Brake problem

Thanks for your reply. By "pulling up the brake" I assume you mean setting the parking brake while pushing on the brake pedal. If I got that right, there's no difference in braking and I can't feel any difference in the brake pedal as I set the parking brake, the pedal still goes to the floor. No lights come on and the brakes will continue to hold the truck on a mild grade, so the brakes don't fail when the pedal gets to the floor. Of course, I've only tried that with the truck empty, loaded might be a different story. Typing this I can't see your reply, but I think you mentioned replacing a check valve in the booster? The booster that I installed was more or less a unit and I'm not sure where the valve is located. Could you elaborate on that for me? Also, it occurrs to me that in installing the ABS modulator (not sure if that's the correct name) and the master cylinder, both were bled, but is it possible that air might be in the lines beyond either of those two parts? The pedal builds slightly when pumped a few times, not much, but I wondered if there might be air in the lines that I'm compressing when I push on the pedal causing it to travel to the floor. Thanks again for your help.