well first off i have a 96 four door 4x4 blazer and when i press the brake pedal now, i have a really loud air sound coming from up under my dash where the pedals are, and the sound is the sound you hear for a second when you first press the brake pedal in a normal car except mine lasts for as long as i got the brake down and its louder than normal, anywayswhen i hit the brake i hear this noise and my brakes dont work at all and then i have to press really hard for them to work andthen the start to work a little,and when i press really hard it makes the car idle funny likethe rpms will drop to like 300 or lessand sometimes it will cut the car off.

so if you have any ideas or sugestions please postem they will be greatly appreciated

 

Brake power booster sounds like it went bad .. My friend just had the same problem in his 91 chevy van, when he hit the brake you could hear air and then it would lose power brakes the more he pressed the pedal... The diaphragm in the booster where the rod goes in prob dry rotted or somehow got torn....I can almost say 100% thats the fault with it...

 

Sounds like the diaphragm in your power brake booster is leaking.

 

would a bad brake booster be caused by a bad master cylinder or do they just go out on there own? what are some possibilities for this too break

 

welp you would`nt hear air from the master just the booster,,, did you start to notice anything wierd with the brakes b4 you heard this air noise? A master cylinder can leak fluid from between where the 2 mount together..If you didnt hear that air i would have orig said Master cyl but because you mentioned air noise, thats why we mentioned booster...

 

I'll put a x3 on the brake booster. One way to check it is to turn the engine off, then pull the check valve from the front of the booster. If you do not hear a rush of air into the booster, then the booster is shot.