Abstract: A retractable flap system is readily attachable to the dump box of a dump truck which includes a tail gate pivotally coupled to the upper portion of the rear end of the dump box. The retractable flap system includes a flap having first and second ends. An attachment bracket attaches the flap to the outer side of the tail gate. The attachment bracket includes a first end which is pivotably coupled to the outer side of the tail gate and a second end which is coupled to the upper portion of the flap. An air actuated ram is coupled to the outer side of the tail gate and to the attachment bracket in order to rotate the attachment bracket and thereby raise and lower the flap. In the raised position the flap is positioned nearly flush with the outer side of the tail gate and the lower end of the flap is positioned in the vicinity of the lower portion of the tail gate. In the lower position the flap serves its normal function of deflecting rocks and debris thrown from the rear tires of the truck.