Clutch Adjustment Oddity

[RLJ]

Can’t figure this one out. 1972 510 with an L20b and a Z five speed. Clutch master cylinder and slave cylinder are relatively new. 
 

Has slave cylinder with the adjustable rod. Will adjust the clutch rod per service manual and everything works fine. After driving about ten to fifteen miles the clutch goes out of adjustment and disengages too much. You can hear it on the diaphragm fingers and shifting will become stiff.  After this happens if you don’t push the clutch all the way to the floor the noise will go away and shifting will be fine. 
Will readjust the slave cylinder rod shortening it and it will be correct. Lasts for a while then the same thing will happen and have to shorten the rod more. Have done this a few times now and still repeats. 
 

Am I doing something wrong with the adjustment? Did it per the service manual. It seems like the rod length increases (it doesn’t, lock nut for adjustment is tight) or the hydraulics start increasing like the slave piston is now in a different place. 

 

The clutch seems fine. Thinking it’s more of a hydraulics issue but can’t figure out what. 
 

Any ideas?

 

[datzenmike]

Check that there is 1/16" of play or looseness in the clutch pedal. Push down on it with your thumb. It should have a small movement then become firmer. The adjustment is the same as the brake pedal.

 

[RLJ]

Good call Mike.

 

Was always checking the slave cylinder adjustment and never looked at the pedal to master cylinder adjustment.  Previous owners mechanic had the pedal adjusted so it was always engaging the master cylinder at least 1/4”! 
 

Adjusted the pedal correctly, then bled the slave to make sure it was at the bottom of its bore. Then adjusted the slave rod for proper play and everything is great. 
 

Drove the car for a bit and clutch adjustment stayed where it’s supposed to be. 
 

Thanks Mike for the good advise to check the pedal adjustment. 
 

 

[datzenmike]

If there is no play it's possible that the clutch master is not fully returning to it's rest position. If this is the case it may not be allowing all the fluid under pressure back into the reservoir. Over time the slave slowly extends from the trapped pressure.

 

Have seen this on brake masters. After a time the front or rear brakes are on and don't release. Loosen the bleeder and fluid squirts out and back to normal. Never seen this on a clutch master but the principal is the same.

[Stoffregen Motorsports]

Do you have the return spring at the slave? The adjustable slave needs a spring.

[RLJ]

Yes it has the return spring. Good point, thanks. 

[Stoffregen Motorsports]

If you want to swing by the shop, I can have a look-see.