An improved device and method of lubrication for a tongue jack, 5th wheel jack, or other jack or other threaded positioning device. Ports are provided in the inner and outer tubes of the jack. The aligned ports provide access to a lubrication cavity in the jacknut. The lubrication cavity may include a grease fitting such as a zerk fitting. When the ports are in alignment, a grease gun can be inserted easily to the zerk fitting to apply grease to the interior structure of the nut as well as to the threads of the jackscrew. The lubricant may be introduced directly at a region of contact between a screw and the load bearing element. Applicant's test results show that this improved lubrication can increase the life cycle of the jack by more than 100%.

A mechanical actuator for translating rotational motion to linear motion. The actuator includes a motor, a screw assembly, a bearing assembly, and first and second lubrication systems. The screw assembly includes a housing, a threaded screw shaft disposed within the housing, a nut assembly, and an extension tube. The threaded screw shaft is rotatable by the motor. The nut assembly is arranged to move in either direction along a longitudinal axis of the threaded screw shaft when the threaded screw shaft is in rotational motion, thereby moving the extension tube between an extended position and a retracted position. The bearing assembly is arranged to provide support to at least a portion of a length of the threaded screw shaft. A pathway of the first lubrication system is remote and isolated from a pathway of the second lubrication system.