No brakes while under boost

[95talonracer]

When I try to brake boost or just when I want to stop anytime right after I let off the gas and there is still some boost there, the brake pedal will not go down at all and it doesn't stop at all until the car hits vacuum. What is causing this?

[Matt D.]

There is a check valve in the line going from the intake manifold to the brake booster that prevents the brake booster from seeing boost and only vacuum. Check that out, it's probably just dirty, but should be an cheap replacement.

[95talonracer]

Well I trimmed the hose to better fit my smim and didnt realize that I cut this portion off. Found my issue. where do you get one of these?

[Matt D.]

I'm unsure because on some cars the check valve is just screw into the manifold and then the hose attached, other cars the valve is inside the hose like a DSM. I'd just buy new OEM hose and start over unless you can extract that valve somehow.

[Halon]

I personally just ran new 3/8" hose and put a regular old 3/8" check valve in there that I had laying around. I have a couple more check valves here if you are in a bind.