air brakes the parking brake shall be a spring-operated system,actuated by a valve that exhausts compressed air to apply the brakes .the parking brake many may be manually enabled when the air pressure is at the operating level per fmvss 121
air brakes <br>the parking brake shall be a spring-operated system,actuated by a valve that exhausts compressed air to apply the brakes .the parking brake many may be manually enabled when the air pressure is at the operating level per fmvss 121