Figure 3.1. Typical Truck.
integrated with other truck components and other car parts is also discussed.
3.3. BOLSTER ASSEMBLY
The truck bolster is a heavy crossmember at the center of the truck set parallel with the axles. The bolster
initially receives the weight of the car body and distributes it to the two side frames. It has three important
parts: the center plate, the bolster ends, and the side bearings.
a. Center plate. The circular raised plate in the center of the truck bolster is a forged or cast-steel female
member that matches a similar male center plate on the car body bolster. A pin from the body bolster fits into
the recessed hole in the truck bolster center plate. This connection permits the truck to swivel beneath the car
while maintaining contact between the center plates. A heavy lubricant must be applied between these plates to
retard wear. When the car is on straight track, most of the weight of the car and its contents is directly upon the
center plate; when the car is moving on curved track, the side bearings support some of the weight as explained
in subparagraph c.