How to identify Geeps and or SD's from one another


nycentral57

nycentral57

New Member
Does anyone know of a sure way to identify GP and or SD locomotives from each other. (Example a GP9 has 3 exhaust fans on her roof, while a GP20 has only 2. I thought it was in the number of fans they had on the roof.
Is there a website I could go to and study pictures to learn this.

Robert.....
 
You just have to make those determinations on you own. We all have our special means to seeing the difference. Some will notice differences in the brake hardware on the trucks, while others will go by roof or side panel details. Some, really just don't care that much. They are all just locomotives.
 
nycentral57 said:
Does anyone know of a sure way to identify GP and or SD locomotives from each other. (Example a GP9 has 3 exhaust fans on her roof, while a GP20 has only 2. I thought it was in the number of fans they had on the roof.
Is there a website I could go to and study pictures to learn this.
Click to expand...
I don't know about a website but the books you need are called the Diesel Spotters Guides.

http://www.amazon.com/Second-Diesel...4549707&sr=1-1&keywords=diesel+spotters+guide

http://www.amazon.com/Diesel-Spotte...4549707&sr=1-2&keywords=diesel+spotters+guide

http://www.amazon.com/Contemporary-...4549707&sr=1-4&keywords=diesel+spotters+guide
 
wright2626 said:
think for the most part gp's have 4 axles, sd's have 6 axles.
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By definition, GP = 4 axles, SD = 6 axles.

Also, GP and SD are purely EMD model designations.

The GP/SD7 to 9 were somewhat of a gradual change with various phases.

The GP30 is the easiest one to spot due to the cab roofline.

Other that that, look for a Diesel Spotter Guide for more specifics.




Sent from my Vic20 using Java Moose
 
nycentral57 said:
Does anyone know of a sure way to identify GP and or SD locomotives from each other. (Example a GP9 has 3 exhaust fans on her roof, while a GP20 has only 2. I thought it was in the number of fans they had on the roof.
Is there a website I could go to and study pictures to learn this.

Robert.....
Click to expand...
If you mean radiator fans, GP7 and GP9's have 4, and GP9 (late) and GP18 have two larger ones. GP20 has 3, two larger ones and one smaller one.
GP 30 and GP35 have two large and one small radiator fan, GP40-50-60 all have 3 large fans. GP38, 39, 49 all have two large fans.
 
Ya know it's my problem. It's the perfectionism in me that make's it absolutely essential to have to identify each and every train. And for what reason? I have no idea. It's not like there's going
to be a pop [quiz at the end of the week. LOLOL I hate this in me. But thanks to all of you who volunteered an answer.
Robert....
 
Oh, you have done it now, opened one of these 822[1].jpg
 
There are identifiers to each model, certainly, but of course there are different things that differentiate between models. The GP38, 39, 40, 49, 50, 59 and 60 are all essentially the same body, but the GP38 will have two radiator fans while the GP40 has three. The GP38 is normally aspirated and has two small exhaust stacks, while the GP39 (while being otherwise identical) is essentially a turbocharged GP38 and the only major spotting difference is that it has one large exhaust stack instead of the smaller two. It's just little things like that. The SD50 and SD60 are virtually indistinguishable from each other externally, with the only real difference being that the SD60 had a new 710-series engine to replace the troubled late-645 series that plagued the SD50. An SD45 has flared radiators, while the SD45-2 has straight radiators. On and on. Little details.

There are also things like the GP33ECO, which looks like a GP60 with an SD70 flared radiator assembly, or the SD26, which is an SD24 rebuild that moved the rooftop "torpedo tube" air tanks to a different location.

Going over to GE, the major spotting difference between the AC4400 and the ES44AC is the thickness and size of the radiator assembly, with most of the rest of the body being very similar.

These are just a few examples of what you have to look for. There's not too many locomotives that just scream "I'M THIS MODEL" at a glance, because most locomotives are the result of progressive design changes rather than being something unique. The GP30 with its unique roofline and the SD24/26 with its rooftop air tanks are two examples of the more unique critters, but for most models you'll have to just learn which specific external details make them different from the others. And for some, like the SD50/60, you just have to look at what's printed on the cab or ask :)

If you're interested in the history of the locomotives as well as how to spot the differences, I'd also recommend "GE and EMD Locomotives" by Brian Solomon. It basically goes through the manufacturing history of all the GE and EMD locomotives, explains the differences in them as one model progresses to the next, and has lots of pictures. It's helpful not just for spotting little differences, but also giving you an understanding of why those changes were made and what they meant. To me it was much easier to remember and understand the differences in the locomotive models once I'd actually read how they came about and wasn't just trying to memorize a checklist of details.
 
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D&J RailRoad said:
Some, really just don't care that much. They are all just locomotives.
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That was me when I started, but there's real pleasure in being able to identify the differences. To borrow a simile from the patron saint of all backpackers, Colin Fletcher, "Walking in nature without being able to identify flora and fauna is like walking through the Louve with half the paintings turned to the wall." I still suck at it, but a couple of months ago I was so proud of myself when I was stopped at a crossing* and unexpectedly saw a pair of RS-3s of the Blissfield and Adrian.

*New Guy: It was the crossing at MLK and Grand River. I still have no idea what they were doing in Lansing (I didn't even know the B&A was a thing). They looked fresh from the factory.



Oh crap!
 
What no-one has mentioned is that Geeps (or GP's for General Purpose) are also called Road Switchers (as distinct from yard switchers which are generally smaller) because their designed use was as main line engines that could also do switching and setting out/spotting duties at industries/depots along the right of way. SD (Special Duty), being longer are not usually considered for that role, but that doesn't mean they don't do it at times.

As the GP's have aged, many, if not most have become yard switchers themselves. And many of the smaller yard switchers, especially on short lines, get used as all round power.
 
There are more technical ways to tell GPs and SDs apart, but my method is to step back and take a look at the general shape of the locomotive in question.
As a general rule of thumb, the GPs are shorter and have 2-axle trucks whereas the SDs are longer and have 3-axle trucks.
 
tootnkumin said:
What no-one has mentioned is that Geeps (or GP's for General Purpose) are also called Road Switchers (as distinct from yard switchers which are generally smaller) because their designed use was as main line engines that could also do switching and setting out/spotting duties at industries/depots along the right of way. SD (Special Duty), being longer are not usually considered for that role, but that doesn't mean they don't do it at times.

As the GP's have aged, many, if not most have become yard switchers themselves. And many of the smaller yard switchers, especially on short lines, get used as all round power.
Click to expand...

SD's were also called road switchers by EMD. The GP7 was in fact designed for mainline use (just in a cheaper, more utilitarian package than the F7/9), and the SD7 followed when the GP7 became so successful. EMD didn't actually anticipate that the GP7 would replace its best-seller F units, but that's what happened. The six-motor version wasn't created to be of any different use than the GP7 except that its six motors would put forth a higher tractive effort, handle steeper grades etc. Thus the "Special Duty" designation. They were both designed for mainline service, just without the fancy dress of the F7/9. Later on it became more common to think of 6-axles as mainline road locomotives and 4-axle as local road switchers, but in fact many railroads for many years continued to use 4-axle diesels for "fast freight", and of course most passenger locomotives are 4-axle. The big difference is in the fact that 6-axles can offer more tractive effort at lower ranges, perfect for heavy freight loads, but as they reach the upper speed range there comes a point where the generator is simply maxed out and with six axles drawing that power it occurs at a lower speed. 4-axle units have less tractive effort to get started with, but with only 2/3 the motors being driven by the generator they can reach higher speeds than the 6-axle units are capable of given the same loads and gearing. This same concept is why railroads use yard slugs. A single 4-axle locomotive has more than enough power to drive eight axles at low speed, so simply hooking up a slug to a GP essentially turns it into a big 8-axle articulated switching unit. Road slugs serve the same purpose, but instead of constant use they help get a train started at slower speeds and then quit providing any tractive effort (or drawing off any power) at higher speeds.

I've seen UP using SD40's for yard duty here locally, and from what I read at least on the early SD's, they weren't any less capable than any of the GP's. The main difference was simply in tractive effort vs. speed. That has obviously changed in recent decades and of course you would never see an SD90 trying to work a yard, but in the early days the GP's and SD's were a lot more closely related.
 
I think BNSF actually has the model name printed on the A end. Of course, if it's flying by at 60mph, it's hard to read....if you're talking 1:1.
 
I do what Louis said, just type the cab numbers into my iPhone and voila!
As has been mentioned there are so very different spotting features, even between phases.
 
tootnkumin said:
What no-one has mentioned is that Geeps (or GP's for General Purpose) are also called Road Switchers (as distinct from yard switchers which are generally smaller) because their designed use was as main line engines that could also do switching and setting out/spotting duties at industries/depots along the right of way.
Click to expand...
On this topic they are called road switchers because Alco had been building their RS-1 Road Switchers for what ... 8 years. So the Alco name stuck. Like using the word Kleenex for all tissues.
 
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