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Discussion Starter #1 (Edited)
I have a 57 Corvette which has just undergone a complete restoration . It has had a (new flywheel from Summit Racing ) and clutch kit installed and it was so rough starting out that I tore it down and replaced the clutch kit with a more expensive McCleod clutch kit . The second clutch kit still did the same thing but it was with the same new flywheel so I started to suspect that the flywheel was defective since there were hot burn marks on one half of the flywheel and pressure plate so I took it to the machine shop and had it checked and refaced but when I put it back in and tried to drive it the same problem existed . I have done everything that I can think of including new engine and trans mounts , checked all clutch linkages , checked to make sure the throw out bearing is not binding , universal joints , etc . Everything checks out good . Now my question : I have a posi rear end and it was making a shutter going around turns so I changed the gear oil and put in the additive for posi but no work was done to the rear end during restoration and I can hear a bumping noise when I back up . Could there be a problem with the posi unit in the rear end making it seem like clutch shutter ? I can't see how there could still be a problem with the clutch . It drives smooth when driving down the road and shifting while moving . It just wants to shake the car apart when starting out . I even thought about an engine balance problem but the engine runs smooth . I've been working on cars for over 50 years and never saw anything like this problem . Any help would be appreciated .
 

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I've owned several GM cars from the 50s and 60s with manual transmissions and never had this problem so a quick search of the internet (below) found a list of things to check.....

Hope you find the problem quickly and cheaply!



Diagnosis of Clutch Chatter
Clutch chatter is best described as a stutter or vibration as the clutch is released. It is most noticable when starting out from a complete stop. Clutch chatter is the most difficult clutch problem to diagnose and repair. Some clutch chatter problems can be caused by a clutch problem, but often the problem is caused by something other than the clutch.

Clutch related Chatter problems
Disc

Clutch Disc related Contamination: Oil on the disc from an engine or transmission leak
Torsion Spring Escaped: usually caused by “popping” the clutch or attempting to push start the car
Pressure Plate Distorted

Pressure Plate Related Warped friction plate: Usually due to excessive heat build up. Can be caused by excessively slipping the clutch
Warped Diaphram Spring: Defective part
Uneven Coil Spring Pressures: Defective part. Very few of this style clutch made today
Release Bearing

Release Bearing Related Damaged or Worn Release Bearing: Usually on very high mileage cars, or can result from extended operation with a defective pressure plate
Grooved release bearing guide
Worn bearing retainer
Pilot Bearing Related Damaged or Missing Pilot Bearing: Part failure

Warped Flywheel: Caused by excessive heat build up. Can be caused by excessively slipping the clutch, or overloading the vehicle. Flywheel may have to be replaced or resurfaced

Actuator Related
Worn Slave Cylinder

Binding Master Cylinder

Worn or Broken Pedal Bracket

Binding Cable

Worn Linkage

Engine Related
Broken Motor Mounts

Worn Thrust Bearing: Excessive crankshaft end play

Poor Engine Performance:Tune Up

Torn Air Flow Tube

Transmission Related
Broken Transmission Mounts

Worn Input Shaft

Worn Input Shaft Bearing:Excessive play

Misalignment:alignment dowel missing or Bolts could be broken or missing

Chassis Related
Worn Shocks/Struts

Worn U-joint or CV Joint

Defective Differential
 

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Discussion Starter #3
I've owned several GM cars from the 50s and 60s with manual transmissions and never had this problem so a quick search of the internet (below) found a list of things to check.....

Hope you find the problem quickly and cheaply!



Diagnosis of Clutch Chatter
Clutch chatter is best described as a stutter or vibration as the clutch is released. It is most noticable when starting out from a complete stop. Clutch chatter is the most difficult clutch problem to diagnose and repair. Some clutch chatter problems can be caused by a clutch problem, but often the problem is caused by something other than the clutch.

Clutch related Chatter problems
Disc

Clutch Disc related Contamination: Oil on the disc from an engine or transmission leak
Torsion Spring Escaped: usually caused by “popping” the clutch or attempting to push start the car
Pressure Plate Distorted

Pressure Plate Related Warped friction plate: Usually due to excessive heat build up. Can be caused by excessively slipping the clutch
Warped Diaphram Spring: Defective part
Uneven Coil Spring Pressures: Defective part. Very few of this style clutch made today
Release Bearing

Release Bearing Related Damaged or Worn Release Bearing: Usually on very high mileage cars, or can result from extended operation with a defective pressure plate
Grooved release bearing guide
Worn bearing retainer
Pilot Bearing Related Damaged or Missing Pilot Bearing: Part failure

Warped Flywheel: Caused by excessive heat build up. Can be caused by excessively slipping the clutch, or overloading the vehicle. Flywheel may have to be replaced or resurfaced

Actuator Related
Worn Slave Cylinder

Binding Master Cylinder

Worn or Broken Pedal Bracket

Binding Cable

Worn Linkage

Engine Related
Broken Motor Mounts

Worn Thrust Bearing: Excessive crankshaft end play

Poor Engine Performance:Tune Up

Torn Air Flow Tube

Transmission Related
Broken Transmission Mounts

Worn Input Shaft

Worn Input Shaft Bearing:Excessive play

Misalignment:alignment dowel missing or Bolts could be broken or missing

Chassis Related
Worn Shocks/Struts

Worn U-joint or CV Joint

Defective Differential
Thanks for responding . That is a long list and I have gone through all of those except for the last one " Rear Differential " . I need to know if the bumping noise that I am hearing when I back up could be caused by something wrong with the posi unit and in turn acting like a clutch problem .
 

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If you have never been into the posi unit, it would be my next place to look. Those original in 57 have different plates and friction material in them than the newer ones and require a special additive= real whale oil. This is no longer available so the posi may be locked up tight.

DZAUTO on this site is the guy. Tom that knows these posi units inside out and backwards from 57 up. He's your man to consult.

Mikey
 

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First of all, since the next step is to tear into the posi ----------------------- DON'T ------------------ yet!!!!!
Locate another rearend center section, ANY gear ratio, preferably a NON-posi center section, and install it and drive it.
If the chatter still exists --------------------- THEN IT AIN'T THE POSI!!!!!

From everything you have mentioned, it sounds like it is in the area of the flywheel/clutch. BUUUUUUUUUUUUT, without being able to drive it and put my hands on it, there is no way that I can really diagnose the problem accurately.
If you want to bring it to me, I'll be happy to try to determine what is going on with it.
 

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I agree here. Clutch chatter and related issues that might seem like clutch chatter are among the most difficult things to diagnose over the internet. Especially since you've already replaced the clutch and flywheel.

I think your best bet now is to seek out some different eyes/ears to look at the problem.
 

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Discussion Starter #8
Which specific Mcleod clutch and pressure plate are you currently using?
I bought it through Summit Racing , their part# is MCL-75117 price $257.14 but keep in mind it did the same thing with the first clutch kit which was a different brand .
 

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Discussion Starter #9
First of all, since the next step is to tear into the posi ----------------------- DON'T ------------------ yet!!!!!
Locate another rearend center section, ANY gear ratio, preferably a NON-posi center section, and install it and drive it.
If the chatter still exists --------------------- THEN IT AIN'T THE POSI!!!!!

From everything you have mentioned, it sounds like it is in the area of the flywheel/clutch. BUUUUUUUUUUUUT, without being able to drive it and put my hands on it, there is no way that I can really diagnose the problem accurately.
If you want to bring it to me, I'll be happy to try to determine what is going on with it.
Hi Tom , I know that you are also a member of the Corvette forum and I have explained the problem on there with no answer to the problem . This is really an unusual problem that I have never seen before with over 50 years of working on GM cars and hundreds of clutches over my lifetime . I have checked everything clutch related besides all of the clutch related parts being new with no logical reason that it won't work . That's why I am looking at the rear since it is the only thing left and it does have a thumping noise like something binding and the clutch shudder is the worst backing up . I do have a spare 1960 non posi rear end that I can change but their is definitely something wrong in the one in the car .
 

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I looked it up, Decent street unit. Bell housing alignment? I know it’s coming off of a restoration, any chance the bell housing mounts are defective or loose?
 

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Discussion Starter #12
I looked it up, Decent street unit. Bell housing alignment? I know it’s coming off of a restoration, any chance the bell housing mounts are defective or loose?
Funny that you should bring up the bell housing . This morning I went to talk to a local drive line specialist ( drive lines are all he does and he has a great reputation ) and he spent a lot of time going over with me everything that has been done and he suspects that it is a warped bell housing. He doesn't like the idea of having the bell housing machined because it changes other specs like the depth of the input shaft. He recommended just buying a good used one . 55-57 passenger cars are the same and inexpensive so that will be my next move . I will keep you posted.
 

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To me, blaming the bellhousing is a stretch. The bellhousing alignment affects the transmission, not the clutch.
 

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Depends. Sometimes the bell is not facially aligned to the block. That being said, the only times I have had this is with a scattersheild. Made the trans a little crooked and clutch chatter when only part of the outside face of one side grabbed. Had a heck of a time sorting that one out. Joe, Sr. At hr clutch in Bensalem figured it out when we brought the clutch up to have him rebuild it. Had to shim the bell parallel to the block, then realign back to center.
 

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Discussion Starter #17
Warped maybe, but if the bell you used was not the bell that was originally installed to the block you are using, it may be out of alignment, meaning it’s not centered to the crank. There is a tool that makes the job easier then it use to be, and you use off set dowels to bring it into alignment.

http://www.colemanracing.com/Alignment-Tool-Bellhousing-P4573.aspx
Just found out today when I went to pick up a used bell housing that I have the wrong bell housing on my 57. Mine is aluminum without the provisions for lower bell mounts and the one that I got is cast iron with mount provisions .I bought it from a fifties junkyard that has a lot of early chevy and corvette parts and the owner has a lot of old corvettes and knows them well . He said that the aluminum bell that I have is for 60-62 corvette and mine uses the cast iron. He also said to use the dial indicators to check it and mentioned the offset dowels .
 

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So how did you have the transmission or bellhousing mounted with the aluminum bellhousing? It won't necessarily make a difference unless the mounting scheme was poor. Stock bellhousings are usually at least fair for runout, unlike aftermarket stuff. But given your problems it certainly won't hurt to measure and correct as needed. Likewise it's unusual to have parallelism problems, although it can definitely happen.
 

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Flywheel bolted to the crank turn the motor over & dial indicate the flywheel it should run true. Had one that was machined improperly it was .040 out of true = clutch chatter.

Pilot bearing in the crank? is it worn out?

Check the trans front bearing retainer for wear from the throw out bearing.

Aluminum trans case? Check the trans to bell housing bolt "ears" many times they are broken off & welded on sometimes causing misalignment.

Your posi clunk during reverse: Rear tires may have different circumferences = the posi unloads when direction changes.
 
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