The Auto Tractor unit went under and behind the automobile. Note the huge bull gear inside the traction wheel. Hub gears from the car mesh with this gear when aligned. There must have been extensive wear on those gears operating in the open. The contraption had to have been noisy as well. No doubt the hub gears had to be replaced frequently. Additionally, there is a smaller gear inside the traction wheel. We can only speculate that it had to do with driving the belt pulley. The additional radiator can be seen on the axle between the traction wheels. Note the hoses near the front of the frame which connected with the car engine. Presumably a car would slide back and stop at the angles on the rear of the frame, and was held in place by the forementioned saddles.
Photo courtesy of the University of Illinois Archives