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The "F7", The Iconic Cab Locomotive

Last revised: December 20, 2024

By: Adam Burns

The All-American F7 defined railroading during the 1950s; nearly every notable Class 1 operated at least one and many rostered dozens, or even hundreds, of these locomotives.  When one pictures Electro-Motive's classic streamlined diesels, the F7 most often comes to mind.

The model debuted directly after the F3; the first examples began rolling out of EMD's factory in McCook, Illinois during February, 1949.  With its predecessor's success, and EMD's reputation firmly established, sales of the F7 took off rapidly. 

During its nearly five-year production run, 3,856 units were produced.  This figure not only made it the most successful diesel ever built up until that time but the F7 also singlehandedly sold more examples than all other manufacturers' designs, combined. 

It proved so reliable and useful that hundreds remained in regular freight service through the 1970s, and in some cases even into the 1980s and 1990s, on short lines and in industrial settings.  Today, numerous F7's are preserved with several examples still operational at museums and tourist railroads.

Photos

Electro-Motive's beautiful A-B-A set of F7 demonstrators, #1950, seen here outside the plant at La Grange, Illinois in June of 1950. Warren Calloway collection.

Overview

There was nothing especially noteworthy about the F7 as a standalone model; it sequentially followed the earlier F3 and produced the same horsepower.  The locomotive's incredible success was simply a combination of timing and EMD's impeccable reputation.

By the late 1940s the industry was rapidly working towards dieselization and EMD had already established itself as the leader in this field with more than a decade of producing high quality diesels for main line service.  

The F7 began production in February of 1949. Internally, it differed only slightly from the F3, largely through internal components.  The model featured an updated generator (D12B) and traction motor (D27C) but continued to carry the 567B prime mover.

These upgraded components had first been featured on the "F5," technically a late model F3 (EMD did not distinguish between its upgraded F3 variants, although railfans have retroactively differentiated these as "phases").  The new traction motor and generator were more rugged and durable than the previous, furthering the builder's efforts to continually improve its product and keep locomotives out on the road.

Santa Fe F7A #345-L in the "Yellowbonnet" livery at Ardmore, Oklahoma; March 22, 1974. American-Rails.com collection.

While intended for use in freight service, with their clean, streamlined design many F7s also found work in passenger service.  Perhaps most notable was the Santa Fe, which often utilized F3s and F7s to lead trains like the Super Chief and El Capitan. 

The railroad was never fond of Electro-Motive's A1A-A1A trucked E units and felt they were not suitable to handle these important trains over the stiff grades found along its Transcontinental main line.  The Southern Pacific carried similar sentiments.

Generally, the F7 was equipped with a 62:15 gear ratio for freight service, offering a top speed of 65 mph.  However, for passenger assignments they were geared for higher speeds (65:12).  In all, EMD offered the model in eight different gear ratios, ranging from 56:21 (passenger) to 65:12 (freight).

Rio Grande F7A #5754 in Denver, Colorado. Date not recorded. American-Rails.com collection.

The F7 was the SD40-2 of its day, the first true "common" model; thousands were built and could be found powering almost any train. When production had ended some 2,393 "A" units and 1,463 cabless "B" units had been produced by late 1953.

Colorado & Southern (Burlington) F7s, led by #702-D, have a southbound freight north of Palmer Lake, Colorado, circa 1960. American-Rails.com collection.

According to an article by Don Strack, published in the November/December 1991 issue of "Diesel Era: Volume 2, Number 6" the, "base price on two cab units was $161,000 and the base price for two booster units was $147,500."  

The F7 was EMD's first cab variant to be produced at its new Canadian subsidiary, General Motors Diesel (GMD) of London, Ontario.  In all, GMD sold 127 examples to the Canadian National, Canadian Pacific, and the Wabash (for its line in southern Ontario between Detroit and Niagara Falls/Buffalo, New York). 

Data Sheet and Specifications

* Steam generators were optional in the F7.  They were produced by Vapor Clarkson; model OK4625 (1,200 Lbs/Hr) for "A" units and model OK4616 (1,200 Lbs/Hr) for "B" units.

Production Rosters

Total Built (F7A) = 2,393

Total Built (F7B) = 1,463

F7A

F7A Rebuilds

F7B

F7B Rebuilds

General Motors Diesel (GMD)

F7A

F7B

Export

F7A

F7B

An A-B-A set of Southern Pacific F7's have Extra 6360 that appears to be making a reverse move in Bay Area of California during the 1950s. American-Rails.com collection.

Sales for the more later, and more powerful, F9 dropped precipitously as the industry realized a handsome freight locomotive mattered little in paying the bills.  Instead, EMD's utilitarian road-switcher series, the General Purpose (GP) and Special Duty (SD) saw increasingly more success throughout the 1950s.

By the following decade, railroads were not only purchasing these locomotives for freight service but had largely switched to C-C trucked variants which offered greater adhesion and tractive effort via two additional traction-motored axles.  Today, the industry continues to predominantly utilize C-C variants in standard freight service.

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.

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

• Solomon, Brian.  Electro-Motive E-Units and F-Units: The Illustrated History of North America's Favorite Locomotives.  Minneapolis:  Voyageur Press, 2011.