70 Years of UNIMOG
70 years ago the official MB Unimog appeared - however, the Legend first began to take shape a few years earlier...
Let's set the scene. November 1945, WWII has just ended, all of Germany's industries and entire economy are on it's knees. All of Germany's automotive companies have been banned from producing trucks and 4x4s with military potential but Mercedes (Daimler) Benz is desperate to help get Germany running again. The key industry to get restarted? Agriculture. Enter Albert Friedich. Head of Aeronautical Engine design for Daimler during the war, Herr Friedich is tasked with designing a machine to help get German Agriculture moving. The only problem is Mercedes can't officially be involved until the bans on production are lifted. The solution; design and build a vehicle without the star on the bonnet and "buy" the design once the bans are lifted.
By December, Friedich had found a factory for his new machine - Erhard & Söhne, who before the war had been jewellers. In January 1946 another Daimler engineer, Heinrich Rößler, joined Friedich and the machine really began to take shape, at this time the phrase "Universal-Motor-Gerät" appeared on the technical drawings, by March the name "UNIMOG" had been coined by another engineer, Hans Zabel, and the prototypes began to be built. Every part aside from the Mercedes sourced engine was a brand new design and had to be made by hand.
(L-R) Heinrich Rößler, Albert Friedrich and Hans Zabel with a 1946 prototype.
The revolutionary design and key reason for the UNIMOG's continual success is it's flexible chassis allowing previously unseen off-road capability and load carrying capability alongside high road speed and operator comfort. Friedich and Rößler managed to design a chassis that seems to defy the laws of physics. Whilst it appears to look like a traditional ladder frame chassis the UNIMOG has a secret weapon - the entire chassis is designed to flex by 30 degrees! They managed this by replacing the traditionally square cross members with tubes and having U shaped chassis rails instead of the conventional box design - these two features allow the chassis to flex without stress, something a traditional ladder frame cannot do.
A rolling chassis, note 3x PTOs and coil springs.
Their ideas didn't stop here, instead of using a big tyres to gain ground clearance, the pair opted to use portal axles. This is where the main axle sits higher than the wheel centre thanks to a pair of gearboxs' at each end of the axle. These also result in less torque on all the other drivetrain components, meaning smaller components allowing the size of the differential casing to be reduced gaining even more ground clearance. Due to the drop in drivetrain stress the transfer box, gearbox and driveshafts can be lighter. This allows the UNIMOG to have a very low centre of gravity - ideal for transversing the steep slopes in Germany's mountainous regions. The portal axles also allowed the UNIMOG's steering components to be safely protected behind the axle away form potential damage. Unlike other off-road vehicles of the time the UNIMOG was designed with 3 difflocks; front, centre and rear. These allow 100% of the power to all the wheels when engaged, so as long as one wheel has grip the UNIMOG will go forwards. Back on the road, the difflocks could be disengaged minimising drivetrain drag. As the UNIMOG was destined to live a hard live the entire drivetrain was sealed to minimise wear and tear. Even the prop-shafts connecting the axles to the gearbox and transfer box are sealed in specially designed "torque tubes."
The UNIMOG's sealed drivetrain - note "torque tubes"
Instead of using conventional leaf springs, Friedich and Rößler designed a complicated system combining multiple coil springs and sophisticated dampers. Aswell as offering great axle articulation, the coil springs offered greater ride comfort over leaf springs. Vital to ensure the operator can use the machine all day, everyday with maximum productivity. Some of you may be wondering how the UNIMOG manages to have a high load capacity and retain it's off-road ability and road manners with the comparatively soft coil spring. Simple - on the rear axle, instead of just one spring the UNIMOG features a shorter "helper" spring within the main coil. So as the weight increases and the main spring compresses, the "helper" spring will engage and keep the load balanced. The dampers help keep everything in check on the road - whilst this system doesn't sound too special nowadays, remember that all 4x4s and trucks of the time only used heavy duty "cart" springs. Just look at the Jeep and Land Rover!
The Unimog could tow and power implements at 330yrds per hour, and then transport goods at 31mph on the road.
When the Unimog was presented to world with its distinctive OX head logo at the 1948 Frankfurt Agricultural Fair they sold 150 in one day. From the drawing board to market in just 3 years the UNIMOG was an immediate success, Friedich, Rößler and Zabel had exceeded Mercedes' exceptions. The UNIMOG had 4 equal sized tyres, had a track the same as two potato rows, was capable of speeds from 330yds per hour (for farm work) to 31 mph on the road thanks to it's specially designed 6-speed gearbox and transfer box coupled to an OM 636 Diesel engine. It had 3 power take offs, (PTOs) where implements could be attached, and could tow many times it's own weight over almost any terrain. All thanks to it's suspension, chassis and drivetrain design. Compared to the tractors of the day, notably the Massey Ferguson TE20 (launched the same year) the UNIMOG was decades ahead in all departments - something that German Farmers, Utility Companies, Fire and Rescue Services and eventually all European Armies where keen to capitalise on.
1955 UNIMOG in forestry, the gentleman is operating a transmission driven winch to pull the logs onto the trailer.
Due to the immediate success and thus demand, UNIMOG production moved to the Boehringer Brothers machine-tools factory in Göppingen. By 1950, 600 UNIMOG ‘70200’s where working on German farms. Later that same year Mercedes where finally allowed to begin building the UNIMOG with production moving to Gaggenau, a war-time truck factory. By 1955 the OX head logo had been replaced by the Three Pointed Star.
1948 UNIMOG advert, note OX head logo forming the "U" for UNIMOG.
All photographs © Mercedes-Benz AG