A method and apparatus for aiding in positioning during assembly of a locomotive wheel with respect to a drive gear mounted adjacent the wheel during assembly and for maintaining the position of the drive gear during locomotive operation. The apparatus includes a lateral stop including a spacer formed of a semi-elastomeric material having a low coefficient of friction and specially adapted to fit into a stress relief groove of an axle between a hub of the drive gear and a hub of the wheel. The spacer is so designed as to be installable on the locomotive axle after installation of the drive gear, to be self-centering on the axle and to inhibit rotation of the spacer with respect to the axle such that the axle will not be marked circumferentially by spacer rotation.