Abstract: An apparatus for adjusting the position of semi-trailer axles in order to attain a desired per-axle loading. Typically, a semi-trailer is towed behind a tractor. The apparatus includes a trailer bed frame having a longitudinal axis generally parallel to the direction of travel; an elongated threaded shaft connected to the trailer frame, parallel to the longitudinal axis; an axle carriage supporting the trailer bed frame; a sleeve having a threaded bore threaded onto the threaded shaft; a sleeve support connecting the sleeve to the axle carriage such that the sleeve may rotate about the threaded shaft, while preventing any relative longitudinal movement between the sleeve and the carriage; a motor for bi-directionally rotating the sleeve; and one or more axles attached to the axle carriage with wheels on each end of the axles. An operator uses a switch proximal the axle carriage to rotate and move the sleeve in a desired direction via the motor, moving the axle carriage longitudinally in unison.