Clutch Cylinders keep failing

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badsamaritan

badsamaritan

10 Year 15 Year
Joined
Feb 16, 2011
Threads
140
Messages
1,290
Location
San Diego, CA
I'm on about my 4th Slave Cylinder, and they consistently fail in the same way. The piston over extends out of the slave cylinder and it pukes all my fluid out. I've tried a lot of different combos but can't find a setup that works consistently. When not ejecting the piston out, everything works and feels fine but I haven't gotten a slave cylinder to last more than about 3mo.

Link to a video showing how far the slave piston currently comes out (new unit I installed today). I set the piston all the way to the bottom of the cylinder and then adjusted the clutch from there. Seems no matter how I adjust the clutch the piston always ends up extending to the very end of the slave cylinder.

A couple of known issues that I need to correct:
  • The AA bracket is pretty terrible. It forces me to mount the slave upside down and at an awkward angle to the clutch fork arm.
  • It will actuate the clutch fine when working
  • I lowered my pedal height to 7-7/8 from the floor to the top of the pad in hopes that lessening the pedal travel would help. No change really
setup:
  • 5.3L Vortec, 56 Corvette Bell, SM420, GM Straight clutch fork, has a Return spring. Clutch is the AA model they sell for LS/SM420 swaps, its the low profile 11"
  • AA Slave Bracket
  • Clutch Master is 75+ FJ40 unit

  • 1779411688914.webp
  • Clutch Slave is the 75+ Beck-Arnley model
  • 1779411731918.webp
 
Last edited:
Link to video I don’t see. Hmm odd I’ve only blown one slave in 25 years. On my v8 swap. Sm465. I use 1978 master and slave. Do you have a return spring on your pedal also.
Maybe you have a partially collapsed rubber hose holding pressure then you pump it up until it pushes it put. Hmm. I have never had an issue with my clutch and slave. Let’s see your video. Mines upside down also. I just flip it up the correct way and gravity bleed mine if I ever have to.
 
I do have a return spring, and it's a hard line that converts to a steel braided AN line. Heres the video, curious if the piston is supposed to extend that far out of the bore?

My current theory is that after driving the truck for awhile, the fluid gets hot and the pedal gets stiff. The next time I use the clutch the piston over extends and comes all the way out of the bore and usually rips the seal
 
Pighead said:
Can you fit a longer pushrod in there?
Click to expand...

I have a pretty long piece of threaded rod that I have been using. It sticks out a ways past the fork arm. I've tried bottoming out the piston and then setting the clutch arm adjustment to see if I could keep the travel limited to inside the slave cylinder but it always over extends
 
badsamaritan said:
The next time I use the clutch the piston over extends and comes all the way out
Click to expand...
Are you allowing the clutch pedal to come all the way up and the slave to retract all the way between shifts? So you're not double pumping the clutch? Do you ride the clutch?
 
charliemeyer007 said:
I think the piston comes out too far. So less pedal movement shorten the yoke.
Click to expand...

I just got back in from the garage...I turned the clutch clevis down about 3 turns and then checked the slave piston and it just barely comes over the edge of the slave cylinder which is a big improvement.
 
I had this problem once.

Added a floor stop for the pedal.

My clutch releases fully about 1” from the floor. However you can go ahead and push the pedal further. So I added a 3/4” stopper.

I rarely clutch mine all the way to the floor, but if someone else drives it they do.

Mine is a 5.3 but Toyota trans, with advance adapter belhousing. GM clutch setup. 4 speed clutch fork.
 
The last 2/3 of the throw do nothing but over extend the piston in MC and slave ? I guess my MC is so tired it doesnt but I could see a new MC possibly causing that. I am happy as long as it throws enough to release clutch. I will say as I get older the clutch, my knee, and a shaky leg need to have a conversation.
 
I will run my pedal to the firewall, especially on technical wheeling. It's never been a problem. My legs are pretty long. On my trail 40 the clutch pedal resistance is real easy to push. It almost feels like it isn't doing anything, but it works fine.
 
pb4ugo said:
I will run my pedal to the firewall, especially on technical wheeling.
Click to expand...
I barely touch my clutch, especially in technical wheeling. It's either in gear or out. My pedal will go the floor but it's a long way, there's no witness marks. I barely move the clutch pedal for regular shifting and usually double clutch it. It's a SM 465 though.
 
Pighead said:
I barely touch my clutch, especially in technical wheeling. It's either in gear or out. My pedal will go the floor but it's a long way, there's no witness marks. I barely move the clutch pedal for regular shifting and usually double clutch it. It's a SM 465 though.
Click to expand...

I do the same. I should say when i use the clutch. I run a sbc, sm420, the tcase has a 2.46:1 low range and 4.88's in the diffs. The 4 wheel disc brakes cant stop it when it's idling.
 
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