Looking for some input on possible brake booster problem.

New master cylinder in the car. While car is in gear and decelerating, when I first press the brake the pedal is very hard. then after I am stopped or if I let off the brake and press it again the pedal is somewhat firm but will keep going to the floor if I keep the same force on it - but there's no decrease is braking ability.
I noticed also that the pedal is only somewhat firm if I am coasting and then hit the brakes. Is this a sign of a bad brake booster, perhaps loosing vacuum?

And secondly what's the physical difference between the power booster for hard suspension as opposed to normal suspension, are these not interchangable?

 

Is the car hard to stop?

You can do a vacuum check on it with a vacuum pump to make sure it holds vacuum. Also if the rod from the booster to the pedal is incorrectly adjusted, the pedal will feel very hard with little braking.

 

Bad master cyl or expanding brake lines

The booster even if disconnected and open will not change and let the pedal float down.

A bad booster will simply increase the amount of pedal pressure needed to stop the car.

size and amount of pressure needed to push activate the brakes