Usually when the master cylinder goes bad it won't hold enough pressure. The place to look is at the individual wheels. See which one(s) is(are) getting hot, then check from there to find the sticking caliper. Over time the brake hoses deteriorate and allow pressure to pass through but won't let it release all the way. An easy way to check is to loosen the bleeder screw and see if fluid will run out on its own. If it won't drip, you need brake hoses.