USING 4WD TRANSMISSIONS
It is safe to say that the majority of 4×4 drivers do not use four-wheel drive as often as they should. There is a misconception that driving in four-wheel drive can damage the transmission. This is true only for driving on dry tarmac in locked-up four-wheel drive, and even then damage is gradual and while it’s happening the driver is warned by an unnatural vibration. Don’t be scared of using four-wheel drive!
Drive to all four wheels should not only be used when in difficulty but to increase tyre adhesion, even if it appears to be adequate. While researching a book in 1994, I was loaned an Isuzu KB260 for a trip into the Maluti Mountains. After the road ahead was blocked by a swollen river I was forced to about turn and head back. It was getting dark and to make matters worse it started to rain. In two-wheel drive the Isuzu handled fine but I wasn’t comfortable because although the surface was firm, occasionally the back would slide out. Then I locked the hubs and engaged four-wheel drive. The Isuzu now drove as if on rails and I felt happy that we were travelling in complete safety. We did not need four-wheel drive but it improved handling so much that we increased our speed from ±50 kph to about 80 kph. Fuel consumption increased marginally and I calculated that for the 60 kilometers we travelled that evening, at a conservative 5% increase in fuel consumption, I spent an extra 92c on fuel! The increase in fuel costs is so small while the increase in safety so huge.
Driving all four wheels offers better all round safety, handling and improved tyre life on anything but a perfect road surface. So my first bit of advice is: Engage 4×4 not because you need it, but because it’s there. And, safety is everything.
When Must Four-Wheel Drive be Engaged?
The key is BE PREPARED. Select four-wheel drive BEFORE you encounter difficulties. If you consider that the terrain over which you are about to travel could not be easily traversed in a normal motor car, then engage four-wheel drive. Even if it is just a rough track and the going is easy, engaging four-wheel drive will reduce wear on the transmission by distributing the pounding to all four wheels instead of just two. If you have free-wheel hubs, lock them immediately you leave the road and you will be able to engage four-wheel drive from inside the cab at a moment’s notice. It is a bit like wearing a seat belt: One does not wait until you need a seat belt before putting it on.
Holding the Steering Wheel
In almost all off-road situations it is not necessary to fight the vehicle, forcing it to change direction. It is far preferable to hold it lightly enough to let the steering wheel slip through your hands should it have to, gently coaxing the vehicle to go in the direction you wish.
Keep your thumbs outside of the steering wheel rim. Steering kickback when hitting an obstacle can jerk the steering wheel around with such force that it can badly bruise a thumb or finger.
In difficult off-road situations, climbing out to inspect the ground over which you are about to drive can prevent bogging down or vehicle damage. This is especially important when negotiating rocky terrain where transmission damage can result if rocks strike the gearbox or axles and expensive body damage can result. I do not subscribe to the opinion that it’s okay for a vehicle designed for off road use to get damaged occasionally.
Avoid Misuse of the Clutch
Engaging the clutch at the wrong moment either to change gear or to prevent a stall can create problems off-road. The beginner should avoid the clutch whenever the vehicle is traversing an obstacle – avoid changing gears and rather let the vehicle stall on a slope than risk a backward slide out of control. Next to hooliganism, misuse of the clutch causes more accidents off-road than anything else.
ENGAGING FOUR-Wheel drive AND LOCKING DIFFERENTIALS
Engage four-wheel drive in conditions where you feel that a two-wheel drive vehicle may spin a wheel and struggle to get through.
Permanent 4WD (Centre Differential Lock)
Lock the centre differential if there is any danger that any of the vehicle’s wheels will lose traction and spin. Also as a safety measure when travelling at high speed on gravel or wet, oil-slick tar. Lock the centre diff whenever low range is engaged, no matter the conditions.
‘Super-Select’ 4WD (Mitsubishi)
Engage four-wheel drive, centre diff unlocked in ALL conditions other than smooth dry tarmac. Locking the centre diff as above.
Rear Axle Differential Lock
Lock the rear axle differential in conditions which are severely undulating, when wheels lift well off the ground.
Many off-road drivers tend to lock the rear diff the moment things become challenging. This robs them of a chance to learn and hone their skills. Just because wheels lift off the ground it doesn’t mean that a rear locker is needed. It just means that a rear locker will make it easier. Try your skills, use the push-pull technique (see axles twisters later in this chapter) and try and get through. If you find it is impossible or you feel that the vehicle is being stressed, go right ahead; stop the vehicle, engage rear diff lock and drive through. I recommend this approach because bad driving techniques are easily masked by a locked rear diff.
In flat soft sand axle diff locks can hinder progress due to the under-steer they cause. This under-steer causes the turn of the front wheels being exaggerated creating a very high rolling resistance of the front wheels, halting progress. Always stop the vehicle before engaging. Failure to do so can wreck the differential.
The Transfer Gearbox
Part of what makes an off-road vehicle special is the transfer gearbox, the second gearbox in which an additional set of gear ratios is available for off-road driving. The transfer gearbox reduces the overall gearing, giving a new set of ratios that are changeable by the gears of the main gearbox. For example, a 5-speed gearbox plus the transfer box provides the vehicle a total of 10 forward gears, and two reverse gears.
Avoid excessive throttle openings when in low-ratio first or second as the high torque loads can destroy differentials and twist off half-shafts. In the case of selectable four-wheel drive vehicles, additional lever/s attached to the transfer gearbox will select four-wheel drive.
Levers on part-time four-wheel drive transmissions:
• Two-wheel drive – high-ratio (normal road driving).
• Four-wheel drive – high-ratio (easy off-road driving and for momentum-critical driving, e.g. sand).
• Four-wheel drive – low-ratio (difficult, slow off-road driving).
Levers on full-time four-wheel drive transmissions:
• Four-wheel drive – high-ratio (normal road driving).
• Four-wheel drive – high-ratio + centre differential lock (easy off-road driving and for momentum-critical driving).
• Four-wheel drive – low-ratio + centre differential lock (difficult off-road driving).
• ABS on/off. (Off-road conditions where engine compression is used to slow the vehicle)
Even for moderate off-road driving it is advisable to lock the centre diff whenever the low-ratios are selected. This will protect the differentials from damage due to excessive torque transmitted when in low-range. The transfer gear lever may have a central position marked “N”. In this neutral position no power goes to either prop-shaft. Neutral is used when the engine is being used to drive auxiliary engine driven equipment via power take-offs. It is also the position which should be selected if the vehicle is being towed.
FREE-WHEEL FRONT HUBS
The sole purpose of free-wheel hubs is to save fuel on the open road. The amount of fuel they save is not measurable under 100 kilometers. Often drivers of part time four-wheel drive vehicles use more fuel than their permanent four-wheel drive counterparts because when the going gets a bit difficult they are often too lazy to stop, get out and lock the hubs and instead battle through in two-wheel drive and use more fuel.
I once did a trip to confirm this. Having driven my Land Cruiser FJ79 from Johannesburg to Cape Town (±1500kms) three times, and had measured its fuel consumption each time, on the fourth drive I left the front wheel hubs locked for the entire way. I anticipated a slight increase in consumption but it turned out less than even I had thought: Approximately 0.2 liters per 100 kms higher than the already established average; an extra three liters for the entire trip.
Driving with the hubs locked does not damage the transmission.
Some think that they must be unlocked when driving on a tar road. This is untrue. I suggest locking them once the long, high-speed tar driving is complete and the gravel and off-road driving lies ahead. In this way the driver will be able to select four-wheel drive from inside the cab. Then, when the trip is over, and you are on the road to go home, unlock them to get any fuel savings that may result.
ELECTRONIC TRACTION-CONTROL (ETC)
Traction control, fitted to many modern 4x4s, is an electronic traction enhancing system developed to improve traction by taking the energy created by tractionless, spinning wheels, converting it into pulling power which is then transmitted to wheels with good traction by use of the ABS brake system or hydraulics. The driving techniques for vehicles with traction control are not the same as for those without.
The fundamental difference in driver technique is in the use of the accelerator. The technique of easing the throttle during wheel spin will cancel out any effect that ETC may be having. In this case ETC might as well not be there. Should the driver keep the throttle open, a well set up ETC will activate, braking the spinning wheels and transmit power to the wheels with traction. Therefore it is safe to say, if you have a vehicle fitted with ETC and a fully-locked up four-wheel drive system, both techniques will work. Of course the beauty of this is that should the first technique fail, try the second. The best of both worlds!
As technology in traction control advances so does the effectiveness of these systems. Some of them, for example the one fitted to the Jeep 2005 Grand Cherokee, is so effective that it is almost impossible to spin a wheel. All four spin, or none at all. The system is so ‘clever’ that it takes much of the fun out of difficult off-road driving.
ELECTRONIC SAFETY DEVICES
Modern 4×4 are endowed with safety features not dreamt of a decade ago. One of the most common has a remarkable effect on off road performance. This is the anti-skid system, sometimes called ESP. It is remarkable how it will correct a slide on corrugations or during a violent swerving action. The first one I drove was fitted to a VW Touareg. Here is what I learnt: When on uneven ground select the suspension height to ‘off-road’ and set the shocks to ‘sport’. This prevents bottoming on big bumps. And, turn off ‘ESP’. With ESP turned on, the Touareg likes to go in a straight line; try and turn and it bogs itself down. Since then I have driven several, one being the Fortuner. It does much the same thing and if left on, in thick sand, quickly bogs the vehicle down immediately the steering is turned. Most ESP systems will switch off when low range is engaged. Check your vehicle’s ESP equivalent and experiment the next time you go out.