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Locomotive Descriptions and Phases - EMD SD38-2, SD40-2, SD45-2

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CBNS #3366, a Phase 2c SD40-2 originally built as BN #8151. The rear-most radiator fan has been replaced with an older fan.

The SD38-2, SD40-2 and SD45-2 were introduced in 1972 as replacements for the SD38, SD40 and SD45 respectively. They retained the same respective horsepower ratings but received a host of mechanical and electrical upgrades, with the most visible difference being the longer frame with HT-C trucks. Internally, the most significant upgrade was the use of solid-state modular electronics. While the SD38-2 and SD45-2 were relatively slow sellers and ceased production in the late 1970s, thousands of SD40-2 variations were built as it became the most popular locomotive of the late 20th Century, with peak production in the late 1970s and the last variant (the full-cowl SD40-2F) built in 1988.

The SD38-2 and SD40-2 were very similar externally, with the relatively long frame and short hood resulting in large "porches" at either end. The SD38-2 had two radiator fans and two exhaust stacks, while the SD40-2 had three radiator fans and a single turbocharger exhaust stack (changed to a flat silencer housing on later units). The SD45-2 had a single exhaust stack and three radiator fans spread out over a distinctively longer hood that filled the extra frame length. "Tunnel motor" variants, the SD40T-2 and SD45T-2, rode on a still longer frame and had a redesigned radiator area with low air intakes, internal fans and roof-mounted radiator grills. Wide-nose units built for CN were otherwise similar to other SD40-2's, but the full-cowl SD40-2F built for CP was in fact closely derived from the SD50F built for CN, and its carbody and general construction had little in common with other SD40-2's.

Transition: From late SD38/SD40/SD45 to early Dash-2 series

On all six-axle Dash-2 units, the frame was lengthened by just over 3' to accommodate the longer HT-C trucks while keeping enough room for the standard 4000-gallon fuel tank. Depending on the thickness of the pilot end plates (0.75" or 1.5") the overall length was either 68' 8.5" or 68' 10", compared to 65' 8" or 65' 9.5" for the SD38/SD40/SD45. The SD40T-2 and SD45T-2 were built to an overall length of 70' 8" with 1.5" end plates.

The HT-C truck looked superficially similar to the earlier Flexicoil, but it was a substantially different design, with an all-new frame casting, taller primary springs, stiff rubber pads for the secondary suspension (in place of large coil springs), unequal axle spacing (79.625" for the outer axles and 83.75" for the inner axles), and all traction motors facing the same direction (the reason for the added length). The bolster centers were offset outward by 1.25" from the center axle on each truck and were 2.75" closer to the end plates than on earlier units; excluding tunnel motors, this made for bolster centers of 43' 6" and a distance between the center axles of 43' 3.5".

Conrail units were built with Flexicoil trucks but retained the same frame, leaving a large gap between the trucks and fuel tank. Railroad diagrams list the bolster centers on Flexicoil-equipped units as 43' 6", but as the Flexicoil trucks had even axle spacing with the bolster lined up with the middle axle, such a dimension would put the trucks too far toward the ends and cause clearance issues with the steps and draft gear. I haven't confirmed the dimensions definitively, but photo measurements suggest that the Flexicoil trucks were located the same distance from the end plates as on the earlier SD40, which would give truck centers of 43' 0.5".

On all six-axle Dash-2 units, the front section of the hood (housing the inertial air intakes and blower duct) was lengthened by roughly 8". On the SD38-2 and SD40-2, this added length was not enough to compensate for the increased frame length, and the result was significantly larger platforms at either end - with the rearmost wheel entirely out from under the end of the hood. On the SD45-2, however, the rear of the hood was also lengthened to fill up the extra frame length, and the added space was used to house longer, narrower radiators that did not require the canted intakes used on the SD45. The longer radiators resulted in three very widely spaced rooftop radiator fans.

At the start of EMD Dash-2 production, almost every part of the cab and hood was changed in some way. Compared to previous SD units, the following changes were made:

Cab and cab sub-base


Underframe and walkway


These phases are based on the SD40-2 phases by Scott Chatfield, with added details based on my own observations and on the phase details described in the GP40-2 roster compiled by Robert Sarberenyi. I have also added a number of sub-phases based on an excellent SD40-2 roster compiled by Brian Bennett.

These phases do not apply to Canadian (GMD) SD40-2 and SD40-2(W) production, which followed a different (though similar) sequence of detail changes. However, a few EMD SD40-2 orders (BN 7167-7205, 7206-7235 and 8074-8089) were built by GMD in Canada when EMD was at capacity. Unlike other GMD SD40-2's, they were built to BN specifications and were virtually identical to their US-built counterparts, except for having a smooth (rather than ribbed) blower duct and HT-C trucks cast by Dofasco instead of Rockwell.

Numbers correspond to the illustrations shown below.

Phase 1a1 1a2 1b1 1b2 1c1 1c2 2a1 2a2 2a3 2a4 2b1 2b2 2c1 2c2 2d1 2d2 3
Inertial air intakes 1   Ridge added along top Ridge added along bottom
Frame side sill Narrow over air reservoirs Engineer's side rear sill notch moved rearward when notched fuel cut-off housing present Narrow over entire length
Pilots 2 Straight upper end plate corners, straight coupler cut levers Notched upper end plate corners, raised coupler cut levers Narrower anticlimbers
Battery box covers 3 Bolted, small louvres Larger louvres Horizontal rib added (bolted version only) Latched, lift-off tabs
Phase 1a1 1a2 1b1 1b2 1c1 1c2 2a1 2a2 2a3 2a4 2b1 2b2 2c1 2c2 2d1 2d2 3
Radiators, fans 4 Square wire grid intakes; curved grabiron behind fans; flat-top radiator fans Corrugated intakes; relocated lift ring and flag holder aft of intakes Angled grabiron behind fans (late Phase 2b1) Q-type radiator fans
Hand brake 5 Ratchet Wheel (some units retained ratchet)
Cab side 6 Riveted side panel with 11 rivets along top/bottom Riveted side panel with 13 rivets along top/bottom Welded side panel
Cab sub-base 7 Hinged sub-base doors Sub-base doors with lift-off tabs
Short hood 8 81" standard length or 116" "snoot" with sloped section ahead of flat section near cab (1)88" standard length or 116"/123" "snoot" with constant slope on top; circular vent on engineer's side Bolted hatch added on top
ECAFBElectrical cabinet air filter box, located on the left behind the cab
Separated from cab Flush with cab (appeared on CNW Phase 1c2 units)
End handrails 10 Flush with pilots, inward-facing central handrail stanchion supports Wrap around pilots slightly, outward-facing central handrail stanchion supports (appeared on CNW Phase 1c2 units)
Phase 1a1 1a2 1b1 1b2 1c1 1c2 2a1 2a2 2a3 2a4 2b1 2b2 2c1 2c2 2d1 2d2 3
Trucks, underframe 11, 12   Revised center axle shock strut (inconsistent until Phase 2a3); deeper angled stepwell plates with narrower steps (2); revised fuel tank vent pipe Revised air reservoir piping on conductor's side (appeared on some late Phase 2a4 units)
Jacking pads 13 Tall (no casting holes after late Phase 1a2) Short
Dynamic brakes 14 Batten strip at rear of dynamic brake housing No batten strip Dynamic brake housing moved rearward
Exhaust 15 Raised exhaust stack Silencer with opening at rear Silencer with opening at front
Blower duct Flat, wide, two ribs Angled "laundry chute"
Phase 1a1 1a2 1b1 1b2 1c1 1c2 2a1 2a2 2a3 2a4 2b1 2b2 2c1 2c2 2d1 2d2 3


  1. Short hood, Phase 2a1: Same as Phase 2a2 except circular vent mounted lower
  2. Angled stepwell plates appeared on BO Phase 2a1 units

Other details


These two drawings illustrate typical early (Phase 1a2) and late (Phase 2d2) SD40-2's built to similar Family Lines specs. The headlight/gyrating light arrangement and horn type (on both units) as well as the non-standard MU boxes and cab strobe lights (on the Phase 2d2 unit) represent railroad-specific variations.

Phase 1a2 -  Phase 2d2


Biel, Charles. (2013). EMD SD40-2. Retrieved November 2014 from

CNRPhotos. (2006). Data Sheets - Motive Power. Retrieved January 2010 from

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

Sarberenyi, R. EMD's GP40-2 - Original Owners. Retrieved November 2014 from

Southern Railway. (1980). Diesel Electric Locomotive Diagrams - 1980. Retrieved November 2014 from

Unofficial EMD Homepage. (2005). SD40-2 Order Numbers. Retrieved November 2014 from