The above sketch came from a reprint of a Heisler marketing booklet originally published in the 1920s. The following text accompanied the sketch.
"A patented 3-way swivel--- perfectly flexible in its action, while rigid and sturdy in construction --- holds each wheel in contact with the roughest track. Every wheel is gripping the trail, carrying its full share of the locomotive's weight, and delivering it's full share of the hauling power."
The photo above shows the partially disassembled Cass 6 middle truck. Most the stuff between the truck sides are part of the gear drive. The design of the gear drive for the model is covered in the Universal, Gears & Shafts section. The design of the wheels, axels, truck framework and brakes are covered in this section. The following links lead to information on the trucks.