'81 4 spd. I bought last Sept. came with a Centerforce clutch. Very heavy pedal effort. Centerforce tech said geometry was off. Just took it all apart and measured- Pivot ball in there was too short by 1/8". Calculations came out to needing exactly GM short ball stud height. Flywheel is stock thickness. The stud I took out was shorter than the GM short stud (by 1/8"). So only thing I changed was the ball stud.

Thought I found the problem till I got the bellhousing back on tonight to check the pedal effort. Couldn't get the linkage to the fork to line up- the linkage was overshooting the fork by about an inch. Tried to adjust it out at the clutch pedal rod, but I had to spin the nut so far up the rod, the clutch pedal was near the floor by the time I had it all hooked up and that was a worthless setup.

Now I'm stumped. Thought maybe the clutch plate was higher than stock moving the throwout bearing rearward and pivoting the fork linkage point forward so it wouldn't line up with the linkage. But a different Centerforce clutch I have laying around that worked fine in my '71 is actually higher by 1/4". It seems to me putting in that clutch would actually make the problem even worse.

Far as I can tell, it has the original bellhousing, fork, flywheel and linkage. Anyone know if there's any difference in those parts between a '71 and an '81? Ideas?

 

See if this gives a clue.
Click this open and look at post #9:

http://forums.corvetteforum.com/c3-t...-question.html

I wouldn't expect any dimensional differences in the geometry. The frames under our C3's are near the same, throughout the generation.

Good luck.

 

Don't overlook the throwout bearing...there are different lengths for different pressure plates. The wrong one could be causing your geometry problems.

 

The link you gave me should get me straightened out. I've eliminated the bearing, but still need to check the z bar and fork to make sure they aren't bent. Thanks.

 

I did change the ball stud to the stock short stud (needed 1/8" longer) 'cause that's what my measurements came out to. Problem solved, right? When I put it back together, the clutch rod was now overshooting the fork by about an inch! Trying to adjust that out only made the clutch go to the floor.

Zbar and fork are perfectly straight. Ready to tear my hair out again, when I thought the ONLY thing I haven't checked is the clutch rod. But what could be wrong with that? Jacked up my '71 to measure that one that I know is stock and works perfectly and amazingly that rod is 1 1/4" SHORTER! And there is only one size for all those years.

Looks the like the paid professional idiots that put this together for the P.O. put in the wrong stud, then when the linkage wouldn't go together, they dug up a longer clutch rod. "There, it fits" like the idiots in that commercial pounding wooden blocks around the battery to make it fit. But why do I have to stand on the clutch to change gears? "It's a high performance clutch- yeah..... that's the ticket!"

Also realized these morons ruined the zbar and charged the owners to do it. (I have the receipts) Dawned on me today why it looks different. They apparently couldn't figure out where the return spring was supposed to go- so they pulled the zirk fitting and shoved a piece of metal rod into the hole and welded it with the worst weld I've ever seen- all to make a place to attach the spring and the other end goes to a bolt on the steering box!

Looks like I'm finally home free- at least when Wilcox gets the new rod to me. Thanks for all the help.