Both agricultural and military heritages combine to deliver what is probably the toughest truck on the planet — the Mercedes-Benz Unimog.
The vehicle we know today as the Mercedes-Benz Unimog was first produced in 1946 with the intention to be a versatile farm tractor which could also deliver produce to market and transport agricultural supplies back to the farms.
In common with most tractors, the Unimog was and still is, equipped with a power take off (PTO) which enables the operation of various pieces of auxiliary equipment for which there is an extensive range as diverse as snow ploughs to grass mowers.
Since the second half of the twentieth century the Unimog has become synonymous with military use as well as expansive civilian applications such as forestry, electricity transmission line construction and maintenance, and Unimogs have also been applied to mining work and emergency services such as the SES here in Australia.
The Unimog’s rugged architecture belies the advanced technology which underpins the truck’s impressive capabilities.
The Unimog’s chassis is fully welded to achieve life-long resistance to torsional stress which is important as the combination of the coil spring suspension and the flexible chassis allows for axle articulation of up to 30 degrees.
Components such as the engine and the transmission have three mounting points to allow the chassis to twist. Power for this 5023 model Unimog is from a 5.1-litre four-cylinder twin turbo diesel engine generating 231hp (170kW) and providing a maximum of 900Nm of torque between 1,200 and 1,600 rpm.
The engine meets Euro VI emissions standards and is mounted separately from the transmission and is connected to it by a shaft to take further advantage of the chassis’ torsional capabilities.
Our test vehicle has the eight-speed Electronic Automated Transmission (EAS) and the optional “Working Gears” low-range mode which enables a total of 16 forward gears and 12 reverse gears ensuring a ratio for every situation.
The driveline can be switched from 2WD to 4WD and have the diff locks engaged while moving at slow speed by the flick of a rotary switch located on the dash.
The vehicle is required to be stationary before selecting ‘Working Gears’ mode which is indicated on the dash by an illuminated logo of a donkey carrying a heavy load.
The transmission also features Electronic Quick Reverse (EQR) which almost instantaneously selects reverse gear if circumstances require it such as entering water that is too deep even for the Unimog’s fording abilities.
The transmission is an automated manual setup that can be operated in full-automatic mode, or when manual mode is called for, the driver can choose to use an innovative fold-out clutch pedal which allows for optimum vehicle control at low speed in slippery conditions where precise clutch control is a benefit.
In manual mode gear changing is via the control stalk on the right hand side of the steering column which is similar to a pre-selection system as the clutch needs to be fully depressed for the transmission to shift ratios.
The Unimog features ‘portal axles’ that contribute to its excellent ground clearance while assisting in maintaining a low centre of gravity and a high degree of vehicle stability on uneven surfaces.
For those familiar with off-road parlance, the front approach angle is 44 degrees, with an over angle of 34 degrees, combined with a 51 degree departure angle at the rear.
In conjunction with its other off road features, this translates into the Unimog being pretty much unstoppable.
The reduction gears at the wheel ends of the portal axles allow for much smaller differential crown wheels which still achieve the low speed abilities of the Unimog (overall gear reduction can be down to 180:1) while having much more compact diff housings to contribute to the remarkable ground clearance.
Great if you need to go rock crawling and not damage the underneath of the truck.
The front and rear coil spring suspension provides up to 30 degrees of axle articulation, a limit which we experience for ourselves at the Mercedes-Benz testing facility located near the Black Forest (which is actually very green when we visit) at Otigheim near the German town of Gaggenau where the Unimog was manufactured until 2002, before transitioning to the Daimler truck plant in Worth.
Mercedes-Benz have constructed a diabolical test course at this German facility, which would likely break any vehicles other than Unimogs, Zetroses or armoured tanks.
The people at the test facility start by acknowledging the Unimog’s tyres are all due for replacement and that traction may not be optimal. We set out to tackle the most exteme obstacles anyway with plenty of in-cab assistance from the resident experts.
The Unimog has a maximum climbing angle of 45 degrees, which initially seems to be nothing less than facing a sheer cliff when assessed from the driver’s seat. The side tipping angle of 38 degrees seems like laying the truck on the ground and demonstrates the low centre of gravity which is achieved despite the truck’s ground clearance of almost half a metre.
The chunky 46-inch diameter tyres are mounted on 20-inch rims and feature a central inflation system which allows the driver to drop or raise tyre pressure to aid low speed driving in tricky conditions. A screen in the cab details each tyre’s pressure which can be specified by the driver or generalised by selecting between Highway, Cross Country, Sand/Mud/Snow or Emergency.
The ability to “air down” and also pump-up from the comfort of the cab demonstrates the value of this feature especially when driving in bad weather.
There are no exposed drive shafts under the Unimog and the entire drivetrain is encased in sealed torque tubes that protect the drive shaft components from contaminations such as the dust, water, rocks and vegetation typically encountered when driving off-road. The airlines for the central inflation system are also protected within the torque tubes. This is a valuable feature when taking into account the Unimog’s standard 800mm fording depth.
The test truck has the optional 1.2 metre fording spec, so naturally we test this to the limit ourselves, creating some impressive bow waves for the benefit of the photographers.
We’re also turned loose in the Mercedes-Benz Zetros 6×6 truck which is powered by a 510hp engine backed by a six-speed Allison automatic transmission. The long bonnet of the Zetros blocks vision when coming over the crests so it’s a leap of faith to commence the steeper decents unsighted.
The semi-forward control driving position of the Unimog eliminates this problem and provides good forward vision, which can be almost as daunting as not being able to see what‘s about to happen.
The Zetros is no longer manufactured in right hand drive configuration; a real shame given that means we no longer get it in Australia. Ascending the 60 per cent concrete staircase in the Unimog the theme from Rocky is playing in the mind, overscored by the mantra “don’t back off, don’t back off!”
After achieving the summit, the first trip down the 80 per cent (36.6 degrees) version of the stairs is only slightly confronting and the mountain goat-like stability of the Unimog quickly secures our confidence and subsequent descents are completed without riding the air operated disc brakes at all, although we did make use of the two stage engine brake to help maintain a steady down-hill speed.
Despite its rugged no-nonsense appearance the Unimog is surprisingly agile with a turning circle just slightly wider than 16 metres.
As many Unimogs are custom-made to suit buyers‘ applications, specified weights are generalised rather than being quoted specifically. The people in the know at the test facility suggest a typical tare weight of around seven tonnes, and a payload of around five tonnes.
The Unimog for a number of years has been unversally considered the World’s Most Capable 4×4 Truck. After our experiences in Germany, we see no reason to disagree.
Article with thanks to Staff Writer at Prime Mover Magazine