The pressure washer that I have used and own recommends that the highest pressure is not used for car cleaning. My washer, a Karcher, has three lances with different pressures available. The lowest is for applying the washing liquid, the second is for car washing and the like and the third, the highest pressure, is for driveways etc.. I wash the wheels and therefore the brakes with the car lance and have had no problems. The thing I do not pressure wash is the door mirror glasses as I don't want to force water into the electrics behind the glass.
Vic.