A GP7 is also a foot or so shorter than a GP9.
Jim
The wheelbase is identical. The GP7 is 55' 11" over the draw bar buffers. The GP9 is 56' 2" over the buffers. I suspect this is a change in vender supply issue or the ability to mount alignment control couplers.
Modeling BNSF and Milwaukee Road in SW Wisconsin
I have been told that the controls of GP7s would not MU with anything but other EMD products, and GP9s were more universal in MU capability.
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Is any of this true?
-Kevin
Living the dream.
"I have been told that the controls of GP7s would not MU with anything but other EMD products, and GP9s were more universal in MU capability.
.Is any of this true?"
I believe not true.
I know the Western Pacific MU'd GP7 with Alcos and GE's
Baldwins could not MU with other brands because it used a hydraulic MU system and an adaptor was made to connect to the others electric MU systems
Most electric MU's used 27 pin plugs. Where other arangements were mounted there were adaptor plugs.
Discussion Here
http://cs.trains.com/mrr/f/13/t/267753.aspx
I tried to sell my two cents worth, but no one would give me a plug nickel for it.
I don't have a leg to stand on.
jrbernier The wheelbase is identical. The GP7 is 55' 11" over the draw bar buffers. The GP9 is 56' 2" over the buffers. I suspect this is a change in vender supply issue or the ability to mount alignment control couplers.
DSchmitt"I have been told that the controls of GP7s would not MU with anything but other EMD products, and GP9s were more universal in MU capability. .Is any of this true?" I believe not true.
It may have been somewhat true when built. In the early 1950s the MU connections were not completely compatible between builders, although (except for BLW) they were very close. Most of the problems were in the lesser features, operating sanders, or having the dynamic brakes operational on all units. Sometimes loco A could control all the features on loco B, but not vice versa. Jumper cables were also a work around. It did not take long for most railroads to retrofit their fleets to be fully compatible. Switchers, in the rare cases where they had MU, were an exception and generally would not MU with road power.
John
The three inch difference in length over draft gear buffer faces between the GP-7 and the GP-9 may be due to the fact GP-7s had a buffer casting while, the GP-9s buffers were fabricated from steel plate.
No examples of "hydraulic" MU are evident, even on locomotives with hydraulic transmissions. MU control was either pneumatic as in Baldwin and early Fairbanks-Morse locomotives, or electrical in the rest of dieseldom. As much as each manufacturer wanted their products to dominate, the railroads made it abundantly clear that they wanted interchangiblilty across all brands of diesels, regardless of builder. This led to standardization on the 27 point jumper cable by the time the GP-9 had replaced the GP-7 in EMD's catalog in 1954. Earlier power was retro-fitted to provide maximum flexibility in locomotive utilization.
One limiting factor in early first generation compatibility was the differences in braking equipment "schedules". These sets of characteristics governed the operations of the air brake systems and all were not compatible with each other, regardless of builder. The 6 schedule as used on the early post war production gave way to the 24 schedule as the GP-9 replaced the GP-7. The 26 schedule came along to replace but, operate with the 24 at the beginning of the second generation.
Most of these factors exhibit no visual cues on a locomotive that a modeler would duplicate but, would be evident in the way locomotive consists would be built. Sometimes, these limitations are included in the special instructions section of the employees timetable. Often locomotives with special characteristics are segregated by numbering group, as the Union Pacific did when it put its "fast forty" SD-40-2s in the 8000 series.
For someone modeling the early postwar diesel era, the effort to keep pure consists of like locomotives together could make you bring back steam!