedal push rod) to compensate for all normal clutch wear.
The clutch pedal should have free travel (measured at clutch pedal pad) before the throwout bearing engages the clutch diaphragm spring levers (Pressure plate fingers). Lash is required to prevent clutch slippage which would occur if the bearing was held against the fingers or to prevent the bearing from running continually until failure.

Chevrolet and Corvette

1. Disconnect spring (E) between clutch push rod and Cross Shaft Lever (z-bar)
2. With the clutch pedal against stop: loosen jam nuts sufficiently to allow the adjusting rod to move against the clutch fork until release bearing contacts the pressure plate fingers lightly.
3. Rotate upper nut (B) against swivel and back off 4-1/2 turns. Tighten lower nut (A) to lock swivel against nut (B).
4. Install return spring (E) and check clutch pedal free travel. Pedal free travel should be:
a. Chevrolet - 1" to 1-1/2"
b. Corvette (STD) - 1-1/4" to 2"
c. Corvette (HVY DTY) - 2" to 2-1/2"
 
Thats the same spec as the service manual. Hopefully that's it. I get pretty quick engagement now when letting off the clutch. Much sooner than before.
 
I've seen that happen-- if the fingers on the diaphragm are not even, the T/O bearing (obviously) hits the higher ones first. That can cause a vibration or chatter you can feel in the pedal.
 
I've seen that happen-- if the fingers on the diaphragm are not even, the T/O bearing (obviously) hits the higher ones first. That can cause a vibration or chatter you can feel in the pedal.

Hopefully it will be ok for a while. Clutch doesn't have many miles on it.
 
I've seen that happen-- if the fingers on the diaphragm are not even, the T/O bearing (obviously) hits the higher ones first. That can cause a vibration or chatter you can feel in the pedal.

Can bent fingers/binding throwout bearing cause the clutch not to engage?

I opened it up and shifted into second at about 5000rpm's. When I let off the clutch, it did not engage until I let the RPM's down to about 3k....then it acted like I dumped the clutch with heavy wheel spin. Did this 2x in a row. The clutch held firmly in first gear while accelerating.

The clutch works well during normal driving. I was able to shift at 5400k before. Something just ain't right in there. I don't have any oil/gear oil leaks.:confused:

Wonder if jumping on it is causing an alignment issue....like a busted motor mount?
 
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:shocking: Man O man....that goes back a few decades....the upper RPM's are hard on a diaphragm cultch, it don't wanna engage again....

something about centrifugal forces....

which I don't understand why other designs don't suffer the same shit....

:crap:
 
Back in Ol' Red's early days with the L-88 installed, I was cruising with the PO. The original diaphragm clutch stuck to the floor somewhere close to 8000 RPM. 3 things happened. He got a new clutch, the original didn't work quite right anymore, a Lakewood bellhousing was installed, and the factory 30 pound flywheel was swapped for the factory 12 pound on.

When we pulled that original clutch the fingers looked like the wave- all over the place.
 
Back in Ol' Red's early days with the L-88 installed, I was cruising with the PO. The original diaphragm clutch stuck to the floor somewhere close to 8000 RPM. 3 things happened. He got a new clutch, the original didn't work quite right anymore, a Lakewood bellhousing was installed, and the factory 30 pound flywheel was swapped for the factory 12 pound on.

When we pulled that original clutch the fingers looked like the wave- all over the place.


8000rpm would be enough to scare me into a scatter shield. That baby must rip!

I am thinking new clutch. I don't think a lakewood is in my future. She rarely sees 5500+ with my hyd roller lifters. Maybe time to replace my 33#(?) flywheel with a much lighter aluminum one. Wonder how the BB would respond to that...puts out 530+ tqe at 3700. I think the heavier flywheel gives more energy to propel the drivetrain during deceleration.
 
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The lighter 'wheel will let it wind faster (less inertia) and make it more difficult to get rolling. The real benefit is it winds like a SBC. The LS-7 winds really good, but I still have to play footsie with the clutch to get rolling. It's either launch it hard and burn tires or slip the clutch.

The L-88 was a crate motor from GM that was installed after the original L-89 spun a main bearing. warranty thing in '71. And it really was bad azz. Showed tailend lights to every one of the muscle cars of the day. PO said the only one he got a little worried about was a Hemi Cuda, and it turned out to be no deal.
I've had the LS-7 above 6000 a couple of times- it just keeps pulling. :yahoo:
 
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