ZF clutch pedal pressure?

[Allen English]

I need some help. After driving my car about 30 miles yesterday the clutch pedal got real stiff and at one point I could barley get the thing to push in. RCR built my car so I don't know much about the system, but I am thinking we have air in the system? At this point the car is near undrivable because of this problem. Any advice would be appreciated.

We have the external slave cylinder set up.

 

[Eric]

Hello Alan,

I had a very similar issue on my CAV with the ZF Transaxle.

The clutch pedal would get rock hard after the car warmed.
I could not drive it due to the lack of clutch action.
Please keep in mind that my car was four years old and not recently
constructed as yours is.

I called Ian at CAV Canada and he was spot in with his diagnosis.
He said that the ZF output may not be centered into the
pilot bearing/bushing on the back of the crank.

After replacing the external slave, bleeding, and much frustration
I removed the ZF unit and found that the throwout bearing
was almost frozen on the output shaft of the ZF unit and the
throwout was burned a blue steel color. Ian was correct.

I replaced the output shaft and the throwout and then machined the bellhousing so it was flat on both sides centered the bellhousing on the engine with a dial indicator and offset dowel pins.

After re-assembly with a new clutch disc and bronze pilot bushing all has been operating well.

I am not saying that this is your issue and I hope it is not your issue but it certainly was mine.

Please keep me informed because I hope that ypur clutch issue
has a much easier cause and solution.

I can E. Mail pics of the work and parts if you are interested.

Eric

 

[Eric]

Hi Allen,

Two things.

#1) Sorry for spelling your name wrong.

#2) Maybe I was not clear. My ZF output was secure into the pilot bushing but the issue was that the bellhousing/ZF unit was not aligned
properly with the back of the engine. This caused excessive friction
on the throwout bearing/clutch which was corrected after proper centering and alignment...


Regards, Eric

 

[Tom]

Eric,
Do you mean to say the ZF's input shaft?

I better add this to my list of 'things to check' on mine.

Tom

 

[Allen English]

Hi Eric,

Yes it seems after disconnecting the slave cyl. I was able to move the clutch pedal with ease as I expected. I went to the trans and tried to move the lever on the clutch shaft, but it was not going anywhere.

Please send pictures if you can. I am really bummed if this is the problem.

 

[Eric]

Gulf

Hello Tom,

Maybe input shaft?

There is a sleeve around the shaft on the front of ZF that throwout
rides on. It was burned from heat as well as was the throwout
so both were actually replaced prior to reinstall of the the Zf unit.

Difficult to check unless you seperate the ZF from the bellhousing/engine.

Eric

CAV GT #105
07 Corvette
69 Camaro

 

[Eric]

Hi Allen,

I doubt that you will be able to move any clutch linkage by hand
even if all was good. Takes a bit of pressure with assist.

Can RCR give you some advise regarding this issue?

I will send some pics through your regular e mail because I have not
yet figured out out to post pics on this site.

Eric

 

[Mike Drew]

Randy Grubb (CAV owner) told me a couple of weeks ago that his CAV bellhousing was defective from new, and machined improperly so that the ZF input shaft was not centered on the pilot bearing in the back of the crank! He thought to check it before installing it and found it was grossly off, not something I ever would have thought to check. He had to completely remake the thing.

Sounds like that's your problem too. :cry:

 

[Allen English]

Since I unhooked the slave from the transaxle and the pedal moves freely that would prove the problem is in the bell housing. Am I correct?

 

[Randy V]

Is this a condition that manifests itself with heat?

In other words - when everything is all cooled down, does the heavy pressure seem to be the same or less?

 

[Allen English]

I'm not sure Randy.

Maybe heat was what started this to happen, but thats hard to say for sure. Right now the pressure is pretty hard and it did seem to be worse about 15 miles into the drive. Since the cool down I would say the pressure is slightly less.

 

[Jim Rosenthal]

It does sound like a centering problem, but wasn't your car assembled at RCR? Unlikely Fran would let something like that get out, if he knew of it. They are very careful at RCR.

 

[Allen English]

Fran, is working with me on this. They didn't drive my car so there is really no way Fran could have known there was a clutch issue.

All is good... (-:

 

[Ian Clark]

Allen, the symptoms and effect of disconnecting the master indicate the kind of issue experienced with an off center bellhousing. I'm fairly certain that will become evident after pulling the drivetrain and separating the engine transaxle.

We've had our run of it with bell housings machined to tolerances that don't ensure concentric assembly. This is not a unique problem as offset dowel pins are readily available to correct the run out. The offset dowel pins originated with the steel "explosion proof" bell housing required in drag racing I believe.

So we ALWAYS trial fit and check the bellhousings for run out before final assembly no matter who made the bell housing or adaptor. This has been covered in depth in an old posting of mine years ago, maybe I can find it and resurrect it here, important info.

Cheers

 

[Allen English]

Hi Ian,

I have the car back together now. The bellhousing run-out checked OK. I drove the car about 10 miles the other day and everything seems to be working good with the clutch now.