Abstract: A system for temporarily releasing spring actuated emergency brakes on semi-trailers without the necessity for the operator to leave the cab of the tractor for movement within marshalling yards comprises an air receiving valve centrally positioned at the front of the trailer a specific distance from the kingpin and connected to the emergency air system through a valve which seals the gladhand when the system is in use, an air injection probe extendibly mounted on a trolley which travels on an arcuate track mounted below and ahead of the fifth wheel of the tractor such that the probe travels in an arc at a distance from the center of the fifth wheel equal to that between the receiving valve and the king pin, a sensing switch for sensing alignment of the injector probe with the receiving valve, a drive mechanism for moving the trolley to align the injector probe and receiving valve, an air actuated cylinder for extending and retracting the injector probe to make and break contact with the receiving valve, a sol