power brake problem

[63Burb]

I converted my 63 to front disc brakes with a complete 72 front suspension. It has a stock power brake booster with the correct brackets from a 64. The master cylinder and proportioning valve are for a 72. The 350 came out of the same 72 GMC with power brakes so it has the correct vacuum line that runs from the carb base. The vacuum line and the check valve are the only brake parts on the entire truck that aren't new.
The problem is that I have good manual brakes but absolutely no power assist. The booster is getting vacuum from the engine and will hold vacuum after the engine is turned off. I'm really out of ideas here. Any help would be welcome.

 

[williamb82]

well if the booster is holding vac it should be assisting. only thing i can think of is the diaphram has come loose from the shaft, but that would cause a vac leak i would think. sounds like a faulty booster to me. you do have the check valve installed the correct way right? make sure you can blow through it towards the engine. if thats right then id say bad booster. if not flip the check valve around.

 

[dvalentine]

Check that the thrust rod off the brake pedal is fully depressing inside the master cylinder.
Mark the rod when fully depressed, then disconnect the rod from the pedal and see if the rod will go in further.
If it does, THATs' your problem..

Val