power brake problems

[71broncrollsport]

i recently installed a power brake booster assembly on my 71 with the chevy disc brake conversion and stock rear drums. when i run the engine and depress the brake has almost no resistane on the pedal and the pedal returns very slowlyand i have no brakes. when the engine is not running the brake pedal feels firm and returns normally. any ideas on what my problem is? its a 71 with a mstly stock 302 and auto trans

 

[S_bolt19]

make sure your vacuum lines are all tight on their ports and that you don't have a crack in one of the lines. That is where I would start.

 

[andre]

TRY THIS RUN ENGINE FOR TWO MINUTE AND REMOVE BOOSTER HOSE

IF YOU CANT HEAR VACUUM THERE A LEAK OR VACUUM HOSE BLOCK OR WRONG PLACE

IF YOU HEAR VACUUM THEN MY HAVE WRONG MASTER CYL

DID SAY IT NOW REAR DISQ BRAKE MASTER CYL NOT THE SAME HAS REAR DRUM BRAKE

PORPOTION VALVE MAY NEED TO BE CHANGE TOO

BEST BET IS GET SOME ONE THAT MADE THIS TO SEE WHAT DID HAVE TO CHANGE