• Unbuilt Dash-7 types

  • Discussion of General Electric locomotive technology. Current official information can be found here: www.getransportation.com.
Discussion of General Electric locomotive technology. Current official information can be found here: www.getransportation.com.

Moderators: AMTK84, MEC407

  by Allen Hazen
A recent addition to the collection of operators (etc) manuals available on-line at George Elwood's marvelous "Fallen Flags"rail photo site is a General Electric "Locomotive Service Manual" for "Series-7 Road Locomotives." (It is "GEK-30150/First Edition/August, 1978" and on "Fallen Flags" as about ten PDF documents.)

The first section has general data and general appearance drawings of ... the various Dash-7 models: all NINE (or perhaps ELEVEN) of them catalogued at the time. In addition to the B23-7, B30-7, B36-7, C30-7 and C36-7 that were actually built, there is tabular data for the B18-7 (FDL-8 engine rated at 1800hp), the C23-7 (FDL-12 rated at 2250 hp: same engine as in B23-7), and the B28-7 and C28-7 (both with FDL-12 rated at 2750 hp). ((COMMENT: My recollection is that the Dash-7 line, as originally announced, had slightly less powerful "intermediates": B26-7 and C26-7. Since the FDL-12 had been tried, in some L&N U23B, at the 2750 hp rating as early as 1973, it's a little surprising that GE didn't go for the higher power from the start.))

There are five pictures (semi-diagrammatic side views) illustrating these models: one for the B18-7, and one each for the 12-cylinder BB models, the 12-cylinder CC models, the 16-cylinder BB models, and the 16-cylinder CC models. Picture captions reveal a further option: the pictures for the 16-cylinder types are labelled as representing a B33-7 and C33-7 as well as the previously noted "X30-7" and "X36-7" model pairs. ((COMMENT: I don't recall ever seeing any other indication that GE was offering a 3300 on a Dash-7 type.))

As for the appearance of the "alternate history" Dash-7s...

(1) B23-7 and B30/36-7 are both two feet longer (overall: truck spacing unchanged) than their U23B and U30/33/36B ancestors. The B18-7 shows the same two-foot stretch between the truck centers and the couplers. (The picture, but not the tabular data, suggests that the B23/28-7 would have been shorter than the 16-cylinder models: the picture was obviously obtained by literally CUTTING and pasting!)

(2) The "1966 carbody" (late U28B and U28C through end of domestic U series) types (except for the U34CH) have a central equipment blower in front of the engine, revealed on the outside by the large square air intake high on the side of the long hood between the cab and the engine compartment. The C30/36-7 has this same configuration, but four-axle Dash-7 (until the B30-7A1 for the Southern) seem to have had the central air blower at the rear: no intake vent in front of engine compartment. B18-7 would also have been like this. The C23-7 and C28-7, on the other hand, have the forward location of the central blower with the tell-tale vent. (The ventis the same distance in front of the engine as on the 16-cylinder C-7 types: the distance between the cab and the vent is longer by the equivalent of the width of two engine-compartment doors. ... The C23-7 and C28-7, in other words, look (in this respect) like the C30-7A GE finally built for Conrail in 1984.

One other oddity. The "Rotating Electrical Equipment" sectionof the manual talks about the GTA-11, but NOT about the GT-581. I think I have read elsewhere that the B18-7 was supposed to have the DC generator: either GE changed their minds about this or (more likely?) felt the likelihood of B18-7 sales was low enough that it wasn't worth wasting pages on its idiosyncracies in the general service manual for "Series-7."

  by MEC407
Thanks so much for finding and sharing this information. It's somewhat gratifying to know that the B18-7 actually existed on paper, and not just in my fantasy world. :wink:

  by Allen Hazen
MEC 407--
So, just which kind of B18-7 inhabit your fantasy world? B18-7-DC, B18-7-AC? Or maybe the Super-7 rebuild? (All, I assume, in Yellow and Green!)

  by MEC407
All of the above. The more the merrier. :wink:

  by MEC407
The "New Series" Operator's Manual from May 1979 mentions the "never builts" as well: B18-7, B28-7, and C28-7.


  by Allen Hazen
MEC 407--
I'd looked at the operator's manual, but thanks for redirecting my attention to it!

The data is much the same as in the service manual (including the same minimum curvature quoted for the B18-7 as for the longer 4-axle units!) with a couple of puzzling exceptions:
>>>>Heights vary -- up to 16 feet for the C30-7 -- on types actually built: perhaps they were quoting heights of actual units with assorted options?
>>>>Length between truck centers for the 12-cylinder and 16-cylinder BB types has gone from 36'2" in the 1978 service manual to 37'2" in the 1979 operator's manual! I've seen other published figures suggesting that GE varied lengths on 4-axle Dash-7 units, so maybe this reflects an actual change in specification and not just a typo. ((???Since the two-foot length increase of the B23/30-7 over the U23/30B, on the earlier figures, was entirely at the ends, maybe spreading the truck centers half of this distance made for better tracking???-- note that a NON-professional is making this suggestion.))

I've got some drawings in old model railroading magazines:
>>>>"Model Railroader" for July 1983 has a drawing of a BQ23-7, showing it as 36'2" between truck centers. The BQ23-7 was built early in the B23-7's production history (10/78-1/79), so it is plausible that it employed the originally specified B23-7 frame.
>>>>"Railroad Model Craftsman" for August 1998 has drawings by Eric Neubauer of a B30-7 and a B36-7. (In another article on a GE locomotive type, "RMC" claimed the drawings were based on measurements of an actual unit-- GE not being generous with product information-- so I tend to think of "RMC" drawings as more credible than average for things in railfan/model-railroad publications.)
>>>>>>>>The B30-7 is from Southern Pacific's first order (1977?), and the drawing shows it as 36'8" between truck centers!
>>>>>>>>The B36-7 is from Conrail's 1983 order, and shows it as 37'2" between truck centers. Both units are shown as 62'2" in overall length: The B30-7 has 12'9" from truck center to pulling face at both ends, the B36-7 has 12'9" at the front and 12'3" at the rear.

The operator's manual has, at the end, two cut-away drawings showing equipment location. The cetral air blower in the BB unit is in the radiator compartment, aft of the fan.

  by trainiac

Your drawings do not deceive you! I've assembled some B23-7 spotting features (which also apply for the most part to the B30-7) and there are indeed multiple length and truck center dimensions:

Phase 1: 62' 2" overall length, 36' 2" truck centers (equal front and rear truck-to-pilot distance), plain jacking pads
Phase 2a: 37' 2" truck centers (rear truck moved rearward 1 foot)
Phase 2b: New jacking pads (flat metal strip on underside)
Phase 3: 61' 2" overall length, 36' 8" truck centers (rear truck 4" closer to pilot than front)

BQ23-7 units have Phase 1 spotting features, while B30-7A and most B36-7 units have Phase 3 spotting features.

The 4-axle units are also substantially shorter in height than the 6-axle units (4 or 5 inches). This is because the frame is thinner and rides lower over the trucks.

  by Allen Hazen
Michael Eby--
Thank you! Sources like the "Contemporary Diesel Spotter's Guide" tend to give only one length per model, and it is only by comparing different sources that I got any impression of the complexity of the situation. (I think there are similar complexities in the internal anatomy of Dash-7 locomotives as well. The latest Kalmbach incarnation of the "Guide" says for eachtype whether it had a GTA-11 or a GTA-24 main generator, and I ***suspect*** the evolution of the design is more complicated: that the newer wheelslip control and its associated GTA-24 alternator may have been introduced in the course of production, without a change in model designation for the locomotive as a whole. But I don't have any detailed information on that.)

The height difference between BB and CC units goes back to the U25B and U25C, I think, and runs through to the Dash-8: in all of these, the end platform/walkway heigth of the CC types is about five inches higher than that of the BB types, with the height of the hoods and cabs, measured from the platform, being the same. The "North American" cab finally forced a change: it is so high, measured from the platform, that GE had to redesign the frames on the "Dash-8 40M" to lower the platform.

Do you have a document with all your spotting-feature observations on various GE types? It's the sort of thing that might usefully be posted as a file at the "GElocos" site or at Will Daviss site.

  by trainiac

I've found out a lot of these spotting features through drawing these locomotives--that's also how I found out about the lowered frame you mentioned on GE units equipped with the North American cab. I've posted these and other details I've found at


The drawings are at


I'm in the process of a long-term update in which I'm incorporating finer distinctions (such as the ones we've discussed here) into the drawings, so I haven't written up spotting features for units I haven't yet drawn or for which I drew generic versions a long time ago.
  by Storknest
Sorry to dig this up again but I have a few questions I thought interesting in case I ever came across a reason to model one of the unbuilt types.

1 - What is the correct length for the B23-7 and B28-7? The drawing on page 5 makes them look shorter than the B3x-7 types but page 6 data lists the same length.

2 - What would be the reason for buying one of the unbuilt ones?
A - B18-7 a branch line switcher like the U18B?
B - B28-7 a skipped step between B23-7 and B30-7?
C - C23-7 heavy transfer, drag and hump service where speed was not a priority like the U23C or more like why the B23-7 was built, competition?
D - C28-7 a skipped step between C23-7 and C30-7?

3 - Why did they drop the 25 types (U25B, U25C) like the they had in the Universal Series?

  by Allen Hazen
Re 1: The B23-7 was actually built, and was the same length as the B30-7 (though, if you go over previous posts in this string you weill see that these weren't all the same!). The B30-7A, which had a 12-cylinder engine, was based on the same idea ("let's raise the rating of the engine and get something more powerful than a B23 without using 16 cylinders") as the B28-7, and was also as long as a B30-7 or B36-7. So the data are probably correct and the picture wrong: I think the picture was done on the cheap by snipping the length of two engine-compartment doors from the picture of the B30-7.

Re 2: Well, nobody DID buy any, so the reason for buying one can't have been that convincing!
I assume that the B18-7 was directed at the same market as the U18B, but that market was drying up (only one U18B was built in 1976, I think, and EMD's GP15-1 didn't sell particularly well).
The B28-7 and C28-7 would have been a bit less powerful than the reasonably successful B30-7 and very successful C30-7, but probably somewhat cheaper (and maybe a bit better on fuel consumption) because of the 12-cylinder engine: no one ordered any. GE finally managed to sell higher horsepower 12-cylinder units when they offered the B30-7A and C30-7A in the early 1980s: not too many, but the economy was soft in the early 1980s, and they might have sold more if times had been better.
C23-7 was clearly intended for the same market as the U23C, but this market had effectively already dried up: no U23C were built for U.S. service after 1971 I think.

Re 3: The U25B and U25C had the 16 cylinder engine at its original 2500 horsepower rating: the models were discontinued at the end of 1965 when a more powerful version of the engine was introduced on the U28B and U28C, and in 1967 those models were discontinued and replaced by the U30B and U30C. It would certainly have been possible for GE to build a 2500hp locomotive in the 1970s, probably using a 12 cylinder engine. (The U50C, built for the Union Pacific around 1970, had two 12 cylinder engines rated at 2500 hp.)
Such a locomotive would have been only 250 hp more powerful than the U23B or U23C, so i assume nobody (either at GE or at the railroads that could have bought it) saw much point to it.
  by mp15ac
Regarding the two foot increase in length of the four axle Dash 7 units vs their U series versions was to increase the size of the end platforms. With the four axle units usually being used in switching moves it was most likely seen as an improvement over the U series design.

As for the lack of orders for the C23-7, its interesting to note that EMD received no orders for the SD39-2 either.