Hi, looking for advice. I have 03 wrx fairly stock but after hard acceleration my breaks go rock hard when going imidiatly to the break. Also if I’m on boost n tap the break it’s stiff again.

breaks are fine during normal rush hour driving I.e. off boost

From what I can find I either have a bad break booster / servo or bad check valve.

how can I test and tell which it is or has anyone experienced this before and have any advice?

thanks in advance.

Have you changed any pipes recently?

theres a pipe that comes from the brake servo with a valve in it it’s on the right hand side of th3 intercooler which causes such problems if not put back in right way or gone faulty

just a guess but this is what mine did wen I crushed 5he valve taking it out with a screw driver when changing for some fancy pipes long time back lol,

Thanks zany, only coolant pipes have been changed by me but u never know what people have done over the years. I will investigate this further!