AAR type A switcher truck Wikipedia
The AAR type A switcher truck is a diesel locomotive truck introduced by EMD and installed as standard equipment on most EMD switcher locomotives and on those of other manufacturers. It was designed by Martin P Blomberg and its US Patent was filed on Jul 6, 1937 and approved Nov 15, 1938 under U.S. Patent 2,137,074. It was designed for switcher service where the more complex high-speed passenger locomotive trucks were not needed. The truck uses drop equalizers but does not have swing hangers as used on the Blomberg B and others. A combination of coil springs, and leaf springs, positioned fore-and-aft inside the drop equalizers, give a good balance of damping. The wheelbase is 8 ft 0 in (2,438 mm).