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"SD40" and "SD40-2": A Timeless Design

Last revised: December 16, 2024

By: Adam Burns

The SD40 series was EMD's turbocharged models in its new 645 line.  The standard SD40 sold more than 1,200 examples, illustrating the industry's desire for higher horsepower six-axle designs.

However, the builder could never have envisioned its "Dash 2" variant - the SD40-2 - would go on to become one of its all-time best sellers.  Interestingly, as Louis Marre and Jerry Pinkepank note in "The Contemporary Diesel Spotter's Guide," EMD had believed its higher horsepower SD45 would hold this status.

During the 1960s the horsepower race was on as GE, EMD, and Alco cataloged increasingly more powerful models.  However, railroads soon realized higher horsepower also equaled higher maintenance.

The SD40-2 offered a fine balance of power and efficiency that sparked a firestorm in sales.  As a result, the model remained in production for nearly 15 years and ultimately sold more than 4.000 examples.  The series' success spawned several variants which included the SD40A, SDP40, SD40T-2 "Tunnel Motor," and the SD40-2SS.

While there are a few SD40s officially preserved so many, especially "Dash 2" models, remain in use there is little need to visit a museum.  In addition, the quality of EMD products can still be seen today as even Class 1s continue to rebuild and operate SD40-2s today.

Photos

Rock Island SD40-2 #4793 lays over at the engine terminal in Kansas City with other power, circa 1975. American-Rails.com collection.

Overview

No other second-generation locomotive compared to the SD40 series; its two flagship models defined EMD's dedication to quality during this era.  The SD40-2 became the industry standard throughout the 1970s and 1980s and remains in regular service today.  In many ways, the SD40 was EMD's curtain call.  By the late 1980s GE overtook the company as leader of locomotive manufacturing.

Development

In his book, "EMD Locomotives," author Brian Solomon notes that in late 1965 EMD advertised nine new models equipped with its latest model 645 prime mover, offered in a range of horsepower ratings, sizes, and wheel arrangements.

The SD40 was introduced in January, 1966 when Chicago & North Western #867 rolled out of La Grange.  This model was EMD's turbocharged, 16-cylinder variant and could provide 3,000 horsepower.  

By this time railroads were realizing the benefits of high horsepower, high tractive effort locomotives.  The SD40 would go on to sell more than 1,200 examples while the even more powerful, 20-cylinder SD45 sold another 1,200+ units.

Visually, the SD40 closely resembled the earlier SD38.  It was 65 feet, 9 ½ inches in length sporting standard Flexicoil trucks, the Spartan Cab, and EMD's now-classic road-switcher carbody.

A keen eye, however, will note the SD40's additional rear roof radiator fan (three) and rectangular turbocharger stack located slightly forward of the dynamic brake blister.

A trio of Union Pacific SD40-2's lead trailers eastbound over Sherman Hill at Dale Junction, Wyoming, circa 1982. Mike Bledsoe photo. American-Rails.com collection.

Success

When the SD40-2 debuted with Kansas City Southern #637's completion in January, 1972, railroads soon realized the model provided an excellent blend of power and incredible relability. 

The locomotive quickly became loved by shop personnel and even more-so by engineers who have stated the locomotive is a joy to operate in service.

From a sales perspective the SD40-2 quickly eclipsed the SD45, which ran into a combination of relability issues and increased maintenance as a result of its gas-guzzling 20-cylinder prime mover.

SD40-2

On January 1, 1972 Electro-Motive unveiled its new "Dash 2" line.  This was not a specific locomotive model but an upgrade to the builder's current catalog.  In his book, "Locomotives: The Modern Diesel & Electric Reference," author Greg McDonnell notes that EMD noted 40 refinements. 

Nearly all of these were "under the hood."   Its most notable was the upgraded electrical system which included transistors, printed circuit boards, and solid-state modular components which replaced a labyrinth of old relays, switches, and interlocks commonly been found on all previous models. 

The new computer system controlled everything from voltage regulation, battery charging and excitation and throttle response to wheel-slip control, dynamic brakes, and the locomotive's sanders.

The SD40-2 also featured EMD's latest AR10 alternator; its rectifier - with four banks of solid state silicon diodes - could quickly convert AC to DC for the traction motors.  It also predominanely eliminated flashovers, a typical issue with DC generators.

Union Pacific SD40-2 #3213 at Salt Lake City; August 14, 1980. American-Rails.com collection.

Not only was the AR10 more efficient but also required fewer overall components, which also decreased maintenance.  With less circuitry the SD40-2 did not experience nearly the same amount of wheel slip issues.

While similar to its predecessor, the new model was noticeably longer, by three feet, to accommodate EMD's latest HT-C truck.  In doing so, the SD40-2 featured extended "porches" fore and aft, and was its trademark feature.

The new C-C truck offered greater adhesion by having all traction motors mounted in the same direction.  This design eliminated torque reversals which commonly caused the truck to tilt and one axle to unload, which resulted in wheel slippage.

Southern Pacific SD40R #7347, sporting a special livery honoring the 1984 Olympic games being held in Los Angeles that summer, is seen here on display at Los Angeles Union Passenger Terminal. Mike Bledsoe photo. American-Rails.com collection.

The HT-C was also equipped with EMD's new modular WS10 wheel-slip control system, which further reduced slippage and "...increased average all-weather dispatchable adhesion from 18% to 21%."

The SD40-2's other improvements were related to the 645E3 prime mover and included stronger pistons and chrome-plated stainless-steel piston rings. It also featured refinements to the engine, turbo, and camshaft bearings.

Other notable advancements included an airtight hood that kept out dust, dirt, and other particles from reaching internal components.  To cool these critical areas the model sported a single air intake for electrical cooling, with a pressurized cooling system.  

Union Pacific SD40-2's #3662 and #3157, along with Milwaukee Road SD40-2's #148 and #141, with a westbound at Cheyenne, Wyoming, circa 1983. Mike Bledsoe photo.

Variants

SD40A

This type featured the longest frame in the SD40 series at 70 feet, 8 inches, utilizing the frame of an SDP45.   The extra length allowed for a larger fuel tank capable of holding 4,000 gallons in place of the standard 3,200 gallons found on a typical SD40.  A total of 18 units were produced between August, 1969-January, 1970; all for Illinois Central.

SDP40

The SD40's passenger variant, the SDP40 featured a steam generator at the rear for passenger car heating.  Only six were produced domestically for Great Northern while Ferrocarril Nacional de México (NdeM) acquired fourteen.

SDP40F

Covered in greater detail here, this model was produced only for Amtrak in 1973-1974 sporting a "cowl" carbody, steam generator, and a variant of the HT-C truck.

Southern Railway SD40 #3185 at the former Nickel Plate Road's Homestead Yard in Oregon, Ohio (Toledo) during the early Norfolk Southern era; December, 1988. American-Rails.com collection.

SD40T-2 "Tunnel Motors"

The success of the SD40 series led to numerous spinoffs.  Most notable was Southern Pacific's "Tunnel Motors." 

This variant was requested - originally with the SD45T-2 of 1972 - to alleviate cooling problems with locomotives operating in high altitude environments where they encountered numerous tunnels and/or snow sheds, predominanetly Donner Pass.

Ultimately, EMD engineers remedied the problem by moving the air-intakes near the bottom of the carbody to draw in cooler air and placed the radiators at the very top of the carbody. While only the Southern Pacific acquired the more powerful SD45T-2 (along with subsidiary St. Louis Southwestern), the Rio Grande also ordered the SD40T-2.

Milwaukee Road SD40-2 #142 and Soo Line SD40-2 #762 lead open autoracks through Des Plaines, Illinois on May 7, 1986. Ray Weart photo. American-Rails.com collection.

SD40-2F

This was a very late era variant ordered by Canadian Pacific and delivered in November, 1988 - more than two years after the final SD40-2s had been built for NdeM. 

The SD40-2F, numbered 9000-9024, featured a full cowl carbody but were otherwise standard SD40-2s.  They were the final in the SD40 series produced.

SD40-2SS

This variant saw only nine units produced.  They featured the Super Series ("SS") wheel slip control system as well as sporting EMD's higher-capacity AR16 traction alternator and a larger turbocharger.

They were built only between April-May, 1978 and included Burlington Northern #7049-7053 as well as Union Pacific #3805-3808.  BN's examples are identical to standard SD40-2s while UP's featured a slightly longer carbody and larger radiators.

A trio of Missouri Pacific SD40-2's, led by #3124, have southbound freight FWSA (Fort Worth - San Antonio) at the north end of Bergstrom Siding in South Austin, Texas on February 14, 1980. Mike Bledsoe photo. According to Mike's son, Steve Bledsoe, "Engineer Joe Covert called our house from the Austin depot to let my dad know that he had three 'Screaming Eagles' and would be heading south in a few minutes. So off we went. At the time the MoPac locomotives with the eagles on the side were becoming fewer and fewer." American-Rails.com collection.

Other Variants

Beyond specific model variants, the SD40 series was produced in a wide range of optional setups at customer request, which did not warrant specific designations.  The Southern and Norfolk & Western acquired many with high, short hoods - standard practice for both railroads.

While not officially an EMD cataloged model, the 123 units produced for Canadian National at the London, Ontario plant featured the railroad's patented "Wide" or "Safety Cab."  As a result, many railfans have dubbed these the "SD40-2W" although EMD/GMDD gave them no special moniker.

There were also SD40-2s ordered by British Columbia Rail, CP Rail (Canadian Pacific), Kansas City Southern, Southern Pacific, and Union Pacific with extende noses.  Lastly, Conrail ordered its SD40-2s with the older Flexicoil truck.

Data Sheet and Specifications

* Some SD40-2s carried the D78 traction motor.

Production Rosters

SD40

Total Built = 1,268

Reused Serials

SD40X

Total Built = 9

SD40A

Total Built = 18

SDP40

Total Built = 6

SD40-2

Total Built = 3,982

SD40-2SS

Export

SD40

SD40-2

SDL40-2

SDP40

General Motors Diesel Division (GMDD)

SD40-2

SD40-2W

SD40-2F

GMDD Export

SD40

Total Built = 10

SD40-2

Total Built = 85

Milwaukee Road SD40-2 #141 at the company's shops in Bensenville, Illinois on May 23, 1981. American-Rails.com collection.

The railroad was wary of the HT-C design after witnessing Amtrak's issues with the modified version equipped on the SDP40F.  Ultimately, it was proven the truck was not the issue.  By the time production ended on the SD40 series, more than 5,700 units had been built.

While the locomotive will one day eventually disappear from the American landscape the model's success and longevity has proven unmatched, even among comparable moden GE designs. 

Railroads, even Class 1s, continue to rebuild SD40s for active freight service, a testament to the product EMD engineers conceived more than a half-century ago.  As a result, it is safe to say they will still be around for years to come.

Sources

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

• 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.

• Solomon, Brian.  GE and EMD Locomotives:  The Illustrated History.  Minneapolis:  Voyageur Press, 2014.