why does my van skip when I brake?

Are you referring to a pulsating brake pedal while braking ? If this is happening then your brake rotors are likely warped. The mfg usually has a minimum runout and the rotor are likely beyond that limit. If this is the case then the rotors will have to be resurfaced or replaced.. Most brake rotors are so thin when they are made that there isn't much extra metal on the rotor to dress it and it still remain within specification. Brake rotors are not as expensive as they were years ago.. I call them "disposal" rotors and almost never machine them any more.. once I take them off then they go in the garbage can.. The amount of labor it requires to machine a rotor in most cases cover the cost of a new one.. Good luck Chuck