The Stovebolt Site Forums The Shop Area General Truck Talk 1959 Apache Master Cylinder leaks inside resevoir!

Alright got a little issue. I've redone all my brakes except the master cylinder that i just cleaned up. When I pump the brakes it builds up pressure but as soon as I release my foot off the break I can see all the brake fluid fill back into the reservoir and I loose pressure again. It comes back in through a second drilled whole never saw this on a master cylinder before usually just has the one. Did I just reassemble it wrong? or should I weld this hole shut? And thankyou for any help.
-Mitch

THe brake fluid is supposed to come back to the master cylinder. Are you pumping the brake pedal several timees to get pressure built up? If that is the case, you are compressing air in the lines and wheel cylinders and need to bleed the brakes.

No I bled the brakes a few times and no change. But i reset the shoe adjustment on all the wheels I was thinking maybe the shoes have to much play.

Did you tighten up the brake shoes until the drums would stop turning by hand, and then back off the shoes just enough so the drums do turn?

No I left them backed off all the way. I'm thinking thats the problem or theres an internal leak in the master cylinder. But all the cars and trucks I've worked on pre 1955, and I never saw this pressure release hole or whatever it is.

do you have a shop manual? following the bleeding/adjustment procedures there and consulting the end of the brake section re problems is better than 'thinking' .... there's at least one hole, called a compensating port, don't remember if it's 2 but if that's the way it was when you started, that's the way it should be and not the source of your problem - but improper adjustment when you did the bleeding could well be, and could also mean you now have weeping wheel cylinders because the wheel cylinder pistons were made to move too far when you first attempted to bleed, which should be done after adjusting the shoes up tight

Bill

You have to ajust the brake shoes (bring them up to the drum) first. Adjust them until you can't turn the drums. Then back them off just until the shoes allow the drum to turn. I can just hear the shoes drag a hair when I turn them. You want to adjust them as close to each other as you can. I'll bet after you do this, they will probably work.

Have your drums been turned? Are the drums still within specs? If they have been turned out too far you may get some wheel cylinder leaking problems.

Builder has it right about adjusting the brakes. It is usually about 4-5 clicks to back it off. Even if there is some rubbing it's ok. Surely when you cleaned up the master cyl. You put a kit in it? That hole is a compensating port & is nessesary.