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The latest 'Mog makes the best even better


The latest Unimog looks familiar, but hides significant powertrain changes behind that rugged façade.


The latest Unimog range was released in Europe in 2014 and retained the previous model numbers of U4023 and U5023. Gross mass ratings for the U4023 are 7.5-10.3 tonnes, depending on vocation and for the U5023, 12.5-14.5 tonnes.

Because post-2014 Unimog models have Euro VI emissions compliance that isn’t necessary in Australia there was no legal reason to hurry the introduction of these vehicles Down Under: hence their delayed arrival here.

Carried over from the previous generation are the design of the familiar cab sheet metal, flexible chassis, high-ground-clearance portal-hub axles, all-coil-spring suspension, eight-speed main transmission and low-range gearing, but virtually everything has been upgraded and strengthened.

Inside that familiar envelope is a revised powertrain. The trigger for the engine change was Euro VI emissions levels that dictated cooled exhaust gas recirculation (EGR), a diesel particulate filter (DPF) and selective catalytic reduction (SCR).

Mercedes-Benz chose the Euro VI-compliant, four-cylinder, OM934 5.1-litre engine with 170kW and 900 Nm as the new powerplant for both Unimogs. The previous powerplants were smaller 4.25L and 4.8L engines.

Even with a cab lift, it was clear that accommodating a larger engine and all the Euro VI emissions equipment, plus a larger radiator under that snub nose was going to be difficult. M-B engineers went a step further and located the new engine a full one-metre aft.

This central engine relocation meant redesigning the flexible Unimog frame, fitting a long shaft to drive the coolant radiator fan and redesigning the transmission connection to the engine.

Bonuses from this redesign were improved weight distribution: shifting some engine weight off the front axle and allowing easy location of an engine power take off right at the back of the cab – not underneath it. Previous transmission PTO choices remain.

At the same time cab length was extended by 120mm, to improve cab volume and 120mm-taller cab mounts were fitted to the chassis, to allow increased airflow around the relocated engine.

Cab upgrades include a new dashboard, multifunction steering wheel, adjustable steering column and a more powerful heating and ventilation system. The Unimog transmission-shift mechanism has been modified to give quicker gear changes, via steering column control.

Externally the higher-set cab scores redesigned three-step access and a new grille, projector headlamps and three-piece bumpers. Lifting the bonnet reveals heat exchangers, fan and necessary plumbing, while engine access is via cab-tilt.

Engine fluids and air cleaner condition are monitored by sensors, so there’s no need for the traditional physical daily check: just as well, because it’s a climb up to the bonnet.


The new Unimog generation

The first new-gen Unimog for Australia was specified by Daimler’s Manager of Special Vehicles, Philip Leslie, who’s never happier than when extolling the virtues of the company’s all wheel drive models.

“I chose a specification that I thought would cover most Australian-market needs,” Philip Leslie said.

The new demo truck has all the regular standard Unimog equipment, plus low-range gearing; automated-shift transmission; gearbox oil cooler; factory-designed and fitted central tyre inflation system (CTIS); two-line air trailer brake connectors; compressed air filling connection at the front; heated air dryer; anti-skid coating on bumper; front implement-mounting brackets; front winch brackets; centre seat with seat belt; front and rear cameras; heavy-duty alternator, 28V/150A, dirt-protected and capable of deep-water fording; hydraulic system, single spool valve and two-line rear connection rear; and special parts for water fording ability to 1200mm, including extended breathers.

Other bits and pieces that Philip thought might be useful include an air-suspended passenger seat to match the driver’s one; power windows; Bluetooth radio; 240-litre fuel tank; vertical exhaust; ‘puddle’ lights at the underside of the doors; high-performance engine/exhaust brake; bodywork sub-frame; battery isolation switch and a 32-pole electrical connector for bodybuilders.

The truck rolls on 395/85R20 tyres, but there’s a range of rubber available, up to 455 section.

This specification should suit the demo truck for most applications, with an ability to pull a trailer (up to 30+ tonnes GCM) and accept a winch or other hydraulic attachments.

As such, the evaluation vehicle had a RRP around $237,000 plus GST, but with less ‘fruit’ in the basket the bargaining started around $220,000.

The demo truck was fitted with a tray body, on which was strapped a 1.8-tonnes concrete block.

From the outside the new ‘Mog doesn’t look radically different from its predecessor. It’s only when you peer under the bonnet or the back of the cab that you notice the changed powertrain layout and capped PTO outlet on the new engine.

However, inside the cab, all is different. The dashboard is still flat, allowing easy walk-through in the cab, but the layout and switches are up to date.

The new automated transmission and engine retardation controls are far less confusing than before. A right-hand wand with integrated knob controls direction and manual selection of gears when required. The same wand is moved to activate the exhaust brake and then the combined engine brake and exhaust brake.

Normally the truck operates in two-pedal mode, but the clutch pedal can be swung down for use when engaging a PTO or manoeuvring in very demanding off-road conditions.

The tyre inflation system works in three modes that are regulated from dashboard and steering wheel switches. Three lower-pressure settings can now be manually selected: Cross Country; Sand, Mud, Snow; and Emergency. Appropriate vehicle maximum speeds are displayed for each of these settings: 70km/h; 30km/h and 15km/h respectively.


On and off road

Our brief test was held on some gravel roads and demanding fire trails around the Victorian town of Anglesea. Increasing numbers of Unimogs find their way around Australia as go-anywhere motorhomes, so we were as interested in on-road behaviour as we were with off-road.

Unimogs have been gear-limited to around 90km/h on highways, but motor racing legend Larry Perkins has a ‘Mog, for which he developed an overdrive box.

Our test vehicle was fitted with final drive ratios of 6.94:1, for which the recommended maximum speed is 90km/h. However, there is an option of 5.31:1 diffs, for about $1700. With these higher-speed diffs the new ‘Mog should be happy cruising at 100km/h plus.

There is some-off-road gearing compromise, but even with these quick diffs the Unimog should have plenty of deep reduction gearing for most situations.

We checked out the new vehicle on some corrugated gravel and were very impressed with the ride quality and handling. Noise levels were low and the cab ambience was more car-like than truck-like. Long distances on outback gravel shouldn’t worry the new Unimog.

Exhaust braking was powerful enough for most on-road situations and engine braking on top of that almost brought the ‘Mog to a standstill.

Off-roading ability was a foregone conclusion, because the Unimog has always been the best 4×4 medium truck in the world. If anything, the revised weight distribution and suspension settings have made it more capable.

A fat, rotary dial controls front axle engagement and rear and front diff lock operation in a logical sequence. All wheel drive and the diff locks engage and disengage instantly, without any hang-up.

Although the all disc-braking system operates without grabbing we found it best to use engine and exhaust braking, in conjunction with a few downshift flicks of the gear wand, to control downhill speed.

Even while running the box in ‘auto’ mode it’s possible to shift up and down manually at any time. However, the computer protects the engine from over-revving if a wrong selection is made.

The outgoing Unimog required a fair amount of driver familiarisation, particularly in operating the pre-selection, clutch-actuated-shifting gearbox.

The new electronically automated shift mechanism is much more user friendly and allows the driver to concentrate on track and vehicle orientation, rather than having to focus carefully on gear selection.

That said, a Unimog driver’s seat is no place for an off-road novice: it’s a tall, heavy vehicle with amazing off-road ability and can be put into places where nothing can venture to extract it!

The Unimog isn’t cheap and its off-road ability is beyond a level that most people require, but if you want the best…


Previous models

The Unimog has been around in various forms since the original 1948 25hp model. It’s an off road legend, being the most capable civilian 4WD vehicle in its class. Characteristic of the Unimog are a flexible ladder frame, live front and rear axles, single tyres, long-travel coil springs, torque-tube enclosed propeller shafts and ‘portal hub’ axles.

Portal hubs are drop-boxes with reduction gears at the wheel ends that increase ground clearance under the axles. The fact that some reduction is carried out at the hubs means that the crown wheel and pinion gears can be smaller, allowing a less intrusive axle ‘bowl’. Both axles have air-actuated differential

At a time when many vehicle makers adopted independent suspension – including most military light truck makers – the Unimog stuck with live axles, because of their superior wheel travel and tyre contact on highly uneven surfaces. (The military sees an advantage in independent suspension, because a land
mine can blow off one wheel end and the vehicle may still be low-speed driveable.)

The original Unimog had manual main and low range transmissions, worked by levers, but the 2010 U4000 and U5000 models on sale in Australia used Mercedes-Benz’ AutomaticShift.

The transmission stick was replaced by a centre-console actuator that was electronically linked to the main eight-speed forward and six-reverse gearbox.

Moving the shift lever forward or backward signalled the driver’s need to shift up or down and the electronic control unit analysed engine torque and rpm, and selected and displayed the correct gear for the load and road conditions.

Low-range gearing doubled the number of ratios and was selected by a dashboard switch. Maximum speeds were between 6.5km/h and 86km/h on road and in low range, 1km/h to 14.7km/h. The U5000 model had an additional range, providing 24 forward ratios and giving off-road speeds between 3.2km/h and 36km/h.

The Unimog could cope with gradients up to 100-percent, or an angle of 45 degrees.

Unimogs ran on a wide range of tyres, from multi-purpose tyres and high-traction deep-treaded tyres to extreme sand tyres. The rear wheels ran in the track of the front wheels, resulting in lower rolling resistance and better traction. With tyrecontrol® (Mercedes-Benz’ optional central tyre inflation system) tyre pressure could be adjusted to suit the terrain while driving.

The 10-tonnes-GVM U4000 had a tyre size range from 335/80R20 to 425/75R20 and the 14-tonnes-GVM U5000 was shod from 365/80R20 up to 455/70R24 sizes.

U4000 and U5000 Unimogs had the same running gear and looked identical, other than for the latter model’s larger tyres. Both were available with 3250mm or 3850mm wheelbases; with two- or three-seat short cabs or seven-seat crew cabs.

Both models were powered by Mercedes-Benz’ four-cylinder, turbo-intercooled diesel engines: either a 4.25-litre, 130kW/675Nm OM904LA or 4.8-litre, 160kW/810Nm
OM924LA in the U4000 or the OM924LA only in the U5000. Both engines had selective catalytic reduction (SCR) emissions control for Euro 5 compliance and 18-litre AdBlue tanks. Standard diesel capacity was 145 litres, with a 180-litre option and a 160-litre tank on crew cab models.

In addition to tyre pressure control, the Unimog options list included a dual-line trailer braking system, hydraulic kits for tipping bodies and implements, DIN76 060 front mounting plate, winches and several PTOs.


Off road in the Unimog

Our first taste was a brief run in Mercedes-Benz demo U5000 Unimog. This truck was actually a South African specification model and was fitted with the previous-generation Telligent® shift transmission. Unlike the Australian-specification models it required a clutch depression for every shift.

The truck was loaded to around 10 tonnes GVM and made light work of the demanding off-road course at Victoria’s Anglesea Proving Ground.

Although the Unimog looked somewhat ungainly on its portal-hub axles its centre of gravity was reasonably low, so the test truck handled severe side slopes with ease. Low-range gearing allowed it to walk at low speed up slopes that were impossible to stand on and provided excellent engine braking for descents.

The latest model was noticeably quieter than its predecessors and automated shifting took all the guess-work out of picking the right gear for different conditions.

A water bath around 800mm deep served only to wash the chassis and running gear, and to festoon it with weed – a prepared Unimog is rated to wade through water up to 1200mm deep.

Our next encounter was a much longer fire trail drive where we had ample time to appreciate the ease of operation and the ride
quality of the Unimog.

On this occasion we met up with Unimog afficianado, Jim Curtin, who runs a company called Unimog Expeditions, from the NSW Southern Highlands. He has two Unimogs and the one we checked out is a crew-cab he’s fitted with a custom motorhome body.

This vehicle has the Australian-specification AutomaticShift transmission and virtually every off-road extra you could want for, including fore and aft winches, dual spare wheel carrier and extra fuel and water tanks. The truck was specified with central tyre inflation, which allows pressures front and rear to be varied on the run.

Shifting is automated, without the need to depress the clutch to activate the next gear, but for severe off road and load conditions it’s possible to select clutch pedal operation.

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