Krauss-Maffei ML 4000 C'C ​​'

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Krauss-Maffei ML 4000 C'C ​​'
Southern Pacific 9011 ("Hood Unit") in Enzen (August 1964)
Southern Pacific 9011 ("Hood Unit") in Enzen (August 1964)
Numbering: Denver & Rio Grande Western:
4001, 4002, 4003
Southern Pacific:
first series: 9000, 9001, 9002
second series: 9003–9017 taken over
by D & RGW: 9021, 9022, 9023
After 1965: 9100–9120
Estrada de Ferro Vitória a Minas : 701-716
Number: First series (Cab Units): 6
Second series (Hood Units): 15
Brazil: 16
Manufacturer: Krauss Maffei
Year of construction (s): First series: 1961
Second series: 1964
Brazil: 1966
Retirement: until 1968 (USA)
until 1980s (Brazil)
Axis formula : C'C '
Gauge : 1435 mm (USA)
1000 mm (Brazil)
Length: First series: 20,100 mm
Second series: 20,610 mm
Height: 4,729 mm
Width: 3,275 mm
Service mass: First series: 150 t
Second series: 162 t
each with full supplies
Wheel set mass : First series 25 t
Second series: 27 t
Top speed: 113 km / h
Installed capacity: 2 × 1,470 kW (4,000 hp)
Traction power: 2,604 kW (3,560 hp)
Starting tractive effort: 400 kN
Driving wheel diameter: 1,016 mm
Motor type: Maybach 870
Motor type: 2 × 16-cylinder V-engine with exhaust gas turbocharger and charge air cooling , 4-stroke, water-cooled
Rated speed: 1585 revolutions per minute
Power transmission: hydraulic

The ML 4000 C'C ​​' was a diesel locomotive built by Krauss-Maffei , which was procured from 1961 by the US railroad companies Denver and Rio Grande Western Railroad (D & RGW) and Southern Pacific Railroad (SP). 21 locomotives were produced in two series. In addition, 16 locomotives were built on meter gauge for the Brazilian railway company Estrada de Ferro Vitória a Minas .


In the early 1960s , the two railway companies were looking for new ways to get more powerful locomotives because of the steadily growing trailer loads for freight trains . The demands in operation were enormous: train weights of up to 12,000 t had to be transported over the ramps of the Sierra Nevada or the Rocky Mountains. In the D & RGW route network, heights of 2,800 meters had to be overcome on the route through the almost ten kilometer long Moffat tunnel . To date, these have been mastered with seven to twelve diesel-electric locomotives of the types EMD F9 and EMD GP9 with 1,750 HP and EMD SD24 with a maximum of 2,400 HP each.

Although the American railroad companies asked EMD to develop more powerful locomotives, EMD did not meet these requirements for the time being. With the construction of the diesel-hydraulic Krauss-Maffei ML 3000 , however, the companies became aware of a 3,000 hp locomotive from the German manufacturer. In addition to the required power, the hydraulic power transmission promised further advantages through a lower power-to-weight ratio and better utilization of the wheel-rail friction than was possible with the diesel-electric locomotives of American manufacturers in the early 1960s. It was thus possible to design and build a stronger and more powerful locomotive with a given maximum possible weight.

D & RGW initially approached Krauss-Maffei with this perspective. However, for economic reasons, the manufacturer needed another order, which is why the Southern Pacific also took part in the procurement. Both railways initially bought three locomotives each. The vehicles had a nominal output of 4,000 hp, making them the world's most powerful single- frame diesel locomotives of their time. The fact that an American railway company procures traction vehicles in Germany was also a sensation among experts in the USA and Europe at the time.

Testing in Europe

Krauss-Maffei tested the first locomotive on the track Münster-Emden, and on the Semmeringbahn in Austria which said slopes to 2.5%. The locomotive started a train with 867 t on such an incline and accelerated it to 26.5 km / h. The test drives were successfully completed in July 1961. All six locomotives were still being exported to the USA in 1961 .


United States

Denver & Rio Grande Western

The locomotives were classified under the numbers 4001 to 4003 and mostly used in twos or threes in front of freight trains with a trailer load of 4,000 to 7,000 t on the routes across the Rocky Mountains. In continuous operation, however, the machines proved to be prone to failure. A main problem was the comparatively high proportion of full load operating hours. At D & RGW it amounted to up to 45% of the operating hours, while Krauss-Maffei had only assumed a share of up to 10% for the development of the ML 4000 - based on experience in the operation of the Deutsche Bundesbahn. Therefore the locomotives only carried a small amount of cooling water. This amount was not enough during the full-load mountain drives through the Moffat tunnel , so that the engines overheated. Problems also arose from the poor compatibility of the compressors installed by Gardner Denver , which were designed for low-speed US diesels with around 800 revolutions / minute, while the Maybach engines of the ML 4000 ran at up to 1,600 revolutions / minute. There were also problems with the lubrication of the exhaust gas turbine.

On the demanding route network of the D & RGW, which on the route from Denver to Salt Lake City reached heights of 2,800 meters (Moffat tunnel) and 2,270 meters ( Soldier Summit ) and comprised numerous tunnels, the ML 4000 was loaded beyond its performance limits, so that machine failures quickly increased. The D & RGW staff disparagingly referred to the locomotives as “Damned Krauts” (“damned Germans”).

The three machines were therefore already sold to the Southern Pacific in February 1964. The locomotives were delivered in the yellow / silver / black color scheme of the D & RGW and kept this color scheme even after the sale.

Southern Pacific

Southern Pacific 9104 ("Cab Unit")

The Southern Pacific also received its first three locomotives in 1961, which were provided with the usual red and dark gray color scheme of this company. At first, the locomotives made a strong impression. It was possible to make train operations more efficient with the more powerful locomotives. Therefore, in 1963, 15 locomotives of the second series were ordered from Krauss-Maffei and, in 1964, the three D & RGW machines were also taken over, which kept their original colors but were given the Southern Pacific lettering.

The SP stationed all of their diesel-hydraulic locomotives together in Roseville (California) . Initially they drove in the Sierra Nevada and Oregon mountain lines, but because of the increasing difficulties with the air intake in the numerous galleries and tunnels, the locomotives were used on the flat lines of the San Joaquin Valley from 1965 onwards . Usually a freight train was led by a Krauss-Maffei and an EMD GP9 or an EMD F7 .

After all, after the German locomotives went into operation, US manufacturers also began building diesel-hydraulic locomotives that were equipped with Voith transmissions . For example, in 1964 the SP also procured three ALCO DH-643 locomotives for comparison with the ML 4000 C'C ​​'.

The Southern Pacific took all Krauss-Maffei locomotives out of service from 1967 to 1968 when an extensive overhaul was due. Although the diesel-hydraulic drive was certified to be reliable and competitive in terms of maintenance costs, the engines of the locomotives were too complicated and difficult to access for the US mechanics.

Remaining after the end of operations

In 1969 a KM, No. 9113, formerly the 9010, was converted into a camera car. The SP wanted to use it to film its routes for a computer-aided driving simulator . The locomotive was provided with a stable structure for the film camera on the driver's cab side . A drive unit was removed. In their place a generator was installed to supply the film equipment with electricity. The fuel for this was taken from the original locomotive tank. The second motor at the rear end was shut down, but remained installed in the locomotive. The equipment of the driver's cab was retained because the push locomotive was to be controlled from the camera car. In 1984 the camera car was taken out of service and handed over to the California State Railroad Museum in 1986 . In 2008 the locomotive was acquired by the Pacific Locomotive Association and restoration work began. This makes it the only diesel-hydraulic locomotive that has been preserved in the USA.


The railway company Estrada de Ferro Vitória a Minas (EFVM) purchased sixteen ML 4000 C'C ​​'locomotives for meter gauge between 1966 and 1969 , with the numbers 701 to 716. These were approved for a top speed of 78 km / h and were the most powerful diesel locomotives on meter gauge at the time of procurement. They remained in service until the 1980s.



The locomotive received two 16-cylinder - Maybach -870- diesel engines . Their power was increased with supercharging to 1470 kW each at 1585 revolutions per minute. Each row of cylinders had its own turbocharger . The speed of these engines was unusually high for the US-American conditions, usually working with speeds of up to 1000 revolutions per minute. The motors operated two drive units, each working on three axles of a bogie .


Each drive unit was equipped with a three-stage Voith fluid transmission . These were provided with a hydrodynamic brake and the reversing gear .


The heat was dissipated via hydrostatically driven fans, which were located under the roof of the engine room . The cooling water circuit included the engine blocks, the heat exchangers for the hydraulic oil of the fluid transmission and the heat exchangers for the engine oil. When driving through tunnels, a water spray system could increase the cooling if hot exhaust gases made this necessary. The cooler soil air was sucked in in tunnels using suction lines.


The locomotives originally had a pneumatic multiple control . This was later replaced by an electropneumatic one so that the locomotives could also be operated together with other types of locomotive from the railway company. However, the control system caused a few problems that contributed to the early decommissioning in 1968.

Structure and chassis

The first and second series differ from each other here. The first series had a self-supporting structure with an engine room and an end operator's cab. The second series was designed with narrower, removable stems and a circumference on both sides. The locomotives of the first series were called cab units, those of the second series were also called hood units. In the case of the locomotives of the second series, an adapted version from ALCO was used instead of the Krauss-Maffei bogies.


The air brake was prescribed by the customer. So the Type 26 L from Westinghouse Airbrake Company was used . Each locomotive had two brake compressors, which were driven by the auxiliary gear. In the first series driven by V-belts, in the second series using an interposed hydraulic control clutch. Each bogie had four brake cylinders, each acting on three brake pads. The two brake pads on the outer wheel and one brake pad on the middle axle were actuated by a cylinder. So there were two cylinders on each side of the bogie.

The hand wheel of the handbrake was located on the rear wall of the driver's cab and, as a spindle handbrake, transmitted its power to the two blocks of a wheel on the central axle via a chain. It was weakly dimensioned and primarily intended as a parking brake (securing the stationary locomotive), and not to stop the locomotive.

In addition to the pneumatic brake, a hydrodynamic brake was also installed, which was used as an inertia brake on slopes. This was connected to each fluid transmission with a hydraulic double clutch. The primary paddle wheels sat on the extended turbine shaft of the hydraulic transmission, while the secondary paddles were built into the housing.


  • Chronicle of the Railway - 1945 to the new millennium . Heel Verlag, Königswinter 2006, ISBN 978-3-89880-548-3 , pp. 160-161.
  • Yearbook of the Railway System, 18th episode , Hestra-Verlag Darmstadt 1967, pp. 91-105.
  • Stefan Alkofer: The big misunderstanding . in: Modellisenbahner Spezial No. 15 Hightech from Germany, Fürstenfeldbruck 2012, pp. 6–23
  • B. Hollingsworth, A. Cook: The Handbook of Locomotives . Orbis-Verlag für Publizistik, Munich 1993, ISBN 978-3-572-00626-7 , pp. 326-327.
  • Louis A. Marre: Diesel Locomotives: The First 50 Years . Kalmbach Publishing Co., Waukesha, WI 1995, ISBN 0-89024-258-5 , pp. 384-385 .
  • Horst J. Obermayer: The V 200 series (EJ Special 5/93) . Merker-Verlag, Fürstenfeldbruck 1993, ISBN 3-922404-46-4 , table p. 81.
  • Brian Solomon: Southern Pacific Railroad . MBI Publishing 1999, ISBN 0-7603-0614-1 , p. 118.

Web links

Commons : Krauss-Maffei ML 4000 C'C ​​'  - Collection of images, videos and audio files

Individual evidence

  1. Stefan Alkofer: The big misunderstanding . in: Modellisenbahner Spezial Nr. 15: Hightech aus Deutschland, Fürstenfeldbruck 2012, p. 10
  2. Stefan Alkofer: The big misunderstanding. in: Modellisenbahner Spezial Nr. 15: Hightech aus Deutschland, Fürstenfeldbruck 2012, p. 12
  3. ^ Yearbook of the Railway System, Verlag W. Teigeler, 1970, p. 173