Help! C3 '81 with wrong clutch fork pivot ball

[clive d.]

This 81 has bellhousing 464697 ( inside says [621] ). Am renewing clutch, P/P and fork. The fork pivot stud that is in it is 1 3/8 tall, and the parts suppliers say I need a 1 1/2 tall pivot. GM Corvette Repair Manual indicates a difference between L48 and L82 applications. This car is one of the first cars built at Bowling Green (per VIN). In '81 there was only one engine, L-81. Clutch Diameter is 11". Car has 90k miles and I believe this the original clutch and pressure plate. How can this be ????
According to GM Corvette Parts Book, the 1 3/8 was only used in 1975.
I don't want to take trans out a second time. Anybody know about this ?

 

[bill81vette]

1st welcome to CAC!!!!
2nd, is your clutch slipping or are you looking to just change the clutch????as far as what size the pivot ball was,our resident engineers would have to chime in as to what will work.
if there is only one size available,I don't see why you can't adjust for it.

 

[clive d.]

1st welcome to CAC!!!!
2nd, is your clutch slipping or are you looking to just change the clutch????as far as what size the pivot ball was,our resident engineers would have to chime in as to what will work.
if there is only one size available,I don't see why you can't adjust for it.

This is a clutch and P/P replace, no failure of any kind preceding. Extreme wear on ball end of stud. SEVERE wear on fork tips from pressing on t/o bearing. Fork spring that retains t/o bearing is broken off one side. Same spring that captures the ball end of stud is broken off (one of the two tabs). Could the wrong ball have caused this damage ? How do I get an engineer to look into this ? Is there any documented history that this short pivot was used on this application in 1981 ? There is no evidence that any previous owners have dis assembled this clutch/pr.plt/bellhousing in the past 30 years.

 

[SVO]

If this clutch pivot ball was in use before you removed the old clutch set-up, and if you didn't have clutch engagement issues outside of wear, and if your replacement clutch parts were replacement in kind, then you shouldn't have issues that couldn't be adjusted out. Since you seem to indicate that it's all back together, try it and see if it works properly.

If the new clutch ass'y, bell and transmission is already installed, may I ask why, at this late point in the project, are you concerned about the pivot ball height? Just curious why you would be throwing the red flag at this point.

 

[bill81vette]

We have on this forum,several VERY knowledgeable people who were involved in the build of corvettes at one time in their life!!!!

 

[bill81vette]

I have to agree with SVO,
and I was wondering to myself when I 1st read your original post,if this could be adjusted thru the linkage...
I do wonder however.if the wear on the parts in question,are from some one at some point in the vettes life,if some one didn't constantly ride the clutch?????

 

[2VettesMike]

Having gone down part of this road before a couple of comments/suggestions:

The factory pivot ball isn't adjustable in terms of length, some aftermarket are adjustable.

As long as the flywheel isn't turned to make it thinner and renew the clutch surface a replacement pivot the same length as the original should do fine.

The reason to my understanding for more than one length GM pivot ball is to correct clutch geometry when either the flywheel is resurfaced or aftermarket clutch/PP assy's or both are used.

For example if the flywheel is thinner from being turned you can run out of clutch rod adjustment before you get full engage/release of the clutch.

Good luck, hope this helps.

Mike

 

[SVO]

If the clutch fork pivot ball is badly worn, it should be replaced. If it is a 1 3 /8" high pivot ball, I'd replace it with another 1 3/8" pivot ball. The damage to the clutch fork you describe sounds like normal wear and tear on a high mileage fork. If the tips of the fork is badly worn, it should be replaced with a new proper Corvette fork. As far as the wrong pivot ball causing all this damage, I would say that is highly unlikely. Also, keep in mind you can get T.O. bearings in different heights to help get the correct linkage geometry.

 

[JohnZ]

The #3729000 clutch fork pivot ball was released initially in 1957 for Corvette usage, and Services every Corvette application through 1981; the shorter one wasn't released, cancelled and replaced in the same year by the #3729000 because it worked just as well. If the rest of the linkage parts are correct and installed properly (including the 1-1/4" throwout bearing), the 1.48" pivot ball will work just fine.