Stovebolt.com Forums The Shop Area Driveline 1953, 153-A brake master cylinder question

I believe she is a 1/2 ton with a low ratio transmission. But my question regards the brake master cylinder. I have had issues with the pedal going down to the floor, but only when driving not sitting still in the yard. I have bled them and overhauled a wheel cylinder. I replaced the master over a year ago. I noticed the fluid in the master will shoot out if the cap is removed and press the brake. It even bubbles out around the cap (there is no gasket or "O" ring on the cap.
Is this normal for the master to shoot oil around inside when pressing the brake pedal?
Thanks,
Glenn

I've been watching for somebody knowledgeable to reply, because I wonder about this too. I just rebuilt my master cylinder - original 1949 single piston - and it also shoots fluid up when you press the brake pedal. My brakes work fine, so I'm assuming it's normal. My cap has a cupped bottom, which would cause the upward fluid flow to be reversed and shot back down. Sorry I don't have a picture handy.

yes if you don't have the lid on the brake fluid reservoir and you pump the brake, it will squirt when you release the pedal. so always pump slowly and put some cloths around your MBC. Also when bleeding the brake never, ever and I mean never, ever, fully compress you brake pedal. even if you have rebuild the MBC, there is a very good chance you damage the cups in the mbc and you're back to square one.
that could be the reason, why your pedal goes down to the floor when driving. I assume you have power brakes? so the extra vacuum pull with the engine running will give you the "strength" to push through the remaining resistance in the MBC.
on second hand.. have you also bled your MBC when installing it, or only ate the brakes?

It has original brakes so no power assist. When I replaced the master I bled the cylinder at the connection to the brake line (the line had fluid at the end and so I bled at the connection point). I am not aware of doing damage to any cups in the master. I.E. if a wheel cylinder ever was to blow the brake pedal will go to the floor so I can't understand why it would be make that way.
Also the surge of fluid is when the pedal is compressed, not released.
I checked with a local mechanic and he verified the squirting is normal, but I do know the cap should seal the fluid from coming out but do not know if there is supposed to be a gasket or "O" ring on the cap?

I believe there should be a flat metal gasket between the flange of the plug and the body of the MC. What kind of pedal height do you get on the first easy push in the yard?