Balky Clutch

[JJames]

When I press the clutch pedal, the clutch disengages and all shifting is smooth, unless I push the clutch pedal down the last inch or two, at which point it partially re-engages and shifting is either impossible or noisy (ouch).

It is a new slave and a two year old wilwood master. Replaced the old slave because it was leaking.

Never had this problem with the old slave cylinder.

Any thoughts?

 

[fastfrontier17]

When I press the clutch pedal, the clutch disengages and all shifting is smooth, unless I push the clutch pedal down the last inch or two, at which point it partially re-engages and shifting is either impossible or noisy (ouch).

It is a new slave and a two year old wilwood master. Replaced the old slave because it was leaking.

Never had this problem with the old slave cylinder.

Any thoughts?

How old is the clutch and did this start recently, or since installed?

 

[JJames]

Clutch is six months old. This started with the new slave cylinder.

 

[fastfrontier17]

Clutch is six months old. This started with the new slave cylinder.

Sounds like you might need to bleed the system. Just my $0.02.

 

[jumpinjan]

Did you see any fluid leaks? Test the slave while parked, and push the pedal down to the floor a few times. Look for leaks
Jan

 

[hartmandm]

Have a helper do the clutch pedal and you go under the car and see what is happening during that last couple of inches of clutch pedal travel. Is the clutch slave arm continuing to extend farther, or is it retracting?

Mike

 

[PETER CLAYTON]

Does the new slave cylinder have the same bore size as the original? If it is a smaller diameter then throw may be excessive causing the clutch fingers to "overthrow" which could allow the pressure plate to partially retract an cause the drive plate to drag.

 

[JJames]

Thanks to all. It appears to be sorted.
1. Bled system again, no improvement.
2. When the pedal is pressed to the bottom the slave continues to extend.
3. The master in use is the Wilwood 260-2636, 5/8" bore.

It appears that the new slave is more robust, or just operates properly and when it was put in place with the Wilwood that was installed two years ago, it was pushing past the point of clutch disengagement and 'cramming' the whole works forward so that the clutch was partially re-engaging. I tested this by jacking up one rear wheel and moving the clutch pedal down in increments and then checking for free wheel spin with the car in gear. About 2" from the bottom, I had free spin and then it tightened up after that.

The resolution was to do some geometry and determine that the Wilwood push rod had to be shortened about 3/8" to lower the pedal and put full pedal extension in the sweet spot for disengagement.

It appears to be working!

Thanks again to all who chipped in.

 

[jumpinjan]

Here are my old release-arm photos that I post now & then. It gives one the idea of where the arm & slave rod should be & length.
Jan

 

[Tim R]

It sounds like you have got it sorted now but we had EXACTLY the same problem on my son's Series V. We tried multiple slave cylinders, repeated bleeding of the system, numerous pushrods (including an adjustable one) until we finally tracked down the problem.

It was that the centre bearing in the clutch plate was too big (too long by about ⅜" compared to the previous one).
When you put your foot right down the bearing gets pushed as it is meant to be to free the clutch to spin but because it is physically too long the actual bearing edge hits the driven plate (see wear marks in photo) which is why it then feels like it isn't disengaged. I did have all the exact measurements and how to cure this recorded but when our old website crashed that data was lost.
It sounds like you have cured the problem yourself but when you have it apart again I would check the length of the centre bearing against another one. If it is too long it will foul when you push the pedal right down. You may be able to see shiny rubbing marks on your own driven plate when you take it apart.
Good Luck,
Tim R

 

[JJames]

Thanks, I will do that.

Jumpingjan. Nice pictures. Where did the adjustable slave push rod come from?

 

[Jay Laifman]

It sounds like you have got it sorted now but we had EXACTLY the same problem on my son's Series V. We tried multiple slave cylinders, repeated bleeding of the system, numerous pushrods (including an adjustable one) until we finally tracked down the problem.

It was that the centre bearing in the clutch plate was too big (too long by about ⅜" compared to the previous one).
When you put your foot right down the bearing gets pushed as it is meant to be to free the clutch to spin but because it is physically too long the actual bearing edge hits the driven plate (see wear marks in photo) which is why it then feels like it isn't disengaged. I did have all the exact measurements and how to cure this recorded but when our old website crashed that data was lost.
It sounds like you have cured the problem yourself but when you have it apart again I would check the length of the centre bearing against another one. If it is too long it will foul when you push the pedal right down. You may be able to see shiny rubbing marks on your own driven plate when you take it apart.
Good Luck,
Tim R

I don't know if it is the same here, I suspect it is. In the Porsche 356/912 world, the clutch fingers get pushed in to release the clutch plate. The fingers push along a pivot point. When the fingers are pushed flat, the clutch is pulled back and the clutch plate can spin. If the fingers are pushed BEYOND flat, it starts pushing the clutch back in again. So the key with adjusting those 356/912 clutches is to feel where the clutch pedal goes "over center" and adjust the clutch cable length.

I'm assuming it is the same thing here. The clutches on our cars had various pieces that were not exactly the same through the years. This includes the pedestal for the throw out bearing, the arm for the TOB, and the bell housings. When mixing the parts, things like this will happen.