Abstract: The sliding transmission disk of a motorcycle automatic transmission is provided with a shaft sleeve having a spring seat. Located at the bottom of the spring seat is a receiving frame in which a compression spring and a turning and sliding member are disposed.The turning and slding member serves to prevent the compression spring from being acted on by a twisting force of the sliding transmission disk, thereby enabling the compression spring to rebound effectively to stabilize the decelerating action as well as the braking action of the motorcycle. The drive belt of the motorcycle is enabled to retrieve with precision so as to permit the motorcycle to be accelerated again after the decelerating and the braking actions.