I'm in the process of replacing most of the braking components. New drums, shoes, all 4 rear wheel cylinders, all hard brake lines and new master cylinder too. I can't get anymore air out of the brake lines. I've ran 2 large bottles of dot 3 through. Pedal goes right to the floor. It stiffens up with a couple pumps but I can still spin the rear wheels by hand while Wifey is standing on the brakes. I'm really frustrated... any idea what to check?