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Clutch Trouble

1K views 12 replies 4 participants last post by  V8CarreraGTS 
#1 ·
First about my car..
Porsche 944 with a 302 Chevy using a 19# steel flywheel; stock HP Camaro pressure plate (10.4") a Chrysler spring center disc (because I need 1" x 23 spline) a McCleod 1300 series bolt on throw out bearing mounted on an adapter plate that is attached to a Chevy steel scatter shield that adapts the Porsche torque tube to the transaxle. I am using the stock pedal and clutch master cylinder (3/4" bore) with a pedal stop to give me about 1/2" travel at the clutch. The pedal ratio is 5:1.

The problem. The clutch pedal feels perfect with the engine off both down and up. With the engine running pushing the pedal down is good but letting it up it feels like it has binding linkage although it is hydraulic. It is so bad it makes it difficult to drive. The stock pedal has an additional spring much like later model Corvettes that is suppose to help pedal feel and help make the pedal snap completely up. I have adjusted this spring to the point of keeping the pedal down to almost having no force and it doesn't make any difference.

I originally had a Speedway Motors pressure plate but engagement was harsh. I think that it was this problem causing it. But being this PP has so much more spring force it was not easy to feel it.

I have maybe 30 miles on the car since I got it running so nothing is worn out. I just had it all apart again last weekend and I couldn't find anything wrong but it still does it. I can't figure out how it can be perfect without the engine running but terrible with the engine running.

Anyone hear of anything like this?
 
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#4 ·
Could be a problem with throwout bearing, pressure plate mismatch.


The area of the fingers of the pressure plate, that the throwout bearing come in contact with, need to have an arc , or a curve to assist in smooth engagement as the fingers are moved closer to or farther from the flywheel as the clutch is being applied or released . Either the fingers need to have an arc or the bearing face needs to be cone shaped (to form same arc)
If both are flat, this could cause a weird engagement issue with engine running as the engagement would be "abrupt".


Also, the disc could be a problem as it may have "crush" built in and with a Hi Po setup, you may not want that.
"Crush" is built into a disc by using a steel frame for mounting the friction material on , that is wavy, or Bellville shaped, so that as it is crushed between the pressure plate and flywheel , it allows some movement of the clutch pedal before the disc is completely flattened out. This gives the disc a little wiggle room to slip before the clutch pedal is let all the way out as it will slip but still have usable torque before it is completely flattened out.
The Bellville shape frame plate provides spring tension in between the friction material, and as the clutch is applied, this gives the clutch a sifter gentler feel while applying.
 
#5 ·
Yes, I understand how the t/o bearing contacts the pressure plate and how the disc works. The disk is also a HP disc with small damper springs so it fits the flywheel. Both parts are factory OEM type units. The TO bearing is contacting the diaphragm properly and I have watched the contact throughout the travel -- only not with the engine running.

Being a Mechanical Engineer these are relatively simple concepts.

First I thought that I was pushing the diaphragm over center so i adjusted it just enough to disengage the disc. It felt good at first but after I backed the car out of the garage it had the same problem.

I'm wondering if I have a problem with the t/o bearing when it retracts. I should have taken it out and disassembled it.

I remember my first car, 1964 GTO had this type of problem when I first drove it and that turned out to be the trans bearing retainer being worn and rusty. But this, being hydraulic, doesn't have that set-up. But maybe it is damaged inside, but I still cannot figure out why it is different with the engine off VS running.
 
#7 ·
The T/O bearing incorporates the bearing retainer and T/O bearing support.
I think the problem wasn't noticeable with the Speedway Motors PP because of the significantly higher clamping pressure. (much higher pedal effort than the OEM Camaro one)

I changed the PP because after I bought the Speedway Motors PP the clutch chattered a lot. And when I called Speedway Motors they ended up telling me that this PP could cause this because of the way it engages. I'm thinking that the chattering was caused by this problem.

 
#10 ·
I need to check the lines. I was thinking today that maybe the line is being kinked when the engine is running, I doubt it but I need to look. I have a -4 braided line from the master to the slave and nowhere for a restriction.

I have already googled the bearing and read through pages and pages of forums but haven't found this problem. Mostly everything is about leaks.
 
#13 ·
I took a closer look today. I had one of my sons push the clutch pedal with the engine off and running and I initially didn't see anything. But after running it the last time and shutting it off this is what I saw. (see below) It never stopped where i could see this. Look at the diaphragm fingers in relation to the bearing. I see that I have a bad pressure plate. Now I need to take it apart and swap out pressure plated to find out if this is the cause.

 
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