Pneumatically actuated parking brake

A vehicle parking brake system pneumatically actuates an air cylinder (46) to mechanically lock a wheel brake (12) in an applied position in response to a parking demand request. The air cylinder (46) includes an extendable shaft (42) that supports a lock member (62). When a parking demand request is initiated by moving a hand control (56), an air chamber is pressurized with air from a parking reservoir via a valve assembly to apply the wheel brake. Air pressure is released from the air cylinder and the lock member is moved into engagement with a brake component to lock the wheel brake in the applied condition. The wheel brake remains locked even if pressure is released from the air chamber (26). When a release command is initiated, the air cylinder is pressurized and the lock member is moved out of engagement with the brake component.