Milwaukee Road’s EMD SDL39 diesel locomotives came from the road’s desire to replace aging Alco RSC2 units in branchline service.
The Milwaukee Road custom-ordered the lightweight SDL39 specifically for use on its light-rail branch lines. The railroad bought five of the locomotives in 1969, Nos. 581-585. It followed with an order for another five in 1972, Nos. 586-590. Mechanically, the 2,300-hp locomotive is an SD39, an oddity itself, with a 12-cylinder 645E prime mover, but on a shorter (and lighter) frame. At 55 feet, 2 inches they were in fact slightly shorter than the original GP7.
To accommodate this change, the SDL39 came with a smaller 1,200-gallon fuel tank and short-wheelbase trucks commonly used on EMD export locomotives. Significant spotting features include a single turbo exhaust stack and two cooling fans over the radiators. Scale drawings appeared in the September 1990 issue of Model Railroader.
The SDL39 weighs about the same as a four-axle GP38. However, by adding the two extra axles, the axle loading weight drops 61,000 pounds to a little more than 41,000 pounds. This gives the units a distinct advantage when operating over light rail on branch lines. In deference to this, the units were geared for operation up to 65 mph.
On the Milwaukee they initially operated on secondary and branch lines in South Dakota, Minnesota, and western Wisconsin. Later, they worked around the Twin Cities, often paired with SD10s (a Milwaukee designation for rebuilt SD7s) or GP38s.
One unit, No. 581, was wrecked on the Milwaukee Road at Sacred Heart, Minn., in 1983 and subsequently scrapped. The remaining nine locomotives went to the Soo Line with its 1985 acquisition of the Milwaukee and saw black patches applied over the Milwaukee Road lettering. Then the units landed with spin-off Wisconsin Central Ltd. in October 1987, four through a direct sale and the remaining five through WC’s Oxford Leasing subsidiary. While on the WC, some received that road’s maroon-and-cream paint scheme.
Later, when deemed surplus by WC successor Canadian National, they found new homes on the FEPASA, Chile’s largest railroad, as its Nos. 2341-2349.
