Master/Slave cylinder leakage?

So I bought a 1965 MG MGB a month and a half ago from a guy who had kept it in a barn for about 7 years. One of the major issues with it was that the clutch would occasionally pop out. The car still ran but the clutch peddle took some force to move.

Anyway, to the point. I took apart the master and slave cylinders, cleaned them out, honed the slave(it was slightly pitted), and put it all back together. So I put in the fluid and then pumped the clutch/opened the valve on the slave to let out any air in the line.

Now I should, after a while, get the fluid spurting out, signaling that the line is free of air. However, no fluid comes out. What is more, the level of the fluid is almost empty. So I kept at is and to no avail.

The loss of fluid is to great to be just the nice clean cylinders filling up with fluid, so where is it all going? All my connections are tight and I have looked everywhere for a leak not finding one. Any ideas?

Did you look under the dash at the firewall where clutch pedal rod passes thru? Sometimes clutch master cylinders will leak at the rear seal allowing the fluid to run down the firewall under the carpet.


As far as I can tell there is no leakage. I tore the carpet out(it needed replacing) so its just the bare metal. There is no leakage there, or anywhere else as far as I or my friend can tell.

Since you’ve checked the carpeting and firewall as Tester sugested, I would keep going. The clutch master, and slave cyl. can hold a LOT of fluid. Bench bleeding might have been an option, but is not worth takeing them off to do it now. Sounds like you’re doing everything right if the fluid’s going down, just keep going

p.s. Did you check the “outside” of the firewall too?

So I got a chance to work on the B after class today with my friend. With our combined footpower we pumped the clutch/“bleed” the line for nearly 30 min. to no avail… So after taking out the masters piston and all that to see if I put something in wrong(I didn’t) I took apart the slave while still having the hydraulic hose attached. To my surprise I found that there was indeed fluid pumping into the cylinder, simply not enough to force the piston back and forth.

As we both got frustrated with my B my friend had the brilliance(maybe) of turning off the music because it was annoying. We both heard a distinct noise like air being forced in and out of a tight space. We now think that it is coming from the cap at the top of the master cylinder. I don’t know what this means, but it seemed rather important. I have no idea where to go from here, any ideas on what might be the problem? At first I thought it might the a bur or something on the piston, which is keeping it from sliding freely. But now, I simply don’t know. The piston did seem rather stiff as I ran it in and out of the slave, but I have no idea if it is sposed to do that.

If you bled this system for 30 minutes the slave should be full by now, and should be operating normally, but apparently isn't.

I think I know what’s wrong. We have had other shops bring us cars that they couldn’t fix, and they had a problem similar to yours.
It took them forever to bleed the system and it never would build enough pressure to actuate the slave cyl. and disengage the clutch. They had rebuilt the clutch masters and slaves, and we found that the seals (cups) had been INSTALLED BACKWARDS.

It will still pump fluid this way, but not very much on the down stroke, and not enough to ever actuate the slave cyl, but pumps lots of fluid and air backwards into the fluid res. on the upstroke which is why you hear air escapeing there.

Take the piston back out of the master and check the orientation of the seals (cups) Make sure the “open” side of the seals or cups are faceing foreward. I think you will find that they are backwards. It’s an easy mistake to make if you didn’t look at the old ones before you took them off, so don’t beat yourself up.
I would also check the seals on the slave cyl. at the same time, since it would be logical for you to have installed both the same direction when you rebuilt them.

p.s. When you have the cups/seals oriented on the piston correctly, and you are puting the piston back into the cylinder, BE VERY CAREFULL. THIS is the point where the seals most often get “nicked” and a nicked seal will also cause you problems down the line.
GENTLY rotate the piston and cup as you gently feed the cup into the cyl. bore. Use your FINGERS to do this. NO sharp tools allowed here.

So I took apart the master again, and the seal was indeed backwards. I fixed it, and put everything back together. However, there is still little pressure when you push down the clutch peddle. I tried bleeding the cylinders again, and this time I have a steady stream fluid coming out of the nipple on the slave. But, when I close off the nipple and pump the clutch the push rod in the slave still does not move back and forth. Any ideas?

From 11-17-09 post: I would also check the seals on the slave cyl. at the same time, since it would be logical for you to have installed both the same direction when you rebuilt them.

The slave seals are all that’s left. Like I posted before, IF the seals are backwards on the master, then you probably installed them backwards on the slave cylinder also.
The only other possibility is a nick on one of the seals, and it/they are by-passing fluid. All it takes is one very minute scratch. You must inspect them very carefully.