Technical Need Hydraulic Clutch Help ASAP

Hi guys. I'm thrashing on my latest 32 Tudor project and the clutch has got me stumped. The clutch takes an excessive amount of pedal pressure to disengage. I'm talking two men and a boy to get the job done.

I'm running a set of RJays hanging pedals with 1961 GM truck master (with 1 1/8 bores) and a matching '61 GM slave (with 1" bore). The trans is a 1939 Ford. This is the exact set up (other than a different brand of hanging pedals) that I ran on my gold Caddy powered truck a few years ago.

Having used the set up before, I'm going crazy trying to figure this one out. The master and slave are matched and the pedals ratio seems OK?

I don't think it's a mechanical issue with the pressure plate. I can but a 13 inch long bar over the trans lever and manually disengage the clutch. It's looks to operate normally through the inspection hole. It disengages hard this way, but I'd expect it to with only a foot and a half of leverage.

Any thoughts are appreciated as I need to button this thing up ASAP as it goes to interior on a few days.

I've included pics of the pedal assembly and of my slave mounting.

Thanks in advance.

 

Btt

 

Are all the pivot points lubed?

 

Yes sir!
All points are lubed.

 

Just thinking out load it seem the master has to large of a bore or the pedal ratio is wrong.

 

I see what your saying Saltflats, but people have been using this master and slave for this application for decades. The pedals are the only unknown since they are different that the set in my truck.

I did call RJays and spoke with them today. He said they have sold a lot of these pedals with no complaints. They do include the master with pedals so you think there would have been other complaints of the ratio was wrong for this master and slave combo. Although RJays was helpful, he was stumped and didn't have any good suggestions.

 

Is the slave mounted where its travel is in the ark of the clutch lever.
Hard to type what I am trying to say. But does it start below and go to center then over center? If that makes sense.

 

Is there some type of joint under the boot of the slave cylinder? The push rod looks to be at an awfully sharp angle coming out of the cylinder in that picture you posted. I would think it all needs to be a straight line for proper performance.

 

Your final pedal ratio works out to about 3.5 to 1. I believe that is most of your problem. A master with a much smaller bore will help or alter the ratio of the pedal assembly or both

 

I agree with K13 - looks like the rod is bound - boot looks distorted - maybe break it free at clutch fork and test

 

The boot is distorted in the picture. I had pulled the slave to check the bore size and just thrown it back in. It's not even bolted down in the pic. The shaft is aligned properly with the lever. It comes straight out of the slave and pushes the lever in the proper arc.

How do you calculate pedal ratio @RICK R 44? The pedals were designed, manufactured and sold as a kit with the master cylinder by a respected vendor. I understand that that doesn't mean it correct, but damn...

 

The only thing I can think of is maybe you still have air in the system.

 

A longer arm on the clutch shaft would help improve things.
Make it as long as you can so it will disengage the clutch just before the slave runs out of travel.

 

It looks like the rod is going into the cylinder at a angle. This will cause some pressure problems but it will ultimately do damage to the cylinder. You need a 7 or8 to 1 ratio on the pedal and movement of the cylinder. There is info on the Internet, can't think of the website at the moment


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Thanks @Pete Eastwood. I had thought about that. The lever is 3.5 inches now. I could probably add another 1.5 or 2 inches but would be surprised that would make enough of a difference. ????

AND AGAIN GUYS, THE PROBLEM IS NOT THE ALIGNMENT OF THE SLAVE. When fully installed (which it is not in the picture) it is straight with the clutch lever and pushes in the proper arc of the lever.

 

Probably not best to YELL at people that are trying to help you that make a suggestion based on the shitty picture you posted.

 

How does the push rod mount to the slave? the clutch arm will swing in an arc and bind a piston with a solidly mounted push arm. it should be a ball end in a pocket like a master cylinder.

you may have to break everything down, remove clutch and throwout bearing and see if all components travel freely.

 

Sounds like you can change the clutch lever longer or shorten the pivot point at the pedal.

 

Went back & looked at the pedal photo & have to agree with "RICK R 44"
looks like the pedal ratio is way wrong, needs to be closer to 6 to 1.

 

Granted we are working from a photo but the pedal ratio kinda looks like about 4-1. If I put 50# force on the 4-1 pedal that will be 200# on a 1 1/8 master cylinder and the output is only 202psi, or 200 X .99, the .99 value being the area of the 1 1/8 bore. That 202psi x the area of the slave bore (1") is 202 x .78 or only 157# pressure applied to the clutch lever. Doesn't that slave need to be bigger than the master, or is my thinking all wrong?

 

Most race cars...don't flame me guys...
Use 1" bore slave..3/4 " bore master...and a pedal ratio of 6 to 1.....
Simple math to calculate pedal ratio..measure from the pivot to the clevis..then from the clevis to the foot..
Simple formula...12" foot to clevis..2" clevis to pivot =..6 to 1 ratio..
More info..
Power brakes...4 to 1..big bore master Cuz the booster dies most of the work..
Manual brake..6 to 1 smaller bore master Cuz your leg does all of the work..
6 to 1 equals more leverage...

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That was my first thought Fordors.
Or the cylinders need to be turned around.

 

Thanks for the help and the info guys!

Since the master and slave are a matched set from a factory GM application, I'm totally buying into the pedal ratio being the problem.

Now the question becomes how can I modify the pedal ratio without changing the mounting bracket where it mounts to the firewall? I'm trying to avoid getting back into the paint again. I can slice and dice the anything inside the firewall no problem. Do I need to move the pivot point of the pedal closer to the center line of the master?

 

You said that you've used this setup before, but I have to ask since you are having some issues. When used is the original truck, they had a Z linkage that swapped over the brake / clutch linkage alignment. So when you use the master with aftermarket pedals like you have the brake and clutch bores no longer match the "brake" and "clutch" cast into the casting. One bore - the brake one - has a residual valve. The clutch bore does not. So you need to swap the the the innards from bore to bore to get them matched for your pedal setup. At that point you'll actually have your clutch attached to the bore marked brake. I always file off the "brake" and "clutch" markings off the casting after swapping over the innards. Having the residual valve in the clutch circuit could be causing some problems. You most likely know this, but thought I'd through it out as I've used a number of these master cylinders.

 

Wow, 2 more responses while I was typing my last response. THANKS!

Just for the record, I did swap the guts on the master as you need to do when using this set up.

Since this combo of slave and master have been widely used in hot rods, I'm leaning towards modifying the pedals. Just need to figure out what to do...

 

You would move the hole in the pedal up in the master push rod pivot point.

 

Just another question you are sure that the cylinder didn't pump all the way up and were at a fluid lock?

 

The lever distance for the GM clutch is about 6.5 ". You have doubled the force required to operate the clutch with your 3.5" arm.

 

Everything seemed to bleed out fine and the clutch does disengage, it just takes WAY to much pedal force.

So if I get this right, I'd have to cut the side mounts and move the pedal pivot down and then redrill the holes for the master clevis somewhere near the green dot in the photo?

 

Lots of responses so far. To me, it does look like there's some "misalignment" in the slave cylinder-adjustment rod-bellcrank setup. I'm not familiar with the old Ford trans at all, but could there be wear on the collar the throwout bearing rides along; I've seen that in other applications. What about different lengths in throwout bearings; I know with GM's there are at least two with the older, more common, clutch setups. Good luck.
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