A method of employing a hydraulic unit of a brake system containing brake lines extending between a master cylinder and wheel brakes and valves which are actuatable by exertion of magnetic force and which have removable electrical coils and when unactuated assume their blocking position, including the steps of removing coils from the valves; connecting the hydraulic unit, toward the master cylinder or the wheel brakes, to an air source of adequately high pressure; switching the valves to their open position by the exertion of magnetic force of a permanent magnet; positively displacing the pressure medium contained in the hydraulic unit from the air source by air and caught.