Abstract: A hydraulic modulation valve for use in conjuction with a tractor power-takeoff shaft to prevent an instantaneous loading of the hydraulic clutch controlling the operation of the power-takeoff shaft is disclosed wherein the supply line leading from the valve spool to the hydraulic clutch is in flow communication with a modulation chamber. A yieldable spring-loaded piston is moved within the modulation chamber from an initial position to an operating position to allow the hydraulic pressure to increase from zero pressure to a working pressure for the hydraulic clutch. A bypass line bleeds hydraulic fluid from the inlet end of the modulation chamber to slow the rate at which hydraulic pressure is increased within the modulation chamber.