Locomotive Descriptions and Phases - EMD/GMD GP7, GP9

The GP7 marked EMD's first serious entry into the road switcher market in 1949. Although it was late to the party, with similar road switchers from ALCO, Baldwin and Fairbanks-Morse having been in production for several years by that point, it ultimately became the most successful of the earliest road switchers. Together with the GP9, it accounted for thousands of first-generation locomotives and was a common sight on railroad for much of the last half of the 20th Century. The general design was retained up to the end of GP18 production in 1963.

The proven 567-series engine and swing-hanger GP (or "Blomberg") trucks were carried over from the streamlined F series, but in place of a structural carbody, the GP7 used a solid underframe with a narrow hood on top. The radiators were split into two sections (at the front and rear of the hood) and dynamic brakes (if present) occupied a raised housing in the center of the hood with a central rooftop fan. The short hood or "nose" was the same height as the engine compartment, and although the hood was angular, the cab retained an arched roof similar to previous EMD switchers. The GP9 was an evolutionary change, with the biggest difference being an increase from 1,500 to 1,750 horsepower.

Many GP7's were retired by the 1980s, although some were rebuilt and continued in service. As the later 567C engine used in the GP9 was more easily upgraded with 645-series engine components, many rebuilt GP9's remained in service well into the 21st Century, even on class-1 railroads such as CN and CP.

Phases - GP7

These phases (as well as those for the GP9) are based on those compiled by Scott Chatfield. I split Chatfield's original Phase 2 into four sub-phases based on minor details. A singled order by MP used GP7 components inside a GP9 Phase 1a carbody, and these units are sometimes referred to as "Phase 4".

Transition: Phase 3 GP7 to Phase 1a GP9

Very early in GP9 production, the coupler pocket and striker plate was changed from a curved, cast housing to a welded version with a flat angled plate on top.

The following detail changes were made to the carbody:

• louvers under the cab removed
• 2 louver groups added to the 1st and 2nd engine room doors
• louvers removed from the 4th door from the long hood end
• lower louver group removed from the door closest to the long hood end

Additionally, the air reservoirs received a different pipe arrangement. The piping on the rear reservoir of the GP7 was an L shape on both sides, extending rearward then vertically behind the side skirt. On the GP9 this was changed to a horizontal pipe between the reservoirs on the left side, and a vertical pipe that went straight under the side skirt on the right side. (There were additional changes in the pipe routing above the level of the side skirt.) The air reservoirs were supported at the top by curved brackets on the GP9 rather than simple straps and bolts as on the GP7.

Length Differences

The overall length of the units is commonly listed as either 55' 11" or 56' 2" for the GP7, and 56' 2" for the GP9. The difference in length can be attributed to the coupler pockets, with the coupler extending either 23.5" or 25" from the pilot face, as the length over the underframe (52' 0") didn't change. As far as I can tell, the difference was related to the type of draft gear used: 23.5" for the M-375 or MS-485 style (longer and shallower), and 25" for the heavier-duty M-380 draft gear.

Without seeing the underframe, one way of spotting the difference on the GP7 is in the striker, on the pilot above and behind the coupler: The M-380 version has a vertical rib up the middle from the end of the striker to the pilot face. This draft gear is listed as an option in EMD specifications for the GP9, but not for the GP7 in the initial specifications of 1949, so it evidently was made available partway through GP7 production.

When the coupler pockets were changed from cast to welded on the GP9, the M-375 / MS-485 version was moved outward so that both versions resulted in an overall length of 56' 2". I believe that early GP9's with cast coupler pockets and M-375 / MS-485 draft gear were still 55' 11" in length, but I haven't confirmed.

Phases - EMD GP9

Phases - GMD GP9

Although relatively few GP7's were built for Canadian railroads, several hundred GP9's were built by GMD, largely for CN and CP. While the phase details were generally the same as on US-built units, the order in which they changed was slightly different.

References