7at11

In sorting out my brakes, I have found that the end of my vacuum booster Flexes, like an eigth of an inch? Anyone ever have this problem? The whole master cylinder moves with it, I am thinking this may be my problem. Can somebody check this? ( I had a buddy watch it while I pushed the pedal a bunch ) I can't imagine it's normal, but can't keep replacing parts in a crap shoot fashion.....