Master cylinder needs replacing. I just did this on a Bravada yesterday. His car had brakes but they felt weak and soft. Constant no pedal feel and the pedal would go all the way to the floor. If I tried to press the pedal to the floor as fast as possible, it still wouldn't lock up. If it was a booster, you would still have full braking ability, it would just be troubled. With a failed booster I can still get the brakes to lock up