how do the brakes feel over all? the pedal mushy and push to the floor or normal firm feeling? or maybe hard as a rock?
if its mush the master is going bad, or it needs to be bleed. rock hard means the boosters not working right. engine off if you pump the brakes the pedal should get harder and harder with each push as it uses up the vacuum in the booster. they can rust and leak out the vacuum on ya running and cause a hard pedal.