Soft Peddle

Are there residual pressure valves in an A body's braking system, or could they be suspect for trapping air if installed? My '72 has issues with what feels like air in the system (pedal can be "pumped up"), but every time I bleed it, no bubbles. I took it to a local Firestone and the braking effect was better, but it still gives a couple state inspectors fits because it doesn't start slowing down the moment they start applying brakes.