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Diff lock makes the difference uit Leisure Wheels; 23; Jul - Aug - Sep 2003
Text by Braham van Zyl

Driving differential-lock equipped two-wheel drive vehicles off the beaten track or even on off-road 4x4 routes is a new concept waiting to be explored by adventurous owners of these vehicles. But there are a few things to keep in mind.

Sales of raised-body bakkies with the aggressive looks of a four-wheel drive vehicle, but with two-wheel drive, differential lock and a more attractive price, are on the increase. And for owners of these vehicles, there are new off-road opportunities opening up.

The greatest advantage of this new generation of off-road vehicles is perhaps its ability to handle dirt roads better than sedans. So owners of raised-body 4x2s can get to remote guests farms much easier than people with low-slung passenger vehicles. And while on the farm, they could use the opportunity to test a few of the easier 4x4 trails.

By knowing what a differential-lock is and following a few basic rules, 4x2 drivers are able to tackle many a route previously rated for 4x4s only.

So, what is a differential lock, or diff lock for short?

In layman's terms it is a device that locks the two independent rotating sideshafts of your vehicle's rear axle into a solid steel bar, allowing both rear wheels to turn at the same revolutions, for equal traction on each wheel.

The driver can decide for himself when to engage or disengage the diff lock, but some of the older models feature a partial locking devise incorporated in the rear axle, called a limited slip diff, which automatically sends a portion of the torque to the wheel that’s not spinning.

It will take you some time to get used to the vehicle's steering action when the diff lock is engaged, as it tends to understeer somewhat – thus trying to move in a straight line rather than following the direction you’re trying to steer it in.

The most important rule in 4x2 off-road driving is not to attempt a trail alone. Always have a companion vehicle or two along, and be prepared for emergencies.

For instance, few of today's 4x2s have proper recovery hooks. Fit them to the front and rear of the chassis before you do any off-road driving. Never attach a tow rope to the ball on the towbar, however, as many a case has been reported where that recovery rope has snapped the towball right off.

Do not be surprised, but the most important recovery tool is a spade. It is surprising to see what manpower and a spade can achieve when you get stuck. We have recovered many a 4x2 with only a spade, the vehicle's standard jack and lots of commonsense.

The second important rule in 4x2 off-road driving is to walk a difficult section of the trail if you aren’t sure if your vehicle will make it. Rather play safe, than get stuck or damage your vehicle.

The biggest secret of driving any off-road vehicle is in the grip of the wheels. Deflating the tyres improves l traction in off-road conditions. You only need to deflate a 4x2’s rear wheels, as opposed to all four on a 4x4.

It is not easy to recommend tyre pressures for every occasion, as not all tyres perform the same at the same pressure. Therefor you will have to experiment to find the best pressure for your type of tyre.

But as guideline - in sand the minimum pressure is 0,8 bar. On shale you need at least 1,8 bar to protect your tyres from the needle-sharp rock ledges that can damage the sidewalls, while you can go down to 1.2 bar on sandstone terrain.

Extra weight above the rear axle will also improve grip. It not only prevent excessive wheel spin, but will also improve vehicle stability while driving off-road. We use sandbags, which are usually filled at the route we are doing.

By deflating your 4x2's tyres and adding extra weight on the back you will minimise spinning of the wheels and your vehicle will be able to climb most of the hills a 4x4 can manage.

As a 4x2 does not have a low-range gearbox, you don’t have the same amount of engine breaking and cannot go down declines as steep a 4x4 can. The problem is that the front wheels will lock if the brakes are applied on too steep a decline, sending the vehicle into a skid.

If things get tough going down, use the handbrake and apply less pressure to the brake pedal. However, rather play it safe and stay away from routes with steep downhills.

Trying to see what’s going on in the road a few meters ahead while concentrating on driving at the same time take some practice. So you have to decide what to do at an obstacle before you get there. The eye-feet co-ordination needed on a hiking trail, also applies to off-road driving, except that your boots are replaced by the vehicle's steering wheel and foot controls.

Take your left foot from the clutch pedal as soon as the vehicle starts moving. In off-road driving you tend to be nervous and normally keep your foot close to, or on the clutch. Make it a habit to push your left foot back towards the seat instead of keeping it too close to the foot controls. If your depress the clutch when the vehicle stalls on an incline or decline, it will start rolling and you could lose control. Rather let it start with the clutch out. In which case you merely turn the ignition key in first gear until the vehicle starts moving again.

Two wheel drive vehicles do not perform too well in sand or mud. Rather avoid soft sand and deep mud and use the vehicle for exploring the back roads of the countryside where you may be surprised by many an undiscovered gem.

More and more travel and off-road magazines nowadays include information about 4x2 opportunities. A Cape Town based tour operator, Ekspl˘r SA, organises special trips for these vehicles. Information is available on website, or phone 021 975 6531.

Many trail operators discourages two-wheel drive vehicles on their routes, as the rear wheels tend to dig holes and damage the tracks. The lack of low range also means that some obstacles have to be tackled at speed to get through, which could mean damage to the vehicle. Make sure the route is suitable for your vehicle before driving all the way there, only to be turned away.