Hydraulic Clutch Installation, CJ7

[Captainlance]

I'm installing a hydraulic clutch mechanism in my wife's 1984 CJ7 that I'm restoring. YES, I have searched and read as many postings as I can find, but I still have a problem that I don't see a clear answer to, maybe someone here can enlighten me. The Jeep has a AMC 258 i6 / 4.2l and Tremec/Spicer T-176 . I used a Centric slave and master cylinder for the clutch, the slave bolted right up to the bell housing with existing holes. The assembly has been bled, and I exchanged the clutch pedal from a YJ onto the CJ pedal assembly, so I would have the pin for the push rod.
PROBLEM: slave cylinder travel is only 5/8 of and inch, yes the clutch disengages, but the pedal is VERY low in engagement, barely 2-3 inches off the floor..

SUGGESTIONS?
Any ideas?

Thanks!
Lance

 

[tarry99]

Sizes matter when it comes to Hydraulics & pressure & volume...........First off what bore sizes have you used? Master and Slave?

Common is you want a larger bore at the master pushing fluid to a smaller bore at the slave.... that will increase the travel at the slave as the oil volume pushed from the larger bore will push the smaller bore slave cylinder push rod farther....

Pedal ratio Usually about 5-6:1 and travel at the pedal is also important.......these are all basics.

Sometimes the loss of travel in fluid volume is directly connected to the travel you have at the pedal...............and when you say the pedal is only 2-3 inches off the floor I assume you're also meaning travel off the floor & that is where I would start..........perhaps the pushrod from the pedal arm to the master is too short? By lengthening that rod it will raise the pedal and add travel...........the correct throwout bearing and collar length is also important...............on hydraulics you want enough travel in the pedal to push the master cylinder piston as far as it will go in the bore or until it hits the stop.........any wasted motion in the linkage will lessen overall travel & therefore lessen the travel at the slave.................

5/8" of travel at the slave is bare minimum.......and here is why.......the hydraulic clutch system is basically 1:1 excepting when you have a larger bore pushing volume to a smaller bore.....which will increase travel
( depending on bore sizes ) but really not that much..............now here is the important part, once the travel at the slave pushrod gets to the clutch fork the ratio inside the bellhousing now turns to 2:1........meaning that if your slave pushrod is moving 5/8" or .625" the fork inside that is moving the throwout bearing is now only moving half of that or 5/16" or .312"...........a standard clutch pressure plate needs anywhere from .400"-.600" of travel to fully release.....add in .100" of free play at the pedal and the system at the throwout bearing needs say .700"...........which means at the slave you really need to be able to move that over 1" or even as much as 1.400"..............anything short of that and more than likely the Transmission will grind going into gear and as the clutch face wears will get even worst......
Hope this all helps!

 

[Captainlance]

Thanks for the reply. The master/slave combo bores are unknown, they were a matched pair sold by CENTRIC. What I did find was that if the slave rod was fully retracted by hand, it was 1.2 inches away from the clutch fork (which is the original fork.)
SO, I measured it up, found it to be Chinese... 8.8mm in diameter. A real common size...(NOT). I took a piece of 3/8 hardened rod and cut it to 5.25 inches, an inch longer than "stock'. I machined the ends round as per the original and installed. Now I have lots of pedal and about an inch or slightly more of movement. tomorrow, I'll visually check the plate movement with an endoscope through the fork hole in the bell housing.

"Old cars are fun"... or so they would have me to believe. You would think after restoring over 2 dozen of them over the years, I would know better.
Should have taken up tennis or fishing...
Lance