Hydraulic Clutch adjustment

[69gmachine]

There have been several posts on Hyd clutch installs, and I've noticed some of them go together without a hitch while others can't seem to ever sort it out. I'm hoping I've finally resolved mine, and this may be at least part of the problem with others as well. After doing a search on the 5.0 Tech forum, it occured to me that the problem may be in the pivot, which is not adjustable on my bellhousing. I haven't put the tranny back in yet, but I've added a washer under the pivot as an adjustment and installed the slave cylinder with 1/2" stand-offs to properly locate it. I'm off to get a 26 spline clutch centering tool before I press the pedal. Keeping my fingers crossed. I'll report back if it's successful.

 

[10secgoal]

The half in stand offs will put you aligned with the wrong hole on the fork. You will want the one closest to the clutch. There should be a washer specially made for that hole. This will give you more throw in the clutch for the same slave movement.

 

[69gmachine]

The standoffs replicate the thickness of the mounting flange of the transmission to locate the slave cyl for and aft, not laterally. I am using the inside hole of the fork with a hardened washer over the end of the CNC pushrod to engage the fork.

Now the really bad part... even with two washers under the pivot it doesn't have enough throw to engage.

Next question: what presssure plates have been made to work? Maybe mine simply needs too much travel to release? The disc is from Mcleod because that was what was recommended by a shop that I felt was knowledgeable in putting together clutch combinations that will hold up to the torque of my engine in the stock 10.5 diameter size, and because I couldn't find a similar disc from Centerforce for the 26 spline input in a 10.5 diamter. They did want me to buy the matching pressure plate also, and maybe I should have, but the Centerforce has almost no miles on it, and I just couldn't bring myself to set it aside and replace it with yet another new part that might not be any better. They did have me mike the thickness of the old disc to make sure they were compatible, and they were identical.

 

[Rusty67]

I think the centerforce presure plate requires the same amount of throw for full release as a stock Ford clutch. You need between and inch to and inch and a half. How much travel are you geting now ?

 

[69gmachine]

Wow! That's a lot. I only have 3/4" of travel at the slave cylinder, but that seems to be all it's capable of given a 3/4" dia MC and 7/8" dia slave cyl. I measure about 1 1/16" travel at the master cylinder, so mathematically, what I measure agrees.

I've been devising a lever arm using an inverted manual brake pedal to increase the travel at the fork from what I get from the slave cylinder. What I can't figure out is how so many people are able to make the same basic arrangement work for them???

 

[Rusty67]

Maybe they are preloading the clutch to get it to work properly. We all know where that leads.

Maybe this will help you ?
http://www.moderndriveline.com/md_faqs/hydraulic_1.shtml

 

[10secgoal]

You HAVE TO have full travel of the slave to work. I just went thru this with a company and they wasted a ton of my time. Their bore on the MC was too small to provide the volume to get the slave to travel the full amount. Take the pushrod out and have someone press the clutch. You should see the slave come all the way out. If you don't, just stop. There is a problem. If you DO get full travel, but not when hooked up to the clutch fork, you have air in the system. Now for the million dollar Q. Is it a genuine JMC MC ? Not by CNC. But by JMC ?

 

[Rusty67]

I just realized I said an inch and a half before. I think it was inch and an 1/8th or 1/4.

 

[gjz30075]

I've got the genuine JMC kit on my '66 (JMC master,etc) and I just finished up bleeding it. I've got 1" travel at the slave and the engagement/disengagement point is pretty close to the floor. I'm preloaded somewhat but I can see that the slave piston could move out another 1/8" or so for really complete travel. It was tough bleeding to get it to where it is now, but 10secgoal has got it right; the slave has got to travel the maximum distance for a properly working clutch, which is a function of the master and NO air in the system.

 

[10secgoal]

Since this may come into play later for 69gmachine. This is how I bleed them, and it has worked for me everytime.
Make sure the master is disconnected from the pedal. If not, it will trap a little air that you will never get out. Then gravity bleed just like the directions say. This will get 96.8945% out of it. Then with the slave off, and the rod out, slowly push the piston back into place. Hold the slave so the bleeder is at the very highest point. I like to rap the slave a little with the back of a screw driver to make sure any and all air bubbles are at the top.


Then for preload I put it all back together. I tighten the nut again the arm until it doesn't move when I give it a good push. It it moves a little, I give 'er a little more. If you only have 3/4 of an inch movement, don't give it so much preload it disengages the clutch. If you do, it won't take much to burn the clutch up in 4th gear.

 

[69gmachine]

You HAVE TO have full travel of the slave to work. I just went thru this with a company and they wasted a ton of my time. Their bore on the MC was too small to provide the volume to get the slave to travel the full amount. Take the pushrod out and have someone press the clutch. You should see the slave come all the way out. If you don't, just stop. There is a problem. If you DO get full travel, but not when hooked up to the clutch fork, you have air in the system. Now for the million dollar Q. Is it a genuine JMC MC ? Not by CNC. But by JMC ?

The MC is by AFCO, not JMC or CNC. It is a 3/4" bore and I'm fully depressing the rod such that it hits the stop on the back of the MC. If the JMC master has more travel, it might be enough to disengage the clutch, but it would mean I would have to have the clutch pedal sticking way too high up to have the requisite travel.

Thanks for the replies. It's nice to feel like I might be able to solve this. I'd really like to observe someone's car with the JMC kit to see how high the pedal rides without depressing the clutch.

 

[69gmachine]

Since this may come into play later for 69gmachine. This is how I bleed them, and it has worked for me everytime.
Make sure the master is disconnected from the pedal. If not, it will trap a little air that you will never get out. Then gravity bleed just like the directions say. This will get 96.8945% out of it. Then with the slave off, and the rod out, slowly push the piston back into place. Hold the slave so the bleeder is at the very highest point. I like to rap the slave a little with the back of a screw driver to make sure any and all air bubbles are at the top.


Then for preload I put it all back together. I tighten the nut again the arm until it doesn't move when I give it a good push. It it moves a little, I give 'er a little more. If you only have 3/4 of an inch movement, don't give it so much preload it disengages the clutch. If you do, it won't take much to burn the clutch up in 4th gear.

I believe I have it properly bled because when I do the math (MC radius squared*pi*distance=slave radius squared*pi*distance) I get .78" travel for the slave when I have 1 1/16" travel at the master. This agrees nicely with my measured travel of the slave at 0.75".

 

[69gmachine]

OK, to get 1.25" travel at the slave, I need 1.7" travel at the master, and the AFCO master at best can get 1 1/16" and more than likely only 1.0".

So I've decided that rather than put a JMC master in with sufficient travel, which would elevate my clutch pedal higher than I want, I will proceed with my design for a lever with a pivot at the bottom. The slave cylinder will engage the lever at 1.9" up from the pivot, and the lever will engage the clutch fork at 5" up. That results in 1.75" travel at the clutch fork with .75" travel at the slave. I should be able to adjust the pedal down in height to ride just a little higher than the brake, which I think is an improvement. I will also use the outer pivot on the clutch fork where the factory cable clutch locates if necessary to lessen the chance of over travel.