so sometimes when i drive my break pedal goes soft. i cant figure out why. and usually its at the moments i need them the most. when i hit my break pedal and theyre working fine it sounds like air is leaking out of somewhere a "psssst" noise. now i dont know if it is suppose to do that but i sure as hell know my break pedal shouldnt hit the floor sometimes. any ideas? thanks!

 

If you have rear antilock brakes, the sensor will cause this.

 

A bad diaphragm in the vacuum booster will make the wooshing sound also, but typically makes the pedal get hard not soft. When the pedal gets soft does it just go to the floor? My old buick does this when low on brake fluid, has a couple leaky cylinders. So i guess start in the most obvious spot and check your brake fluid if you havent.

 

x2 with what hairybox is saying(XD...hairybox)

 

master cylinder could b going bad