b. Bolster ends. The truck bolster interlocks at both ends with the truck side frames, tying them together
and preventing lateral movement. The interlock is made by bolster guides that ride up and down the columns of
the side frames. The bottom of the bolster has, on both ends, built-up, shouldered spring pockets that seat unit
clusters of coil springs upon which the bolster rests. The springs are seated at the bottom in matching pockets
either on a spring plank or in the side frame itself. In a spring-plank truck, a steel plank runs across the truck,
beneath the bolster, and interlocks with the two side frames. It is important to note that the same number and
same size of springs are used on both sides of the truck; however, the number and size of springs vary with
different type trucks depending upon the loads and speeds for which they were designed. The typical freight car
truck has five coil springs beneath each end of the truck bolster.
c. Side bearings. Special steel plates, fabricated as part of the truck bolster, with flat bearing surfaces are
designed to make contact with similar bearing surfaces on the bottom of the car body. The truck side bearings
are located on the top of the bolster between the side frames and the center plate. These bearings steady the car
and prevent most of the side-to-side rocking motion that develops as the car moves over uneven track or around
curves. When the car is moving at a slow rate of speed around a section of track that curves to the left, the left
side bearings make contact with the bearing surfaces of the car body; when the car is moving at a high rate of
speed, the right bearings make contact because of the centrifugal force acting on the car body. When the car is
on straight, level track, none of the side bearings are in contact with the car body bearing surfaces. A heavy
lubricant should be applied to these bearing surfaces to reduce wear.
3.4. SIDE FRAME
The side frame of the truck, shown in figure 3.2, is a cast-steel, dual-trussed member, having two
connecting columns to which the truck bolster interlocks. A journal box is cast integrally with the side-frame
on each end. The bottom truss is cast to fit either the spring plank or the springs themselves; between the
columns and the journal boxes on the top truss, brake-rig lugs are cast to provide a means for hanging brake
beams. The truck side frames are subjected to severe stresses and strains when the car is under load and being
pulled at a high rate of speed. They should be inspected frequently and carefully for cracks or chips because a
failure of either frame would cause the car to derail.
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