Yeah, its got to be the master cylinder. The symptom of a bad bomb is that it takes a whole lot of pedal pressure to activate the brakes, in other words, you can't get the pedal any where near the floor. Probably a shot rubber piston seal, otherwise if the cylinder were pitted, you'd usually see some sign of fluid leakage. you might try to find a rebuild kit if the cylinder is not pitted. I suppose another source of your symptoms might be a blown piston seal on the booster behind the cylinder, which is the gadjet that provides the power braking effect. Try the brake cylinder first, as its the cheapest fix. The booster is a $150 item. Bob H.