Hydraulic Clutch parts help requested

[Brian Diehl]

As many of you remember I'm putting an ISM and Eaton Autoshift in my MCI 96A3.  This weekend I got my clutch linkage, pedal assembly hooked.  Since I could pull the clutch arm myself by arm force alone I was hoping a cable pull setup would work.

Well, actuating the clutch with just a cable pull is not going to work.  It simply takes too much force to be realistic.  So, I need to go hydraulic.  I need a master cylinder and slave cylinder to make this work.  Does anyone have ideas of appropriate parts?  I'm not even sure where to start looking and will appreciate any and all ideas.

Thanks guys!

[skipn]

Brian,

   Just for reference: What is the travel distance on the clutch arm?

   (could make a diff on solutions)

   Skip

[Brian Diehl]

The travel distance at the end of the arm is 4".

[Stan]

Brian: To et any significant mechanical advantage with hydraulic takes too much travel at the pedal end. It is easy to do with air. A little 4" diaphragm will give you about 1200 pounds of force so you can use a link to get whatever travel you need. An air brake or air throttle assembly at the front gives you good control.
tried hydraulic on a bus clutch without success but the air system worked great. HTH.

[Brian Diehl]

I have the air brake valve from the Freightliner I got the engine out of.  I also have an air cylinder already mounted on the clutch arm.  It takes about 85lbs of pressure to move the arm.  Maybe I'll run some airline temporarily and try the brake valve to see how it works.

However, I wanted to use hydraulic so even without air pressure I could still push the cluth in.  Maybe that isn't mandatory...

[Hartley]

Just make sure that you can't shut the engine down with the transmission in gear or have an auxillary air supply for the clutch system ( mini compressor ) with a T- and check valve.....

One of the BIMBA air cylinders from a belt tensioner would probably work.
Be sure to add a return spring to disengage the clutch linkage when you let off...

[Stan]

Brian: If you need 85 pounds of air pressure on your cylinder, you should use a larger cylinder in order to have better control with the brake valve. If it is 85 pounds of force needed then the hydraulic idea is definitely not feasible. To get it down to 22 pounds at the pedal, for 4" of travel, you would need 16" of pedal stroke.

[Brian Diehl]

The air cylinder is mounted in from the end of the arm.  I think it is only working 8" of leverage.  It took 85lbs of air pressure to get the cylinder to pull up the arm.  I believe the cylinder is 1 1/2" in diameter, IIRC.

[rv_safetyman]

Brian, I started out using Volvo truck parts for my hydraulic clutch.  The slave cylinder and Volvo arm on the clutch cross shaft work very well.  The Volvo clutch pedal assembly and master cylinder worked OK at first.  I had to change the geometry a bit to get it under the dash and that resulted in very heavy clutch pedal.  I also had to modify the reservoir and that turned out to be a real problem. 

I am now using a normal car type master cylinder and activating it with a brake treadle valve which activates a brake chamber that pushes the hydraulic master cylinder.  I have been playing with master cylinder bore sizes to balance force/activation throw, and sensitivity.  The system works pretty well, but is a bit too sensitive.  I am still refining the system.  I am on my third master cylinder and they don't give them away at NAPA.  I have not tried the newest unit.  I am hoping it will make the system more manageable. 

One of the issues I ran into is over-pressuring the hydraulic system.  I now have a pressure gauge in the system to monitor the full application when you need to engage the clutch brake. 

If you go with hydraulic and use hose, be sure to specify two wire hose.  That hose has much higher pressure rating than is required (system pressure is well under 1000 PSI), but the two wire hose resists expansion better and allows better control (at least on paper).

Stan says that a pure air system worked for him.  I talked to folks who tried that approach and said that they could not get it to work.  They said that they had almost no control of the system.  Stan, can you give us more detail?

[Len Silva]

Brian,

Since you already built the mechanical (cable) set up, how about air assist?  HB sells the system for $750, kind of pricey in my estimation.

These are the same components that Eagle used and there are probably a few laying in peoples junk boxes.  I sold one last year for $100.

You can see it here:
http://www.hbindustries.us/air.htm

Len

[Stan]

Jim: After the hydraulic clutch design that was unsatisfactory, I did the air system without out much pre engineering. The brake valve I used came out of a Mack truck with a dual braking system so I just hacksawed the bottom section of to reduce the height for more clearance under the floor. I pulled in a 3/8" plastic air line through the original clutch rod conduit and mounted a 4" (IIRC) brake type air can to a bracket (using tapped mounting bosses on the side of the transmission) that connected directly to the clutch arm. All air was through the brake valve (no QR valve) and it was so smooth I could climb up on blocks like I had an automatic transmission. I carried a spare diaphragm with me but never used it in several years. It should last at least as long as a brake or throttle diaphragm.

When stopping, you set the parking brake so even if you leave it in gear with the engine stopped, you can put it in neutral to start. Only once, I got in trouble by just reaching in the door and pushing the start button (bad habit) while it was in gear. That got the transmission in a bind but it was my own fault for not being in the driver's seat before starting the engine.

This was done on a MCI 5A which doesn't have a clutch brake so it was always hard to get into first or reverse with a hot transmission but it was like that before the mod. I no longer own the bus so I can't take any measurements.

My original reason for changing was that I had to stand up to push the clutch pedal down and couldn't find the cause. When I pulled out the long clutch rod I found the problem. The rod is actually a piece of steel tubing with solid threaded ends welded to it. Some mechanic had adjusted the rod by twisting the tubing instead removing the pin and turning the end. When the rod came out it turned into a long spiral so it was obviously binding in the wooden bearings in the tunnel.

[Brian Diehl]

I'm going to try the air since I have all the parts I need to test it with.  I'm going to test with the brake valve right next to the transmission for the shortest air run possible.  If it works, then I'll hook it up to my cable directly and see how that works. 

[Stan]

Brian: All that is needed for the air supply is a bleeder type air regulator with a range that that gives full travel on the clutch arm with whatever type of air motor you are using. An air throttle foot control would take up less space than a brake valve. I didn't mention it in my previous post but there was not enough room to mount the brake valve in my bus in the clutch pedal position so I had to mount it farther back under the clutch pedal arm. This resulted in a pedal travel of 2" which probably gave me better control than the approximate 1" of travel on a brake pedal directly.