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Southern Pacific -9152.jpg
Southern Pacific #9152, formerly #9020.
Type and origin
Power type Diesel-hydraulic
Builder American Locomotive Company (ALCO)
Order number S-3374
Serial number S-3374-01 – S-3374-03
Model DH-643
Build date September 1964
Total produced 3
AAR wheel arr. C-C
UIC class C′C′
Gauge 4 ft 8 12 in (1,435 mm)
Length 75 ft 10 in (23.11 m)
Loco weight 378,000 lb (171,000 kg)
Prime mover ALCO 251C, (x 2)
Engine type V12 Four-stroke diesel, (x 2)
Aspiration Turbocharger
Displacement 8,016 cu in (131.36 L)
Cylinders 12 (x 2)
Cylinder size 9 by 10 12 inches (229 mm × 267 mm)
Transmission Voith hydraulic
Loco brake Straight air
Train brakes Air
Performance figures
Maximum speed 77 mph (124 km/h)
Power output 4,300 hp (3,200 kW)
Tractive effort 95,000 lbf (422.58 kN)
Operators Southern Pacific Railroad
Numbers 9018–9020 (later 9150–9152; final 9800-9802)
Locale North America
Scrapped 1973

The ALCO C-643DH, also known as the Century 643DH, was a twin-engine diesel-hydraulic locomotive, the first diesel-hydraulic road unit built in the United States. It had a C-C wheel arrangement and generated 4,300 horsepower (3,200 kW). Only three were built, all for Southern Pacific Railroad in 1964 (#9018–#9020). The Alco C-643DHs joined 21 Krauss-Maffei ML-4000 diesel-hydraulics already on the Southern Pacific's roster. These hydraulic-drive diesels spent most of their service lives in the flat San Joaquin Valley in California.

Dissatisfaction over the poor performance of diesel-hydraulic locomotives, as well as their use of foreign-made components (the hydraulic transmission was of German Voith design), eventually led Southern Pacific to scrap the C-643DHs in 1973.

Original owners[edit]

Railroad Quantity Road numbers Notes
Southern Pacific Railroad
9018–9020 renumbered 9150–9152

See also[edit]


  • "ALCO 244 and 251 Diesel Engines". Pacific Southwest Railway Museum. Archived from the original on 13 January 2006. Retrieved 20 February 2006. 
  • Kirkland, John F. (1989). The Diesel Builders, Volume Two: American Locomotive Company and Montreal Locomotive Works. Interurban Press, Glendale, CA. ISBN 0-916374-81-5. 
  • Pinkepank, Jerry A. (1973). The Second Diesel Spotter's Guide. Kalmbach Publishing Co., Milwaukee, WI. ISBN 0-89024-026-4. 
  • Strapac, Joseph A. (1993). Southern Pacific Historic Diesels, Volume 2: Diesel-Hydraulic Locomotives. Shade Tree Books, Bellflower, CA. ISBN 0-930742-15-X. 
  • Strapac, Joseph A. (2001). Southern Pacific Historic Diesels, Volume 8: Alco Roadswitcher Locomotives. Shade Tree Books, Bellflower, CA. ISBN 0-930742-23-0. 

External links[edit]