page_title: Unimog 406
section_title: Model changes
hierarchical_section_title: Unimog 406 / History / Model changes
caption_attribution_description: The compressor unit for controlling the brakes of the freight cars is on the loading bridge of the truck. Sabo Oil in Horn, Switzerland, June 23, 2016. (3/4)
context_page_description: 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 with a closed two-door or four-door cab, as Cabrio and as an OEM part. 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.
context_section_description: 1964
  Due to a shortage of OM 352 diesel engines, the first 1766 series production Unimogs as well as the prototypes were fitted with the precombustion chamber injected OM 312 diesel engine, detuned to 65 PS (48 kW). In 1964, OM 352 engines were available for the Unimog 406 and they were used instead, also detuned to 65 PS (48 kW). This power output turned out being insufficient for many applications the Unimog was used for, later Daimler-Benz decided to offer more powerful variants of the OM 352 engine for the 406. Further changes in 1964 included a Rockinger trailer hitch, an indentation in the front bumper for the front PTO, a compressed-air tank with a capacity of 27 litres instead of 20, uprated springs, new portal axles and new rims without the four apertures at an angle of 90°.
  1965
  In this year, the Unimog 416 production was started as well as the Unimog 406.130 / 406.131 OEM part production. The 406 was fitted with new mudwings, a new clutch and rectangular tail lights. Due to DIN and ISO standards which intended that the PTO shaft had to be underneath the trailer hitch, Daimler-Benz offered a PTO-relocating-gearbox for the rear PTO shaft.
  1966
  For the Unimog 406 production, 1966 was an important year. A tilting mechanism was added to the cab. The cab was also fitted with a new removable bonnet and a new windscreen, the air louvres for the heating and ventilation system next to the headlights were removed and replaced with smaller louvres near the indicators. The production of the U 65 came to a close, it was replaced by the more powerful U 70, now offering 70 PS (51 kW). Starting with the U 70, the four door double cab was offered for the first time. The drivetrain was improved with ruggedised reduction gears, new portal axles and axle stubs as well as optimised torque tube welding. Modifications of the electrical system included an electrical thermostat and a new alternator with an external governor. Also, the main brake cylinder was replaced. Some parts of the interior were changed as well.
  1967
  1967 brought only minor changes, the driver and passenger seats were upgraded, the rear-view mirror was modified. The portal axles were improved slightly.
  1968
  In 1968, the F-Gearbox was replaced with the G-Gearbox. Both are basically the same sliding gearboxes, however, the G-Gearbox  has an additional intermediate gearbox. Furthermore, the 406 received a new governor for the compressed-air system and a new oil tank for the steering system as well as new outside mirrors.
  1969
  With the 1969 model changes, Daimler-Benz introduced the hinged windscreen for the Cabrio and a new closed cab with a bigger ventilation flap. The model U 80 was added to the model range in addition to the U 70. Also, the doors were made sturdier.
  1970
  The steering system was replaced with a hydraulically assisted ball-and-nut steering in 1970, the mechanical steering system was still offered as an option. New safety regulations required a roll bar for the 406, also, the closed cab models were equipped with two additional rear windows. The brake cylinders were upgraded again.
  1971
  In March 1971, the U 80 was replaced with the U 84. It was fitted with bigger, rectangular indicators, new tail lights, upgraded portal axles and a new aluminium bed.
  1972
  The 1972 changes were a removal of the ventilation louvres above the windscreen and the introduction of a plastic coolant reservoir.
  1973
  The last major changes were made on 2 July 1973 when the drum brakes were replaced with disc brakes. With the introduction of the disc brakes, a dual-circuit brake system was installed and the rim colour was changed from red to black. Also, the steering system was upgraded and the radius of the exhaust pipe was increased to 35 mm.
  1974 – 1989
  The most important improvements for the Unimog 406 were completed by 1974. In 1974, the exhaust silencer was modified, followed by a new step for the cab in 1975 and a constant-mesh version of the gearbox in 1976. The all-wheel-drive switching mechanism was upgraded to a pneumatic version in 1977, the chromed mouldings on the f
caption: Unimog 406.121. This model has two additional rear windows.
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