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to haul longer and heavier trains at relatively low speeds. After
World War I, however, this "drag freight" philosophy began
to change as shippers demanded faster service. As the speed
of freight trains increased, it was found that most freight car
trucks were unequal to the task. Truck springs that cushioned
loaded cars provided a harsh ride when the car was empty, and
vice-versa. In addition, experiments showed that the 39' spac-
ing of rail joints set up harmonic oscillations in trucks at cer-
tain speeds which were so severe that, in extreme cases, the
wheels were actually being lifted up off the track.
24
25
24-25: Two slightly different versions of the ARA 70-ton
truck with 5'8" wheelbase, one by Symington and the
other by American Steel Foundries. The ASF truck had
Barber Lateral Motion devices.
Freight Car Trucks - 10
A variety of measures were taken to address these problems.
Truck spring stiffness and spring rates were modified. A num-
ber of different trucks designed to improve riding qualities
began to appear, and these efforts continued through the
1930s and into the post-World-War-II period. Friction snubbers
were also developed which could replace one spring on each
side of existing trucks and provide some improvement in riding
qualities at modest cost.
Barber lateral motion devices
As the cushioning effect of lateral motion in trucks had long
been recognized as desirable, the Standard Car Truck Co.
26
26: This cross section drawing reveals how the self-
centering rollers in the Barber Lateral Motion device made
limited sideways motion between the side frame and
bolster possible.
index contents
MRH-May 2013