Bloody Clutch Hydraulics--- not bleeding.

[Wade Nelson]

I've got a clutch hydraulic system I can't get to bleed.

New slave, new flex line, new master cylinder because the old system was leaking fluid (somewhere!) and often required I pump it up to have a working pedal.

I've installed dozens of clutch hydraulic cylinders, masters and slaves, in everything from Triumph TR-3's to my current 280ZX. Never run into one I couldn't get bled.

Till today.

Here's my theory. I've always thought "bench bleeding" a fresh master cylinder was a waste of time, because most of the fluid drips out while you're trying to connect the lines, makes a mess, and eats paint off of whatever it drips onto. Why bother?

I suspect my new master cylinder sat on the shelf so long the piston is 'stuck" down at the end of the throw. If I'd "bench bled" it a bit, worked it back and forth a bit, I might be able to bleed it now. At least it would have lubricated the seals...

How to get it to return, other than to reverse bleed it, pump fluid from the slave BACK to the master? I'll have to take the slave off the transmission so I can move the shaft back and forth to pump it...

Right now the pedal moves to the floor, effortlessly, and most times just sticks there. I opened the bleeder screw (on the slave) and tried a gravity bleed, let it bleed a bit, saw the reservoir go down, so it SHOULD have given me SOME pedal...but it didn't.

It doesn't get firm no matter how much I pump the pedal, nor does any fluid leave the reservoir.

NEXT time I'm gonna do the bench bleed thing...put my finger over the output hole and make sure I'm getting pressure...

TIPS FOR DOING THIS JOB:

Remove the windshield squirter bottle, disconnect it's wires, move it and the injector resistor pack out of the way to replace the master. Get upside down under the dash to pull the hairpin and pin security the master cylinder rod to the clutch pedal assy.

Loosen the flare nut fitting to the master BEFORE removing the two bolts securing the master to the firewall. Re-install in opposite order --- get the flare fitting STARTED, THEN bolt the master to the firewall loosely, install the pin and hairpin, tighten the master to the firewall, THEN tighten down the flare nut

ALWAYS USE A FLARE NUT WRENCH or else you'll end up using VISE-GRIPS on stripped off flare nuts.

The hardest fitting to work on is the one by the starter, connecting the hard (metal) hydraulic line to the flex line.

Loosen the fitting on the hard metal line using a 10mmflare nut wrench BEFORE you take the clip off securing the flex hose.

Install the flex hose USING A COPPER WASHER to the slave cylinder, use a vise or other to hold the slave and really get it snug and install as a single unit. Do NOT attempt to connect this under the car as you'll never get it tight enough.

Again, get the flare nut fitting STARTED before locking the flex hose down with the clip; it sits in some little "dents" so it can't rotate while you tighten the flare nut down 1/4 turn at a time..aggh! If you can't get the clip on, you don't have it all the way through the bracket.

Normally I'd offer some tips on bleeding the system but...not today!

[Wade Nelson]

LESSONS LEARNED:

It's very seldom I figure out where I went wrong the same day. Guess today's my lucky day!

So here's lessons learned --- and how I got this system to bleed properly...

1) Go ahead, bench bleed your master. Or at least get some fluid in it and exercise it, moisten the seals.

2) Gravity bleeding works a lot better when gravity is on YOUR side, not the bubbles. Jacking one side of the car can create high points in the hydraulic lines from which bubbles WILL NOT escape under the power of gravity alone. If the car's level, normally there are no high spots and a gravity bleed will work just fine.

3) Reverse bleeding --- if you've got a system full of air, it's pretty easy to grab the shaft of the slave (clutch) cylinder and push it back, forcing any air/fluid BACK towards the master cylinder --- and perhaps unjamming a MC piston "stuck" at the end of its travel.

4) A pedal too far: Personally I love a clutch that disengages right at the top of the pedal stroke. Well, I went too far, extended the rod into the master cylinder an eensy bit too far -- so the piston never returned fully "home" and NEVER uncovered the port that allows fluid from the reservoir to re-fill the space in FRONT of the piston. So with no fluid to push, the piston did nothing but pump air.

Shortening the rod by 1/2" made the problem go away, got SOME pedal, and then was able to bleed it normally. I'm going to re-lengthen it just a tad now that it's working.

5) One-way valve, one-man bleeders. These work great. Around $7 at the auto parts store. A clear hose with a one way valve you put onto the bleed screw on the slave cylinder. Fluid can go out, but air can't get sucked baack in. Truly makes bleeding a one-man job.

Well there it is, five tricks to help you when a hydraulic system proves difficult to bleed.

Edited July 10, 2013 by Wade Nelson