My brake pedal is to the floor no matter how much I bleed the system. Is it bad master cylinder or is it bad brake booster?

 

I had a ford explorer and the Master cylinder broke on it. The brakes only worked about 10% and the pedal droped right to the floor. When did the problem first start? Mine broke when I did a huge 4 wheel burn out in the rain, I worped my rotors, killed my pads and busted MC. Thats a ford for ya.

 

Seem like the master cylinder is busted on my car. Without the key in the car, I can pump the brake peddle and it will firm up. Soon as I start the car, after two pumps it's about 80% to the floor. Looks like I need to stop by the parts store tomorrow morning for one. I wonder if a 300ZX turbo one would fit on the max?