Problem With Rebuilding Clutch Master Cylinder

About a month ago a posted a couple messages about a clutch slave cylinder, and then a master cylinder for a '96. I replaced the slave cylinder, but couldn't get any pressure when trying to bleed the system. I bought a master cylinder kit, which had no instructions. I think I replaced everything in the correct order, but still can't get any pressure when I pump the clutch pedal.

This is the order I put the parts back into the cylinder - spring (fat end first), rubber cup (cupped end facing spring), metal washer (the old one was solid plastic, but the new metal one has a hole in it, the piston, and then the retaining clip.

I filled the cylinder with fluid, pumped it about 100 times, but get nothing at the slave cylinder, and the fluid level in the master doesn't go down. Thanks for any help.

Jim

Reply to
mjb920
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Fair notice: I'm a 626 owner/driver, not Miata. However, the Miata and 626 use virtually identical clutch plumbing, differing only in the length of the hose and exactly where it runs along the firewall. This advice works perfectly (based on my experience) on the 626, and should work just as well on the Miata.

Try it as "Spring, finger over "output" hole, pour in brake fluid, add rubber cup facing spring, etc...", load the reservoir with BF, and use a screwdriver or chunk of dowel to pump like a madman. At each "push" stroke, uncover the output hole. Before each "release", seal the output hole with your finger so it can't suck air instead of drawing fluid from the reservoir like it should. Repeat until either your arms fall off (That'll seem like the most likely thing to happen... if it does, put 'em back on and keep at it!) or until every "push" cycle spits an unbroken stream of BF from the output hole, from "starting to press", to "bottomed out". Keep the reservoir topped up throughout the process!

Once you're at that point, you'll need something to plug the output hole. I've fond that a suitably sized short chunk of wooden dowel "screwed" into the output hole works well. Remount the MC on the car, and remove the slave - As you know, simple task - two bolts and unscrew from the line. Open the slave up like you're doing a rebuild, but instead of rebuilding it, pour it full of brake fluid, THEN reassemble, doing your best to avoid spilling the contents. Set it aside for the moment. remove the dowel (or whatever plug was used) from the MC, and connect the line to it. Repeat the "pump like a madman" process on the master, only substituting "The other end of the line" anyplace my instructions say "output hole". A helper is a Good Thing(TM) for this step.

Once you've got straight fluid coming from the end of the line, cap it with your thumb, get your helper off the clutch pedal, have him/her hand you the slave cylinder after filling the opening the line end is going to go into with brake fluid, then screw the slave onto the line. Now bolt the slave back to the tranny. From that point, it's just like bleeding brakes - "pump pump pump hold! Open bleed screw, repeat" until there's no more air in left in the system. With the "prefill/prebleed" operation described, that's a very short amount of time, since there's very little, if any, air in the line when you start.

Due to the way the line is run, clutches are usually a pure pain to try to bleed unless you've gotten rid of practically all the air before you begin. Starting from a dead-empty MC attached to a closed system is an great exercise in futility, since it just squeezes air into the line on the downstroke, then sucks it back out of the line on the upstroke - you can sit there literally all day like that and make no visible progress.

My 626 is the same way (using the same clutch MC, line and slave) - After opening the clutch hydraulics, trying to get a solid fluid column from master to slave from an "empty" start will take forever, *IF* it can be accomplished at all before you lose every last trace of anything resembling patience. Prefilling off the vehicle turns it into "minor pain in the butt, but doable". Last time, I ended up stripping the entire system - MC, slave, and lines, off the car, doing the rebuild, pre-filling, and the entire bleed sequence (with the slave held higher than the master so that trapped air bubbles could rise up the tubing and get vented from the slave, rather than returning to the MC to undo all my progress) and had the bleeding done in about 5 minutes. Put everything back on the car as a unit (by feeding the slave down amongst the engine parts to where it belonged on the end of the hose) in about

15 minutes, and the whole job was done, including the rebuilding that was needed, in less than an hour.

Clearances on the miata may be a bit tighter than on the 626, but I suspect you'll be able to pull the same stunt, should you so desire.

Reply to
Don Bruder

Jim,

When you say you pumped it 100 times, were you opening and closing the bleeding screw each time? Just pumping the pedal without bleeding the air will do absolutely nothing, not matter how many times you attempt it. Clutch systems are a pain to bleed by hand, a mighty vac or similar vacuum creating system, makes the job much easier but, one way or the other, you've got to bleed all the air off before it will work and before you'll see an appreciable drop in the fluid level.

Tom

92 Red (gone but not forgotten) 05 Vette (red, but of course)
Reply to
Tom Howlin

Just pumping it, first with the bleeding screw on the slave cylinder closed, and then I tried it with it open. But never depressing the clutch with it open, closing it, and then releasing the clutch. You are talking about the screw on the slave cylinder?

Reply to
mjb920

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