Page 82 - 39. MRH13-05-May2013
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35
35: An ARA truck with a combination of coil and elliptical
leaf springs. Motion dampening was provided by the
inherent friction of the leaves in the spring. Note that this
particular truck had double-truss side frames, with the
lower chords boxed-in, but was not self-aligning and still
employed a spring plank.
this truck interlocked so that the truck was self-aligning; no
spring plank was required, resulting in a significant reduction
of unsprung weight. Though distinctive in appearance, the
National B-1 truck conformed in all respects to ARA/AAR speci-
fications. Competitive in price and performance, it was widely
adopted by many railroads in the 1930s and 1940s until it was
rendered obsolete by trucks with built-in friction snubbers such
as the Barber S-2 and ASF A-3 (see below).
Coil-elliptic trucks
Several truck manufacturers, notably Gould and Buckeye,
began in the late 1920s to offer ARA/AAR standard trucks with
a combination of coil and elliptic springs (35). The Pennsylvania
Railroad also applied coil-elliptic spring packages to many of its
later ARA type trucks (36). The advantage of this arrangement
was that elliptical leaf springs had inherent friction between
Freight Car Trucks - 14
36
36: Applied to a car built in 1936, this Pennsylvania
Railroad truck with coil and elliptical springs was a direct
descendant of the ca. 1920 2DF8 design, which the
Pennsy continued to use long after other railroads (and
the ARA itself) had abandoned it because its side frames
tended to crack.
the leaves so that they tended to act as snubbers and damp
out excessive jolts and oscillation.
AAR Self-Aligning Spring-Plankless trucks
The need for further research and development in the design
of freight car trucks continued into the early 1930s, but owing
to the effects of the economic depression, individual truck
manufacturers lacked the capital to pursue it on their own.
This led to formation of a consortium of truck manufactur-
ers under the Four Wheel Railway Truck Agreement. All of
those who participated in that agreement contributed to the
research, and all were able to employ the resulting improve-
ments without paying royalties.
The outcome of this initiative was the Self-Aligning Spring-
Plankless Double Truss truck, whose innovations combined to
MRH-May 2013
