Brake Booster filling with boost? Hard pedal after full throttle.

[jefo]

Hey guys,

In my 89 caravan turbo on 17psi the brake pedal goes hard after a pull. It goes makes to normal after a few seconds though.

What do I need to replace to fix this?
Also, is there a valve I can put inline with the booster line as well to prevent this as a safety measure?

Thanks,
-Jeff

[going4speed]

Might be the check valve on the booster. Cheap to fix.

[turbovanman²]

Check valve on the booster is no good or you have a leaking diaphragm.

[jefo]

The weird thing is it holds vacuum after the engine is off, so I am guessing it is boost pushing past the valve.