How to bleed a JMC hydraulic clutch linkage?

"Howard Juneau" wrote in message news:PzQih.2067$ snipped-for-privacy@newsread4.news.pas.earthlink.net...

punch a small hole in the lowest part of the hose, then open the cap. That should cause the JMC to bleed out.

And how will he get to work again afterwards?

Some people claim to bleed their kit no prob, some claim it's not possible and give up. I don't know what it is or why, but I've seen both kinds of posts numerous times.

I have done it at least five times and each has been a little different. But the main commonality is that it takes alot more pumping than you ever thought possible, if bleeding brakes is your frame of reference. Just one caveat -- my personal experience is with a '65 Mustang, '65 bell housing, '96 Mustang GT T-5 with Medatronic iron bearing retainer, JMC master cylinder, braided flex hose, McLeod hydraulic throwout bearing, and McLeod diaphragm clutch. Just so you'll know. But I've bled this setup installed in the car, as well as with the TO bearing/slave cylinder assembly sitting on a footstool with C clamps to hold the TO bearing down, and I have like I said experienced a slightly different process each time. But the main commonality is to keep at it longer than you ever thought possible.

Here's my procedure: with the system assembled and the bleeder screw open (which in the case of a hydraulic TO bearing is at the end of a hose -- here's a pic:

fill the fluid reservoir. Stick a clear polypropylene tube on thebleeder screw and route it to your drip pan or whatever. Pump tentimes -- which you can do by hand -- then pull the pedal up to itsat-rest position. When you do this you will see the fluid level dropin the reservoir. Refill the reservoir and repeat. Pretty soon fluidwill come out the bleeder screw, so at this point you should close thebleeder after each set of pumping, while you're pulling the pedal upand refilling the reservoir. The reopen it for the pumping. You repeatthese 10-pump sets 20, 30, maybe 40 times, until you see no air bubblesin the polypropylene tube. Then do it some more. You can't overbleedthe system, and you will be amazed how many more sets you can do andstill see bubbles.

180 Out

Thank you very much for taking the time to post your procedure. It was clear, well-written, and very entertaining as well. I particularly enjoyed "You repeat these 10-pump sets 20, 30, maybe 40 times, until you see no air bubbles in the polypropylene tube. Then do it some more..." You helped us (my nephew and I) start a potentially frustrating task with a light-hearted attitude. As it ends up, however, after trying your procedure for a while, we invented our own.

Our hardware was different from yours. We have the JMC master cylinder and a JMC slave cylinder actuating the linkage designed for a cable linkage on the bellhousing of a Tremec TKO 5-speed. We were working on my nephew's '69 fastback. (I have the same arrangement on my '67 coupe). You couldn't use our procedure with your hydraulic release bearing except on the bench.

What we ended up doing is taking what I call an "Aussie" approach, i.e., we stood the process on its head and did it from "down under". Here's what we did:

Disconnect the slave cylinder from the bracketry that attaches it to the bellhousing, and remove the pushrod and dust bellows from the slave cylinder.

Rotate the slave into a position where the hydraulic line is on the upper side and the bleeder valve down. Leave the bleeder valve was closed for the entire process.

Put the clutch pedal in the full up position to allow the master cylinder's piston to move into a position that opens a port to the reservoir. Place something (e.g., a rolled up shirt or towel, a wrench, a piece of wood, a 50 lb rock, etc.) between the clutch pedal and the floorboard to hold the pedal in the full up position. Lifting the pedal does not force the piston into the proper position, but it allows it to move into the proper position and one would hope and can expect it to move into that position further into this process if it does not go there at this point.

The pumping for the bleeding process will be accomplished completely with the slave cylinder, so we'll need a means to pull the slave piston as well as to push it. We'll accomplish that by pushing about a half inch of fuel line tubing into the cylindrical recess in the slave piston where the pushrod resided. Then a 5/16" bolt, long enough to be used as a handle, will be treaded into the hose to expand it enough to grip the inner wall of the cylindrical recess.

To thread it in, it will be necessary to pull the piston out far enough to expose a 1/4", or so, of the piston wall to be able to grip with the fingers, possibly with a paper towel in the fingers, to keep the piston from turning while threading in the bolt.

If the system has air in it, the piston should be able to be pulled out far enough to expose the aforementioned 1/4" of piston by wedging the tip of the little finger into the piston's recess and pulling.

After threading in the bolt, use it as a handle to push and pull the slave piston in and out to pump fluid down from the reservoir and to pump air out through the reservoir. Pump as slowly and smoothly as you can, but movement will tend to be jerky due to "stiction" between the seals and the slave cylinder walls. Fast movements will tend to squirt hydraulic fluid out of the reservoir, splattering on adjacent surfaces, ruining the paint, so take whatever precautions you deem judicious.

Repeated pumping, with reasonable pauses to allow air bubbles to travel up the hydraulic line, and for fluid to flow down will eventually clear the line of air. Keep a close eye on the fluid level in the reservoir. (If you are looking at the reservoir from directly above, while your buddy is pumping the slave cylinder, then you'll need to keep a closed eye on the reservoir!)

It requires actually requires surprising little pumping, at least compared to the multiple applications of 20, 30, or 40 sets of ten pumps that it takes to bleed by pumping the master cylinder.

This method uses very little fluid. The up side is that the fluid costs very little; the down side is that it does not flush the system of old fluid. I suppose this method could be modified to force some fluid out the bleeder valve for flushing purposes only.

Please accept my sincere thanks for your help, one80out, and for your cheerful and entertaining approach to writing about the subject.

replying to Howard Juneau, Lee wrote: I simply have to write a note about the method above. Like many folks, I've probably bled hundreds of brakes, clutches, etc. but I simply couldn't get the JMC unit to have full travel. I did what Howard suggested and was done in :20. Thank you!