C4+3=/=C7

Hi, I purchased a 1984 Corvette project car with the knowledge that the clutch slave cylinder was bad. The previous owner included both the master and slave cylinders, new in Duralast packaging. As soon as I got the car running, I replaced the slave cylinder with the new unit provided. However, the head of the fitting was rusted and posed an obstacle to replacing the master cylinder and I decided to see if it would work. After replacing the slave, I was able to drive it for a few miles- after which point the master cylinder had leaked out the brake fluid through its seal at the firewall and I could no longer put the car in gear.


At this point, I took a torch to the clutch line fitting at the master cylinder and used a toothed wrench to turn it (it stripped under normal conditions. I managed to get the line fitting out of the master cylinder, but noticed that the threads on it were mostly stripped. I installed the new master cylinder and managed to get the line installed--despite the state of the fitting--with no leaks. Without bleeding the clutch at the slave cylinder, I took the car on a quick spin around the block. I recall an irregular squeaking noise when the pedal was pressed in, but I don't know if that is relevant. The master cylinder and line didn't leak, but I had to pump the clutch or shut off the car to change gear and decided to bleed the slave cylinder at the bleeder valve.

At this point, a friend was helping me to pump the clutch and keep the reservoir full. I was under the car releasing the fluid after he pumped the pedal. Maybe the third time after I had opened the bleeder valve and as he was pumping, he told me that the pedal suddenly got to hard to push in.

When I went up, the pedal was stuck down. When I compressed the slave by hand with the hydraulic line attached, the pedal would move back up. However, the pedal could not be modulated nearly as much as usual and would not come back all the way. I detached the pedal from the master cylinder rod to verify that that pedal assembly itself was functioning properly, and it was. With the line detached from the bottom, the master cylinder would push some fluid out of the line although the pedal still wouldn't move all the way back. However, there were no visible leaks with everything put together. I also can't crank the car as if something is interrupting the starter, which I assume is related due to the simultaneous timing.

If anyone has any thoughts or experience I'd really appreciate any help on this matter because the line likely can't be used again if the master cylinder is the source of the problem. These parts represent a significant cost for this car that I'm trying to rescue and I'd like to avoid trashing them if it can be helped. Thanks.‎

frank j. moran

To bled that unit you have to disconnect the slave from the bell housing, raise the slave/bleeder screw up at a 45 deg. angle, then have your helper actuate the clutch pedal while you open and close the bleeder. The objective is to get the slave bleeder screw facing it's elevated level to have any air move to the top of the slave where the bleeder screw is..

C4+3=/=C7

Thanks, that is actually what I did per the service manual. Actually, the problem arose as my helper was actuating the pedal; as he pumped the clutch, it suddenly lost much of its travel and wouldn't move the slave cylinder.

Danlb

I think that if you have the slave rotated 45* so that the bleeder is at the highest point you must also have it rotated so far that the clutch actuation rod cannot be seated in the slave cylinder, so the slave has reached the limit of its travel, thus the hard pedal. This can be determined by the fact the piston can be seen extended to the snap ring that retains it in the cylinder. The slave cylinder is retracted by the pressure of the clutch pressure plate thru the clutch fork pushing the rod back into the cylinder. You stated the clutch pedal raised when you manually pushed the piston back into the slave. I replaced the clutch master and slave on my '84 recently and used the gravity method to bleed it. I removed the slave and rotated it so that the bleeder port was the highest part of the slave and made sure there were no loops or bends in the rubber portion of the clutch line. I then opened the bleeder and let gravity do its job while watching for bubbles. Have your helper stationed at the master and keep pouring fluid in as the level drops, which happens fairly quickly. Once there are no more bubbles close the bleeder and bolt the slave in place on the bell housing. Make sure the master doesn't over flow when the slave piston is pushed back in the cylinder.

Good luck and let us know when you get it working like it should.

C4+3=/=C7

Thanks for the advice! Your procedure is actually quite close to what I did. The real problem I'm facing here, though, seems unrelated to the slave cylinder. I ruled it out by disconnecting the hydraulic line at the slave, after which the symptom of extremely short pedal travel and seemingly little compression of the master cylinder persisted. A lot seems to point to a broken master cylinder, but I'm just grasping at straws because:
-the master cylinder is brand new
-it was working after installation
-it was able to push fluid through the detached line
-I'm hoping to salvage the line itself.

I may take the master cylinder and attached hydraulic line out of my sidelined '85 tomorrow and replace the '84's with it to see if that fixes the problem. If it does, then I know what I need to change. If not, at least I know that the master cylinder is fine and I'll keep looking. The real issue seems to be whatever's causing the pedal to be stuck in the middle 50% (or less) of travel. I will try to post a video tomorrow. I will be sure to let you know of any progress.

tl;dr: someone was in the car stepping on the the clutch pedal, I was under the car bleeding the detached slave, and suddenly the clutch pedal wouldn't move all the way up or down in the middle of pumping it.

C4+3=/=C7

Sorry to revive this old thread, but the problem's been solved. It was actually a matter of the stock aluminum master cylinder spacer between the firewall and master limiting pedal travel. I replaced it with a couple of thinner nuts and the pedal travel is now normal, allowing the clutch to disengage and the transmission to go into gear. I should have tried this a while ago!

The good news is that I think I've found the source of slippage in my '85: the total lack of any spacer behind the master cylinder! This meant that the master cylinder rod had to be depressed to attach it to the fully released pedal. Hopefully that's it. Thanks again.