I just bought a used 1999 Ford Taurus. The brake pads and shoes have been replaced on the car and thought that they need to be bled. We bled the brakes and got all the air out of the system but I am still having to press hard to stop. I have start braking halfway down the block before a stop sign! There is an "air" sound on the inside of the care when pressing on the brakes. Could this be bad wheel cylinders and the master cylinder together or could it be the brake booster or does something need to be adjusted?