SD7

From RailroadfanWiki

The Electromotive Division SD7 is a 6 axle, 1,500 HP diesel-electric locomotive built by EMD from 1952 to 1953. Like the 4 axle GP7, it uses a 16 cylinder 567B prime mover rated at 1,500 HP.

The SD7 was the first 6 axle freight locomotive built by EMD. Prior to the SD7, the only 6 axle locomotives built by EMD were it's passenger E units. Though Alco and Baldwin had been building 6 axle freight units for years, EMD regarded them as curiosities and didn't think the market for a 6 axle road switcher was big enough. Interest continued to grow however, and in 1952 EMD built it's first 6 axle road switcher, the SD7. Unlike the E units, which rode on 6 axle A1A trucks with the center axle unpowered, the SD7 used six axle C type Flexi-coil trucks on which all 3 axles were powered, the first unit to use this truck. EMD still regarded these units as "curiosities", so they called them SD's, or "Special Duty" locomotives. With 6 powered axles, the SD7 could pull more than a standard 4 axle GP7.

188 SD7's were built, the most going to Southern Pacific (44 units), who ran them up until the early 1990's as rebuilt SD7R's. Though their ranks are thinning, a few SD7's can be found on shortlines and museums. The first SD7, SP #1518, is preserved in operating condition at the Illinois Railway Museum in Union, IL.

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