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Athearn Ready-to-Roll HO scale SD40T-2

Read this review from the July 2019 issue of Model Railroader
Athearn Ready-to-Roll HO scale SD40T-2

More prototype-specific detail and a dual-mode SoundTraxx Econami decoder highlight this HO scale SD40T-2 “tunnel motor” diesel from Athearn Trains. The plastic model has many enhancements compared to the previous Athearn Ready-to-Roll SD40T-2 that we reviewed back in the January 2008 issue.

Prototype. In 1972, General Motors Electro-Motive Division and Southern Pacific RR collaborated on the SD45T-2 to work on the railroad’s most mountainous routes. Exhaust gases tended to collect in the ceilings of tunnels and snow sheds, which could cause a diesel locomotive with conventional high-mounted air intakes to overheat. The SD45T-2 “tunnel motor” had air intakes at walkway level to draw in cooler, cleaner air for more reliable operation.

Electro-Motive also applied the tunnel motor concept to its 3,000 hp SD40-2, resulting in the SD40T-2. From 1974 to 1980, 312 SD40T-2s were built. Southern Pacific purchased 229 SD40T-2s, and its subsidiary St. Louis Southwestern rostered an additional 10. The Denver & Rio Grande Western bought the last 73 units.

The tunnel motors worked through the 1990s, with some receiving Union Pacific paint after the SP merged into the UP in 1996. All were removed from the UP roster in the early 2000s, but several found second careers on shortline and regional railroads.

The model captures the prototype’s distinctive air-intake grills.

The model. Our review sample is accurately decorated for SP no. 5387, which was originally built as D&RGW no. 5387 in 1978. In the late 1980s, those two roads merged, and in the early 1990s, no. 5387 received the SP “Speed Lettering” scheme. The locomotive was sold not long after the SP/UP merger. Still wearing remnants of its SP paint, no. 5387 now works the rails for the Alabama & Tennessee River Ry.

The model’s paint is smoothly applied and all lettering is straight, opaque, and faithful to prototype photos from the 1990s, including “DRGW” under the cab numbers. Small warning and maintenance stencils are legible under magnification. Electro-Motive Division builder’s plates are on the side sills under the cab.

The Athearn SD40T-2 also matches prototype dimensions. The short hood length of 88 scale inches is correct for this ex-D&RGW prototype. The plastic body shell has well-defined molded detail, including engine access doors, grills, and the two radiator hatches on each side of the long hood.

The see-through air intakes are standout features. The 2008 review noted that the worm gear assembly was visible inside the hood. Thankfully, Athearn has corrected this on the new release by moving the gearbox farther forward, making it less visible through the grills.

The rooftop dynamic brake fan grills are also see-through, with separate fan detail visible underneath.

Handrails and stanchions are made of flexible acetal plastic. One of the stanchions came loose when I removed the model from the box, but it was easy to press back into place.

Other separate parts include sand filler hatches, windshield wipers, m.u. hoses, and grab irons. Prototype-specific details include a bracket-mounted Nathan P3 air horn, frame-mounted bell, Positive Traction Control cabinet in front of the blower housing, and a nose-mounted Gyralight.

The model rides on blackened metal scale 40"-diameter wheels. The plastic HT-C truck sideframes have separately applied brake cylinders.

Much of the model’s heft comes from its die-cast metal chassis. Mounted in the body shell, LEDs provide the lighting effects.
Mechanism. After removing the coupler boxes, I removed two additional screws from the underframe at each end of the fuel tank. Then I lifted off the body shell.

The motor and flywheels are mounted in the center of the die-cast metal chassis. Drive shafts transfer power to the truck-mounted gearboxes.

The SoundTraxx Econami decoder is attached to the chassis above the mechanism. The dual-mode decoder works on both Digital Command Control (DCC) and direct-current (DC) layouts. Leads run from the decoder to light-emitting diodes (LEDs) in the body shell. Two leads run to a 1⁄2" x 13⁄8" rectangular speaker enclosure over the rear truck.

Measured by our workshop force meter, the mechanism produced a tractive effort equivalent to 49 free-rolling HO scale freight cars on straight-and- level track. During a hill climb test, the model pulled 12 HO freight cars up a 3 percent grade. It also negotiated 18" radius curves and no. 5 turnouts.

DCC performance. During speed tests on our DCC test track, the model accelerated smoothly from 4.5 scale mph to a prototypical top speed of 74 scale mph. The decoder supports 128 speed steps for finer slow speed control. Performance can be further fine-tuned with acceleration/deceleration momentum, three-point or 28-point speed tables, and forward/reverse trim. These and most aspects of the decoder are adjustable via configuration variables (CVs) as described in the free Econami diesel user manual at

The Econami has the same excellent sound and almost all the features of a top-of-the-line SoundTraxx Tsunami2 decoder. These features include Flex Map technology for easy function mapping and button-controlled braking. However, while the Tsunami2 features three braking modes (independent, train, and dynamic), the Econami has only a single braking mode.

Pressing F0 turned on the directional headlights and ditch lights. Pressing F5 turns on the nose Gyralight, while F6 turns on the rooftop beacon.

Other user-triggered effects include the bell, coupler, dynamic brake fan, manual engine notching, and long and short horn blasts. The horn on our sample was correctly set for a Nathan P3, but there are 15 additional horn sounds to choose from.

I easily programmed the locomotive address to its cab number (5387) and set up an advanced consist with another six-axle diesel. The Athearn SD40T-2 supports CVs 21 and 22, which allow function control under the advanced consist address.

DC performance. Like most dual-mode sound-equipped locomotives, the SD40T-2 requires a lot of voltage to get moving. At 7 volts the diesel engine sounds started and the lights illuminated. The headlights and ditch lights are directional while the beacon and Gyralight are always on.

Once I advanced the throttle to 10V the tunnel motor started moving at 3.5 scale mph. At 12V the model reached 28 scale mph, and at 14V, the power pack’s maximum output, the locomotive attained its top speed of 50 scale mph.

The only sound effects in DC mode are the diesel engine rpm, which raise or lower with the throttle setting, and a brake squeal triggered by quickly decreasing the throttle.

With its accurate detailing and realistic sound, one (or more) of these tunnel motors would look and sound right at home hauling tonnage on an HO scale mountain railroad.

Price: $199.98 (DCC sound), $139.98 (DC, no sound)
Athearn Trains
1600 Forbes Way, Suite 120
Long Beach, CA 90810
Era: mid-1970s to present (mid- to late 1990s as detailed and decorated for SP no. 5387)
Road names (multiple road numbers): Southern Pacific (speed or Roman lettering), Denver & Rio Grande Western, St. Louis Southwestern (Cotton Belt), and Union Pacific
• 21-pin NEM DCC plug (DC version)
• All-wheel drive and electrical pickup
• Five-pole skew-wound motor with dual brass flywheels
• Light-emitting diode (LED) headlights, ditch lights, nose-mounted Gyralight, and rooftop beacon
• McHenry scale knuckle couplers at correct height
• Minimum radius: 18" (22" recommended)
• Roadname/roadnumber-specific short hood length (81", 88", 116", or 123" as per prototype)
• RP-25 contour blackened metal wheels in gauge
• SoundTraxx Econami dual-mode decoder (DCC version)
• Weight: 15.6 ounces

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