B2200 brake problems, pedal goes to the floor.

hey guys, i am having a problem where when i press the brake pedal while driving the pedal is going to the floor. i checked the fluid level and it is fine, also the pads and shoes are fine. i pulled the master cylinder off and checked out the plunger guy behind it that moves when i pressed the brake pedal. when i press the brake pedal there is a hissing noise(air escaping) from the plunger. anybody know what name the part is that i need to replace? is it just a diaphragm or is it the whole assembly(eek!)

thanks in advance.

1990 mazda B2200, 5 spd, abs.

By plunger are you referring to the piston in the master cylinder? If so I would recommend replacing it with a rebuilt cylinder (they are cheap) and the installation is simple. My 2 cents anyway.

that is always the best solution, but also check your brake lines to see if any of them are plugged.

the hissing nosie is coming from brake booster that is the bolted to the fire wall also check for leak at capliers and wheel cylinder pull rubber boot on the wheel cylinder on rear brake for fuild in them that is bad if every thing is ok replace master cylinder and bleed all brakes