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Bachmann Standard Line Union Pacific "Centennial" DDA40X Locomotive
Fans of high-horsepower locomotives will find the new and imroved Union Pacific "Centennial" DD40X a welcome addition to their roster.

Product Review: Bachmann Standard Line
Union Pacific "Centennial" DDA40X Locomotive

by Gary Quale/photo by George Riley

Many years ago, Bachmann released a Hong Kong produced model of the then largest ever US diesel locomotive, the Union Pacific "Centennial" 6,600hp DDA40X locomotives. Bachmann has recently reissued a significantly upgraded model of this unique locomotive.

The Union Pacific initially ordered 25 of these locomotives back in 1968, and added 22 more to the order before the first unit was delivered. They were numbered 6900 through 6946. The lead unit was rushed to completion so it could participate in the May 10, 1969 celebration of the one hundredth anniversary of the "Golden Spike" ceremony that marked the completion of the first transcontinental railroad. These locomotives were given the name "Centennials" in commemoration of that event. The remainder of the initial order was delivered between June and December 1969, with units 6925 to 6946 following in June 1970 to September 1971.

The DDA40X Centennials were built by by General Motors' Electro-Motive Division. The "X" indicated experimental as these units served as testbeds for several new features that would later become standard in the Dash-2 product line, including modular electronic controls, advanced excitation of the traction motor fields, and capability to self load-test using the dynamic brake resistors. At 98 ft 5 in long, they are the longest diesel locomotives ever built and this required EMD to go to an outside fabricator to build the frames. The frame included an 8,000 gal. fuel tank, the largest ever used on a diesel locomotive.

The Centennials used two 16 cylinder 645E3A engines. The first three units were briefly equipped with 20% fuel injectors that gave them a 7,000hp rating. After about a year, these were replaced with the standard 10% injectors, restoring a 6,600hp rating. The Centennial units were equipped with the high speed 59:18 gear ratio (instead of the 62:15 on most EMD locos) for operation at over 80 miles per hour.

Bachmann Standard Line Union Pacific "Centennial" DDA40X Locomotive

There were minor detail variations between the locomotives as delivered. The most visible external difference between the first 25 units and the second 22 was the door with a small oval window on the left side at the rear of the long hood. The first series had this door high on the side, and had a tall, narrow window on the left half on the door. On the later series, this window was wider, centered on a narrower door, and mounted in a lower postion. The first three units were unique in having a 45o cut out on upper left corner of the door below the windor door; all the later units had a rectangular door. The 6900-6902 were also unique in having two rectangular sander valve covers below the walkway under the large rear sand boxes, a feature not repeated on the subsequent units. The Bachmann model includes all of these details as appropriate for Centennials 6900, 01, or 02.

Other changes were made over the service lives of these units. The units were delivered with a rectangular metal box that looked like an anti-climber centered under the front walkway. This cosmetic detail was removed from most of the 6900s by 1972, leaving just the edge of the deckplate protruding above the pilot. The units were delivered with Cullen rotating amber beacons mounted near the center of the cab roof. These were replaced with a strobe light on most units. The units had Leslie S-5T-RF five trumpet Super Tryphon horns mounted between the first and second radiator fans for the forward engine as delivered. Starting in 1978, the UP began relocating the horns to the center front of the cab roof on a 12" tall bracket, at which time some of the Centennials received Nathan horns. Metal cab window shades replaced the original canvas around 1979. The Bachmann model has all these features as appropriate to an as-delivered unit.

Painting also had some changes. The large UP medallions originally applied were lettered "UNION PACIFIC RAILROAD." The word "railroad" was officially eliminated from the corporate name in 1970, and was painted out on some units as an interim measure before new shields were applied. By about 1975, all of the fleet had the new style medallions. Around the same time the UP started painting the green anti-glare and no-skid area on the nose gray on some units and by the late 1970s all units had gray on the noses. Starting in June 1980, the UP began to paint the vertical sections of the handrails on road units used for switching in a contrasting color. White had been used on yard unit handrails since 1976, but the new spec called for yellow on road power. This spec was changed to white in February 1983. With the exception of the nose color, the Bachmann model has the paint features of a unit operating in the mid-1980s.

Bachmann Standard Line Union Pacific "Centennial" DDA40X Locomotive

The 6900s were primarily used in long distance fast freight assignments, and some units ran as much as 21,000 miles in a month. The units had run up high mileage by the mid-'70s and were requiring more maintenance. The UP initiated a special overhaul program in the spring of 1976, and over the next year the major drive train components were reconditioned on all of the fleet. A similar program started in late 1979. Many of the changes listed above would have been made during these overhauls.

The Centennials high power and the traction motor advanced excitation allowed them to accelerate trains up to speed more rapidly than any other power on the UP. When older GP-30s, GP-35s, or GP-40s were MU’ed in front of a DDA40X, the Centennial would often be pushing the smaller power as it accelerated the train, leaving the GP with a dented walkover plate. The UP rebuilt 35 SD40-2s in 1976 for fast freight service and equipped these units with 59:18 gearing like the Centennials. These modified units became known as the "Fast Forties." The UP frequently ran "Fast Forty Sandwiches" of a Centennial, a high speed SD40-2, and another Centennial. Impressive power!

Following a downturn in traffic, the Centennials were put into storage beginning in late 1980 and into '81. Traffic increased again in the mid-80s, and 25 Centennials were brought back into service in February and March of 1984. However, the high mileage and desert storage period combined to reduce reliability, and the resurrection lasted only about a year. The #6936 was the last Centennial to haul a regular freight run on May 6, 1985. Thirteen of these locomotives survive today. Eleven are on public display, one is a stripped hulk, and best of all #6936 is still operable in the UP’s "Heritage Fleet" and is used for special occasions.

Bachmann has improved the body shell on the new models. The detail on the radiator grills along the upper sides of the long hood is much improved, and these grills and the exhaust stacks are blackened to represent weathering from use. The contour of the fuel tank is improved, and the air reservoirs are now in more realistic high relief. The cab side windows now have silver colored frames. The model comes with nicely detailed handrails of a tough, pliable plastic. Lettering in much crisper than on the earlier version, and now includes the correct black edging. Bachmann currently offers four different numbers on their Centennials, 6915, 6927, 6932, and 6943 for those who want to make a sandwich.


Bachmann Trains
1400 East Erie Avenue
Philadelphia, Pennsylvania 19124

#62106 EMD DD40AX Centennial

HO scale, MSRP $130.00

Bachmann has made major improvements to the mechanism. The old single power truck with a spur gear drive has been replaced with two flywheel equipped, skew-wound can motors each driving one truck for a 16 wheel drive. The RP25 wheel sets conformed to the NMRA standards gauge. E-Z Mate Mark II couplers are factory installed. A pair of constant intensity LEDs light the headlight in the nose and the number boards and the beacon above the cab. The Bachmann Centennial comes with a factory-installed dual-mode DCC decoder connected by a standard 8-pin plug. The bottom of the removable fuel tank has two speaker grills cast in, and there is a recess in the underside of the die-cast frame to accommodate two speakers for those that want to add sound to their models.

The Centennial weighs 1 lb. 7 oz., and produced a drawbar pull 2.7 oz. without slipping. Out of the box, our sample began to crawl at a smooth 0.2 smph at 5.0 V and 0.05 A in the DC mode. Outstanding! Full speed running light was 105 smph at 12 V and 0.07 A. Current draw at 12 V with the locomotive stalled and wheels slipping was 0.5 A. In the DCC mode with a Digitrax control system, speed step 1 yielded 0.36 smph and speed step 99 produced 154 smph.

Fans of high-horsepower locomotives will find the new and imroved Centennial a welcome addition to their roster. The new Bachmann Centennial is an excellent operating and well-detailed model of a significant prototype.


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