Clutch fork push rod travel

I have swapped my clutch release mechanical linkage for a hydraulic system. I'm using a Wilwood 7/8" master cylinder with a Novak 3/4" slave. This setup gives me plenty of travel at the slave (possibly more than necessary). I am wondering if someone can tell me what the normal (including free play) linear travel distance of the clutch fork push rod is from fully engaged to fully released? I failed to measure this travel distance on my setup prior to doing the swap. While I am not having trouble with the clutch release I do not want to drive the release bearing against the clutch fingers any more than necessary for adequate release.

 

I'm not sure of the actual measurements. When I setup mine I used the Novak knowledge site for some additional help with fork travel etc.

http://www.novak-adapt.com/knowledge/clutches_etc.htm

 

I email Novak and they sent me the following:

"Our slave will travel nearly 2", but 1-1/4 is usually adequate for comfortable AMC clutch release. Use that numbers as your touchstone and you can + or - a bit either way, but shouldn't have to."

I have almost 2" of travel at the slave with full cycle of the clutch pedal from upper stop to floor. Looks like I can reduce my pedal travel by 1/3.

 

Normal pressure plates requires about .500 to as much as .750 in travel including free play to fully release the throw-out bearing. As mentioned you should also have some free-play or air-gap of about 3/8"-3/4" in the system to keep the throw-out bearing off the fingers at highway speed. Keep in mind that the ratio changes at the throw-out fork fulcrum ball to 2:1...........Meaning 2 inches of travel at the slave cylinder is now only 1 inch at the throw-out bearing.

 

That was my real problem, (originally) I did not know the fork ratio so had no idea how far the throw out bearing was really moving... To add to the problem, at full engagement (pedal out), the fork boot was holding the bearing slightly against the fingers and I couldn't get the free play I wanted. Eventually I figured that out and trimmed the boot. It was only after making these posts and reading yours did I finally realize I had another fork laying on the bench. I measured it and it has a 1.76 ratio (.568 multiplier) so my 2 inches of travel gives me a bit over 1 inch of release bearing travel. As you mention it takes between .5 to .75, taking that and what Novak told me regarding sufficient slave travel of 1.25 inch which translates to 0.71 release bearing travel indicates everyone is in agreement and I can quit obsessing over it....
I think what I will do with some of the excess travel is increase the free play a bit.
Thanks for the input....

 

A little extra free play is OK but keep in mind that to much and you will not have enough throw / travel on the pedal to fully release the clutch when the pedal is pressed in.............Its all about a little compromise a little here and there.

 

My ultimate goal with the conversion to hydraulic was to find a happy medium between pedal travel and pedal force. But you don't get something for nothing.... Now that I have all this info I'm going to start adjusting the relation between the two...

 

And if your willing to play with it long enough that's an easy goal to obtain...........when you convert to hydraulics .........ratio's are a little less important as compared to fluid volume and the relationship between bore sizes and the moving of fluid between the MC and slave to get the necessary end travel & pressure result.............Larger bore = more volume but less pressure as compared to a smaller bore moving less volume but with more pressure. Think of it as a closed system whereby movement at one end with an unequal bore size will get a different result in movement at the opposite end. Good Luck!

 

After a considerable amount of drilling, grinding fabricating and bleeding (blood and brake fluid) I finally got it like I wanted it... Typically one doesn't really think about the forces and pressures associated with the brake and clutch systems. It becomes obvious when you start working with pedal travel vs master cylinder piston travel. I mounted the clutch master cylinder in the firewall hole originally used for the wiring harness pass thru grommet. This location puts both master cylinders ( brake and clutch) at the same level. I fabricated two 3x8 steel plates to mount the slave cylinder. One plate on each side of the fire wall and then thru bolted. For some reason the pedal feel (engage/disengage) was not linear and indistinct (as if it had air in the system). It turned out that (once I had a helper to push the pedal while I observed the process) even with the amount of metal (stoutness) added by the two steel plates the firewall deflection was still considerable. I had to add a strut from the pedal bracket to the steel plates. This fully resolved both the feel of the pedal and the linearity of engagement.
I guess it is no wonder why the clutch brackets on these mid 70s Jeep crack the frame mounts and noticeably lift the body off the frame when the clutch is depressed...

 

Not to hijack this thread but does anyone know what the standard pedal ratio is for the clutch, I have a different pedal in mine (not Jeep) and its always been heavy, thought it may be the pedal ratio as the MC/slave are equal sizes like Novac suggest.

 

The pedal on my 74 is around 12 inches from swing point to center of pad. The jack shaft (was) connected to a hole around 3 inches from the swing point. So I guess the pure ratio is 4. I'm not sure that the cross shaft did not also provide a bit of mechanical advantage as well. Looking at it from a different stand point, that of pedal swing distance to clutch fork push rod movement, 7 inches of swing gave me 1.4 inches of travel and that is a pure ratio of 5. Somewhere I read a ratio of 6 is a good starting point. Since I was initially unsure of where I was going with the conversion I used unequal M/S and fabricated a bracket that has a connection point about 2.5 inches from the swing point, that provides a ratio of 4.8. My pedal is about the same now as it was with the mechanical linkage (just smoother). So...I guess with the unequal M/S combination factored in the ratio is about back to factory. That's a long way of saying I think the factory ratio must be somewhere between 4 and 5...