EMD F7 - History

History

The F7 was the fourth model in GM-EMD's successful line of F-unit locomotives, and by far the best-selling cab unit of all time. It succeeded the F3 model in GM-EMD's F-unit sequence, and was replaced in turn by the F9. Final assembly was at GM-EMD's La Grange, Illinois plant or GMD's London, Ontario facility.

The F7 differed from the F3 primarily in internal equipment (mostly electrical) and some external features. Its continuous tractive effort rating was 20% higher (e.g. 40000 lb for an F7 with 65 mph gearing, compared to 32500 lb for an F3 with the same gearing.

A total of 2,366 cab-equipped lead A-units and 1,483 cabless booster or B-units were built. (Note: the B-unit is often referred to as an "F7B", whereas the A-unit is merely an "F7".)

The F7 can be considered the zenith of the cab unit freight diesel, as it was ubiquitous on North American railroads until the 1970s (even longer in Canada). It powered some of the most famous trains in North America.

Many F7s remained in service for decades, as railroads found them economical to operate and maintain. However the locomotive was not very popular with the yard crews who operated them in switching service because they were difficult to mount and dismount, and it was also nearly impossible for the engineer to see hand signals from his ground crew without leaning way outside the window. As most of these engines were bought and operated before two-way radio became standard on most American railroads, this was a major point of contention. In later years, with the advent of the “GP” type “road switchers”, Fs were primarily used in “through freight” and “unit train” service where there was very little or no switching to be done on line of road.

The F7's eventual successor, the F9, was more powerful but mechanically similar.