I have a ej1 w/ abs and the brakes feel as if I have manual brakes. So I replaced my brake booster with a known working one the same as mine thinking that would solve my problem but it didn't. So here is where things confuse me. The check valve was on backwards; it had the arrow pointing towards the brake booster. Flipped it around started the car and have no pedal pressure. I turn the car off remove the check valve and the brake booster side blows off. When I have the car running and pump the brakes it builds pressure in between the check valve and booster when the check valve is in the right direction. Replaced the check valve with a known working one and get the same results. I'm wondering if the MC went out.

Cliffs:
Feels like manual brakes
Replaced brake booster same problem
Check valve on backwards flipped in right direction
Check valve builds pressure between the valve and brake booster only works if backwards even with known working valve
Possibly MC bad?

 

Any ideas?