I meant brake.... LOL... Happened just yesterday, I was driving kinda fast and needed to use the breaks but they felt as if the car was turned off, after boost went down and vacuum took place then they worked but not as they should. Now the pedal is stiffer than usual but it does not bottom out. Maybe brake booster???

 

The brake booster wont be effective without vaccum. You can use a vaccum pump to test booster or with car running slowly depress pedal a listen for leaks.

 

I don't know how the turbo system works but im going to guess that there is supposed to be a one way check valve in the large vacuum line to only allow vacuum in one direction and to keep vacuum in the booster while the intake manifold is under pressure?

 

Under what circumstances does a person need to use boost and brakes at the same time, except when trying to launch in a roll race?

Brakes use vacuum, something there is none of in the intake tract when the engine is under boost (by definition). They were not meant to be used at the same time, that's just how it is. That said, the few times I have brake boosted while rolling, I have never had a real issue getting the brakes to work. You can also use your e-brake to brake boost.

 

theres a check valve in the brake booster vacuum line, maybe yours is missing or failed?

 

is ther suposed to be a check valve?......(TII swap and i dont got it) sorry dont mean to thread jack

 

Some t2's had the valve in the line at the BMC visible from the outside. Others had a valve that slid inside the hose and you cant tell without taking it off.

Even without the valve, when the engine is in boost, there is no longer any vacuum, so there won't be much of any assist left when you hit the brakes.

 

What I meant to say was that I had to use the brakes suddenly...

Let me make the picture clearer:

I'm doing about 90mph on my daily driver, boost is up and I had to use the breaks all of the sudden and the pedal was as stiff as a rock... It was not until after a few seconds that the pedal became more or less soft but not like it is supposed to... Under other circumstances I could have f@cked my **** up... Now under normal driving the pedal still feels harder than what it used to be... So in other words I had to wait for vacuum to build so I could use the breaks. It is my best understanding that the booster is supposed to have at least some vacuum stored for these type of situations so it might be the booster diaphragm...

BTW for burnouts I use the break line lock (which is not faulty)... LOL

Check valve is fine... Gonna check the booster... Thanks for the pointers guys, just wanted to make sure if my assumption could be accurate before doing any work... Once again RotaryResurrection thanks!!

 

thats why theres a check valve. you should be able to idle the engine, shut it off and still have power brakes for 2-3 applications of the pedal.

if you dont its a booster/check valve issue

 

As soon as you let off the gas(to hit the brakes)there is vacuum present and no boost. Are you hitting the brakes with your left foot while the right one is still floored???