cscott1

Situation/background:
I removed the transmission/clutch/flywheel to diagnose a vibration in the engine. When that work completed, I reassembled everything a couple times. The first time was with the same parts, and the clutch would not consistently fully engage (bad test drive!). I decided to replace the slave cylinder, and give it another go. As far as I can tell, the slave cylinder is fully bled. I've gone through 5-6 rounds of pumping the pedal, opening/closing bleeder, and each time produced a fair amount of fluid. This time around, since I know more about the problem, I have more details around the symptoms

Symptoms (car completely on jack stands):
I can pump the pedal several times, shift into 1st, continue to hold pedal to floor, and for about 5 seconds the wheels don't move (clutch disengaged). However after that time, the clutch slowly engages (hydraulics lose pressure). I can consistently produce this behavior. Shift to neutral, brake (stop wheels from spinning), pump pedal to build pressure, shift into 1st, and within ~5 seconds tires begin to spin.


I know that an obvious course of action here is to just replace the master cylinder & hydraulic line (slave has been replaced), but I'd really like to KNOW what's wrong. So far, my only thought is to use a vacuum pump to see if I can slowly draw in fluid. The idea being that if fluid is coming into the pump, then its being displaced by something. However, I don't think that has a good chance of success because any leak that would be noticeable at a small vacuum would be squirting under pedal pressure.

Any suggestions for diagnosing this?

TIA

cscott1

When the hydraulic line is disconnected (isolating the master), I can't get the pedal to move. Is that a valid test? If the leak was between the fitting and master cylinder, wouldn't the pedal eventually move?

Pharcyde50

iTrader: (11)

I would replace the master also. I've had good luck bleeding the hydraulics and hitting with a mitty vac at 10psi to pull out a few more small bubbles.

My master was leaking around the dust boot.

jmd

iTrader: (4)

With a speed bleeder or a 90deg spark plug boot and some hose with the bleeder barely cracked at all, submerge the end in the reservoir pointed down. Then pump the pedal for a couple minutes. If you do it right,
Fluid will flow out the top of the slave under pressure.
Any air will fall out of suspension at the reservoir.
The pressure will dislodge air in the slave and line.

It is impossible for the mityvac at the reservoir method to accomplish the same as the jmd method. But you will probably get someone to tell you how neat leaked air bubbles from the reservoir to master hose connection made them feel.

Oh and did you shim the slave?

cscott1

I've bled the slave at the bolt quite a few times. Does the technique you describe do something differently? Is the conventional method (open bleeder) known to leave air behind?

I did not shim the slave, but I I have an OEM replacement style clutch and an OEM (replacement) slave. The clutch feels like it works properly until the pressure drops. Would it ever work correctly if it needed a shim?

I'm just asking all the questions so I can learn the reasons behind what you suggested. Trying to learn to fish.