[POWERBRAKEBOB]

IF the master is sucking air in, then there is no venting between the booster and the master. Perhaps someone put sealer in between? They must vent.
I do HYDROBOOST conversions, and can build for the C-4's. With a HYDROBOOST booster, I run a c0ommon 1" master, even one from a C-5 can be used. Gives outstanding braking performance, AND a firmer pedal