Brake fluid coming out cap

[1971ford]

I've been having tons of brake problems lately on my highboy. Power brakes, drums all 4 corners (stock highboy).
First I had a leak in the right rear wheel cylinder so I replaced both rear wheel cylinders and put all new hardware (springs) on both rears.
But still my master cylinder seems to be spewing brake fluid out the cap... I thought it wasn't pressurized, what could possibly cause this? simply a bad cap seal?
Making me mad because It's probably working at stripping my freshly POR-15'd chassis/inner fenders.

[Hemmi06]

Something to consider: While filling the MC do you take the cap and set it down metal cover side down? If you do some of the residue brake fluid will sneek behind the rubber seal and pool into the cap. You turn it over and place it back on MC and all the fluid that snuck behing the rubber comes out. I have been there done that and was wondering where the fluid was comming from!!!

[1971ford]

That is exactly what I do... hmmm That might be it, but I think more is leaking than residual fluid could cause. It's not a massive leak but there are a few drops of brake fluid on my inner fenders and frame.
I will wipe the MC/frame/inner fender dry tomorrow morning and check it as soon as i get to school to see if it is coming out of the cap for 100% sure. I won't take the cap off either.

[fordman]

a clog in the brake system will also push fluid out between the cap and master. i have also heard others say they sanded down the edge of the master to make it stop leaking on them.

[1971ford]

THere shouldn't be any clogs. We have bleeded all 4 corners 4 times now. Its almost a daily routine
The rear wheel cylinders are new, the only thing brake wise not replaced are the front wheel cylinders but they still bleed fine and don't leak. hmm

[ScreaminZ]

You might see if you can buy just the seal for the cap. Those seals get old and hard and don't seal well against the rough casting of the master cylinder. Mine leaked all over the place too if i filled it up too much or took turns too hard. I replaced the cap and seal and all is well now.

[mrtleavitt]

I doubled up my MC gasket and no problems for the past year. You can get a new one in the "Help" section of Autozone.

[1971ford]

Doubling it up sounds good! I have a spare cap I think. I'll do that