AAR type A switcher truck
EMD#AAR Type A bogie trucks were first fitted to locomotives sold in 1935; they were successful and standard on EMD switchers into the 1970s; they were also used on other makers locomotives. Their design was a colaboration by Martin Blomberg at EMD and the originating foundry General Steel Castings; see U.S. Patent 2,137,074 filed on Jul 6, 1937 then granted Nov 15, 1938. Intended for lower-speed shunting, this bogie truck has a basic suspension system with drop equalizers, secondary leaf springs and primary coil springs, which provide adequate damping and relatively simplified maintenance; it does not have swing hangers as may be seen in higher-speed designs such as the EMD#Blomberg; as of this 2019 writing, these bogie trucks remain in service on operating locomotives in North America.
Wheel sets on this bogie truck are typically for 56.5 inch (1.435 m) standard gauge rails; wheel diameter is typically 40 inch (1.016 m); wheel base is 96 inch (2.438 m); early factory builds had Plain 6.5x12 journal bearings allowing 62750 Lbs (28.46 tonne) GRL per axle; later factory builds and rebuilds typically have APcGG 6.5x12 conical bearings allowing 70000 Lbs (31.75 tonne) GRL per axle; various trac motors (EMD#D17+D27+D37+D47+D57+D77+D78...) and gears have been used, though rebuilds typically have D78s with a 62~15 AxleBull~MotorPinion ratio; maximum stable speed is typically 45 MpHr (72 KpHr).