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Locomotive Phases - EMD SD38, SD39, SD40, SD45

The SD40 was introduced in 1966 as an evolution of the SD35. It marked the introduction of EMD's 645-series engine, which used the same engine block dimensions as the 567 series but incorporated modified power assemblies with a larger cylinder bore. The SD40 also used an alternator-rectifier electrical system, addressing one of the biggest reliability concerns of the SD35, in which the DC generator required nine stages of transition to handle a 2,500 horsepower output. Along with the SD40, which used a 3,000 horsepower 16-cylinder turbocharged engine, three other variations were introduced: The SD38, which used a 2,000 horsepower Roots-blown engine (replacing the SD28); the SD45, which used a 3,600 horsepower 20-cylinder engine; and, a couple of years later, the SD39, which used a 2,300 horsepower 12-cylinder engine. The SD38 initially used a DC generator but later (in the SD38AC) used the same AR10 alternator as the SD40.

While only a few dozen each of the SD38 and SD39 were sold, the SD40 and SD45 both sold more than 1,200 locomotives, marking the first time that EMD's SD series out-sold their GP counterparts. The SD45 also marked the end of EMD's horsepower race of the 1960s, with the comparative reliability and versatility of the 3,000-horsepower SD40 paving the way for the hugely successful SD40-2. While (despite popular myth) the SD45 was no less fuel-efficient than the SD40 on a per-horsepower basis, the 20% increase in horsepower and fuel consumption came with neither an increase in fuel capacity nor in tractive effort at low speeds (where weight/adhesion was the limiting factor).

In 1972, EMD introduced an updated "Dash-2" series, replacing the SD38, SD40 and SD45 with the SD38-2, SD40-2 and SD45-2 respectively. An SD39-2 was apparently cataloged but never built.

While some SD40's and SD45's were retired by the 1990's, many more continued in service into the 21st Century, often in modified or rebuilt form. Many SD40's received upgraded Dash-2 (modular) or Dash-3 (microprocessor) electrical systems. A number of SD45's were downrated from their original 3,600 horsepower rating, either through derating the original 20-cylinder engine or replacing it with a 16-cylinder version.

Transition: From SD35 to SD40

The biggest change from the SD35 was a longer underframe, with the length over the coupler pulling faces increased from 60' 8" on the SD35 to either 65' 8" or 65' 9.5" (depending on whether the end plates were 0.75" or 1.5" thick). On the SD45, the 20-cylinder engine and longer radiators (with flared intakes) took up all the additional frame length, but on the three other models, the shorter hood left "porches" at either end that, while not as long as on the later SD40-2, still left several feet of empty walkway space. The longer underframe allowed for a significantly longer fuel tank, with a standard fuel capacity of 4,000 gallons (although smaller tanks were sometimes used). The walkway side frame was 5" tall above the air reservoirs, compared to 3" on the SD35, and air piping was relocated inboard of the air reservoirs (as on the last SD35 orders for SOU).

The increase from 2,500 to 3,000 horsepower necessitated a larger radiator section with three 48" fans in place of the one 36" and two 48" fans on the SD35. The SD40 adopted general hood dimensions and radiator design of the last two SD40X demonstrators, but also lengthened the front hood section (housing the inertial air intakes and equipment blower duct) by about 15". The taper of the dynamic brake hatch was made steeper at the rear than the front (to make room for the longer radiator intakes). Aside from these changes, the cab and hood were very similar between the late SD35 and early SD40. As on the SD28, the SD38 used the same hood design as the SD40, but incorporated shorter radiator intakes with only two 48" fans and two exhaust stacks in place of a single turbocharger stack.


These phases are based on the SD45 roster compiled by David Thompson, with added details based on what I have observed. I have relabelled Thompson's Phase 2b1 as a variation of Phase 2a (Phase 2a3) since the single change in this phase (U-shaped nose grabirons) actually appeared on some earlier units as well. However, there are still two Phase 2b variations, since I have added a subphase for revised traction motor cable routing that appeared in the middle of Phase 2b.

These phases are very similar to those for the GP38 through GP40.

Phase 1a1 1a2 1a3 1b1 1b2 1c 2a1 2a2 2a3 2b1 2b2 2c 3
Dates 1965-12 -
1966-02 -
1966-03 -
1966-10 -
1967-01 -
1967-06 1967-07 -
1967-11 -
1967-10 -
1968-07 -
1970-02 -
1971-03 -
1971-11 -
Cab sub-base doors Smooth Ribs on conductor's side Ribs on both sides Ribs made full-width (rather than ending before door edges)
Handbrake Short hood Long hood end (SD38, SD39, SD40);
Long hood, engineer's side (SD45)
Rear hood doors (SD45) 1-2-4-1 grouping (same as SD40, with added door) 1-2-2-2-1 grouping (rearmost door on right shortened for handbrake)
Truck brake cylinders Low-mounted 3 low, 1 high All high
Fans Flat center cap Open-top
MU receptacle housing Short, wide, angled side Tall, narrow, angled bottom
End plate Small tabs at bottom steps, end plates do not extend below steps Angled extensions at bottom steps, end plate extends to bottom of pilot Straight edges (as on Dash-2 units)
Footboards Flat plate on side extending behind pilot end plate (as on SD35) Beveled plate on side flush with pilot end plate (as on Dash-2 units)
Fuel tank supports Triangular brace Pentagonal brace (rectangle with angled corner)
Phase 1a1 1a2 1a3 1b1 1b2 1c 2a1 2a2 2a3 2b1 2b2 2c 3
ECAFBElectrical cabinet air filter box, located on the left behind the cab
No (unless subsequently added) Yes
Short hood grabirons Top-mounted, straight Bottom-mounted, U-shaped (appeared on some units starting with Phase 1c)
Radiator intake subscreen Diamond mesh Square wire grid
Rear traction motor cables Split and cross underframe Similar routing to front (appeared earlier on all SD39 production)
Dynamic brake roof vent No (unless subsequently added) Yes (additional side vent on SD45 only)
Blower duct Flat Two horizontal ribs
Front taper on dynamic brake housing Short, angled Longer, nearly straight
Handrail stanchions bottoms not lined up revised front corner handrails (SD38, SD39, SD40);
bottoms lined up (inconsistent on SD45)
Phase 1a1 1a2 1a3 1b1 1b2 1c 2a1 2a2 2a3 2b1 2b2 2c 3

Other details


Electro-Motive Division. (1965). Handrail Application, SD45, Part no. 8364878. [Drawing]. Retrieved July 2015 from

Electro-Motive Division. (1970). Handrail Application, SD45, Part no. 8449399. [Drawing]. Retrieved July 2015 from

Electro-Motive Division. (1966). Hoods and Cab Application, SD38/SD39/SD40/SD45, Part no. 8389735. [Drawing]. Retrieved January 2013 from

Electro-Motive Division. (1967). Underframe Assembly, SD45, Part no. 8393345. [Drawing]. Retrieved January 2015 from

Electro-Motive Division. (1971). Underframe Assembly, SD45, Part no. 8449100. [Drawing]. Retrieved January 2015 from

Foster, Gerald. (1996). A Field Guide to Trains. New York, NY: Houghton Mifflin.

Sarberenyi, R. EMD's SD45 and SDP45 - Original Owners. Retrieved January 2017 from

Unofficial EMD Homepage. (2004). SD40 Order Numbers. Retrieved April 2010 from

Unofficial EMD Homepage. (2006). SD45 Order Numbers. Retrieved April 2010 from