Maybe it's me but my point is: if I press on the brake pedal with the engine off (no Vac) the pedal starts to have back pressure fairly soon and does not go all the way down before it gets hard. With the engine running and Vacuum on the booster the pedal goes down fast with no back pressure until it seems to go to the end of the master cylinder, not to the floor. But it will not go any further and does not have the feeling of brake pressure.
Why would there be a difference in using the booster and not?