User:Ocelotarian/Unimog 411

The Unimog 411 is a vehicle from the Unimog series produced by Mercedes-Benz. Daimler-Benz built 39,581 of these vehicles between August 1956 and October 1974 at the Mercedes-Benz plant in Gaggenau. The design of the 411 is based on the Unimog 401. The 411 contains a ladder frame as part of its design and was developed to function as a carrier, tractor, and universal utility vehicle. Like the 401 the 411 runs on a car engine with 30 horsepower (22kW).

Altogether there were twelve different models of the 411, offered in variants with three different wheelbases (1720 mm, 2120 mm, and 2570 mm). Additionally, there were convertible and closed cab versions. The closed cab was present in two versions, with that of the Type B similar to the cab of the Unimog 401, and that of the DvF type similar to the cabs of the Mercedes-Benz trucks of the 1950s and 1960s, with headlamps in the grille and a chrome trim.

During its long production phase, the Unimog 411 was revised several times. Due to the number of changes that the 411 series had undergone, the four different types were distinguished from each other through the designations of 411, 411a, 411b, and 411c. Although the 411 was technically based on the 401, it also adopted design features from the other Unimog series. One such example is the axle construction of the 406 series, which was used after 1963 in a modified form of the 411. As the last classic Unimog the 411 had no direct successor, but was the inspiration for the technical design of the Unimog 421, which was placed in the same product segment.

Development
The design of the Unimog 411 was not completely novel, as Daimler-Benz based it on its predecessors, the 401 and 402. There were some different designs considered by the Unimog engineering department headed by Heinrich Rößler in the 1950s, such as fitting the Unimog 411 with a 40 horsepower (30 kW) diesel engine and a 80 horsepower (59.5 kW) gasoline engine. These ideas would be implemented in later models. The developers hoped in particular to fit the 411 with an all-steel cab. The engineering department focused primarily on the demostration, testing, and improvement of such. The main changes of the 411 from its predecessors include an increase in engine power of 20%, reinforced shock absorbers, and reinforced crossheads in the engine. Additionally, starting in 1959 plain bearings were used in place of roller bearings for manual transmission, and larger tires with a dimension of 7.5 to 18 inches (or an optional 10 to 18 inches), which required a new wheel arch. The front wheel arches on the 411 were set higher than on the 401, so that the tires would not grind against them when the steering wheel was turned. The front of the 411 was also redesigned, so that the flaring on the hood was wider. Furthermore the radiator grille was made smaller, and painted in the same color as the body of the vehicle.

Convertibles from the 401 series were starting in June 1955 equipped with the cab of the later 411 series. The 411 was presented at the DLG exhibition in September 1956 in Hanover. Since several modifications were made to the Unimog 411 during its production, Daimler-Benz classifies the 411 series into four types to distinguish technical changes. These four types are the original 411 (1956-1961), 411a (1961-1963), 411b (1963-1965) and 411c (1965-1974).

Daimler-Benz set itself a goal of selling 4,000 Unimog 411 vehicles per year. In order to meet this goal customer concerns were taken into account with the further development of the series. However, the 411 ended up as a rather small vehicle with a 34 horsepower (25 kW)  diesel engine, which was considered for some applications as too weak. Analysts at Daimler-Benz warned that the annual production rate of the Unimog 411 would fall below 3,000 vehicles after 1960. This production rate was reached in 1964. Therefore Daimler-Benz introduced the larger Unimog 406 in 1963. The 411 was moved from its position as the core product of the Unimog range to a lighter series. However, the Unimog 411 remained in development, and starting in 1963 a modified form of the 411 was produced with the axles of the Unimog 406. These axles were more stable, cheaper, and easier to maintain. Since 1967 the 411 had the same bumper as the Unimog 421.

After the introduction of the 411c in 1965, the 411 series was no longer developed on a large scale. The last major innovation was a model with an extra-long wheelbase in 1969. In March 1966, the Unimog 421 was presented and placed in the same segment as the 411, as it was a similar vehicle to the 411 design-wise but with a more modern appearance. The 421 was meant to be a low-cost addition to the 406 series, as it had a 2 liter pre-chamber engine of the OM 621 type with 40 horsepower (30 kW),  but already in 1970 the Unimog 421 was much more popular than the similar, but older and weaker 411, and was preferred by customers. Despite this the Unimog 411 remained in production unchanged. In October 1974 production was ended, after 39,581 vehicles had been produced. In 1975 some additional vehicles were produced, presumably for a military customer.

Sales
The Unimog 411, in its introduction to the West German market in 1956, cost in its basic version as a convertible 12,500 DM. It initially had the engine model of the OM 636.914, which produced 30 horsepower (22 kW). Since for some customers the Unimog 411 was too expensive, in the years 1957 to 1959 a "savings model" was offered, named the U 25. The U 25 received the independent design number 411.116. It lacked a windshield, side windows, windscreen wipers, a hood, and other small parts. The seats and engine were from the Unimog 2010. The U 25 was a failure, and only 54 units were sold. In the late 1950s the 411 series was exported to the USA, where Curtiss-Wright distributed the 411.112 and 411.117 models; the brand name of Mercedes-Benz was retained. In 1965 the basic version cost 15,300 DM. The greatest number of Unimog sales was received by Daimler-Benz in West Germany. In 1962, worldwide sales of the Unimog 411 reached 54,870,000 DM.

Prototype for the French Army
At the request of the French army, Daimler-Benz built a prototype based on the 411 series with a gasoline engine in 1957. The prototype was given the chassis number 411.114 75 00939 and was assigned to the 411.114 model, which had a extra-long wheelbase. The prototype had a wheelbase of 2120 mm, the transmission and clutch of the Unimog S, and tire dimensions of 7.5 to 18 inches. The four-cylinder engine used was the M 121 with a displacement of 1897 cc, 65 horsepower (48.5 kW), and a maximum torque of 128 N m. The top speed was 90 km/h. A distinguishing feature of the prototype was its reinforced windshield. The French army tested the prototype over a span of approximately 9000 hours, and decided not to order it as it had a high center of gravity. Using this prototype as a base, Daimler-Benz developed more military vehicles with a payload of one ton.

Westfalia Cab
Like the previous Unimog 401 and 402 series, a Unimog 411 with a closed cab was made available, which Westfalia manufactured in Wiedenbrück. At the start of production of the 411 series in August 1956, the Type B cab, which had been already built for the Unimog 401, was modified for the new Unimog 411 chassis. This had the model number 411.520, and was nicknamed the "Froschauge". This cab was built only 1107 times, on the 411.111 (with a 1720 mm wheelbase) and the 411.113 (with a 2120 mm wheelbase) until it was discontinued in October 1961. Already in 1957 Westfalia had a new cab for the Unimog 411. The model was designated as 411.521 and called the DvF type. It was built specially for the 411.117 and the 411.120, which both had a 2120 mm wheelbase. The DvF cab was significantly larger than the Type B, with a 30% larger volume and a larger loading platform. The windscreen was undivided and its ergonomics had been considerably improved. This shape followed the truck design of Mercedes-Benz in the 1950s and 1960s, with with headlamps set on the outer rim of an elliptical radiator grille, and a rich chrome trim. Unlike the convertible models the front bumper was more rounded and bent at the ends. Daimler-Benz fitted the DvF cab with a heater upon request. However, the DvF cab had a drawback in that there was a high heat load caused by the engine's waste heat. The cause of this was the engine cover, which extended into the passenger compartment and did not sufficiently isolate the cab from the engine. The production of the Unimog 411 was discontinued in 1974, but Westfalia continued to build the DvF cab until 1978.

Westfalia tested a fiberglass hardtop convertible version of the Unimog 411 in the mid 1960s. It offered better protection from the weather and gave better visibility to the sides. Although brochures were printed and the hardtop version was included in the official Unimog catalog, few units were sold. It is unknown how many units of the hardtop version were produced.

Prototype 411
1957

In 1957, the 411 was extensively modified. The trafficators were removed and replaced by the more conventional car turn signals. Other external changes included the new Mercedes badge on the hood and modified tail lights. The engine power was increased in March to 32 horsepower (24 kW), and the gearbox could be delivered synchronized upon request. In July new springs with a wire diameter of 19.5 mm were used instead of 18 mm for the rear axles, and in September a three-spoke steering wheel was installed by Fulmina. In May 1957, the convertible models had their side panels replaced, using polyvinyl chloride instead of Cellon. In May Mercedes-Benz introduced the U 25 model. The new Westfalia cab type DvF was presented at the International Motor Show Germany in September, and in October a new trailer brake system was made available.

1958

Starting in March or April 1958  the Unimog 411 was fitted with a 60 liter fuel tank instead of just 40 liters. Other changes were mostly small, including a modified brake system, a combined preheat and start switch, a stronger auxiliary drive system, and hinged windows on the DvF type.

1959

In January, the previously optional equipment of the synchromesh unit was made standard. The U 25 was discontinued in 1959 without a replacement.

1960 In January 1960, the chassis numbering system was changed so that the first numbers were no longer in the 55 to 95 range. Instead, chassis numbers were to begin with "01". The design of the hood was changed. Latches were installed, which made external knobs superfluous. Additionally, the mirrors were moved down and no longer attached to the A-pillar. In anticipation of the introduction of the three-point-mounted cab in October 1961, the rear suspension of the cab was adjusted in March 1960.

411a
1961

In October 1961 the Unimog 411 was redesigned and the original 411 was replaced with the 411a, which began production on the 9th of October. The 100 mm side members of the original 411's ladder frame were replaced with 200 mm side members. Additionally, a new hydraulic system was introduced and the cab was given three-point storage, which increased the comfort of the occupants. The 411a can be distinguished from the original 411 by noting the position of the headlamps, which were now attached to the radiator grille instead of the frame itself. The platform had four instead of three side boards per side, and had a distance of 30 mm from the cab. The production of vehicles with the Type B Westfalia cab ended in October 1961.

1962

The indentations on the hood which were no longer needed for the knobs were removed, and all vehicles received a new turn signal system from Bosch. The rear window of the convertible was enlarged, and the DvF type cabs were outfitted with two-piece headlight trim rings.

411b
1963–1964

The production of the 411a was discontinued in March, in favor of the new 411b. The most significant change was the replacement of the old axle manufactured by Erhard & Söhne with the axle of the Unimog 406. The windscreen size was increased from 410 mm to 450 mm, and the convertibles were given a triangular window behind the A-pillar. In the rear, the fenders were painted completely black. Other technical changes included a modified exhaust system, an optional hydraulic power steering assist, and a new, two-stage main brake cylinder.

411c
1965

Production of the 411b continued until February 1965,  when the manufacture of the 411c began. The main difference was an increase of 2 horsepower (1.5 kW) to engine performance. Daimler-Benz continued to use the OM 636.914 for the engine model, however the nominal speed was increased from 2550 min−1 to 2750 min−1. Additionally, the cylinder head, injection pump, and throttle body housing were changed. This resulted in an increase of performance, to 34 horsepower (25 kW). In order to keep the car's speed at nominal speed equal, the gear ratio of the axles was changed from 25:7 to 35:9. The rear of the convertible top, the tachometer, the V-belt pulley for the compressor, and the taillights were also modified.

1966

In April 1966, the standard color of the Unimog 411 was changed from Unimog Green (DB 6286) to Truck Green (DB 6277). The side wall hinges of the Unimog 421 were installed, and the rear spring support was cast. A handle was built into the A-pillar of the DvF type cab. 1967

The most important change in 1967 was the instalment of the Unimog 421's bumper on the 411. Pivot bearings were installed on the front axle, and a door handle guard was added to the convertible versions.

1968

The frame was given a new mounting plate bracket, and welded front and rear cross bars. The thermostat was modified and the DvF type cabs received new exterior mirrors.