A reciprocating drive assembly is disclosed for use in a fluid mixer to impart reciprocating movement along a longitudinal axis to a shaft carrying a mixing head. The drive assembly includes a housing, a flywheel mounted for rotation about a rotational axis, a crank member projecting from the flywheel, and a yoke supported by the housing for movement along a yoke axis parallel to the longitudinal axis. The yoke is releasably connected to the shaft and has a linear race formed therein for receiving the crank member. Guide assemblies are connected to the housing and to the yoke for sliding engagement therewith along guide axes parallel to the yoke axis. The yoke is between the guide assemblies. The crank member is caused to translate linearly within the race, thereby urging the yoke to move along the yoke axis to effect longitudinal reciprocating movement of the mixing head.