Abstract: In a transfer set, a retention hook rigidly secured for rotation with the tailgate of the truck body for rotation therewith. Entry of the trailer body into the truck body automatically triggers pneumatic elements to lower the truck tailgate causing the retention hook attached thereto to capture a trailer body retention pin secured to the outside of the trailer body. A solenoid operated directional control valve prevents the inadvertent release of the trailer body when the truck body is lifted away from the truck frame to empty contents therefrom. A single pneumatic actuator releases the truck tailgate and, when the trailer body is retained in the truck body, also the trailer tailgate.