Car: 87 gta, 4 wheel disc

I've been trying to find why my car won't stop. When I push the brake pedal my dad noticed brake fluid was squirting out the end of the combo valve that has the (air bleed off) and the screw in fitting that has a spring on it. The fitting is on the very front of the combo valve. I think the o ring is shot so i'm going to replace that if I can find one the same size. But my question is, would that cause the brakes not to work? It doesn't shoot out much but its a small stream. As the car is rolling I can press the brakes hard and pump them and it will hardly stop. Also, can you use a combo valve off a front disc/rear drum car on a 4 wheel disc car?

If that isn't the prob I think it might be the booster from what I've read on here.

Thanks for the info!

 

thats the problem, with a leak, you cant build the pressure needed to properly work the calipers/drums.

you can use the drum/disc valve, but the brake pressures wont be ideal.