EMD Road Switchers

Four Axle General Purpose (GP) Road Switchers

The following tables illustrate the various spotting features of EMD GP7 and GP9 units purchased by the Pennsylvania Railroad. The basis for these tables are from a Jim Williams presentation at the May 2000 annual meeting of the Pennsylvania Railroad Technical & Historical Society.

EMD GP7 vs. GP9

EMD GP7, Class ES15 / ES15ms

The EMD GP7 is a four-axle (B-B) road switcher diesel-electric locomotive built by General Motors Electro-Motive Division and General Motors Diesel between October 1949 and May 1954.

Power was provided by an EMD 567B 16-cylinder engine which generated 1,500 horsepower (1,119 kW). The GP7 was offered both with and without control cabs, and those built without control cabs were called a GP7B. Five GP7B's were built between March and April 1953. The GP7 was the first EMD road locomotive to use a hood unit design instead of a car-body design. This proved to be more efficient than the car body design as the hood unit cost less to build, was cheaper and easier to maintain, and had much better front and rear visibility for switching.

This was the first model in EMD's GP (General Purpose) series of locomotives. Concurrently, EMD offered a six-axle (C-C) SD (Special Duty) locomotive, the SD7. The GP7 was replaced by the GP9 model in GM-EMD's GP sequence.

The GP7, GP9 and GP18 locomotives share a similar car-body that evolved over time. Most GP7s had three sets of ventilation grills under the cab (where the GP9 only had one), and two pair of grills at the end of the long hood (where only the pair nearest the end was retained on the GP9). However, some late GP7s were built with car-bodies that were identical to early GP9s. Early GP7s had a solid skirt above the fuel tank, while late GP7s and early GP9s had access holes in the skirt. Many railroads later removed most of the skirt to improve access and inspection.

Locomotives could be built with the engineer’s control stand installed for either the long hood, or the short hood designated as the front. Two control stands for either direction running was also an option, but one end would still be designated as the front for maintenance purposes. The GP7 was also available with or without dynamic brakes, and a steam generator installed in the short hood was also an option. In the latter case the 1,600 US gallons fuel tank was divided, with half for diesel fuel, and half for boiler water. One option available for locomotives without dynamic brakes, was to remove the two 22.5 in × 102 in air reservoir tanks from under the frame, and replace them with four 12 in × 150.25 in tanks that were installed on the roof of the locomotive, above the prime mover. These "torpedo tubes" as they were nicknamed, enabled the fuel and water tanks to be increased to 1,100 US gallons each, although some railroads opted for roof-mounted air tanks and 2,200 US gallons fuel tanks on their freight ‘Geeps’.

GP7 8572 was assigned to Lewistown as of 1956 per photo on pages 90 and 93 of "Trackside..." (#65).

GP7 8581 was assigned to Lewistown as of 1957 per photo on page 63 of "Pennsy 1950s Last Great Decade".

EMD GP9 / GP-9B, Class EFS17m

An EMD GP9 is a four-axle road switcher diesel-electric locomotive built by General Motors' Electro-Motive Division produced between 1954 and 1959 and it is powered by a sixteen-cylinder engine which generated 1,750 horsepower. The GP9 succeeded the GP7. The lettering "GP" stands for "general purpose". This locomotive type was offered both with and without control cabs; locomotives built without control cabs were called GP9B locomotives.

EMD GP30, Class EF22

The EMD GP30 is a 2,250 hp (1,680 kW) four-axle road switcher diesel-electric locomotive built by General Motors Electro-Motive Division of La Grange, Illinois between July 1961 and November 1963. A total of 948 units were built for railroads in the United States and Canada (2 only), including 40 cabless B units for the Union Pacific Railroad.

It was the first so-called "second generation" EMD diesel locomotive, and was produced in response to increased competition by a new entrant, General Electric's U25B, which was released roughly at the same time as the GP30. The GP30 is easily recognizable due to its high profile and stepped cab roof, unique among American locomotives. A number are still in service today in original or rebuilt form.

The GP30 was conceived out of the necessity of matching new competitor GE's U25B. The U25B offered 2,500 hp while EMD's GP20 and its 567D2 prime mover was only rated at 2,000 hp. The U25B also featured a sealed, airtight long hood with a single inertial air intake for electrical cooling, with a pressurized cooling system which kept dust out of the engine and equipment area. Finally, the entire GE design was optimized for ease of access and maintenance. The U25B demonstrators were receiving much praise—and orders—from the railroads that tested them. Meanwhile, ALCO had been producing the 2,400 hp RS-27 since 1959, though it had not sold well.

EMD's engineering department pushed their DC traction system for an extra 250 hp. The 2,250 hp wasn't quite equivalent to the GE and ALCO offerings, but EMD hoped the railroads' familiarity with EMD equipment would improve their chances. The locomotive in which the 16 cylinder, 567D3 would be fitted, was improved along the lines of the U25B; sealed long hood, central air intake, and engineered for easier maintenance access. The frame and trucks of the GP20 were carried across; the extra equipment for the centralized air system required more space behind the cab, and since the locomotive was not going to be lengthened, extra space was achieved vertically by raising the height of the locomotive, giving room for the central air system, turbocharger and electrical cabinet all behind the cab. This extra height behind the cab meant that the body style used for previous GP units was not suitable.

EMD GP35, Class EF25

The EMD GP35 is a 4-axle road switcher diesel-electric locomotive built by General Motors Electro-Motive Division between July 1963 and December 1965 and by General Motors Diesel between May 1964 and January 1966. The locomotive's power was provided by an EMD 567D3A 16-cylinder engine which generated 2,500 horsepower.

Many railroads traded in Alco and EMD F units for GP35s, reusing the trucks and traction motors. Some railroads had EMD reuse the Alco trucks on the GP35s.

Four Axle Super Duty (SD) Road Switchers

EMD SD7, Class ES15a

An SD7 is a 6-axle road switcher diesel-electric locomotive built by General Motors Electro-Motive Division between May 1951 and November 1953. It had an EMD 567B 16-cylinder engine producing 1,500 horsepower for its six traction motors. 188 were built for United States railroads. Starting in August 1953 a total of 26 SD7s were produced which used either the 567BC engine or the 567C engine. T

This was the first model in EMD's SD (Special Duty) series of locomotives, a lengthened B-B GP7 with a C-C truck arrangement. The two extra axles and traction motors are useful in heavy, low speed freight service. 

Many SD7s both high and short-hood can still be found in service today on shortline railroads and industral operators, although most Class 1 roads stopped using these locomotives by the 1970s and 1980s. Some remain in rebuilt form on some major Class I railroads, as switcher locomotives.

The PRR purchased these units specifically for use on 5h3 Madison Hill grade, a 1.5 mile 5.89% grade in Indiana.

EMD SD9, Class ES17m

An SD9 is a 6-axle road switcher diesel locomotive built by General Motors Electro-Motive Division between January 1954 and June 1959. An EMD 567C 16-cylinder engine generated 1,750 horsepower. This model is, externally, similar to its predecessor, the SD7, but this model, internally, features the improved and much more maintainable 567C engine. The principal spotting feature are the classification lights on the ends of the locomotive, above the number board. The SD9's classification lights are on a small pod, canted outward. The last phase of construction had a carbody similar to the SD18 and SD24, and used two 48-inch cooling fans instead of four 36-inch cooling fans.

Purchased primarily for use as hump pushers and heavy yard switchers.

EMD SD35, Class EF25a

An EMD SD35 is a 6-axle road switcher diesel-electric locomotive built by General Motors Electro-Motive Division between June 1964 and January 1966. Power was provided by an EMD 567D3A 16-cylinder engine which generated 2,500 brake horsepower. A 3,000-US-gallon fuel tank was used on this unit.

EMD SD40, Class EF30a

The EMD SD40 is a 6-axle road switcher diesel-electric locomotive built by General Motors Electro-Motive Division between January 1966 and August 1972.

Like its predecessor in EMD's catalog, the SD35, the SD40 is a high-horsepower, six-axle freight locomotive.

EMD SD45, Class EF36

The SD45 is a six-axle road switcher diesel-electric locomotive built by General Motors Electro-Motive Division between 1965–1971. It has an EMD 645E3 twenty-cylinder engine generating 3,600 hp on the same frame as the EMD SD38, EMD SD39, EMD SD40, and EMD SDP40.