Method of preventing a vehicle brake system from developing a vaccum in a low-pressure area thereof

A method of preventing a vacuum from developing in a low-pressure area of a vehicle anti-lock brake system of the type including a tandem master cylinder, wheel brakes, and a hydraulic control unit, said hydraulic control unit comprising normally open electromagnet valves and normally closed electromagnet valves, said tandem master cylinder being connected to said wheel brakes by primary hydraulic pressure lines via said normally open electromagnet valves, said wheel brakes being connected back to said tandem master cylinder by low-pressure lines via said normally closed electromagnet valves, said low pressure lines passing through a low-pressure area, said method comprising the steps of:

• opening normally closed electromagnet valves periodically when brakes are not applied and each time said vehicle's ignition is shut off, to thereby equalize pressure in said tandem master cylinder and said low-pressure area and thus eliminate a vacuum trapped in said low-pressure.