Master cylinder overflows

[ares360]

I think 3rdowner is right, I think it just holds pressure until it all leaks out.

Duckryder,
It will leak out if it is not running too. All I have to do is start pumping the brakes and wait.

[fordman]

ok yep the master is bad and not letting excess pressure go by. replace the master.

[ares360]

not the bypass valve or whatever?

[DGrant09]

Ours would over-flow when I was told to clean the gasket really well, or replace it, tighten the cap spring and then clean the lip of the MC where the gasket seats with emery cloth. Even though our MC was replaced this past year, the lip had developed pitting and corrosion. It has been dry for several months since I did this.
Is there some sort of "bypass or relief valve" used to relieve pressure?? I thought it was the brake spring assembly opening up or loosening thus relieving the hydraulic pressure on the system.
Dan

[DBossMan]

I had the same issue with a new MC a year or two back. I replaced the cap and gasket until I found a pair that did not leak. There's a lot of crap parts out there.

Tim

[DuckRyder]

There's a lot of crap parts out there.

Boy, you got that right! Even buying name brand stuff isn't a guarantee, but it does help some.

Unfortunately it isn't usually an option for us with the trucks, but I have gotten where buy nearly everything at the dealer for our newer stuff, including batteries. I will on occasion go with an OEM IF I can verify it is an OEM.

[ares360]

I took the gasket out and cleaned it up. sanded the top of the lip and tightened the clamp. now it is just holding pressure.

[fordman]

thats good that that worked.

[ares360]

except the pressure will not release and it is probably going to do the same thing

[fordman]

let me summerize all that i know. this isnt saying that you have done something wrong. its just a list of things to check.

drum drum master cylinders are for drum drum apllications only they cant be used with disc brakes.
disc drum master cylinders are for disc drum applications only also. and shouldn't be used with drum drum brakes.
the lines for the front brakes are hooked to the back of the master cylinder.
the lines for the rear brakes are hooked to the front of the master cylinder.
line clogs can create pressure and not let the brakes bleed.
clogs can be from dirt and or from collapsed rubber hoses.
wheel cylinders/calipers can stick and not let fluid in or out to move shoes/pads. this can also be a blockage to the brake system.
some master cylinders have a pressure valve in them. and can at times be bad or get stuck and not relieve the pressure.

i hope this list helps in some way. i dont know what for sure could be wrong without checking it myself.

[ares360]

it's definitely a drum drum mc
all of the lines are hooked up correctly
have been bled

drums could be sticking
need to find the pressure valve to check that

Pretty sure it is the pressure valve.

Thanks