The same principle is applied to bleeding the booster as a wheel cylinder. You start bleeding at the master cylinder, then go to the booster, then the wheel cylinders.This may sound crazy, but when I worked at a garage in the early 70's we were working on the brakes on a 2 ton truck- relined the brakes and rebuilt all the wheel cylinders. We got it all done and all that was left was to bleed the brakes, and we couldn't get a pedal. Bled them again, got a good pedal, let it set a few minutes-pedal would go to the floor. The old timer there said "let me show you boys something". He told us to open ALL the bleeder screws. Then he had us pump the brake pedal until just fluid came out the booster,then closed that bleeder screw. Then to the left front wheel, same thing- right front wheel, same thing. Then did the rear wheels the same way, and no air was in the system. We had a full pedal and it stayed that way. Just a thought (Paul Van Scott), if nothing else works to get a good pedal.