Bad Brake booster?!

[alpalwal]

A month or so ago I did a bunch of work on my car... I put in a new motor, put on new brake pads, rotors, and stainless lines all the way around....

since then, the brakes have completely sucked.

If I start the car with my foot already on the brake pedal, the pedal doesn't move in at all which leads me to believe there is a problem with the brake booster.

I have 2 check valves in by brake booster line right now, and both allow vaccuum from the engine to flow and pull air from the brake booster..

I have no idea what else my problem can be besides a spontaneously bad brake booster.. any other suggestions of tests or parts I need to fix?

89 240 with ka-t and non abs.

[Nissan_240sx]

Check your brake booster hose for cracks or holes. I thought you were supposed to have one check valve in the brake booster line?

[boznuttz]

Give more details. Is the manifold right next to the brake mc? Did you ever BLEED the brake fluid after periodically being exposed to extreme heat? Is there any fluid under the brake booster or behind the pedal behind the firewall? Any fluid leaking from lines?

[alpalwal]

I've bled my brake fluid and there are no cracks in the line.

I don't remember why I have 2 check valves... I know I put the second one in a couple months ago but I don't remember the reason... it shouldn't create a problem though, all it should do is make sure boost doesn't go to the brake booster.

I haven't looked at it recently, but I know when I changed my master cylinder a month or so ago there was some brake fluid leaking down the front of the brake booster. I figured it was from my broken bmc.

[CleanSfourteen]

If I start the car with my foot already on the brake pedal, the pedal doesn't move in at all which leads me to believe there is a problem with the brake booster.

You answered your own question, if your foot is on the brake with the car off and you turn the ignition you should feel the vaccum from the power brakes assist you in pushing the pedal down.

Your brake booster is indeed defective, most likely a busted diaphram.