Figure 3.5. Typical Six-Wheel Truck.
the brake cylinder on the bottom of the car body. These cars have the brake cylinder mounted on the truck side
frame. The cylinder, with all other body-mounted braking apparatus, is discussed in chapter 6.
Most of the rolling stock in service on railroads throughout the world is equipped with four-wheel trucks.
In addition to the wheels and axles, the principal parts of the truck are the bolster assembly, side frame, journal
box, and brake rigging.
Set parallel to the axle, the truck bolster has three main parts: a raised center plate that connects with a
similar plate on the car body, permitting the car to swivel; ends that interlock with the truck side frame,
preventing lateral movement; and side bearings, located on the bolster top midway between the ends and center
plate, to steady the car and prevent most of its rocking motion. The truck side frame interlocks with the bolster.
Cast into the side frame is the journal box with parts that have important functions. The dust guard keeps
dust, dirt, and moisture from entering the box itself from the rear; a wedge distributes the weight of the car and
lading evenly over the axle journal; packing and lubricant keep the journal from overheating; and a lid on the
outer end of the box keeps anything from getting into the box.