Unimog Information

The Unimog, ([ˈʊnɪmɔk], listen (help·info)), is a range of multi-purpose all-wheel drive medium trucks produced by Daimler (formerly Daimler-Benz) and sold under the Mercedes-Benz brand. In the United States and Canada, the Unimog was sold as the Freightliner Unimog. The name Unimog is an acronym for the German "UNIversal-MOtor-Gerät", Gerät being the German word for device (also in the sense of machine, instrument, gear, apparatus).

Unimog Production started in 1948 at Boehringer in Göppingen. Daimler-Benz took over manufacture of the Unimog in 1951, and first produced it in the Mercedes-Benz Gaggenau plant. From 1951, the Unimog was sold under the Mercedes-Benz brand, however, the first Unimog to feature the three-pointed Mercedes-Benz star, was only introduced in 1953. Since 2002, the Unimog has been built in the Mercedes-Benz truck plant in Wörth am Rhein in Germany. The Mercedes-Benz Türk A.Ş. plant assembles Unimogs in Aksaray, Turkey. Unimogs were also built in Argentina (first ever country to do so outside Germany) by Mercedes-Benz Argentina S.A. under licence from 1968 until 1983 (with some extra units built until 1991 off the assembly line from parts in stock) in the González Catán factory near the city of Buenos Aires.

The first model was designed by Albert Friedrich and Heinrich Rößler shortly after World War II to be used in agriculture as a self-propelled machine providing a power take-off to operate saws in forests or harvesting machines on fields. It was designed with rear-wheel drive and switchable front-wheel drive, with equal-size wheels, in order to be driven on roads at higher speeds than standard farm tractors. With their very high ground clearance and a flexible frame that is essentially a part of the suspension, Unimogs are not designed to carry as much load as regular trucks.

Due to their off-road capabilities, Unimogs can be found in jungles, mountains and deserts as military vehicles, fire fighters, expedition campers, and even in competitions like truck trials and Dakar Rally rally raids. In Western Europe, they are commonly used as snowploughs, municipal equipment carriers, agricultural implements, forest ranger vehicles, construction equipment or road-rail vehicles and as army personnel or equipment carriers (in its armoured military version). New Unimogs can be purchased in one of two series: medium series 405, also known as the UGN ("Geräteträger" or equipment carrier),:4 and heavy series 437, also known as the UHN ("Hochgeländegängig" or highly mobile cross country).

The Unimogs characteristic design element is its chassis: A flexible ladder frame with short overhangs, and coil sprung beam portal axles with a central torque tube and transverse links. Having portal axles, the tyres centres are below the axle centre, which gives the Unimog a high ground clearance without big tyres. The coil sprung axles with torque tubes allow an axle angle offset of up to 30°, giving the tyres a wide range of vertical movement to allow the truck to comfortably drive over extremely uneven terrain, even boulders of one metre in height.

Unimogs are equipped with high visibility driving cabs to enable the operator to see the terrain and more easily manipulate mounted tools. The newest Unimog models can be changed from left-hand drive to right-hand drive in the field to permit operators to work on the more convenient side of the truck. The ability to operate on highways enables the Unimog to be returned to a home garage or yard to thwart vandalism.

Unimogs can be equipped with front and rear tool mounting brackets and hydraulic connections to allow bucket loaders and hydraulic arms to be used. Most units have a power takeoff (PTO) connection to operate rotary equipment such as snow brooms, snow blowers, brush mowers, loaders or stationary conveyor belts.

Unimogs are available with short wheelbases for implement carrier operations or long wheelbases for all-terrain cargo carrying operations. Currently, Daimler offeres the 437.4 heavy series and the 405 implement carrier series. Starting in 1951 with purchasing the traditional Unimog from Boehringer, Daimler-Benz started making the Unimog S series in the mid-1950s and added light, medium and heavy series to the model lineup in the 1960s and 1970s, before they successively reduced the available models during the 1990s to end up with the modern implement carrier and the heavy series today.

Originally, the traditional Unimog 70200 was a rather small agricultural tractor, measuring just 3,520 mm in length. It was only offered as a Cabrio with a canvas roof. The engine power output of 25 DIN-PS (18.5 kW) proved to be insufficient for many applications. To accommodate customer needs, a longer wheelbase version, a proper cab and more powerful engines (up to 34 DIN-PS (25 kW)) were introduced soon after Daimler-Benz took over Unimog manufacture; the traditional Unimog evolved into its final stage, the 411-series. Yet, Daimler-Benz decided that an entirely new, more powerful version of the Unimog would be required to meet future customer expecations. This Unimog version would later be known as 406-series.

The military Unimog S series is the first Unimog designed to be an offroad truck rather than a tractor, and it is the only series production Unimog that has an Otto engine.[N 1] Daimler-Benz designed a new frame for it, but it still shares its drivetrain with the 411-series.

With the introduction of the 406-series in 1962, Daimler-Benz layed the foundation for a completely new Unimog model family, the 406-based medium series (in the 1960s known as heavy series). It was produced until 1994. Unimogs belonging to the medium series are the series 403, 413, 406, 416, 426, and 419. These models were offered with three different wheelbases (2,380 mm, 2,900 mm, 3,400 mm) and two engines, the straight-four and straight-six direct injected Diesel engines OM 314 and OM 352, ranging from 54 DIN-PS to 110 DIN-PS (40 kW – 81 kW). The light series 421 and 431 share their frame design with the 411-series, but borrow their drivetrain and cab design from the 406-series, which is why they also count as 406-related Unimogs.

The heavy series Unimogs were introduced in 1974, and first featured the edgy cab, which is still a design feature of the Unimog today. First heavy series Unimog was the 425-series, which was available from 1976.[N 2] Soon after, the 435-series and 424-series followed, which caused a decline in Unimog 406 sales. The 425 was available with a wheelbase of 2,810 mm, the 424 with 2,650 mm and 3,250 mm, and the 435 with 3,250 mm, 3,700 mm and 3,850 mm. The introduction of new engines starting in 1986 caused a shift in the series numbers, but leaving the vehicles mostly unchanged otherwise. The 424 became 427 and both 425 and 435 were joined together and became 437. A derivate of the 437-series, the 437.4-series is still in production today.

In 1988, after declining Unimog sales, Daimler-Benz launched a new strategy that was supposed to increase sales and make the Unimog more profitable, called "Unimog-Programm 1988". New models introduced with this programme were the new light series 407 and medium series 417, which ought to replace all Unimog 406-related series. 407- and 417-series were replaced after just four years, in 1992, with the 408- and 418-series. in 2000, these two models were replaced with the current 405 implement carrier series, making the 437.4 and the 405 the only remaining Unimog series.

Like other trucks, but unlike agricultural tractors, the Unimog is a body-on-frame vehicle with short overhangs. The original Unimog was made with a plane ladder frame and a wheelbase of 1720 mm. Later, the wheelbase was extended several times to accommodate customer needs. Starting in the mid-1950s, with the introduction of the Unimog 404, the frame received a drop. Originally, this was done to make space for a spare tyre, but soon engineers found out that the new frame would improve the torsion performance, which is why all following Unimog series also received a frame with a drop. Several mounting brackets, additional cross members and tool boards were offered as factory options for the frame.

The Unimog has live front and rear axles that have portal gears (portal axles). Such axles have a lifted axle centre, but the wheels centre remains unchanged, meaning that a high ground clearance can be achieved with small wheels and tyres. Unlike "regular" trucks, the Unimog has coil springs with hydraulic shock absorbers rather than leaf springs, as coil springs provide more spring travel. The axles themselves have only one longitudinal pivot point each, the so called torque tubes. The torque tubes contain the drive shafts and connect the axles differential gearboxes to the Unimog gearbox, but being also parts of the suspension system, the torque tubes prevent longitudinal movement of the axles, whilst still allowing limited vertial movement. Lateral axle movement is prevented by panhard rods and transverse links. This design results in extreme axle angle offsets of up to 30° possible.

A wide variety of wheels and tyres were available for the Unimog. Originally, the first Unimog was equipped with 6.5–18 in tyres designed for both on- and offroad use. Later, bigger wheels and tyres with different tread patterns were available, reaching from agricultural tractor tread patterns to massive bar tyre treads to low pressure ballon tyre treads. Until 1973, drum brakes were standard for all Unimogs, until they were replaced by disc brakes, however, until 1989, drum brakes remained an option for Unimogs of the 406-family. The steering system used to be a screw-and-nut system until 1970. Then it was replaced by a power assisted ball-and-nut system for the 406-series.

The classical Unimog is rear-wheel drive vehicle, meaning that the rear axle is directly connected to the gearbox. Turning on front wheel drive automatically locks both axles, without torque compensation. The mechanical lever that turns on all wheel drive has a third position that locks front- and rear differentials. As of 1963, a pneumatic power switch was used instead of a lever. Due to the reduction gears inside the portal axles, the rotational frequency of the driveshafts inside the torque tubes is greater, meaning that the amount of torque they have to withstand is fairly low.

Traditionally, the Unimog has a splitter gearbox. Over the years, three different base gearbox designs were used, all following the same principle, and having four gears and two ranges (called groups) and an additional direction gear. Those designs were UG-1/xx, UG-2/xx, and UG-3/xx. UG is an abbreviation for Unimog-Getriebe (Unimog-Gearbox), the number after the slash resembles the input torque in kp·m (=9.80665 N·m).[N 3] Until 1955, the Unimog base gearbox UG-1 was a constant-mesh countershaft gearbox, it was then upgraded with synchroniser rings to a synchromesh gearbox. However, the synchromesh-version was only used for the 404-series, and the constant-mesh version remained the standard gearbox for the 411-series. In 1957, the synchromesh-version became an option for the 411-series, before it became the standard gearbox for all Unimogs in 1959. The following gearbox versions UG-2 and UG-3 were made as synchromesh versions only.

There are different layouts of the gearbox, namely F-layout and G-layout as well as their upgraded layouts, not having particular names. The F-layout is the original gearbox layout and is limited to the first two gears in the first range as it does not have selector sleeves, meaning that in total there are six forward gears. Instead of a reverse gear, the gearbox has its direction gear, which, in therory, can be used to reverse any gear. Due to the lacking shifting sleeves however, the reverse direction can only be used in the first range, which itself is limited to the first two gears, resulting in only two reverse gears (resulting in 6 forward and 2 reverse gears). To operate the gearbox, there is only one shift lever with a 6-speed H-layout, the gearbox shifts its ranges automatically. An additional shift lever is used for shifting into reverse. The G-layout has an additional reduction gearbox, which can be used in all gears. This effectively doubles the number of gears (12 forward and 4 reverse gears). This reduction gearbox was also available with an additional crawler gear, which can only be used in the first range (20 forward and 8 reverse gears). As of 1976, shifting sleeves were added and a 4-speed-H-layout replaced the 6-speed-H-layout, which allows using all gears in all ranges. With the introduction of the UG-3-gearbox, the standard gearbox-shifter-layout was changed to an 8-speed-H-H-layout, with 8 gears on one lever, without any additional switches. When shifting from "4th" into "5th" gear, the gearbox automatically shifts into range 2 and back into gear 1. Crawler gearboxes were offered as a factory option for the UG-3 gearbox as well, resulting in 24 gears. The design with the additional direction gear was kept, which means that all 24 gears can also be used in reverse mode. Since the highest final gear ratio allows top speeds of up to 110 km/h, and the reverse gear only comes with a small reduction of 1:1.03, the top speed in reverse mode is more than 100 km/h. To prevent such high reverse speeds, a lock for the second range was available as a factory option, allowing only the first range (gears "1" to "4") in reverse mode.

The initial Unimogs were equipped with passenger car engines, the first Unimog series to receive a truck engine was the 406-series in 1963. All engines use the Diesel principle, except for engines used for the Unimog 404-series and the first four Unimog prototypes, which use the Otto principle. The following engines were used as of 1947, with M being Otto and OM being Diesel engines (the list is incomplete):

Complete article available at this page.