EMD "SD7" Locomotives: Data Sheet, Specs, Roster

Last revised: December 17, 2024

When Electro-Motive quietly unveiled the six-axle SD7 in 1952, company officials could have never imagined the new "Special Duty" line would one day witness unprecedented success.

Prior to its introduction, EMD had no interest in a specialized locomotive and instead remained focused on mass produced four-axle variants. At the time this included the streamlined "F" series although the builder had recently (1949) launched its own road-switcher line, the GP7.

The SD7 was the Geep's larger cousin, sporting a C-C truck arrangement that offered greater tractive effort on a longer frame but was otherwise identical. At the time, there was little interest in such a design; comparable models sold by Alco and Baldwin also found little interest.

A total of 188 SD7s were produced during a very short production run from April, 1952 to November, 1953. Interestingly, in a nod to the quality of EMD products, the model's largest buyer - Southern Pacific - rebuilt its entire fleet, which remained in service through the 1990s.

Photos

Burlington Northern (Colorado & Southern) SD7 #6077 (built as #817) and GP38-2 #2154 at North Yard in Saginaw, Texas, circa 1983. Mike Bledsoe photo. American-Rails.com collection.

History

The six-motored locomotive concept was not new when EMD introduced the SD7. As Brian Solomon points out in his book, "EMD Locomotives," General Electric had offered a straight-electric in this configuration as early as 1930 when it produced 42 Class R-2 locomotives for New York Central for its West Side freight operations in New York City (Manhattan).

In addition, Alco had first offered a six-motored RS1 in 1942 for the U.S. Army while Baldwin first cataloged its own six-axle version as early as 1946, the A1A-A1A trucked DRS-6-4-1500. Two years later it unveiled the six-motored DRS-6-6-1500.

Internally, the SD7 was identical to its four-axle counterpart, equipped with a 1,500 horsepower, 16-cylinder model 567B prime mover.

However, it was also unique via a custom designed frame; by contrast, Alco and Baldwin had utilized the same basic frame in developing both their four, and six-axle models. While internally the same, the SD7 was outwardly unmistakable from the GP7.

At a length of 60 feet, 8 ½ inches over couplers, the model was more than five feet longer than its four-axle counterpart. A single locomotive could haul a 5,500-ton train on level track, climb grades as high as 5%, and negotiate curves of 23 degrees.

The SD7 also featured another unique trait, EMD's own Flexicoil truck. This lightweight, high adhesion design offered a surprisingly comfortable ride and was easy to maintain. It provided mechanics straightforward access to the center-axle, which was difficult to reach in Alco's early six-axle truck.

Burlington Northern SD7 #6088, sub-lettered for the Fort Worth & Denver, is seen here in Fort Worth, Texas, circa 1983. Mike Bledsoe photo. American-Rails.com collection.

Reception

In the early 1950s, railroads still preferred four-axle locomotives in main line freight service. As a result, reception to EMD's early six-axle variants was cool.

Nevertheless, there was some interest, especially by Southern Pacific, which tested out the builder's bright red demonstrator, #990, and ultimately purchased this unit. In fact, SP wound up with the largest fleet, 43 of the 188 examples produced.

Data Sheet and Specifications

Entered Production	4/1952 (Milwaukee Road #2200)
Years Produced	4/1952 - 11/1953
Engine	567B
Engine Builder	GM
Horsepower	1500
RPM	800
Cylinders	16
Length	60' 8 ½"
Height (Top Of Rail To Top Of Cab)	15' 0"
Width	10' 8"
Weight	300,000-360,000 Lbs
Fuel Capacity	1200 Gallons
Air Compressor	Gardner-Denver
Air Compressor Model	WBO
Air Brake Manufacturer	Westinghouse
Air Brake Schedule	6BL
Trucks	C-C
Truck Type	Flexicoil
Truck Wheelbase	13' 7"
Wheel Size	40"
Traction Motors	D27C (6), GM
Primary Generator	D12B, GM
Auxiliary Generator	Delco
Alternator	D14
MU (Multiple-Unit)	Yes
Dynamic Brakes	Yes
Gear Ratio	65:12, 62:15, 61:16, 60:17, 59:18, 58:19
Tractive Effort (Starting)	90,800 Lbs at 25%
Tractive Effort (Continuous)	75,000 Lbs at 9.3 mph
Top Speed	55 mph (65:12), 65 mph (62:15), 71 mph (61:16), 77 mph (60:17), 83 mph (59:18), 89 mph (58:19)

Production Roster

Total Built = 188

Owner	Road Number(s)	Serial Number(s)	Order Number	Completion Date
Milwaukee Road	2200-2208	15612-15620	5139	4/1952-6/1952
Milwaukee Road	2209-2211	15621-15623	5201	6/1952, 8/1952
Electro-Motive (Demonstrator)	990 (became Southern Pacific #5308)	15624	7512	10/1952
Great Northern	550-564	16099-16113	5146	5/1952-10/1952
Nevada Northern	401	16824	6397	8/1952
Milwaukee Road	2212-2214	16941-16943	5144	6/1952
Fort Worth & Denver City (Burlington)	850-857	17121-17128	6468	3/1953
Colorado & Southern (Burlington)	810-817	17129-17136	6274	1/1953-2/1953
Bessemer & Lake Erie	801-803	17138-17140	6436	10/1952
Southern Pacific	5279-5293	17144-17156	5157	11/1952-1/1953
Colorado & Southern (Burlington)	818-819	17260-17261	6274	2/1953
Chicago, Burlington & Quincy	400-411	17396-17407	5140	11/1952-12/1952
Minneapolis & St Louis	852, 952	17408-17409	5181	12/1952
Electro-Motive (Demonstrator)	991 (became Baltimore & Ohio #760)	17410	6457	3/1952
Kennecott Copper Corporation	903	17411	6456	12/1952
Great Northern	565-572	17896-17903	5182	3/1953-4/1953
Bessemer & Lake Erie	451-455	17904-17908	5212	4/1953
Fort Worth & Denver City (Burlington)	858-860	17921-17923	5249	10/1953
Denver & Rio Grande Western	5300-5304	18124-18128	5232	5/1953
Chicago & North Western	1661-1664	18223-18227	5185	5/1953
Chicago & North Western	1660	18227	5276	6/1953
Union Pacific	775-781	18284-18290	5244	6/1953
Union Pacific	783-784	18291-18292	5277	6/1953
Union Pacific	782	18293	5278	6/1953
Milwaukee Road	2215-2219	18301-18305	5274	10/1953
Milwaukee Road	2220-2223	18306-18309	6516	10/1953
Central of Georgia	201	18310	6512	5/1953
Chicago, Burlington & Quincy	300-324	18320-18344	5242	5/1953-10/1953
Southern Pacific	5316-5335	18381-18400	5188	8/1953-9/1953
Southern Pacific	5309-5313	18401-18405	5282	7/1953
Southern Pacific	5314	18406	5283	7/1953
Southern Pacific	5315	18407	5286	7/1953
Pennsylvania	8588-8589	18669-18670	5300	10/1953
Baltimore & Ohio	761-764	18683-18686	5303	11/1953

An Electro-Motive photo showcasing new Great Northern SD7 #558 in the summer of 1952. American-Rails.com collection.

Demonstrators

In designing the SD7, EMD intended it to be used in light branch service. The truck itself was lightweight and its additional axle could more evenly distribute the locomotive's weight over a greater distance, a handy trait in territory where rail was generally light.

Interestingly, the Flexicoil proved so successful it remained EMD's standard through the early 645 series which included the SD38, SD40, and SD45. It was finally replaced with the "Dash 2" line, which carried the new HT-C truck.

EMD's second demonstrator, #991, was purchased by the Baltimore & Ohio, which went on to roster five examples, #760-765. Other buyers included the Milwaukee Road, Great Northern, Nevada Northern, Burlington (and subsidiaries), Bessemer & Lake Erie, Minneapolis & St Louis, Kennecott Copper Corporation, Rio Grande, Chicago & North Western, Union Pacific, Central of Georgia, and Pennsylvania.

Interestingly, SP kept their SD7s in service - following an extensive rebuild program into SD7Rs, through the end when the railroad merged with Union Pacific in 1996.

Sources

Foster, Gerald. A Field Guide To Trains. New York: Houghton Mifflin, 1996.

Hayden, Bob. Diesel Locomotives: Cyclopedia, Volume 2 (Model Railroader). Milwaukee: Kalmbach Publishing Company, 1980.

Marre, Louis A. Diesel Locomotives: The First 50 Years, A Guide To Diesels Built Before 1972. Milwaukee: Kalmbach Publishing Company, 1995.

Pinkepank, Jerry A. Diesel Spotter's Guide. Milwaukee: Kalmbach Publishing Company, 1967.

Schafer, Mike. Vintage Diesel Locomotives. Osceola: MBI Publishing, 1998.

Solomon, Brian. EMD Locomotives. Minneapolis: MBI Publishing Company, 2006.