Brake booster hiss

[bcstingray]

The power brake booster I have, used but was to be a good one, has a hiss coming from the back side inside the cab. My truck is a 73 that I switched from manual to power brakes using an 81 up booster. I take it its just bad. Anyone else come across this problem?

[bd]

A continuous hissing sound from the booster is a perforated diaphragm.  Temporarily remove and cap the vacuum hose that connects to the booster then start the engine.  If the hissing stops, replace the booster.

[bcstingray]

I'm pretty sure it's bad. Will the rod that attaches from the brake pedal to the booster rod (81 up booster) fit on a 73-80 booster?

[bcstingray]

Would it matter to put a JB5 booster on a JB3 system?

[bd]

Using a dual-diaphragm vacuum booster is a common upgrade.