Locomotive Phases - EMD GP7, GP9
One detail I haven't been able to figure out is in regards to length. 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. However, it appears the change in length did not occur with the change in coupler pocket design from cast to welded early in GP9 production. I haven't been able to confirm when the change took place, and photo measurements I've taken of several GP7's all suggest a coupler-to-pilot distance of 25" (and therefore a length of 56' 2").
These phases are based on those compiled by Scott Chatfield.
Phases - GP7
Phase 1: 1949.10 - 1950.11
- Dynamic brakes: not available
- No box on walkway behind left side cab
- Fuel tank skirt: Solid
- Sloped pilot plates
- 86" engine room doors
- Hood straps around engine compartment: full-height
Phase 2: 1950.06 - 1953.02
- Dynamic brakes: optional, with 36" fan
- Box added on walkway behind left side cab
- Fuel tank skirt: Slotted - only on units with 1200+ gallon fuel tank (afer 1952.03)
- No sloped pilot plates (after 1952.07)
- Dynamic brakes: 48" fan (after 1952.10)
Phase 3: 1953.03 - 1953.12
- 82" engine room doors
- Hood straps around engine compartment: either stop at top of engine room doors (dynamic brakes) or are absent (no dynamic brakes)
Phase 4: 1954.04
This may be considered more of a de-rated GP9 than an actual GP7 phase as it applies to a single order by MP.
- GP9 Phase 1a carbody, GP7 internals
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:
- 2 louver groups under cab removed
- 2 louver groups added to 1st and 2nd engine room doors
- 2 louver groups removed from 4th door from long hood end
- lower louver group removed from closest door from 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.
Phases - GP9
- Handrail stanchions: fabricated pipe
- Fuel tank skirt: deep
- Radiator fans: 4, 36"
- Louvers under walkway in front of cab: 1 large louver group
- Welded (instead of cast) coupler pocket/striker plate (late Phase 1a)
- Handrail stanchions: stamped channel
- Lower louver groups removed from generator room doors (behind cab)
- 2 louver groups added on 3rd engine room door
- Fuel tank skirt: shallow
- Fuel filler moved forward
- Louvers under walkway in front of cab: 2 small louver sets
- Radiator fans: 2, 48"