Editing EMD SD40-2 (section)

== Appearance ==
As the [[EMD SD38|SD38]], [[EMD SD39|SD39]], [[EMD SD40|SD40]], and [[EMD SD45|SD45]] shared a common frame, so too did the [[EMD SD38-2|SD38-2]], SD40-2, and [[EMD SD45-2|SD45-2]]. It was {{convert|3|ft|2|abbr=on}} longer than the previous models, giving a length of {{convert|68|ft|10|in|2|abbr=on}} over the coupler pulling faces. The SD38-2 and SD40-2 shared the same basic superstructure, since they used the same [[EMD 645|16-645]] engine (in [[Roots supercharger|Roots-blown]] and [[Turbocharger|turbocharged]] form respectively); the [[long hood]] was {{convert|18|in|mm|0}} longer than the SD38 and SD40, but since the increase in frame length was even greater, the SD38-2 and SD40-2 had even larger front and rear "porches" than the earlier models. These empty areas at front and rear are spotting features to identify the Dash 2 models of both units. The SD40-2 can be distinguished from the SD38-2 by its three roof-mounted radiator fans instead of two, and a single large exhaust stack instead of two smaller stacks.<ref name="Foster1996">{{cite book|author=Gerald L. Foster|title=A Field Guide to Trains of North America|url=https://books.google.com/books?id=ZvSHlCxuyH0C&pg=PA56|year=1996|publisher=Houghton Mifflin Harcourt|isbn=0-395-70112-0|pages=56–57}}</ref>

The increase in the frame length between the preceding ''40 Series'' and the ''40-2 Series'' six-axle locomotives was made to accommodate the new HT-C truck design, in which the traction motors all face the same direction, making the trucks longer. After a series of derailments involving Amtrak SDP40F units that were equipped with "hollow bolster" HT-C trucks, applied only to the SDP40F, [[Consolidated Rail Corporation|Conrail]] ordered the SD40-2 units and several orders of SD50s with the older [[Flexicoil]] trucks, but the HT-C truck was vindicated and it ultimately went under most ''[[EMD SD40|40 Series]]'', ''[[EMD SD50|50 Series]]'' and ''[[EMD SD60|60 Series]]'' six-axle locomotives, and this truck is still found under many remanufactured locomotives. {{citation needed|date=January 2022}}

Some SD45 and SD45-2 units have been modified by replacing their 20-cylinder engine with the 16-cylinder removed from scrapped SD40-2 units; this was common on Union Pacific and possibly other railroads. In many cases these are identified by the owner as SD40-3, SD40M-2 or some such. Confusingly, what appears to be an SD45 is labeled as an SD40-2. Older SD40-2 units used in low-power modes such as yard switching or hump service have been de-turbocharged, resulting in the mechanical equivalent of a SD38-2. Units so modified may or may not be re-labeled. {{citation needed|date=January 2022}}

There are several variations of the SD40-2 such as the [[EMD SD40T-2|SD40T-2]]s (Informally: T for tunnel motor; the actual EMD designation is "SD40-2 With Cooling System Modification", as stated on this model's EMD manuals) bought by the former [[Southern Pacific Transportation Company|Southern Pacific]], and [[Denver and Rio Grande Western Railroad|Denver and Rio Grande Western]] railroads; now operated by Union Pacific. The SD45 tunnel motor equivalent, the SD45T-2 model, was also utilized by Southern Pacific. Many tunnel motors were rebuilt and sold second-hand to a handful of American shortlines including, [[Bessemer and Lake Erie]], [[Illinois Railway]] and Missouri and Northern Arkansas, as well as Canadian shortline [[Goderich-Exeter Railway]]. There is the [[#SD40-2W|SD40-2W]] (W for the 4-Window Safety Cab) bought and operated by the [[Canadian National]] railway. High-nosed versions of the SD40-2 were bought by [[Norfolk & Western]], & [[Southern Railway (U.S.)|Southern Railway]]. These units are now operated by the [[Norfolk Southern Railway]] (Resulting merger of N&W and Southern Railway). A narrow gauge version produced for Ferrovia Central Atlantico in Brazil is the [[EMD BB40-2|BB40-2]]. {{citation needed|date=January 2022}}

Three [[B unit|cabless]] "SD40-2B"s were also created from standard SD40-2s by the [[Burlington Northern Railroad]] in the early 1980s. The units had been in collisions and BN decided that it was more economical to rebuild them without cabs. Canadian Pacific also created several cobbled "SD40-2Bs" by created by welding metal plates over the cab windows of many of its ex-Norfolk Southern and some of its original SD40-2s. {{citation needed|date=January 2022}}
<gallery class="center" heights="150" widths="150" caption="SD40-2 production variations">
File:NS 3204 (3246054426).jpg|NS 3204, an example of a SD40-2 built with a high short hood
File:NS Loco No.3408.jpg|NS 3408, which rides on Flexicoil C trucks
File:Ohio Central System Railroad SD40-2 5855.jpg|[[Ohio Central Railroad System]] 5855 was built with an extended rear deck
</gallery>