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Unimog 406
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 now highly collectible Unimog 406 represents the classical Unimog, having agricultural and silvicultural applications with the last of the drum braked 1973 406BT being the most desirable for collectors. 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 forestry 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 German Agricultural Society (DLG)-exhibition in Munich 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 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.
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°.
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.
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.
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Unimog 406
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 now highly collectible Unimog 406 represents the classical Unimog, having agricultural and silvicultural applications with the last of the drum braked 1973 406BT being the most desirable for collectors. 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 forestry 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 German Agricultural Society (DLG)-exhibition in Munich 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 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.
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°.
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.
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.
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