Systems and methods are described for providing a magnetic clutch to limit Z-directional motion of a mass (e.g., a carriage for transporting a robotic mechanism in context of a storage library). According to embodiments, the mass is suspended by cabling, and its Z-directional movement is controlled by a Z-drive assembly. The Z-drive assembly includes a drive gear made of a magnetic or conductive material, and the drive gear is in magnetic communication with a biasing magnet. Embodiments configured the biasing magnet with a particular magnetic moment and a position relative to the drive gear, so that the spinning of the drive gear induces magnetic currents that tend to counteract the motion of the gear. For example, in the event of power loss to the Z-drive assembly, magnetic clutching is used to limit or prevent motion of the mass under the force of gravity.