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Locomotive Descriptions and Phases - EMD GP39X, GP49, GP50

The GP50 was introduced in 1980 as a significant evolution of the GP40-2, and was produced alongside it until both were replaced a few years later by the GP60. It incorporated several features that had first appeared on experimental GP40X units in 1977-1978. An updated 16-cylinder 645-series prime mover (along with revised traction motors and main alternator) provided a horsepower increase from 3,000 to 3,500, and EMD's "Super Series" wheelslip control system employed Doppler radar to more precisely measure the locomotive's speed. The traction motors were wired permanently in parallel with transition taking place within the alternator, and a lower engine speed at idle and during dynamic braking reduced fuel consumption. An exhaust silencer and Q-type radiator fans were intended to meet 1980 federal noise regulations, and appeared concurrently on the GP40-2. The GP39X and GP49 used a smaller 12-cylinder engine and were purchased solely by Southern and the Alaska Railroad, respectively.

Externally, the GP50 retained the same general appearance as the GP40-2, with an angular cab, a straight hood with exhaust stack near the front and three fans at the rear, and a raised blower duct along the left walkway; the most obvious visible difference was the taller radiator intakes. While the overall length remained the same, the GP50 rode on a new, slightly lighter underframe with a roughly 1.5" taller cross-section. This new frame was used on the GP39X, GP49 and the last order of GP39-2's, but was not adopted on concurrent GP40-2 production.

While the high-adhesion "HT-B" truck introduced on the GP40X was optional on the GP50, none were built with it; all were built with EMD's familiar single-shoe, swing-hanger GP design (informally known as the "Blomberg M"). Partway through production, the secondary suspension (in the middle, supported by the swing hangers) was changed from stacked rubber pads to a leaf spring. The rubber pads had previously been introduced because the single-shoe brake system didn't have enough clearance for the larger leaf spring used on earlier clasp-brake versions of the truck; the new leaf spring required less space and restored some of the vertical ride compliance lost with the rubber pads.

As a result of the Super Series wheelslip control system, EMD marketed the GP50 as a potential equivalent to the 6-axle SD40-2. In practice, it partly succeeded; the more advanced control system was not quite enough to compensate for the lighter weight and two fewer axles at low speed or on wet rails. As the GP50 arrived at the start of a slump in locomotive sales, it sold in significantly fewer numbers than previous GP models, although it was still the best-selling domestic 4-axle locomotive of the early 1980s.

Several reliability problems immediately emerged in service - although claims within railfan circles of the model being a "failure" as a result of the "overstressed" engine are rather exaggerated. Several components suffered from quality-control problems as a result of cost-cutting or outsourcing; once these were addressed and the 645F engine refined, problems tended to be electrical rather than mechanical. The electrical system was a stepping stone between the modular electronics of the Dash-2 series and the microprocessor controls of the later 60 series, and failure of the Super Series wheelslip control system would cause the engine to default to the older WS10 system previously used on the GP40-2.

Despite the teething problems, many GP50's had long service lives. As of 2024, most ATSF, BN and Southern units were still in service with successors BNSF and Norfolk Southern (albeit largely either derated or rebuilt). CNW and MP units were retired by UP in the 2000s, after which a number continued in service on smaller railroads.

Transition: From GP40-2 to GP50

Despite many shared dimensions and an overlapping production run, the GP50 rode on a different underframe from the GP40-2 and had largely new sheetmetal above the walkway:

Phases

These phases are the same as those described in Robert Sarberenyi's GP50, GP39X, GP49 roster, with a few details added from my own observations. Most details were also applied to concurrent GP40-2 production, so I've listed the equivalent GP40-2 phases as well.

Phase 1a1 1a2 2a 2b
Dates 1980-05 -
1980-09
1980-09 -
1981-06
1983-09 1985-04 -
1985-11
GP40-2 Phase 2c1 2c2 3
Battery box covers Bolted,
no horizontal rib
Horizontal
rib added
Latched,
lift-off tabs
Frame side sill 5" tall over air reservoirs,
8" tall at ends
5" over entire length
Blower duct Flat, wide, two ribs,
no raised step
Angled, narrow, no ribs,
raised step ("laundry chute")
Exhaust silencer Opening at rear Opening at front
Short hood Bolted hatch added on top

Railroad Variations

ATSF

ATSF purchased 45 GP50's in two main batches, numbered 3810-3839 (Phase 1a2, 1981) and 3840-3854 (Phase 2b, 1985). Typical of ATSF units at the time, the GP50's had a cluttered cab roof, with an air conditioner in the middle, a Prime beacon on the left side, a Leslie RS-3L-R horn on a raised pedastal at the front, and an antenna plane above the inertial air intakes behind the cab. The first 14 units (3810-3823) had Locotrol equipment for mid-train operation, evident externally by the additional antenna on a raised box at the rear of the cab roof. The front sill was an anticlimber (sturdier than the rear sill extension, with the handrail stanchions fastened to the top of the walkway). Following the merger with BN, these units were renumbered into the BNSF 3100 series alongside former BN units.

▼ Illustrations:

BN

The first ten GP50's used by Burlington Northern were ordered by the St. Louis–San Francisco Railroad (SLSF) prior to the merger with BN, intended to be numbered SLSF 790-799. One unit was delivered in SLSF paint but numbered as BN 3100; the remainder were delivered in BN green and black and numbered 3101-3109. These were Phase 1a2 units delivered in late 1980 and were built to SLSF specifications, including a small front plow, a non-anticlimber front sill extension, a red Gyralite in the short hood, a Prime beacon on the cab roof, and a Leslie RS-5T-RR horn. Unlike later units, these first 10 were retired by BNSF in 1997, after which they continued in service on smaller railroads.

In 1985 BN received 53 additional Phase 2b units numbered 3110-3162, built to more typical BN specifications (a front anticlimber, a Prime beacon at the front of the cab roof, a Prime PM-990 horn at the rear of the cab roof, and Type F couplers. The last 5 units (3158-3162) were built with an enlarged cab for a 5-person crew, with the front wall of the cab moved forward by nearly 2 feet (with corresponding changes to the battery box and sub-base doors underneath). While units with the large cab are sometimes referred to as "GP50L", they apparently were given no such model name by EMD; the "GP50L" designation was instead used internally by BN for all GP50's in the 3110-3162 series equipped with the LARS telemetry system.

▼ Illustrations
Phase 1a2, ordered by SLSF:
Phase 2b, extended cab:

CNW

The first production GP50's were an order of 50 units for CNW, built in mid-1980 (Phase 1a1) and numbered 5050-5099. They had CNW's gong-style bell mounted on the short hood, a winterization hatch over the forward radiator fan, a Leslie RS-3L-R horn, and a small beacon on the rear of the cab roof (initially appearing to be a Federal Signal model with a rounded housing, replaced with other versions later).

In 1996, the fleet (minus wrecked units 5051 and 5096) was absorbed by UP following the merger with CNW; some were renumbered briefly to the UP 900 series before all but two were numbered to UP 5510-5557. Seven were renumbered to the 1600 series in early 2002 before all 48 units were retired in late 2002. Most continued in service on smaller railroads or leasing companies.

▼ Illustrations:

MP

Missouri Pacific was the only railroad to order GP50's without dynamic brakes, receiving 30 units built in 1980 (Phase 1a2) numbered 3500-3529. The units were relatively bare-bones in both appearance and specifications, with the only notable spotting features (other than the lack of dynamic brakes) being the bell mounted high on the left side of the long hood, and the additional jacking pads near the corner steps.

Following the merger with UP in 1982, several were numbered in the 50 to 78 range before all were renumbered to UP 960-989 from 1989 to 1992. Ten units (960-969) were modified with the addition of dynamic brakes; plans to convert the remaining fleet were ultimately cancelled. Seventeen were renumbered to the 5558-5587 series and a few to the 1600 series before they were gradually retired over the mid to late 2000s. Unlike the CNW units retired by UP a few years earlier, most former MP units were stored or scrapped in the late 2000s or early 2010s.

▼ Illustrations:

SOU

Southern's GP50's were the last locomotives built with the railroad's traditional high short hood; subsequent locomotives delivered after the merger with Norfolk & Western were closer to NW specs. They were numbered immediately after the railroad's GP40X's (7003-7092) and retained the same features: Nathan P5L horns and large plows on both ends, a bell on the end of the long hood, rigid metal awnings above the cab side windows, platform lights on the upper edges of the hoods, and dual fuel gauges.

The first few dozen were not built in sequence; 7003-7007 and 7017-7035 were Phase 1a1 while 7008-7016 and 7036 and up were Phase 1a2. The last order (7073-7092) also had the inner stanchions moved from the end of the sill to the top of the walkway, and Timken tapered roller bearings on the trucks in place of Hyatt bearings. Southern also ordered six GP39X's numbered 4600-4605; aside from having 2 instead of 3 radiator fans and a shorter engine compartment (with fewer doors and the blower duct / inertial air intake moved rearward) they were very similar in appearance to the GP50's.

While Norfolk Southern retired their three GP40X's in 2001 (after which two were rebuilt as GP40-3's for SLR) they retained their GP50 fleet until the majority were rebuilt either as GP38-3's (in 2004-2007) or GP33ECO's (in 2015-2016). In both cases, they received new cabs with low short hoods; the GP38-3's retained much of the original carbody (with the original engine receiving Roots blowers in place of the turbocharger) while the GP33ECO's received a substantially altered hood housing a new 12-cylinder 710-series engine.

▼ Illustrations:

References

BNSF GP50/L? [Online discussion]. (2001). Retrieved January 2024 from https://www.trainorders.com/discussion/read.php?1,21183

Electro-Motive Division, General Motors. (1979). Model GP50 - 3600 hp General Purpose Locomotive, Specification 8112.

EMD’s 50 Series....lemon or just lore? [Online discussion]. (2021). Retrieved January 2024 from https://www.trainorders.com/discussion/read.php?11,5331410

Peck, D. F. (1980, November/December). CNW GP50. Mainline Modeler, 38-51.

Sarberenyi, R. GP50, GP39X, GP49 Roster. Retrieved April 2010 from http://www.trainweb.org/jaydeet/gp5049.htm

Strack, D. Union Pacific’s Ex-Missouri Pacific GP50 Locomotives. Retrieved January 2024 from https://utahrails.net/articles/up-gp50-letter.php

Strack, D. (2009). UP Diesel Locomotive Roster, Modern Era Index (2000 to present). Retrieved January 2024 from https://utahrails.net/up-diesel-roster/modern-index.php

Toth, C. R. (2024). Norfolk Southern 1982 to Present Diesel Locomotive Roster Summary. Retrieved January 2024 from http://www.nsdash9.com/atroster.html