Abstract: A hydrostatically driven road roller having a swash plate pump controlling the supply of pressurized fluid to a drive motor, a dead man's handle or the like controlling pressurization of the fluid in the fluid system, a manual speed control lever connected to the swash plate pump, and a disconnectible device positioned in the connection between the control lever and the pump. The disconnectible device comprises a piston fixed to a swash plate control shaft, a cylinder movable on and lockable with the piston, and means for moving the cylinder into and out of locking engagement with the piston. Centralizing means are also provided to move automatically the swash plate into a neutral position.