Brakes soft, car stops, but pedal goes almost to floor. At stop in gear, pedal will go all the way to floor if you keep pushing it. Replaced front calipers, complete replacement of rear drum brake assemblies, replaced master cylinder (and bench bled), new pads, new brake hoses, bled lines - no change.

Could it be the booster? Vacuum reads 16 at idle at the hose going to booster - is that enough vacuum? I ask because my vacuum dropped with my mods - was more like 20 with stock cam & heads.

Any info appreciated.

 

Proportioning valve?

 

Did you check for a brake fluid leak? You could have small leak that could give the symptoms you mentioned.