Ford: hard brakes, ford 150, brake booster

Question
I have a 1999 ford 150 4by4
brakes are nomarl and nexts time I have to stop brake peddle maybe hard and no braking pretty scary.

Answer
it sounds like you may have a bad brake booster. to test it with the truck off pump the brakes till the pedal gets hard it should be only about 10 x's. Now start the vehicle and see if the pedal moves down to or equal with the gas pedal.if not the booster is bad .let me know