When I come to a stoplight my brakes "grab". There is no pulsation in the pedal. It is really jerking the car though. It acts as if I pumped the pedal, but I am using steady pressure. I checked the rotors and they are not warped. Most of my braking system is new since I recently put discs in the rear, save the booster. Does this sound like the booster is bad? Tonight I replaced the filter and check valve but no change.

Thanks