When my car is on the brake pedal is fine, but when i turn it on the pedel is really soft and?

Question

ohkay this is what happedn today i just finished my rear brake conversion everyhtin is fine, bleed it and everything it's a 94 del sol with stock front , but the rears are from a 94 integra, i used a 1725 prop vavle , can someone please help me. when i just let it sit without it on the cars brakes are normal, but when i turn it on the brake gets really soft. and the brake is weak

Answer 1

you need to change the master cylinder too

Answer 2

thats due to the vacuum line. when the vehicle is off its only using mechanical forces to apply the brakes, when your car is running it uses the "power brakes system" you have a leak in your vaccuum line check the master cylinder.see your manual for location. should be right in front of the steering wheel on the other side of course under the hood.

Answer 3

Bleed them again,  You must have air in the line

Answer 4

you need a different proportioning valve. When the engine is off, there is no vacuum for the booster, that is why the pedal is hard.