I am finishing a partial restoration of a 1969 L-36 427/390 with Muncie M-21 four speed. The engine and drivetrain were gone through prior to me picking it up, so I have no knowledge of what was done. I have questions on the clutch fork travel, it doesn't seem right to me, though this is my first Vette resto.

See photos below of max travel. Fork lever hits bell housing all the way forward and is not near parallel with flywheel all the way back. First question, what is the correct position?

I also attached photos of in front and back of the clutch fork. Is the position of the retracting springs relative to the clutch cover correct? If not, I guess I have to check if the correct flywheel, clutch disk, etc are in place to get the right stack height forward of the throw out bearing.

Other possibility is the clutch fork pivot ball is the wrong length. See photo.

Before I dive into this blind, any advice or photos to help out?

Thanks in advance!

 

Check the fly wheel thickness I had one once with a high performance steel flywheel that was 1/2'' thinner than stock had to use a Mr Gasket adjustable ball stud to get the fork travel right.
Mark

 

From what I can see from your pictures....

The clutch cover is not stock.

It is unlikely to be a thinner flywheel problem.... that would move the outer end of the clutch fork to the rear, and you could fix that with an adjustable clutch pivot.

It looks like you have a longer pivot stud installed already....
http://www.parts123.com/parts123/yb....0g~Z5Z5Z5GBCVJ
...the shorter one might fix this.
http://www.parts123.com/parts123/yb....0g~Z5Z5Z5GBEJC

Also there seems to be something not quite right with with the spring on the clutch fork around the pivot ball. The spring metal should be flat.
http://www.parts123.com/parts123/yb....0g~Z5Z5Z5AAHLW
In your photo the metal appears to be folded into a right angle. Worth checking out...perhaps not a vette part?

Hope this helps,

Joe

 

Hey Bobs69BB:

First thing I would do is go the the auto parts store and get a "medium" length release bearing. From your pictures I see you are using a "short" release bearing. I'm referring to the length of the collar. The short one you have has the groove for the release fork nearly at the back surface of the bearing. The medium one will have about a 3/8" shoulder before the groove itself.

Ask the parts guy to bring out a couple to look at. (there is a "long" on as well that has about a 5/8" long collar before the fork groove, but I doubt you'll need that).

It'll preclude having to get a longer stud. I had to do the exact same thing with my 68 BB/Muncie....

Make sure whatever bearing you use you have adequate release bearing clearance to the trans front bearing retainer with the clutch fully engaged..

P.S. If you are not sure you have all the clutch pieces installed properly, take it all apart and confirm....

Good luck

 

Hi rainmaninwa

Correct me if you think I'm wrong...

The "medium" release bearing you suggest will make the problem worse.

A longer pivot stud will make the problem worse.

The solution must be the opposite of what you suggest... shorter pivot stud or a clutch set up that has the clutch cover fingers closer to the flywheel.

(a thinner flywheel would also work)

Let me know what you think? I'm not an expert...just thinking of the geometry of the system.

BTW, if you move this post to Tech / Performance.... there are guys there that really know their stuff.


Joe

 

Hi Bobs69BB

On a closer look the clutch fork seems to be correct...so can probably eliminate the fork as a problem.


Joe

 

Bobs69BB:

I guess maybe I didn't totally understand the "problem" you are trying to address.

In any case, in my opinion, the important thing to ensure is that you have enough "throw" on the release arm to fully disengage the clutch driven disk with the clutch pedal "down", and at no locations do the aft edges of the release arm contact the bellhousing. When I look at your pictures, it concerns me because it seems like the fork is already in a "pedal slightly depressed" attitude (outboard end already aft a bit inboard end forward a bit) which is why I suggested the slightly longer release bearing.

Of secondary but similar importance is that with the clutch pedal "up", the clutch driven disk is fully clamped by the pressure plate, and the aft collar of the release bearing has some clearance remaining to the transmission front bearing retainer, so that the release bearing is totally unloaded. At no locations should the font surface of the release arm be contacting the bellhousing.

In addition, at rest with the clutch pedal "up" and the clutch engaged fully as explained above, try to ensure that the release fork fingers that engage the fwd shoulder of the release bearing groove rest more or less in the center of the rounded mating surfaces on the fork fingers.

You are not dealing with stock parts so you have to ensure that all these geometric paramaters are correct.

Basically, all I try for is to ensure that I get full release travel and get everything else centered up reasonably well. And, there is no way to know with the engine out of the car, where clutch pedal "up" or "down" is going to want to position the release arm, so Once it is in the car you'll have to adjust the clutch linkage to match.

 

What make clutch is it? Centerforce?


does this help? This isn't really about the clutch fork it that is your only problem.

 

Actually, I think I've misunderstood the problem.... I believed that the two photos were of the travel of the clutch fork when engaged and released. I see now that perhaps the photos are of the clutch fork free travel only.

If that is the case, then Rainmaninwa is 100% correct. Sorry about causing any confusion.


Joe

 

Thanks all! There seems to be enough going on here that I need to pull everything to check it out. I'll take more pix with it apart this weekend

 

The comment on the clutch not being stock and question if it is Centerforce got me looking, found this photo of a Centerforce below. Pretty sure the side view of mine is showing the Centerforce weights, so I'll assume it is until I pull it apart.

Those familar with Centerforce, is the clutch cover spring height different from stock, requiring to make up the difference in the TOB height or fork ball stud ?

 

I solved the problem I was having. Turns out the clutch is not the issue. I thought the angle of the clutch arm was too far forward when the TOB is touching the springs, but once I measured it is within the 5 - 7 degrees ahead of the flywheel plane (values I got from a Classic Motorsports clutch install guide). It certainly looked like a larger angle, which was deceiving. Also the fork arm is centered in the opening. So the geometry of the flywheel, clutch and ball stud all seem to be OK.

The real problem was a Bubba fix on the outside of the Z-bar. The Z-bar end was not located properly so the linkage was binding, which lead me down the wrong path. With the Z-bar properly seated, everything looks in order.

I guess I will find out for sure when I drop the body and hook up the pedal ...