a hydraulically driven rotary vibrator that includes a motor body and a pair of opposed housings . each housing includes a shaft , and an eccentric weight that are journalled by a pair of anti - friction bearings . the shaft of each housing extends a selected distance beyond a first end of the housing . a gear is attached to the extending end of the shaft . the gears associated with each of the housings are aligned and meshed with each other interior of the motor plate . the gears and their associated shafts are rotated when a hydraulic fluid is introduced into a motor chamber formed in the motor plate . the eccentric weights may be selectively phased for producing a determined vibratory output .