Alco "C-643DH" Diesel Hydraulic Locomotives

The Alco C643DH was one of the builder's most powerful locomotive designs. Built for the Southern Pacific the model was similar to UP's massive C855 design in that it was essentially two locomotives merged into one.  However, it differed in using a diesel hydraulic main generator.  At the time both SP and UP were experimenting with large, powerful single unit locomotives to reduce operating expenese and both had been quite loyal customers to the American Locomotive Company (Alco) for decades, dating well back to the steam era.   Unfortunately, the C643DH was plagued with many of the same problems that UP experienced with its experimental C855. 


Aluminum wiring, for instance, was one such issue.  It displaced copper in a cost-savings attempt.  However, it was completely inadequate and often caught fire.  Following about a decade of service Southern Pacific retired their fleet of three during the 1970s. UP's version lasted no longer and as all three '855's were off its roster around the same time.

"On May 19th, 1968 Southern Pacific DH643 Diesel Hydraulic #9151 led a Pacific Locomotive Association 'Truckee Limited' from Oakland to Truckee and back. Seen here, it is making a photo stop on Donner Pass near Shed 47. Held outside of Sacramento on the westbound trip for at least three hours as Bobby Kennedy's Campaign Train was in the Sac depot, the train did not get back to Oakland until well after midnight." - Drew Jacksich

The C643DH, classed by Alco as ithe DL-643, was produced in the early fall of 1964 as the builder manufactured a set of three for Southern Pacific who, like rival Union Pacific, often tested big horsepower in an attempt to see if they could reduce the number of locomotives needed per train. The SP took this a step a bit further by testing diesel hydraulic designs during the 1960s, which included Alco's design (the railroad also acquired or purchased new 21 German-built, Krauss-Maffei ML-4000s). The C643DH could produce 4,300 horsepower using two 251C model prime movers rated at 2,100 horsepower each. Unlike the C855 which used four B-B trucks, the C64H carried two, standard C-C trucks and weighed much less at only 378,000 pounds (interestingly, at 189 tons the model even weighed less than its six-axle Century line which topped out at over 200 tons).

As you might expect, the C643DH was not a standard model in Alco's catalog although the company would certainly build and test any type of experimental locomotive a railroad requested. Internally, the C643DH was basically two C628s merged together. The model used traction motors (model 752) from General Electric although its main generator was produced by Voith Hydraulic, its notable characteristic.  Additionally, air components came from Westinghouse (brakes and compressor). The locomotive was one of the longest the company ever produced (the C855 ranked first in this category) at nearly 75 feet, 10 inches and was capable of producing an incredible 95,000 pounds of tractive effort, on par with some of the largest and most powerful steam locomotives ever built.

Only three C643DHs were ultimately constructed for Southern Pacific, originally numbered #9018-#9020 (the railroad later classed them as #9150–#9152 and finally #9800-#9802). Unfortunately, the locomotive was not particularly successful. First, the diesel hydraulic transmission performed poorly and due to the fact that it was foreign-made meant parts were expensive and took time to arrive.  Other issues evolved around a lack of proper research and development, similar to the C855.  As a result, the '643s experienced numerous problems and trouble-shooting issues while in service, particularly in regards with the two prime movers functioning as one (timing issues).  Because of the locomotives' problems, crews came to loathe operating them, which provided for an incredibly jarring ride.  Dissatisfied with their performance Espee pulled the group from service after less than ten years and all were retired by 1973.  Interestingly, UP had scrapped their fleet of C855s a year earlier in 1972.   For more information about the C643DH please click here.  

An American Locomotive builder's photo featuring Southern Pacific C-643DH #9019 circa 1964. This particular experimental utilized a hydraulic transmission (Voith) and could produce 4,300 horsepower. SP was never satisfied with their performance and all three examples were retired in 1973.

The Century Line

Model Type Units Built Date Built Horsepower
C-643DH3 (Built For SP)19644,300
C-8553 (Built For UP)19645,500

For a comprehensive look at the American Locomotive Company and all of the motive power types it built from steam, diesel, to electrics consider the book Alco Locomotives by Brian Solomon. Covering more than 175 pages Mr. Solomon's book details the history of Alco from its esteemed 4-6-4 Hudsons and 4-6-6-4 Challengers to vaunted RS and PA series diesel locomotives. If you have any interest in Alco this book is a must have!  Also consider Mike Schafer's Vintage Diesel Locomotives which looks at virtually all of the classic builders and models from Alco PAs to early EMD Geeps.  To read more about other Century models please visit the Diesel Locomotives section of the site, which can be reached from the top of this page.

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Header Photo: Drew Jacksich

Researching Rights-Of-Way

A popular pastime for many is studying and/or exploring abandoned rights-of-way.  Today, there are tens of thousands of miles scattered throughout the country.  Many were pulled up in the 1970's and 1980's although others were removed long before that.  If you are researching active or abandoned corridors you might want to check out the United States Geological Survey's (USGS) Historical Topographic Map Explorer.  It is an excellent resource with thousands of historic maps on file throughout the country.  Just type in a town or city and click on the timeline of maps at the bottom of the page!

Studying Diesels

You will be hard pressed at finding a better online resource regarding diesel locomotives than Craig Rutherford's  The website contains everything from historic (fallen flags) to contemporary (Class I's, regionals, short lines, and even some museums/tourist lines) rosters, locomotive production information, technical data, all notable models cataloged by the five major builders (American Locomotive, Electro-Motive, General Electric, Fairbanks-Morse, and Baldwin), and much more.  A highly recommended database!

Electro-Motive Database

In 1998 a gentleman by the name of Andre Kristopans put together a web page highlighting virtually every unit every out-shopped by General Motors' Electro-Motive Division.  Alas, in 2013 the site closed by thankfully Don Strack rescued the data and transferred it over to his site (another fine resource).  If you are researching anything EMD related please visit this page first.  The information includes original numbers, serials, and order numbers.