Soo I have a 1994 300zx with what I think needs to have the brake booster hose check valve and the fitting that's on the intake plenum replaced see what I did is I said f*** all tht and just blocked it all off with vaccume end cap on the booster a 1/4 npt fitting in the plenum as a block off and I dont think it works for sure but it's what I did to find the issue. I replaced the master cylinder bled it and booster too the brakes where getting wayy too much vaccume soo that's why I blocked off the air to the booster soo that I could see if the pedal was any stiffer WHILE RUNNING. Before all of that when the car was off pedal was nice when the car was running the pedal is soft and goes to the floor with no braking being applied untill I pump the brakes which s why I thought I had air in the lines I bled them multiple times they felt great with it off but I never bled the car while running but I see no point in that anyone else have any opinions on this.

No such thing as "getting wayy too much vacuum" if a vac hose is IN FACT going from manifold to Booster(factory setup) - whether the check valve is good , broke open , and obviously not if broke closed ??
Max vac for most cars (as in all of mine) around 20-22 "Hg @ idle .Ya know
Gotta get much clarification here , for the sake of safety ,man.

My question is clear would a bad check valve cause and or the hose going to and from it cause air to get in the system to the point the pedal has to be pumped till it works because the master is new the booster is new only other object I can mess with has to be the booster check valve?

Also I wanted to know that if I block off the brake booster does it really matter sure makes the pedal stiff I dont mind that at all just want to know if there would be any lack of performance cus tbh I prefer the pedal to be nice and stiff I'd rather my clutch was like that too... all in due time.

Quick question, have you ever tried to stop without the brake booster? I have and it is very very difficult and unsafe.
The check valve serves two purpose; allows the booster to assist one last panic stop if your engine stalls. Second purpose is to prevent positive pressure (from turbo engine) to get into the brake booster.

If your brakes fall to the floor with booster attached the you still have air in the system or malfunctioning part. Just because the BMC is new (possibly rebuilt unit) doesn’t mean it’s working properly. I’d suggest returning the BMC for another and bench bleeding first before installing.

Hope that helps.

itsa300zx wrote: ↑

Wed May 29, 2019 6:16 pm

Quick question, have you ever tried to stop without the brake booster? I have and it is very very difficult and unsafe.
The check valve serves two purpose; allows the booster to assist one last panic stop if your engine stalls. Second purpose is to prevent positive pressure (from turbo engine) to get into the brake booster.

If your brakes fall to the floor with booster attached the you still have air in the system or malfunctioning part. Just because the BMC is new (possibly rebuilt unit) doesn’t mean it’s working properly. I’d suggest returning the BMC for another and bench bleeding first before installing.

Hope that helps.

See I did bench bled and bleed it afterward. Soo the way I have been breaking now I capped off the booster with a vac cap blocked of the npt fitting on the intake plenum that connected to the hose that connects to the check valve and the hose that connects from the check valve to the booster removed I wish I could post the video on here but I really dont know how to on this forum but basically I bled all 4 lines too and only when I turn the car on the booster would make the pedal so soft and useless I'd have to pump the brakes for it to tighten up the master cylinder is bled but if anything I'll take it out and bleed it again.

NO a bad check valve wouldn't do squat to your brakes under normal operation. You have a leak in the system somewhere, may be in your ABS pump not in the booster. The ABS pump should cycle when you start the car, may be loosing pressure there.

Agreed with what NoLimit says, I hate to say but it's time to look for errors and such. Once when bleeding my brakes I'd removed the calipers, and somehow put them on the wrong sides (makes them upside down) without noticing except I could not bleed the calipers, period. Stumped and angry, it took awhile before I finally made the choice to recheck everything despite my confidence...and found my error, everything of course worked after putting them back correctly.
We all make mistakes and can be tired, frustrated, etc., so do yourself a favor and recheck everything including testing replacement parts.