I would inspect everything 1st. Like worn out pad/shoes, leaky calipers and wheel cylinders. I had my master cylinder go out and i lost my front brakes coming down a mountain no less. the master is a pain to change

 

ok..replaced the master cylinder..definately not the problem..i can hear the vaccuum leak on the brake booster now inside the cab. rpms shoot up when i push the brake pedal and no change in braking ability since the new master cylinder. anyway..i need to get this up and running today so any ideas? part is special order only from every store around here and im screwed if i have to wait for it. any advice would be nice

 

any brake experts out there?

 

It's ur brake booster! The Diaphram on the inside is bad,id almost put money down on it! Ill bet you if you pump your brakes repeatedly your RPMs will start to raise =) thats cuz the brake booster is letting the motor suck air from the broken diaphram (thus the HIIISSSSSSSS coming from your feet), iv got 89 with my booster on its way out, soft pedal but not that extreme yet. Before you go swapin parts tho do a little bit of self inspection, have a vacuum gun with guage? (try autozone they rent them =]) pull the line off the intake manifold and use the gun to pull a vacuum on the booster, if it holds a vacuum you've got other problems, if it doesn't make sure the grommet on the out side where the vacuum line comes in isn't bad... but other than that im pretty sure its a bum booster