fixing a booster leak

[yakka10]

I have a VP commodore and my breaks are hard to push down and they make hissing noise. I have never come accross this problem before. How do i check to see if there is a leak or moving forward do you think the master cylinder is dmaged and needs to be replaced.

[Pub247]

I'd say more likely the brake booster whixh is the larger black thing behind the master cylinder is probably stuffed they have large diaphragms inside them that tend to split. It could possibl;y the larger vacumm hose running from booster to engine

[Brett_jjj]

To test the brake booster ,with the car off,pump the brake pedal a few times to deplete any left over vacuum,then press and hold the brake pedal in whilst you start the engine.As the engine starts the brake pedal should sink in a bit further.If yours does not do this,either the booster has a vacuum leak,or theres no vacuum getting to the booster to start with..

[glenn l]

with the hard pedal and hissing sound it sounds like booster, my vn did the same thing. as pub247 said the diaphragm would have sh1t it self.
what normaly happens is the vacume comes from the manifold and it sucks vapours into the booster and the vapours cause the diaphragm to disintergrate.
you can get a new one or get yours rebuilt, i use a place in melbourne called VAC AIR SERVICE, do a great job and great turnaround.