15 is axially moved along shaft 16 towards the center of disc 13 i e closer to the longitudinal rotational axis of the disc then roller 15 will rotate more slowly as will shafts 16 and 17 once again assuming shaft 14 is the driving shaft this increase and decrease of rotational speeds are the same assuming shaft 17 is the driving shaft in order to accomplish this axial movement of roller 15 relative to shaft 16 and therefore radial movement of roller 15 relative to disc 13 the motive assembly 29 is actuated to pivot the shaft 16 about transverse axis a when the shaft 16 is so pivoted the rotation of disc 13 and roller 15 automatically tend to make the roller walk axially of shaft 16 and thereby change its axial position this is accomplished by introducing hydraulic fluid on selected sides of piston 83 so as to move piston rod 84 which is ultimately connected to collar 57 and therefore the other end 27 of shaft 16 this movement is instigated by manipulation of the valve handle or actuator 96 for the speed ratio control valve 92 for example as seen in fig3 the valve body 93 has been displaced upwardly allowing hydraulic fluid to move through the valve body 93 via port.