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Locomotive Descriptions and Phases - EMD/GMD GP28, GP35

The EMD GP35 was introduced in 1963 as a successor to the GP30. With the 16-cylinder turbocharged 567 engine uprated from 2,250 to 2,500 horsepower, EMD caught up to the power output of the competing ALCO C-424 and GE U25B. Although many of the changes from the GP30 were evolutionary - the underframe was almost identical and internal equipment layout was largely the same - the carbody was redesigned to a simpler, clean-lined appearance. The cab roof was lowered, the windshield was flat instead of tapered, the engine compartment doors and radiator intakes were taller, and the rear of the hood was raised to match the cab roofline. The general hood design of the GP35 - 6' wide, 9' 4.25" above the frame, tapered ends, a flat roof, and slightly rounded top corners - was carried through to the SD70 series in the 21st Century.

Several of the external changes from the GP30 reflected changes under the hood. On the GP30, the traction motor blower duct extended from the blower (located on the left side behind the cab) across the underframe to the right walkway, with a raised air duct extending along the length of the walkway. The left walkway contained a raised equipment duct. On the GP35, the air duct was simplified and moved to the left walkway, while the duct on the right side was eliminated. The raised roof of the GP30 was necessary to accommodate the electrical cabinet, which was too tall for the earlier EMD carbody design; the lower roof of the GP35 was made possible by the electrical cabinet being shortened by roughly 6". The carbody of the GP35 was also less expensive to build and provided somewhat easier access for maintenance.

A 1,800 horsepower, non-turbocharged (Roots-blown) version, the GP28, was also produced as a replacement for the GP18. It had two exhaust stacks (in place of a single turbocharger stack) and two 48" radiator fans (in place of two 48" fans flanking a 36" fan) but otherwise looked the same as the GP35 and followed the same phase evolution. Only a few dozen were built as the railroads were already well-supplied with earlier GP7 through GP18 units. Six axle versions, the SD28 and SD35, were built concurrently.

The GP35 sold well, with more than 1,300 built by the end of 1965. However, the increase in horsepower came at a price. The 2,500 horsepower rating pushed the limits of a traditional DC generator, and the resulting electrical system, with sixteen stages of transition using four field shunting contactors for each traction motor, proved complex and unreliable. The 567 engine, while still reliable, was nonetheless nearing its horsepower limit with technology of the time, having nearly doubled from the 1,350 hp of the FT in 1939. In 1965, EMD built a test bed on a GP35 frame (EMDX 433A) that introduced an alternator-rectifier electrical system and new 645-series engine, addressing two of the major shortcomings of the GP35. In 1966, less than three years after the GP35 began production, these improvements led to its replacement by the GP40.

By 2000, few GP35's remained in service in their original form. However, from the 1980s onward, many were rebuilt either in kind or modified and redesignated as GP38 or GP39 variations. In the process, most rebuilds received substantial revisions to the electrical system and had the engine retrofitted with 645-series power assemblies, and as a result a number of them remained in service beyond 2020.

EMD GP28, GP35 Phases

The biggest external change in GP35 production happened in mid 1965, when the underframe was changed from the "fishbelly" profile used on previous EMD road switchers (thicker in the middle than at the ends) to a straight pair of I-beams, which would be used in most subsequent EMD models. At this point, the GP35 adopted the side sill, air reservoir and piping arrangement that had been introduced in the SD35 in 1964. The new underframe was about 1.5" taller, and the increased clearance under the middle of the frame allowed for a simpler fuel tank design placed flat against the underframe instead of extending up between the frame rails.

These phases are based on the GP35 roster compiled by David Thompson.  Some of the units listed by Thompson as Phase 1b2, 1b3 or 1b4 were actually other Phase 1b variations, since they all occurred within a very short time. However, the phase details are the same.

See also SD28, SD35, SDP35, SD40X Phases.

Numbers correspond to the illustrations shown below.

Phase 1a1 1a2 1b1 1b2 1b3 1b4 1c1 1c2 1d 2a 2b 2c
Dates 1963.10 -
1964.02 -
1964.03 -
1964.09 -
1964.09 -
1964.11 -
1964.12 -
1965.02 -
1965.05 -
1965.04 -
1965.05 -
1965.08 -
Central hood doors 1 7 latched 3 latched 7 latched
Central air intake 2 Short, flat perforated sheet Slightly longer Corrugated
MU connector housing 8" high 10" high
Panel under headlight 3 Flat (with headlights) or rounded (with gyrating lights) Rounded regardless of light type
Left side battery box cover 4 2 groups of 3 louvers 2 single louvers
Right side battery box cover 3 groups of 3 louvers, sheet metal extension in front of battery box No sheet metal extension 2 single louvers
Radiator intakes 5 Metal bars Wire screen
Blower duct housing 6 Smooth edges Seam along edges, fewer bolts
Dustbin hatchOn roof behind cab, above central air intake
Flat Raised Flat Raised
Underframe 8 "Fishbelly" profile, approx. 60.5" walkway height Straight profile, narrower side frame,
taller/narrower steps, approx. 62" walkway height
Phase 1a1 1a2 1b1 1b2 1b3 1b4 1c1 1c2 1d 2a 2b 2c

Other details


These two drawings illustrate typical early (Phase 1a2) and late (Phase 2b) GP35's built to similar BO/CO specs. Externally, these represent very generic GP35 variations.

Phase 1a3 -  Phase 2b

GMD GP35 Phases

Twenty-six GP35's were built by GMD in Canada - 2 for CN and 24 for CP. While GMD Phase 1a units shared the same spotting features as EMD Phase 1a1 units, GMD production did not change at the same pace. Later units tended to retain details consistent with older EMD GP35 phases. All GMD production featured vertical steps, a cab-mounted bell, square sand hatches and larger Pyle National headlights, with the front headlight in the short hood and the rear headlight vertically mounted. GMD did not build any GP28's, and no GMD GP35's were built with the later straight frame design.

These phases are of my own making.

Phase 1a 1b 1c
Dates 1964.05 -
1965.05 -
Hood doors 7 latched 3 latched 7 latched
Central air intake Short Long
Panel under bell (cab headlight) Flat Rounded
Radiator intakes Metal bars Wire screen


Electro-Motive Division. (1962). Air duct Assembly and Application, GP30, Part no. 8305561. [Drawing]. Retrieved December 2018 from

Electro-Motive Division. (1964). Underframe Assembly, GP35, Part no. 8346666. [Drawing]. Retrieved January 2013 from

Electro-Motive Division. (1964). Diesel Locomotive Operating Manual for Model GP35, Second Edition. Retrieved December 2018 from

Strack, D. A History of Union Pacific Dieselization, 1934-1982. Retrieved January 2020 from

Strack, D. GP35. Retrieved December 2018 from

Strack, D. UP GP30s. Retrieved January 2013 from

Thompson, D. EMD's GP35 - Original Owners. Retrieved April 2010 from