Abstract: A road compacting drum is equipped with a dual amplitude, rotational, vibratory mechanism. A shaft rotatably mounted on the drum supports eccentric weights. Casings secured to the shaft adjacent the weights have chambers accommodating fluent mass. The fluent mass comprise metal members, as steel balls, shot or liquid metal, that move to a first location in the chamber upon rotation of the shaft in one direction to increase the amplitude of the vibration of the shaft and drum. The fluent mass flows to a second location in the chamber in response to rotation of the shaft in a direction opposite the one direction to generally balance the shaft to reduce the amplitude of vibration of the shaft and drum.