SD7 vs. SD9

(Is anyone getting tired of my diesel-identification threads?)

I've always known that SD7s and SD9s do not merely look like 6-axle versions of GP7s and GP9s. The same identifying features cannot be used to tell them apart. SD7s and SD9s appear to have the same louver arrangement. I know there is an external difference, but without knowing where to look for it, I'm missing it.

 

There are a few external spotting differences...

The quickest and almost sure-fire way to tell them apart is the class lights. SD7s had theirs set more inboard (note how they're almost centered on the angled portion of the hood end), and mounted on a hinged door.
http://espee.railfan.net/nonindex/sd07_photos/1442_sp-sd07-bob_dengler.jpg

The SD9 had them in a more outboard position (closer to the edge of the hood), and they were fixed in place.
http://espee.railfan.net/nonindex/sd09_photos/3916_sp-sd9-bob_dengler.jpg

 

I specifically learned not to use lights to identify diesels in general, since they can vary so much (the headlights on the SP units you showed are perfect proof)!

 

For SD7s and SD9s, I use the class lights, too. Also, the SD7 steps are ladder-like and the SD9s are a more conventional stair-step type. (A more recent example of these step types is the stair-step type on the front of SD45T-2s and ladder or stamped metal type on the rear of the same SD45T-2.) The N Scale Atlas/InterMountain/LifeLike models clearly reflect these differences.

 

That's a good rule in regards to optional headlights like Espee's, but it's generally safe to rely on the SD7/9 classlights as a spotting feature since that's something they were all built with, regardless of RR. It might make it tougher to spot some latter-day SD7/9s however, due to rebuilds and/or mods some might have received (chopped noses, replaced class lights, totally deleted class lights, etc.). Then you'd have to start looking for other little clues to help tell them apart, like handrail stanchions ("pipe" vs. channel), 48" fans and taller sub-base and battery boxes (which made the cab and nose sit higher) on phase IV SD9s, etc.

 

Good call on the steps, Flash.