1966–1975 | Start of light- and heavy-duty Unimog model series.

On the occasion of the 75th birthday of the Unimog we present you some of the key models and developments in its successful history. This chapter on the third decade of the Unimog illustrates how the new model series were created and milestones in the production figures were reached.

More than just a facelift: the Unimog U 421.

Twenty years after the first Unimog prototypes were built and ten years after the launch of the successful model series 411, in January 1966, the Unimog U 421 heralded the launch of a new model series – later also described as the "light-duty model series". It aimed to close the output and weight gap that existed back then between the successful 406 model series (available from 70 hp) and the 411 model series (with 34 hp at the time). Originally designed for passenger cars, the OM 621 was initially available in a 40 hp variant, and output increases up to 60 hp followed later.

Components from the U 411 were largely used for the Unimog U 421, which also explains the visual similarity. Not only did this bring business benefits; it also ensured that it was possible to reuse bodies and implements in many cases. The ingenious feature of the new light-duty model series: it was possible to fold up the cab forwards in just a few steps, which made maintenance work on the engine much easier.

The Unimog 411 series adds extra performance.

Model series 421 proved to be enduringly popular and was produced for over two decades up until 1988. It is among the most successful Unimog model series of all time, with nearly 19,000 vehicles.

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Relevant videos:

Unimog 401 model series – a look-back in time.
Unimog 411 model series – a look-back in time.

Fast towing vehicle instead of a truck.

Also in 1966 Daimler-Benz launched the 403 model series, which was later also produced in a long-wheelbase version as the 413 model series. A major new feature compared with the 406 model series, which was virtually identical in looks, was the 4-cylinder OM 314 engine, whose enhanced-output version with 66 hp enabled speeds of up to 80 km/.

In agriculture in particular the demand for fast towing vehicles for agricultural logistics was high in those years too. The Unimog positioned itself as an attractive alternative to the truck. Versions registered as trucks were also developed for the model series 411, 413, 416 and 421. They allowed a higher permissible speed on the road and a higher overall weight.

Farmhand: Unimog from series 421 used for agricultural transportation.

The brother of the Unimog: MB-trac.

1973 was the year in which MB-trac was born. Like the Unimog before it, it was developed specifically for agriculture and forestry. The MB-trac, which was series-produced on the same line as the Unimog in Gaggenau up until 1991, included many of the components that had been specially developed for the Unimog: from the chassis with all-wheel drive and four equal-sized wheels to the portal axles.

To this day the MB-trac also has many fans in the Unimog community. Both its launch and the end of its production in 1991 still remain the subject of controversial debate to this day.

Non-stop success.

The demand for Unimog vehicles also grew constantly in its third decade, and this resulted in ever more increases in production at the Gaggenau plant. The reason was that thanks to its versatility the all-rounder offered a convincing concept for year-round use, by no means only for agriculture. It also impressed its users in municipalities, in the construction sector and as a transportation vehicle and in applications on rails.

Then there was the constant further technical evolution, in which increasing focus was placed on safety. For example, the open cab of the Unimog was equipped with roll bars even before they became a legal requirement, and it was launched with more powerful brake systems and disk brakes on all wheels – a real innovation in the truck sector.

In May 1966 the 100,000th Unimog then rolled off the line. Just five years later the 150,000th Unimog was celebrated. The 416 model series, which boasted ever-higher-performance engines of up to 125 hp, played a major role in the success of production. The licence productions of model series 426 and 431, which were assembled in Argentina and developed specially for requirements in South America, enjoyed particular success as exports.

Water-resistant: Unimog series 421 during a demonstration on the Sauberg test track near Gaggenau.

Especially practical: drawing of the Unimog series 421 with a raised cab.

Farmers’ favourite: Unimog, series 421 with large-area crop sprayer.

Export hit: Unimog series 421, in Sumatra.

Pre-series vehicle in testing: Unimog U 120 in 1974.

Heavy-duty: Unimog U 150 from series 425 used in transportation.

Sought after by fans: Unimog U 1300L, series 435 as water tender TLF 8W with Schlingmann body.

Imposing: Unimog U 66/403 L with AMAZONE EV 900 large-area seed drill, 1973.

High achiever, rough around the edges: Unimog U 425 and 435.

As was the case with earlier Unimog premieres, in 1974 it was once again a DLG (German Agricultural Society) exhibition where a new era began: that of the "heavy-duty model series" (SBU). Their angular design characterises the Unimog to this day and was even given the Design Award of the Federal Republic of Germany. But a lot had been happening beneath the bonnet, too: alongside the 125 hp engine the heavy-duty model series were bestowed with a completely new type of chassis as of the mid-1970s.

The increasingly powerful engines called for a fundamental revision of power transmission, which, on the Unimog, included a crawler gear as well as high speeds, and also had to serve numerous power consumers such as PTOs. There were also new legal regulations which aimed to restrict noise and vibrations in the cab. And the result was: the engine and transmission were no longer directly bolted and a new 8-speed transmission with a double reduction gear was developed. This facilitated speeds between 0.15 and 80 km/h.

A further technical highlight of the heavy-duty model series was the frame in an offset U design. This design, already used successfully in the Unimog S, enabled excellent torsional flexibility. A huge bonus when driving on off-road terrain.

Production of the heavy-duty model series began in 1975 with the Unimog U 1300, named according to the new designation structure. The variant with a long wheelbase which was launched at the same time and which was given the letter "L", enjoys huge popularity to the present day, due to its robustness and good conversion ability as a substructure for conversion into a travel camper and expedition vehic

A story worth continuing?

Further chapters of the Unimog vehicle’s eventful success story will be published in the coming months. Don’t miss any articles – get a free subscription to the Unimog E-News.