I replaced the master cylinder and bled the brakes, now the brake light is on in the dash. this is a 1994 chev 2500 with 6.5 diesel, it has a hydro boost and a proportioning valve. do i have to hold the propotioning valve pin in when bleeding the brakes? also the pedal goes to the floor if you keep pressing hard on it. it done this before i replaced the master cylinder. the power steering was low and have filled it to full level and turned wheels to each side to bleed hydo boost still have light on and pedal goes to floor with continued pressure, goes part way then stops then goes to floor, the mastercylinder level does not go down. Got the brake light to go out by pushing in pin on proportioning valve, brake pedal still goes to floor with lots of pressure on it,Could it be my rear shoes aren't adjusted high enough?