Page 71 - 39. MRH13-05-May2013
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There was one drawback to the arch bar design, however.
Because it was assembled entirely with bolts and nuts, vibra-
tion could loosen the nuts, and constant working of the truck
could enlarge the bolt holes until the truck would become out
of alignment or, in the worst case, come completely apart. This
shortcoming was becoming increasingly problematic by the
turn of the century, owing in part to the dramatic increase in
car size and capacity that followed the universal adoption of air
brakes and knuckle couplers. The tendency of arch bar trucks
to shake themselves apart could be overcome with periodic
maintenance, but cars that ran in interchange might not be
returned to their owners for months or even years at a time,
and when off-line, their trucks seldom received any attention
apart from journal oiling.
As a result, though the venerable arch bar design remained the
de facto standard (1 and 2), late nineteenth and early twentieth
3
3: John J. Tatum, head of the Baltimore & Ohio car
department and a prolific innovator, designed this
improved arch bar truck in the early 1920s when arch
bars had fallen out of favor with most other railroads.
The spring seat and columns were a one-piece steel
casting and Barber lateral motion rollers were located
between the springs and the bolster.
Freight Car Trucks - 3
century freight car truck development was devoted largely to
finding better alternatives, and a variety of designs employing
pressed steel or cast steel side frames and bolsters began to
replace arch bars. Some railway mechanical engineers remained
reluctant to abandon the arch bar truck, and efforts to improve it
continued until the mid-1920s (3). In fact, the Baltimore & Ohio
was still taking delivery of new steel sheathed boxcars with arch
bar trucks as late as 1928. By that time, however, arch bar trucks
were a lost cause. The Association of American Railroads banned
them from interchange in 1940, though they continued to be
used under company service cars that did not go off-line at least
as late as the 1970s.
Pressed steel trucks
Toward the end of the 19th century, making freight car parts
from pressed steel became both practical and economical,
4
4: The Pressed Steel Car Co. designed this pressed
steel version of the arch bar truck design. It was
assembled with rivets instead of bolts except for the
bolts that held the journal boxes in place.
MRH-May 2013
