Gas tank vent valve?

[Worden18]

Right now my 60 Rambler American is up on blocks while I re-pack the front wheel bearings and double check the brakes.  I had filled the car up and noticed a little bit of gas leaking out of the cap. I pulled the cap off and more gas spilled out and I realized the gasket on the old camp is pretty worn. I replaced it with a new one from my truck which happened to fit on there. It seemed like problem solved. Well I went out there today and noticed it's leaking again, and I gently released the cap only to have a flood of gas come out of there from the pressure.  Is there a plugged gas vent valve somewhere that I need to look at? I had never heard of such a thing but ran across a couple of things online. I need to do something quick before the damn tank explodes.  Any advice is greatly appreciated. I've owned 60 cars and I have not seen this problem.

[Ulu]

Gas caps had vents in 1960.

 

Yours is probably blocked.

[Tooljunkie]

Also, most fuel tanks are intended to be filled 80% for this very reason. 

[linus6948]

The aftermarket fuel tank I put in my 48 coupe came with a one way vent valve that got mounted high in the rear wheel-well, it closes if the car flips over.