The Unimog 406 is a vehicle of the Unimog-series by Mercedes-Benz. A total of 37,069 units were manufactured by the Daimler-Benz AG in the Unimog plant in Gaggenau from 1963 to 1989. The 406 was the first medium duty Unimog, having a larger wheelbase of 2380 mm and more than twice the engine power of the Unimog 401. Unlike the initial Unimog, the 406 does not have a car engine but a heavy duty truck engine instead. Several following Unimog versions were based on the 406. There were eleven different types made of the Unimog 406, which were available in four models (U 65 – U 84) with a closed two-door or four-door cab, as Cabrio and as an OEM part (a "half" Unimog lacking the rear part, as a basis for third party vehicle manufacturers). During its long production period, the 406 received several technical refinements. In 1964, the precombustion chamber diesel engine OM 312 was replaced with the direct injected OM 352. Disc brakes followed in 1973. For many enthusiasts, the Unimog 406 represents the classical Unimog, having agricultural and silvicultural applications. It was successful and the best embodiment of the word Universal-Motor-Gerät considering all prior Unimogs.
The initial Unimog concept was favoured by customers and accessory manufacturers, however, starting in the early 1960s, they desired a "heavy duty Unimog", following the trend of more powerful agricultural tractors beginning in the late 1950s which was due to German agriculture's shift to heavy mechanisation requiring less personnel. It led to the end of the tractor boom in Germany in the mid-1960s, a demand for agricultural tractors with low power output. The most powerful Unimog 411 model at that time was offered with a 25-kW-engine which was considered too weak for several applications. Analysts warned that the demand for the Unimog 411 would pass the zenith after 1960 and fall below 3000 produced units per year. This point was reached in 1964. Also, a decline of the military Unimog 404 production was foreseeable since the Bundeswehr had reached their required number of vehicles for the majority of their regiments and battalions. Therefore, Daimler-Benz decided to create a more powerful Unimog, the 406.
In 1960, the performance specifications were completed. The 406 was still supposed to be an agricultural and silvicultural vehicle and tractor but have a greater wheelbase, a higher top speed, the downbent frame of the Unimog 404 and a stronger engine. Three cabs were planned: The Cabrio cab, a closed cab and a closed double cab. The initial engine concept favoured the direct-injected four-cylinder, diesel engine OM 314 with 54 PS (40 kW). Since Heinrich Rößler, the leader of the Unimog development did not want this engine, it was decided to use the also direct injected six-cylinder OM 352 instead. New tyres had to be developed by Dunlop and Continental, also, the Unimog 406 needed a new hydraulics system for auxiliary devices and a new drivetrain with new axles and a new gearbox for the increased engine power. Several new 1,000 Mp (9,807 kN) sheet panel presses had to be installed in the plant in Gaggenau for producing the closed cabs.
The first prototypes were tested in 1961, prototype 1 was a disguised prototype vehicle lacking the Mercedes-Benz and Unimog emblems with a slightly different cab and the bumper of the Unimog 404, prototype 2 already had the cab of the series production model with emblems but still had the Unimog 404 bumper. The final presentation of the Unimog 406 was at the DLG-exhibition in München 1962, led by the Daimler-Benz board of directors. In the run-up to the presentation on 20 May 1962 a lot of minor Unimog changes and improvements as well as improvisations were made. Daimler-Benz split the truck production in Gaggenau in 1963; while the truck and lorry production was moved to the new Daimler-Benz plant in Wörth, the Unimog production stayed in Gaggenau. More production capacity could be used for the new Unimog 406. In 1963, 800 Unimog 406 were produced, the first 100 of them being pre-series production models.
During the late 1960s, the Unimog 406 was a popular type though the less powerful but cheaper Unimog types (403 with a smaller industrial engine and 421 with a car engine) were introduced Yearly improvements increased the quality of the Unimog, the highest production figures were reached in the first half of the 1970s. With the start of the series production of the heavy duty Unimog types 425 in 1974 and 435 in 1975, the demand for the 406 was declining. The yearly improvements were reduced and since 1979, the 406 had not been changed anymore. Soon it became very unpopular with an average production number of only 380 Unimogs per year during the 1980s. Series production was stopped after 27 years in 1989. With the Unimog 406, Daimler-Benz laid the foundation for the expansion of the Unimog family. 94,215 Unimogs of eight different series belonging to the 406 family were made from 1962 to 1994. The family included similar models all based on the technical and optical design of the Unimog 406 with different engines, wheelbases and applications. In 1965, the first long wheelbase model in addition to the 406 was offered, the Unimog 416. It had the same wheelbase as the long wheelbase model of the Unimog 404: 2900 mm. It was also available with 3400 mm. Later, the conveyance motor models and the more powerful prototypes of the Unimog 406 were also integrated into the Unimog 416 series. Engines with 80–125 PS (59–92 kW) were offered for this model. It was the most popular Unimog of the 406 family with 45,544 units made. In March 1966, the Unimog 421 was added to the Unimog family, a weaker model with 40 PS (29 kW). It was followed by the Unimog 403 in August 1966. The 403 has the OM 314 engine with 54 PS (40 kW) that was initially planned for the 406 and is therefore a cheaper model. With the increasing demand for higher power output, Daimler-Benz offered a 66 PS (48 kW) version starting in 1969 that was followed by a 72 PS (53 kW) model in 1976 for the 403. Optically and technically there are no differences between the Unimog 403 and 406 other than the engine. Since Daimler-Benz also wanted to offer an inexpensive version of the long wheelbase model, they created the Unimog 413. Due to the less powerful OM 314 engine, it was less expensive but also very unpopular, only 633 Unimog 413 were made. From 1969 to 1971, CKD-kits of the Unimog 421 were made for the production in Argentina. These Unimogs belong to the Unimog 431 series.
While the majority of military Unimogs are 404s, some 406-family Unimogs were also made for military use. These are the 426 and the 419. Starting in 1969, completely knocked-down (CKD) Unimog 416 parts were made in Gaggenau and shipped to Argentina where these parts were used to build a licensed version of the Unimog which was given the number 426. In total, 2643 Unimog 426 were made for the Argentine, Chilean, Peruvian and Bolivian military. A version for the United States Army with the type number 419 was made starting in 1986. Approximately 2200 units were planned, in total, 2416 were produced. The Unimog 419 has the same wheelbase as the 406 but comes with a more powerful version of the OM 352 engine with 110 PS (81 kW). Unlike other Unimogs, it was sold under the Freightliner brand name and classified as Small Emplacement Excavator (SEE) tractor that was used as an engineer vehicle. The Unimog 406.145 was a military aircraft tractor.
Technical data:
- engine: 6 cylinders
- capacity: 3400 cc
- horsepower: 82 HP
- gearbox: 4+1
- top speed: 100 km/h
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