Brake booster or check valve?

Reading a thread here the other day got me thinking about the brake booster in my truck. The truck brakes just fine. But as soon as the engine is off, the brake pedal is rock hard. From what I have read, this points to the check valve not holding vacuum when the engine is off. Thoughts on replacing just the check valve vs the entire booster assembly?

Truck is a MT. Unless the parking brake is nice and tight, it's easy for the truck to roll when you start it. This truck is mainly for my daughter so the last thing I need is her rolling into a parked car because she couldn't press the brake pedal. (Part 2 of this issue is adjusting the parking brake)

 

sub'd for interest and knowledge for myself

is there really a "check valve" though? isn't the purpose of the check valve to prevent fluid from going in the opposite direction? that would be bad as it would always keep pressure on the pistons.

also they are power assisted brakes so the pedal is hard when engine is not running.

again, I'm hypothesizing and waiting for someone more knowledgeable than myself

 

When I turn my engine off if I pump the brakes like once or twice the pedal hardens up really fast. Pretty sure it's the same in the families other cars too. I believe this is because you're building pressure in the lines and the booster isn't operating when the engine is off so you're not able to apply as much hydraulic force. I'm also interested if anyone knows more.

 

it is just a one way check valve, pop the line that goes from the intake manifold to the booster off the intake manifold... blow through it and see if there is any resistance, then take if off the booster and hold your thumb over the end and repeat. If it is a booster it can be replaced without disconnecting any of the hydraulic lines off of the brake master cylinder (non ABS). I haven't done one on an ABS equipped Tacoma yet so i cant speak to that.

 

Thanks. I'll try that this weekend.

From what I have read, you should have 2-3 pumps of the brakes with the engine off before the pedal gets hard. Right now on my truck it's immediate. At minimum, you should be able to apply the brakes without too much effort before starting the engine.