Can someone tell me what constitutes a defective power brake booster? I added disc brakes to the front and with drums on rear. The booster,m/c (Corvette style) and disc/drum prop. valve are all new. All lines have been bled more than once.Didnt buy these as a kit. With my car running,the pedal goes 2 inches from the floor before any sign of braking. After I stop the motor,I have about 1/2 pedal. If I disconnect the check valve at the booster to release vaccuum,which by the way is 15 in. at the valve, the pedal goes to the floor. I have replaced the prop. valve and m/c again with same results.Can the booster be bad? any suggestions Please.