Abstract: An improved variable moment vibratory driver system in which a variable moment is achieved by hydraulically shifting the phase of two sets of eccentric weights via a control valve shifter. The mutual phase of the two sets may be changed at any time without stopping the gear wheel rotation unprecedented in conventional devices. The weights are shifted through direct driven meshed gear links which are located in the place of Pecqueur epycyclic gears. An integral electrical wire diagram of the control valve shifter and a hydraulic phase shifter are used to start and stop the variable moment vibrator with reduced gear elements and virtually no vibration.