Hydraulic clutch problem

[oldguy668]

Here's the setup:

Ford racing diaphragm pressure plate
Ford racing clutch disk
Ford OEM flywheel
3/4" bore CNC push type slave
1 1/8" bore CNC master

Last week when I started the engine, I could not get the car into gear due to inadequate clutch arm travel. Having been down that road before, I put it up on the jackstands and checked everything and also re-bled the system. I lengthened the rod out of the slave cylinder by about 1/4", and lengthened the rod from the pedal arm to the master by about 1/4". Those two things took some of the free play out of the linkage but raised the clutch off the floor an extra 1.5". I think I'm all set but I want to check the math before I drop it off the jackstands. If there's someone out there with the same combination of master and slave, can you give me a measurement of the static clutch pedal to floor distance and also the travel distance of the pedal to full disengagement.

One thing that's wierd is the free play inside the CNC master. There appears to be a spring in the bore that keeps the rod off the piston at rest. With the pedal arm ratio, the 1/4" at the master equals about 1.4 inches at the pedal.

[CraigS]

"One thing that's wierd is the free play inside the CNC master. There appears to be a spring in the bore that keeps the rod off the piston at rest. With the pedal arm ratio, the 1/4" at the master equals about 1.4 inches at the pedal".
I haven't worked w/ that MC but I can't see how that is correct. Why would one want to give up 1/4 travel at the MC? That is huge.

[edwardb]

The kind of standard setup for these is a Wilwood 1-1/8 inch MC and CNC 7/8 inch slave cylinder. That yields about 1-1/8 inches of travel at the slave cylinder with full stroke of the clutch pedal. That's approximately the same clutch fork movement of a cable setup, so should work fine. You shouldn't have that much play in the system though. Neither of the two CNC slaves I've used had a spring visible. I'm assuming there's one internal with the piston, but externally all you can see is the little cup area where the pushrod end rests. With the clutch pedal all the way out, both the MC and CNC slave should be all the way out to their stops, and there should be just a slight amount of play in the pushrod at the clutch fork. Similar to how you set up a cable.

[oldguy668]

I can still get the MC out so I can look inside without disconnecting the line. I know I have the right mix of parts because I had the same setup on an earlier build that worked just fine. The only difference is the older version had a Wilwood MC and this one has a CNC....both the same size. That 1/4" of slop in the MC has me stumped.

[CraigS]

Every MC, either brake or clutch, that I have worked on had an internal spring. It pushed the piston out of the MC except that the travel was stopped when the piston hit a snap ring in a groove inside of the bore right at the end. Hate to say it but I think you are going to need to remove the MC and take it apart.

[oldguy668]

I made a bunch of subtle adjustments to the entire system. Disassembling the MC is on my clutch service flow chart right at the branch entitled "Does it Work Now?"

[oldguy668]

No, it doesn't work now. I adjusted the slave pushrod for zero lash, and I adjusted the master pushrod so the pedal is almost in my lap. I bled the system using a vacuum tool, and I still don't get much movement from the slave until I push the pedal down half way. I'm starting to suspect that the master cylinder piston is not returning to the end of the bore. If I was getting a full pump out of a 1.1875" master cylinder, I should be blowing the piston right out of the end of the .75" slave. Anyone suggest something else to check before I rip the master out?

[oldguy668]

I had my numbers backasswards again. I have a 7/8" slave and a 1" master, which is Forte's currently recommended configuration. I also am certain that I have the TO bearing and clutch arm installed right, and I know the lock washer is under the pivot ball. The only explanation at this point is that I didn't bleed the system as well as I thought. I'll try again tomorrow.

[Erik W. Treves]

What pedal box are you using

[oldguy668]

I'm using the standard FFR-issue Wilwood box. This exact configuration worked great in my last build, so I'm convinced I did a sloppy bleed job.

[Erik W. Treves]

ok... so you cut the frame rail and or the pedal to get full travel? assuming so....probably the bleed then.

[oldguy668]

I modify the pedal arm to get full travel and a positive stop. I'm getting 1.4 inches of travel at the MC. I only need about .9" to max out the slave. If everything was okay, I should be blowing out the slave piston. I initially blamed the MC, but there's nothing in it to go wrong except a leak. It has to be air in the system.