like it says i have a 93 coupe ex, and at a traffic light or whatever my brake pedal goes soft sometimes all of a sudden, it has been happening more lately, and i can pump it up to get some pressure but then it will drop back down again, i'm thinking it is the master cylinder, but i'm not sure, the front pads are good, i havnt pulled off the rear drums yet to see how they look but i dont think that could cause it. and my resivoir is full so i know its not leaking.

Help me out, Please.

 

Maybe your booster ?

 

sounds like a master cylinder problem.

 

well the master cylinder is not leaking, is there any way to check it to make sure it is the master cylinder before i replace it and its not the master cylinder?

 

When the car is OFF... does the pedal remain firm or does it get soft?

Does is get harder as you pump and then get soft after letting it sit for a minute

 

There are internally leaking seals in your master cylinder. The leak is not visible on the outside. Loosen your master cylinder slightly and feel behind it for fluid, if it's leaking there you may want to go ahead and get a booster too. Brake fluid contamination can destroy the rubber diaphram in the booster.

 

i replaced the master cylinder, and bleed the brakes, adjusted the rear drums and it works great now.