Hydrema 912D HM (High Mobility) dump truck

By: Geoff Ashcroft

Date: 30.09.2010

Hydrema’s 912D High Mobility dump truck is said to have the lowest ground pressure on the market for a wheeled ADT.

Hydrema 912D HM (High Mobility) dump truck

Hydrema's 912D HM dump truck. Its 800mm wide tyres give it exceptional ground pressure.

Self-levelling front suspension system
Ultra-low ground pressure package
Wide and comfortable cab with good visibility
Makes easy work of steep inclines
Anti-roll device fitted to centre pivot joint

Danish company Hydrema's latest dump truck, the 912D High Mobility model, benefits from front suspension and 800mm wide tyres, offering what is claimed to be the lowest ground pressure on the market for a wheeled ADT

Hydrema produces more ADTs than any other machine in its portfolio, creating a niche market with low ground pressure dump trucks. The four-wheel drive, 10-tonne capacity 912-series accounts for the lion's share.

In addition to the standard model, the firm now offers a Multi-Chassis version that comes without the dumper body and rear tipping towers, allowing a demount body to be fitted to its flat profile chassis.

There is also a 912DS that includes a self-levelling front suspension system and the HM (High Mobility) version that adds wider boots to that specification.

Both the DS and HM models are available in standard rear tip and swivel tip versions.

"Apart from very extreme conditions, the HM version should go just about anywhere that a tracked dumper would go, but without all the hassles and extra running costs of a tracked machine. It also remains road-friendly, offers 365-day availability, and is smoother, easier and much more comfortable to drive than a tracked dumper," says Hydrema UK's sales director Tim Wadsworth.

Shod on Trelleborg 800/45x30.5 tyres, the 912D HM is 2.87m wide, against the 2.47m width of the standard 912DS.

The bigger tyres raise the machine's overall height by 280mm, to 3.03m, but they also add extra ground clearance, allowing the HM to clear 470mm beneath its belly.

The only trade-off is a slight increase in unladen weight. Payload remains unchanged at 10 tonnes, while ground pressure reduces to 11.9psi.

Inside the cab

The D-series cab is wider than its predecessor. More glazing combines with soft-touch materials, improved sound insulation and a better all-round view.

The standard specification now includes air conditioning. An optional heated and air suspended seat, plus heated mirrors, are available too.

Instrumentation is derived from a Windows-based platform and viewed on a 6.4in flat screen PC monitor. The display also works as a rear view monitor when in reverse.

Engine and power

Power comes from a Cat-influenced Perkins E1104-44TA stage 3a engine that uses ACER technology to reduce combustion noise and improve performance. The four cylinder engine is behind a protective hood that can be lifted off for servicing, but only after the body has been fully raised and locked into the tipped position.

A self-diagnostic system records any engine faults and alerts the driver with warning lights.

Gear changing is via a ZF soft shift transmission offering six forward and three reverse speeds. Where sites and haul roads allow, there's enough gearing to push the 912D up to 50kph.

Manual and automatic control is possible, and the clever electronics will enable skip shifting, jumping two gears in the right conditions.

A joystick controller carries +/- transmission controls, neutral button plus directional arrows to select forward or reverse. There's also a small button for the tipping brake, and thumbing this button when stationary applies the vehicle's brakes and dials in full throttle.

All you need to do is pull the joystick back to tip the load. Once tipped, pushing the lever forward to lower the body releases the brakes and drops the engine rpm back to idle, so you can drive off.

The 912D HM also comes with an override for the front suspension. In addition to being able to lock down the front axle when the machine is moved by low-loader, the clearance can be raised by 100mm above its self-levelling working height to help free the machine should it ever sink to its belly.

Performance and handling

I dab the neutral button which informs the transmission we're going to be looking for gears - this unlocks the box - and having selected full auto shifting, I thumb the forward button, flick off the electric handbrake and dab the throttle to ease our fully laden truck away from rest.

The 912D HM is smooth shifting and very quiet.

Easing off the power I notice there is virtually no engine braking in auto mode, and the Hydrema wants to run on, down the first gentle gradient I come to.

Instead of reaching for the big pedal that activates oil immersed disc brakes on each wheel, I flick the transmission into manual mode, hoping that a fixed gear will simply hold the truck back - it does. Full engine braking comes to the throttle pedal.

There is no retarder on board, but it doesn't really need it with an all-up weight of just 18 tonnes. By switching to manual gear shift control, I find that the truck soon needs a bit of throttle pedal to prevent the outfit slowing too much.

The 800mm tyres do their best to absorb most of the bumps, with the remainder soaked up by the front axle suspension and air seat.

Those fat tyres are ideal for straddling ruts and hollows, and with 10 tonnes of stone in the back, the 912 sits firmly planted to the floor.

The Hydrema's centre pivot uses a pendulum bar with hydraulic stabilisers to transfer weight from one side to the other, and it's noticeable when cornering. After an initial lean, the 912 tightens up and continues to corner.

It is said to be much more stable than a traditional ADT, as the centre joint isn't free to rotate through 360-degrees.

Hydrema says it is the only maker to fit an anti-roll device to its centre pivot joint, and as a result, the truck is able to traverse with an angle of up to 34 degrees when loaded and up to 43 degrees when unladen.

The centre joint allows the front and rear sections to oscillate by up to 24 degrees.

Climbing gradients is easy enough in the 912D, and the steeper they get, the more the 912D seems to revel in climbing.

While we were unable to measure the gradients during our off-road assessment, several of them were almost impossible to walk up - not helped by the wet surface conditions - yet the 912D took them in its stride.

Servicing and maintenance

After the initial 100-hour and 250-hour service intervals, the 912D HM only needs detailed servicing every 500 hours. There is, however, a need to make daily checks and greasing on some key items, such as body tipping points.

There's a useful lockable toolbox at the back of the left-hand front mudguard, while the right-hand mudguard carries the truck's batteries.

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