Master cylinder overflows

[ares360]

for some ungodly reason the master cylinder is leaking out the top. I bleed the brakes, no air or obstructions. I am missing something.

[kaptnkaos]

It's probably a bad gasket... mine does the same thing...

They don't make replacement gaskets for the older style MC's (the kind with 2 diffferent size reservoirs)..
at least I've not been able to find one..
Now that I got iot back on ehte road, I'm gonna replace the whole MC with a new style one.

KaptnKA S

[ToughOldFord]

The MC with the two different size reservoirs is the newer style.
Autozone has the gasket, part number 42069 for 9.99. Their website says you can special order at he store or buy it off the site.

[ares360]

yeah, I got the mc at o'reilly's a few months ago and the gasket is new, so that can't be it.

[70shortwide]

i bought one about a year ago, it leaked just like that. they would do anything about it. i never bothered trying to fix it. i went with power brakes right after so i got a new m/c. really ruins fresh paint on the inner fender

[ToughOldFord]

Being new or rebuilt does not eliminate the part from being faulty. In fact with the low quality materials and workmanship available today I'd wager being new might even be a good indicator of the problem. The gasket could be bad (most likely), the cap may not fit flush, or the clamp may not be strong enough.

[ares360]

well the gasket is good and I have tightened up the clamp until you can barely get it on. I think it has something to do with the pump behind the mc.

[fordman]

not an answer . but does anyone think the pressure from a bad bypass value could be causing this?

[ares360]

hey fordman,
you're not too far away from me.

[fordman]

you live down by robert.

[ares360]

nobody else think it could be the bypass valve?

[kaptnkaos]

Hmmm TOF.. ya got me thinkin'...

Now, I can't remember which MC I have, all I know is that it has been on the truck for 20 plus years.
One of the first things I did on the '68 CS when I got it was to go thru the brakes, so I know the one on it is the old style MC.
The gasket I got from NAPA was the wrong one. When I took it back with the MC top, they said the gasket was for the new style and that hey couldn't get the old style gasket.

KaptnKA S

[td]

when i did my power brake swap the first brand new MC leaked like crazy no matter what i tried, so i pulled it off and took it back to the wonderful old school parts store i do all my business with and showed them what it was doing. they ordered me a new one and swap them out and I've had not the first drop leak out of this one so i wouldn't think something is wrong until i tried another MC to rule out that one being faulty. Good luck with it, i know how aggravating that is.

[3rdowner]

Years ago I had a Mustang that kept pumping fluid out through the gasket. It was brand new and I noticed my brakes were very touchy after I replaced the mc. Turns out the new mc was holding pressure everytime you hit the brakes. It would release just enough to drive the car but eventually it would start pumping the fluid out. It would actually empty the resovoir if you didn't refill it. Replacing the mc solved all the problems.

ED

[DuckRyder]

Do you have a sticking brake? A stiking brake an overheat the fluid.

Under what conditons does it leak? Do you have to drive it a ways before it starts?