Where's the Spare
Although a locomotive can't have a flat tire, on occasion mechanical failures with a traction motor assembly may require changing it out.
The traction motors as seen in the photo, are made up of the traction motor, the wheel and axle, and a gear case, which encloses the bull gear located on the axle and pinion gear on the traction motor.
The gear case is filled with lubricant to keep everything moving and cool.
Failure on the road that can stop a locomotive include a seized wheel bearing, loss of one or more teeth on either the bull or pinion gear or a mechanical failure inside the traction motor itself.
Expand the photo for a closer look.....