4×4 Operations section deals with operating 4x4s, and the equipment that is attached to 4×4 vehicles, enabling them to perform specific tasks. On the following pages you will find most things that pertain to 4x4s and off-road driving and overland expeditions.
4x4S HAVE CHANGED a great deal since first produced in any number; but at no time has this change been as swift as in the past 15 years. Between 1948 and 1968, vehicles like the Jeep CJ, Toyota Land Cruiser and Land Rover changed very little; they remained utilitarian, functional machines. In the late 1960s and early 1970s the market changed and Jeep built the Cherokee with power steering; Toyota produced a station wagon with wind-up windows, and Land Rover created a 4×4 with coil springs; the Range Rover. Even the Range Rover, the leader in the leisure 4×4 market for decades, was a year and a half in production before the introduction of carpets.
Comparing the sales brochures (left) of many of these originals with their modern equivalents reveals a completely different marketing strategy – vehicles that were once photographed climbing mountains are now seen in the polished environment of a shopping mall. This illustrates how the image for most 4x4s has changed from rugged work-horse to urban fashion statement. To compound the problem of choosing a suitable vehicle, manufacturers are creating 4x4s without true off-road ability and often advertise them as off-roaders.
It is true that in the modern world comfort is as important as off-road working ability, but many 4x4s are becoming so sophisticated that while being brilliant on road they make themselves less suitable for wilderness travel. Sophistication makes servicing and repairs easy in the city but often impossible elsewhere.
As a result, all civilian four-wheel drive vehicles are a compromise between a town vehicle and an off-roader. Therefore, in selecting a vehicle designed for this double life, the buyer should ask this question: ‘How much time will I be spending on tarred roads and how much off-road?’ and, ‘If I intend to go off-road, do I want to travel into the wilderness?’ What follows is a guide to variations in design and original equipment and features that will be encountered when selecting a four-wheel drive vehicle.
There is an unequivocal sentiment among the general motoring public that 4x4s are a nuisance. Why? Are we really damaging the environment or are we just scapegoats? The perceptions are that 4x4s are: unsafe, gas-guzzlers, environmental hazards, destroyers of roads and altogether unnecessary. Many feel that a 4×4 on the road that is not being used for a 4×4 application should be discouraged or even banned. Maybe a bit of realism will even things out.
‘4x4s are gas-guzzlers and emit unnecessary noxious gasses.’
It is impossible to generalise because there are small ones and big ones, ones with emission control and older ones without, just like regular cars. But how is it possible for 4x4s to be especially bad? To effect the fuel consumption and therefore emissions, three things could add to it: the vehicle’s extra weight, loaded roof-racks, the 4×4 transmission and a larger and higher body that increases wind resistance.
Weight: The average 4×4 is between 100 and 180 kgs heavier than a similar 4×2. At most, that’s 2% of a two-tonne vehicle. Not many 4x4s are over two tonnes, but for this argument, let’s add 2% onto the weight. Roof racks: Especially if they are loaded, racks can increase fuel consumption at higher speeds by up to 25%, this from my own tests. This figure varies considerably between vehicles and rack designs. 4×4 transmissions can cause additional fuel consumption. However the increase is miniscule. Even full-time 4wd systems, have little or no effect on fuel consumption and in all my experiments with 4x4s to disprove this, I have concluded that the difference is bearly measurable.
So, what percentage increase is this really? Is it a 0.1% difference in fuel emissions caused because we drive a 4×4 instead of a 4×2? Is it even as much as this because we drive with loaded roof-racks only once or twice a year and many 4x4s drive in 4×2 on the tarmac?
I cannot help but view it like this: If you feel guilty about the extra 0.1% increase in emissions, make up for it by a few less trips to the store in the family saloon.
‘4x4s are destroyers of roads and tracks.’
No, actually both scientifically and practically, the opposite is true. Scientifically, a 4×4’s tractive force on the road surface (the force exerted on the road surface to set a vehicle in motion) is one-half that of a 4×2. In our world of lumpy roads the figure is even better than this. The result is reduced wear and tear on the country’s roads. While on a good tar surface this variation makes no difference, on gravel roads and on slippery mountain roads it does. So many roads and tracks in rural areas are destroyed each year by rains as the tracks, already worn by vehicles, are subjected to erosion. Serving small rural communities the vehicles that travel these roads are mostly light pick-ups and in the Third World, min-buses. These are almost all 4x2s, not 4x4s. If these vehicles were 4x4s there would be a significant reduction in road surface wear and a reduction in erosion. Surely then, 4×4 is good for the environment? It is the users of 4x4s damaging the environment by thoughtlessness, not the vehicles. I guess you can say the same about guns: It’s not the guns that kill people, it’s the people with the guns.
‘4x4s are less safe than 4x2s.’
All-wheel drive provides improved traction, four times that of a similar 4×2 and as a result there is a reduced chance of wheel spin, more neutral steering and therefore a significant reduction in the chance of skidding and spinning, the main cause of vehicles rolling. In addition, the high driving position gives an improved view ahead. In opposition to this evidence is the fact that most 4x4s (even those just built to look as if they can drive on rough terrain) have a higher centre of gravity and therefore reduced stability, resulting in a higher chance of a roll as a result of a swerve or collision. More alarming though is the tendency of some people to overload their roof-racks making some models far more dangerous. Insurance and vehicle hire firms substantiate this statement in their roll-over accident statistics.
Another spat is that drivers of smaller vehicles complain that they cannot see past the larger 4x4s. This is true, but this is not 4×4 that’s the problem; it’s the vehicle’s size that is the factor here. When people have a go at 4x4s, it’s never because of the vehicle’s four-wheel drive but rather its size. And perhaps many 4×4 drivers drive aggressively and that’s a problem. Again, this has nothing to do with 4×4 or damage to the environment but has everything to do with a large vehicle being driven questionably.
And another debate is, as a pedestrian, if you are hit by a 4×4 you are more likely to die. This argument is because of the 4×4’s larger size. Again it isn’t the fact that it’s a 4×4; it’s the vehicle’s size. On the other side of this argument is the absurd idea that being driven over by a 4×4 is safer because of its increased clearance. Either way, being hit by a vehicle, 4×4 or otherwise, is going to be hazardous.
‘Drivers of 4x4s who do not actually use them in 4×4 terrain should be discouraged from driving them.’
This is an everyday debate from the pens of ill-advised people who want to be seen as tree huggers, irrespective of the stupidity of their arguments. I can’t see why we must take my wife’s Corolla on a weekend family trip, just because we probably won’t need four-wheel drive. My choice would be to leave the Corolla locked up and take the 4×4 because its a smooth, quiet, safe and roomy station-wagon. It has a frugal turbo-diesel engine, spewing out similar emissions as many medium-sized family saloons. But it has four-wheel drive! What’s wrong with that? Now, if I want to I can go a little higher into the mountains and if it begins to rain I can keep my family safe. And in the week I can use the same car because it seats all my kids with their own seatbelts as well as their friends, instead of taking a second car to the swimming pools. I just do not see this argument.
The ideal power plant for an off-roader is able to produce its power at low RPM. Engines that do this can be driven in higher gear ratios in difficult terrain which is advantageous because the higher
the gear ratio, the less chance of wheel-spin and the more delicately the driver can control the engine’s power output. Engines designed with long piston strokes tend to do this.
Good off-road driving technique calls for selecting the right gear for the conditions. If the gear ratio selected is too high, a more powerful engine may still have the torque to get through, but if the gear selected is too low, a big engine could, if not handled skillfully, cause excessive wheel-spin. For a novice driver therefore, high power is often a disadvantage but for the experienced it can be an advantage. For long distance travel, larger engines are more reliable because they rev slower with the penalty of higher fuel consumption.
Petrol Vs diesel engines
It is never an easy choice, but should be. What do you expect from your 4×4? Are you towing? Are you spending lots of time on road and then a short time off it? And when you are off it, what kind of
terrain will be tackled? Once you have answered these questions, and more, you should come to the conclusion that petrol is the way to go, but for one thing: fuel consumption. This is the only significant advantage diesels have over petrols. Diesels are more expensive to buy, more expensive to service, require more frequent maintenance, are slower (a general observation), are noisier than petrols, the fuel smells more, diesel is often more prone to being contaminated with water or other chemicals – the list goes on and on.
If you want to go fast, rev high and pull a trailer, then a diesel is definitely not for you, I don’t care how many kilowatts is produced. Diesels are more prone to overheating and do not like sustained high-rev driving in hot climates – if they did, race cars would have them. So, if you are a more sedentary driver happy that on hot summer hill climbs the engine may lose some of its pulling power and that while idling, the clatter is sometimes intrusive and that if you spill a bit of fuel while pouring out of a Jerry can and you don’t mind the stink, then go ahead, buy a diesel. The additional range of a diesel vehicle, due totally because it uses less of the stuff, is another advantage, which, again, is about fuel consumption. So to summarize, get a petrol and put up with the consumption knowing that because its cheaper to service, at the end of the day, the cost-to-run difference is not all that much.
However, when driving off road, these engines do have their advantages, and as you will see, again, petrol comes out on top. A large capacity petrol engine is a good choice off-road, even if its power output is similar to that of a smaller turbo-diesel. They perform a lot better in the rough but are much thirstier than diesels, especially if the going is slow, through thick sand or on rutted tracks.
Turbo chargers boost power after the engine has, on average, reached 1200 RPM or more. A petrol engine will work at much lower revs, down to 600 rpm in some cases. The difference here is a mere 600 rpm, which doesn’t sound much, but low rev power is a distinct advantage off-road. Turbo-charged vehicles often have to take a tricky climb one gear lower than their petrol counterparts, because at some point in the climb, the revs drop to below where the boost is working, and the engine stalls. Other terrain where small-capacity turbo-charged diesels often struggle is on dunes, where momentum cannot be maintained because of turbo-lag.
Some turbo-diesels are fitted with an intercooler, a radiator which cools the hot air pumped by the turbocharger, which itself is powered by hot exhaust gases, before it enters the combustion chambers. They often increase power output by over 20%.
Like petrol engines, diesels are controlled by micro-processors. This is good and bad. It improves reliability and tuning accuracy. It also means that power output can be increased by the simple matter of adding a computer ‘tuning chip’ such as the Dastek Unichip, a remarkable device. Another advantage of a turbo-charged engine is that altitude has less effect on performance than it has with a normally aspirated engine.
For operations in Third World countries, diesel engines are the better choice for the reason that local truck transport relies on diesel and it is available more often and in more places. In these countries, the fuel is frequently contaminated with dirt and water with the result that fuel related problems cause more breakdowns than any other factor. Ideally, dual fuel filter systems should be fitted. At the very least, spare fuel filters should be carried.
But if you want to be the king off road, nothing beats a big petrol.
The four-wheel driver’s vehicle has two kinds of life: on and off road. However, modifications to improve on-road performance may have detrimental effects on the vehicle’s off-road abilities. Vehicle manufacturers always strive to increase engine power without increasing the engine’s size or weight. One of the ways of doing this is to improve the engine’s capacity to breathe. Increasing the amount of air that can be consumed by an engine during the combustion cycle increases engine power. Fitting free-flow exhaust systems or grinding and smoothing inlet and exhaust valve ports will increase air flow.
Modifications to engine components to increase performance are many and varied. With modern engines, a lot can be achieved with electronics.
Chipping the engine
Almost all currently available diesel engines, whether in a tractor or race car, are controlled by a microchip. By adding another piggy-back computer to override the manufacturer’s settings more
performance can be taken out of an engine. Some chips are so clever that they can be mapped in several configurations, such as limit the revs when your 18 year old takes it out, or extra power at cruise speeds, set when towing. These are just two examples. Each preset is sent to the chip using your cell phone. The chip I am referring to is the Dastek Unichip. I have seen it work and it is phenomenal.
Free-flow exhaust systems
Free-flow exhaust systems consist of big bore pipes and free-flow silencers and are worth considering.
The advantages of free-flow exhausts are numerous:
• They improve fuel economy and thereby increase a vehicle’s range.
• They improve acceleration without negatively affecting the power and torque output rev-range.
• In many cases they are less expensive than a genuine factory part.
Although not spectacular, individually these improvements are noticeable. For example, when fitted to a Land Rover V8, fuel consumption improved by about 1.5 liters per 100 kms. I calculated at the time that for a new free-flow exhaust system to pay for itself in fuel savings, I would need to travel over ninety thousand kilometers!
If your existing exhaust system is due for replacement I recommend investigating fitting one of these systems. It is important to make sure that there are several mounting points and that the job is done well. Exhaust failures are common in rough country.
Are electronics a real threat of just a perceived one, when it comes to vehicle reliability? Many overlanders are concerned that a vehicle’s electronics will let them down, or that if it does, it is not repairable. This should be put in perspective: In my thirty plus years of overlanding, travelling with vehicles both with and without electronics, I have only once been let down by electronics but on several occasions by mechanical stuff. The electronics breakdown was permanent and the vehicle rendered temporarily useless. In this case the electronic failure was because the non-factory immobilizer fitted was incompatible with the vehicle’s electronics and it damaged the engine control electronics. Five days later, all the way from Austria, the spare arrived and within an hour the vehicle was running again. In at least three of the mechanical breakdowns I have experienced, the vehicle was similarly rendered useless. So I reckon the important questions to ask are: Are electronics less reliable than mechanical components? Both can render a vehicle useless for a time. The answer is no. Modern electronics, by and large, are extremely reliable. Can they easily be fixed without spare parts? Almost never. Are mechanical components necessarily more reliable than electronics? In general it is safe to answer this one, no, as well. Mechanical components are if anything less reliable but the difference is that they can, on many occasions, be temporarily repaired or a plan made.
The most common breakdowns on overland trips are, in no particular order: wheel bearings, exhaust breakages, tyres, radiator cracks/thermostat/overheating, tyres, suspension failures and did I mention tyres? Not electronics! Many, if not most, breakdowns are related directly to lack of maintenance.
The trouble is, you cannot even buy a tractor that isn’t controlled by electronics any more. The value of clever electronics in engines is often under-estimated. It radically reduces emissions (without it, no diesel engine could comply with emission regulations), it protects the engine from over-fueling, making it more reliable, it reduces fuel consumption and makes them quieter.
Some vehicles are overdosed with electronics and this worries me a bit. When items like the height of the suspension is affected, then there is always a nagging feeling about being out of control. I guess I still need to see a spring holding up the vehicle, and not a sensor, attached to a rubber tube, attached to a circuit board, attached to a microchip, doing the same job. Thank heaven they aren’t Microsoft-based or we would have real cause to worry.
Then again, there are some that behave as if they are, and horror stories are appearing. The last one I heard (mid 2010) was a Discovery-3 driver who was stranded in the Moreme Wildlife Reserve Botswana for two weeks to wait for a Land Rover mechanic, equipped not with a box of spanners, but a laptop. The vehicle had bumped a tree, cracked the front bumper and broken one of the airbag sensors. This was enough to completely immobilize the vehicle. The bonnet might as well has a large sign: ‘No User-Serviceable Parts Inside’.
Transmission systems for off-road vehicles are unique. Unlike a normal road vehicle where the gearbox is a single unit, off-road vehicle gearboxes comprise three, four and sometimes five units.
1. Main gearbox
Similar to a normal road vehicle’s gearbox but built to withstand heavier torque loads. Many 4x4s are made with a choice of manual or automatic transmissions.
2. Transfer gearbox
Power from the engine is transmitted via the main gearbox to the transfer gearbox which is a two-ratio unit reducing the overall gearing. The result is two individual sets of forward and reverse gears. The high ratio is used for normal driving and the lower gear ratio is used for off-road work or starting off on a steep slope when towing a heavy load. From the transfer gearbox power is transmitted to the front and rear prop-shafts. In the case of full-time four-wheel drive vehicles it first goes through a centre differential or centre viscous coupling. In the case of part-time four-wheel drive vehicles this ‘centre’ component does not exist. For the most part, soft-roaders do not have a transfer gearbox.
3. Centre differential/viscous coupling
Located between the front and rear prop-shafts in full-time four-wheel drive vehicles only, this component distributes the power to the front and rear prop-shafts. Because the front and rear wheels rotate at different speeds when turning a corner this component must permit a differential in rotation speeds. A differential unit is fitted between the front and rear prop-shafts to do this. For off-road driving this differential can be locked, preventing differential rotation, locking the shafts together. This differential lock must not to be confused with differential locks found on axles as the job they do is entirely different.
A viscous coupling, in brief, does the same job as the centre differential but locking is done automatically.
A full-time four-wheel drive with its centre differential locked is the same as a part-time four-wheel drive vehicle engaged in four-wheel drive, the front and rear prop-shaft are attached, as if it were a solid shaft. These shafts drive the wheels via the axle differentials.
4. Axle differentials
These components, one on the front and one on the back, distribute power from the prop-shafts to the wheels. Again, because of the different rotation speeds of the wheels when the vehicle turns, this differential permits this speed differential. (Hence the name differential) All wheeled vehicles have differentials for this purpose. Axle differential locks are fitted to some vehicles and are discussed later.
5. Overdrive unit
Fitted as optional equipment to some older vehicles, the overdrive is a gearbox that adds an additional high gear ratio. Overdrives are built for the relatively light duty of motorway cruising and are not intended for use with low gear ratios.
Manual versus Automatic transmission
There is much debate as to which transmission system is superior for a 4×4. Assuming that the vehicle will have the dual role of city vehicle and off-roader, here are my findings:
Advantages of manual transmission:
• Engine braking down steep slopes is far superior where vehicle control is easier and safer.
• Easier to drive in very uneven terrain where as auto gearboxes tend to surge and can be difficult to control.
• The vehicle can be pull or push started.
• Manual gearboxes are easier to repair and more mechanics understand them.
• Manual transmissions are more economical to run and often less expensive.
• They run cooler when worked hard in heavy sand conditions.
Advantages of automatic transmission:
• Allows very gradual application of power to the wheels which would only be possible by slipping the clutch (with a manual gearbox).
• Technique of rocking, as a method of getting a vehicle out of a near-bogged situation in mud, is easier.
• Sand driving is altogether easier with auto gearboxes.
• More relaxed driving on road and on winding, rough bush tracks where there is a lot of slowing down and speeding up.
• Auto transmissions stress the vehicle less and are often a better choice when purchasing a used 4×4.
Electronic Hill Descent Control (HDC)
Electronic Hill Descent Control first appeared in the Land Rover Freelander and Discovery Series-2 and is now commonplace in many modern 4x4s. HDC in conjunction with the anti-locking brakes (ABS) is used to slow a vehicle on steep descents.
I do not consider HDC a ‘must have’ and while it is useful in some situations it is more of a sales gimmick than a useful off-road tool. The trouble with it is that it engages at a speed that is too fast for most steep slopes. So the driver must use the brakes and transmission to slow the vehicle. In a well controlled descent it does not engage. HDC should therefore be considered as a kind of parachute should things go wrong; Release the brakes, hold on tight and steer the vehicle. HDC will assist in steering control albeit at a potentially unsafe speed. It should also be engaged when driving up steep slopes as it also engages in reverse and in the case of an uncontrolled rearward slide it could arrest a fast, dangerous descent.
Traction Control (TC)
Various systems have been developed to cancel out the wheel-spin that results from tractionless wheels on open differentials, normally accomplished by axle differential locks. These range from electronic traction control working with the anti-lock braking system, first seen in the Mercedes M-class, Discovery Series-2 and Range Rover. Jeep’s first Quadra-Drive is hydraulic powered and does a similar job. These systems are beyond the scope of this book to illustrate in detail, however it is enough to say that they assist traction when wheels leave the ground or spin when the surface gets slippery. They do not, as advertised, make off-road driving easier but instead change the techniques required. Early traction control systems are harder on the vehicle and environment than axle differential locks, which in effect, do the same job.
Some modern TC systems are miracles of engineering. They are so effective that it is sometimes absolutely impossible to even spin a wheel. Either the vehicle moves or all four wheels spin out and the vehicle sticks; there is no in-between. What these systems do is take away the challenge of difficult off-road driving and drivers of vehicles like the 2006 Jeep Grand Cherokee and Land Rover Discovery-3 are rarely tested as their vehicles do all the thinking. See Chapter-5.
Full-time four-wheel drive
Full-time four-wheel drive has been an option for the off-road motorist for many years but only in the last 20 years has it been recognised as the most user friendly type of four-wheel drive transmission. It has been fitted to vehicles such as the Jeep CJ-6 and
CJ-7 and Range Rover since the early 1970s, the Land Rover 110 since the mid eighties, and the Mercedes-G and the Toyota Land Cruiser in the 1990s. The Mitsubishi Pajero/Shogun’s transmission offers the options of part-time, full-time and true four-wheel drive with a system called ‘Super-Select’.
Most full-time four-wheel drive vehicles have a centre differential located between the front and rear prop-shafts to prevent wind-up caused by the different rotation speeds of wheels on sealed surfaces. (In the case of some vehicles with automatic gearboxes it is a self-locking hydraulic viscous coupling).
The advantages of full-time four-wheel drive transmissions are numerous and include safety, even tyre wear and better control and handling. Its only disadvantage is frequent misuse by those who operate it.
The trouble is that a full-time four-wheel drive vehicle with the centre differential unlocked is not operating in true four-wheel drive and drivers operate the vehicle as if it is. Hundreds if not thousands of high-speed roll overs on gravel roads around the world could be avoided if drivers lock the centre differential and drive in true four wheel-drive! More about this in chapter-5.
Contrary to popular belief, the full-time four-wheel drive system decreases tyre wear and does not affect fuel consumption greatly. Although there is no rule for the increase in fuel consumption caused by four-wheel drive while cruising, from my own experiments, I doubt if it is as much as 2% – hardly significant considering the increase in safety it provides.
Selectable/Part-time four-wheel drive
This system is less expensive to produce owing to the absence of a centre differential, which is not required, since the front prop-shaft is disengaged when driven in two-wheel drive.
When a vehicle with part-time four-wheel drive is engaged in four-wheel drive, it is equivalent to a permanent four-wheel drive vehicle with its centre differential locked. With part-time systems, because the rotation of the front axle side shafts and prop-shaft do not serve any purpose when travelling on firm surfaces, free wheeling hubs disconnect these components and will improve fuel consumption.
Part time 4WD vehicles pay a penalty in that the rear tyres (those used for driving the vehicle when in two-wheel drive) wear out before the front. This is especially true of vehicles driven in rough conditions where four-wheel drive should have been engaged but was not, often because the driver did not feel it was necessary.
Super-Select four-wheel drive
Super-Select four-wheel drive is found in the Mitsubishi Shogun/Pajero. This system gives the operator the full range of traction options: Part-time four-wheel drive, full-time four-wheel drive with a centre differential unlocked and then true four wheel drive when this differential is locked. In some respects this is the ideal system. Again, its only disadvantage is drivers not using the system to its best advantage and not engaging full-time and true four-wheel drive when they should. Unless this expensive and complex system is used properly, the buyer has spent his money on nothing more than a gimmick.
Hydraulic viscous coupling
The hydraulic viscous coupling solves all of the problems of axle wind-up while at the same time operating as a non-slip differential. It works like a centre differential which is permanently locked but still absorbs all differential wheel speeds caused when driving on firm surfaces.
DIFFERENTIAL LOCKS: CENTRE, AXLE LOCKING AND LIMITED SLIP
The subject of differential (diff) locks is one of the most confusing and misunderstood aspects of four-wheel drive vehicles. This is illustrated by the way many magazine buyer’s guides indicate this in their expansive charts; Indicating a ‘yes’ or ‘no’ is too simplistic and confuses the issue because not all diff locks have the same function. What a diff lock does depends on which diff is being locked AND what kind of 4×4 transmission is fitted.
For example let’s compare a Defender’s full-time 4WD with a diff lock and an Isuzu Frontier’s part-time 4WD, also with a diff lock. When both of these vehicles are in four-wheel drive with their diff locks engaged, the configuration of the drive to the wheels is different. This is because the Land Rover’s diff lock is locking a centre diff, locking the front and rear prop-shafts together while the Isuzu’s diff lock is located on the rear axle locking the left and right rear wheels together. With the Land Rover, although its ‘diff is locked’, the wheels on the rear axle remain unaffected, driven by an open, unlockable differential. It is in effect in the same configuration as the Isuzu with its diff unlocked.
Differential locks on individual axles
An axle diff lock prevents differential wheel speeds on that axle, preventing wheel-spin on opposite wheels. They help tremendously in sticky situations particularly when two wheels on the same side drop into a trough and the axle is grounded, or when opposite front and back wheels leave the ground when traversing a ditch at an angle. Without axle diff locks, two airborne wheels, one on the back and one on the front, spin helplessly and the vehicle stops.
Axle diff locks can be a hindrance when engaged on flat ground where the surface is slippery but traction is similar on all four wheels. This is because a locked axle differential always causes under-steer. Under-steer causes disturbance and therefore increases the rolling resistance of the tyres which can cause a vehicle to bog down. Typical terrain on which this occurs is on a flat beach. It is not uncommon for the inexperienced driver, who tends to use every tool at their disposal to prevent difficulty, to create more problems for themselves by locking an axle differential. In this case only the centre diff (if you have one) should be locked.
When diff locks are fitted to both the front and rear axles it is imperative that the rear lock is
operated first. A vehicle moving over slippery ground with a locked front axle and an unlocked rear diff will want to spin out and may become very difficult to control. Front diff locks severely inhibit steering control.
Limited-slip differentials (LSD)
A limited slip rear differential does the same and gives the same advantages as a lockable differential but, as the name suggests, the advantage is limited. There is some slip, which can be an advantage and a disadvantage (see the table below).
In most cases limited slip differentials are fitted on the rear axle only. This is usually advisable, for when fitted on both front and rear axles, some limited slip differentials can alter the vehicle’s handling characteristics and cause instability at speed.
Vacuum/Pneumatic differential locks
Until fairly recently the most common type of locking device was
the air-locking diff, so called because it required a compressor to actuate the locking mechanism. These systems are still available
and come from the USA, Australia and Great Britain. The ARB air-locker is one of the best available. Engine-vacuum powered differential
locks are fitted to many vehicles as a standard fitting.
Post-delivery differential locks
Don’t fall into the trap and believe that a four-wheel drive vehicle must have an axle diff lock before it will be effective off-road. It is true that there are some obstacles that only vehicles with a lockable diff will negotiate with ease, but these can in so many cases be overcome with driving skill. However, if you intend tackling the very toughest off-road conditions then axle differential locks are essential.
A rear axle diff lock should be regarded as a ‘nice to have’ item and a front axle diff lock, a ‘I want to be unstoppable!’ item. Steering a vehicle with both axles’ diff locks is almost impossible and the average driver, even with front diff locks fitted, rarely ever uses both.
Automatic locking differentials
Auto-lockers such as the Detroit Locker are automatic locking
differential devices that lock when traction is needed, and disengage when a wheel needs to rotate at a different speed due to the vehicle turning on firm ground. No conscious decision has to be made to lock the differential – maximum traction is permanent. Automatic diff locks are a disadvantage in soft sand when the vehicle is turned, as the locking rear axle tends to cause drag on the outside wheel hampering progress. Contrary to what the manufacturers claim, I do not advise fitting an auto diff lock to a front axle as it can cause severe handling difficulties on slippery surfaces. Because they cannot be manually disengaged when steering becomes difficult, I must assume that they are unsuited to front axles.
Fitted to part-time (selectable) 4×4 vehicles, free-wheel hubs fit on the front wheel hubs and enable the side shafts and prop-shaft to be disconnected from the wheels. The one and only purpose behind free-wheel hubs is to prevent these components from rotating unnecessarily and thereby reduce fuel consumption when driving on a firm surface.
“Can free-wheel hubs, if engaged and operated on the road, damage the transmission?” This is a very common question. The answer is no. However, the opposite is true: if hubs are left unlocked for long periods the following damage can result:
On some vehicles the lubrication of the front hub bearings depends partly on axle rotation which sends oil to the bearings. With the front hubs disengaged, the axle remains stationary and the hub is not effectively lubricated.
Spline shaft damage
Spline shafts are located in the side shafts (in the case of vehicles with independent suspension) and in the prop-shafts (in the case of vehicles with solid axles) that allow for suspension travel as the vehicle moves over uneven ground. In conditions where the drive shafts are rotating, wear will be spread evenly over the splines. Should the drive shaft or prop-shaft remain stationary for long periods, as will occur if the hubs remain disengaged, the splines wear on a single plane. If serious uneven wear has occurred, drive shaft vibration will result. It is therefore important that, should you have free-wheel hubs fitted to your vehicle, drive with them engaged once in a while. If free-wheel hubs are not offered as standard equipment and you wish to fit them, do not skimp – cheap units fail when the going gets tough.
Automatic free-wheel hubs
Automatic free-wheel hubs engage the front wheels automatically when the front prop-shaft rotates under power, i.e. when four-wheel drive is selected in the cab. Old types of automatic free-wheel hubs did not lock when compression braking (descending steep slopes) or moving in reverse. Modern auto free-wheel hubs do operate when moving in reverse and down steep slopes.
Modern auto hubs are engaged simply by engaging four-wheel drive. Auto-hubs have improved and have become as reliable as the manual types. For this reason many manufacturers are fitting these in preference to the manual types. Many serious off-roaders still prefer manual types.
Reduction gearboxes fitted at each wheel hub serve to increase axle ground clearance. While it increases ground clearance it also means that once the vehicle has bogged, it is very much deeper and therefore much more difficult to extricate.
Four-wheel drive transmissions – summary
1. Part-time four-wheel drive transmissions have two differentials; one on the front axle and one on the rear axle.
2. Full-time four-wheel drive systems have three differentials. One on the front axle, one on the rear axle and one in the centre, driving the front and rear prop-shafts.
3. A differential lock on an axle prevents differential rotation between the two wheels on that axle. (Left and right).
4. A differential lock in the centre prevents differential rotation between the prop-shafts. (Front and rear)
6. It is possible to have all three differentials lockable (full-time 4wd), or two differentials lockable (part-time 4wd). This is the ultimate traction configuration.
7. Free-wheel front hubs are used to save fuel. They are fitted to part-time four-wheel drive vehicles only. They cannot be damaged by leaving them locked.
GROUND CLEARANCE AND SUSPENSION
It is a bad idea to take a vehicle manufacturer’s minimum ground clearance claim and base off-road performance on it. For example, a Land Rover Freelander has similar clearance to a Mercedes Geländewagen. The Freelander’s independent suspension enables it to have a reasonable clearance which is measured from the chassis. In the case of the Mercedes, the clearance is measured from the differential housing, hung below its live axles that move up as the wheels ride over obstacles. So when these vehicles go off-road, the Mercedes’s clearance increases and with the Freelander it decreases. It is the suspension type and design that enables a vehicle to keep its clearance off-road, or lose it. In the case of the Freelander and most vehicles with independent suspension, it loses it. In the case of the live axles on the Mercedes, it keeps it. The result: The Freelander has inadequate clearance for driving off road and the Mercedes, which while it is not over endowed with clearance, must rate as one of the best off-roaders of all time.
In addition, clearance should be measured not only under the lowest point of the chassis but in front of, behind and between the axles as well. The front and rear overhangs (approach and departure angles), wheelbase in relation to wheel size (break-over angle) and centre of gravity (roll-over angle) are important factors which affect a vehicle’s off-road ability.
Ground clearance & Suspension
With a low centre of gravity and well-tuned suspension such as the Mercedes Gelandewagen has, at no time during this obstacle did the vehicle feel as if it was going to roll-over. If this vehicle had a roof-rack, I would not have attempted this obstacle. Note the rear wheels firmly on the ground.
The maximum angle a vehicle can approach an obstacle without any part of the vehicle striking that obstacle.
The maximum angle a vehicle can leave an obstacle without any part of the vehicle striking that obstacle.
The maximum angle a vehicle can ride over without striking the obstacle between its axles. The longer the wheelbase the larger this angle is. On some vehicles, parts of the transmission protrude below the chassis and this has a detrimental effect on the break-over angle. So, if you are fitting protective equipment or towing apparatus to your vehicle, it is important to consider the negative effect it may have on these angles and therefore the vehicle’s off-road ability.
The maximum climb angle, which can be represented as degrees from horizontal or a percentage of a one-in-one slope (100%=45 degrees) Figures supplied by manufacturers are based on a traction-perfect flat surface. In the real world, things are very different.
The choice of wheelbase should be determined by the kind of work the vehicle is likely to undertake and the loads to be carried. Long wheelbase vehicles can carry heavier payloads and have a higher seating capacity. They handle better on the road, on corrugations and on fast unsurfaced roads.
Short wheelbase vehicles have a few advantages when off-road. An improved break-over angle is the most significant. They are generally lighter, more manoeuvrable and more economical. Short wheelbase is a disadvantage on gravel roads and corrugations as they tend to have less straight-line stability and are more prone to slide.
This is the angle at which a vehicle will roll when traversing a slope at right angles. This value is a result of the distance of the vehicle’s centre of gravity above the ground. Anything above 40° is good and below 35° is poor.
CHOICE OF SUSPENSION
No compromise made to improve off-road ability or on-road comfort is more noticeable than those made to the suspension. The type and rating of the springs, the configuration of the axle location and the axle design all have a significant effect on a vehicle’s ability off-road and comfort both off and on the road.
Two types of axles are fitted to off-road vehicles – independent and live/solid beam axles.
Solid/live axles versus independent axles
If the vehicle is going to spend most of its time in the bush or will be worked hard in very rough country, rigid, solid beam axles, also known as ‘live axles’, are stronger and perform better than independent suspension.
When a wheel on a solid axle rides over an obstacle and lifts, it lifts the part of the vehicle closest to the ground (the differential) with it, thereby increasing ground clearance and clearing the differential over the obstacle. Because solid axles are very heavy, independent suspension reduces the unsprung weight contributing to ride comfort on-road.
With independent suspension, as a wheel rides over an obstacle the differential is left in a vulnerable position closer to the ground. Although independent suspension is able to offer superior axle articulation because the axle is independent of the differential, this is rarely the case with the current range of vehicles. In general, vehicles with the best axle articulation are those with solid axles and coil springs front and back.
No single compromise to the suspension system is more noticeable than axle articulation. Axle articulation is the suspension’s ability to allow the wheels to move vertically, to drop into deep ruts and follow the contours of the ground without leaving it and losing traction. Articulation is therefore very important to an off-road vehicle but to a road cruiser it is a curse because it allows the body to roll uncomfortably as the vehicle is cornered. In general, independent suspension gives less articulation and body roll than does solid axles.
SPRINGS AND SHOCKS
Three types of springs are fitted to off-road vehicles – coil springs, leaf springs and torsion bars. Solid beam axles are either fitted with leaf or coil springs while independent axles are fitted with coil springs or torsion bars, or both. Another system, based on pneumatic cylinders in place of springs, permits variable ride-height adjustment from the cab. This highly sophisticated system is controlled by a computer and is fitted to top-spec 4x4s like the Range Rover and Land Cruiser V8.
independent front suspension showing the suspension as it is fully extended.
Coil versus leaf springs
Coil springs make for a better ride both on and off the road. This is because they absorb vibration better than leaf springs and suspension designers can take advantage of unrestricted axle articulation offered by coil springs.
Coil spring designs require axle location arms to locate the axle to the chassis – a job which leaf springs do themselves. These arms come in the form of radius arms at the front, trailing arms at the rear and panhard rods or similar to locate the axle laterally. These suspension systems can absorb irregularities in the road surface so efficiently that vehicles get damaged often long before the driver realises the damage he is doing. One of the philosophies behind maintaining the production of 4X4s with leaf spring suspension for so long was the fact that an uncomfortable ride limits the driver’s endurance before limiting the vehicle’s.
Some vehicles, often those equipped with leaf springs, have heavy duty nylon straps attached to the chassis and looped around the axle at each hub. These prevent spring and shock breakages where suspension travel over uneven ground allows the axle to drop too far.
Shock absorbers control the oscillation of the road springs. When operating on rough surfaces they work hard because axle travel is greatly increased which in turn increases shock absorber temperatures. Shock absorbers are a vital part of the suspension system and in most cases, those supplied by the vehicle manufacturers are the minimum required for safety and vehicle control.
If you use your 4×4 off-road and on gravel roads and are considering improving the ride, handling and off-road performance, upgrading the shock absorbers is the first thing to consider. Gas shock absorbers and other suspension modifications are discussed in detail in Chapter-3.
These diagrams illustrate the variations in suspension systems fitted to off-road vehicles.
Front coil springs with a solid axle are almost always combined with a similar setup on the rear. This setup offers the best combination for off-road ability. Examples: Land Rover Defender, Mercedes Geländewagen and Unimog, Toyota Land Cruiser, 80 and 105 GX, newer Nissan Patrol, first and second generation Range Rovers and the first Toyota Hilux. The unusual combination of solid axles all-round with coils on the front and leaf springs on the back is found on the Toyota Land Cruiser 70 and 79 series.
Front independent coil springs or torsion bars with solid rear axles are found on vehicles such as the first and second Mitsubishi Pajero, Isuzu Trooper, Ssangyong Musso and bakkie-based vehicles like the Nissan Hardbody and Sani, Ford Ranger, Mazda Drifter, Isuzu KB and Frontier, all but the first generation Toyota Hilux.
Leaf springs on front and back axles are found on older designs such as the Land Rover series I,II and III, first Toyota Hilux, all early Land Cruisers, Suzuki SJ40, Jeep CJ, old Chevrolet Blazer, first Nissan Patrol, SVM and even the current Ford F250. This design is very old fashioned and not seen much any more.
Many years ago I predicted that all-four wheel independent suspension would become the most popular solution for 4×4 designers and this is now evident in most modern 4x4s, both those designed to go off-road and those that just look as if they can. Until the mid nineties just about the only vehicle fitted with this was the VW Syncro Bus. Then the Mitsubishi Pajero paved the way and today it is found on almost all ‘soft-roaders’. Now the third generation Range Rover, Discovery-3 and the Jeep Grand Chreokee among many others have all taken this route. This is because this system is best for on-road comfort and safety. While it works well off road, the penatlies are load carrying ability and axle articulation.
As engineers have developed systems they have managed to improve the design of independent suspension so that it can almost match the off-road performance of solid axles. While the die-hards (I am one of them) who love solid axles off road hold onto their older designed 4x4s for as long as possible, it will not be long before we are forced into accepting that this is the suspension of the future. Already, if we want a Land Rover with solids axles our choice is limited to Defender, and Toyota lovers are limited to Cruiser pick-up. The choice of station-wagons with pure solid axle suspension is now limited to just the Nissan Patrol.
MORE TO CONSIDER
Diesel turbo failures
Why is it that petrol engines seem to last so much longer than the average turbo-diesel? The answer is anything but simple. Try as I may, being simplistic about this issue isn’t going to help, so here I am going to get a bit technical. So, if you own or are planning to purchase a turbo-diesel vehicle, understand the pitfalls because some are very costly. I am not advocating staying away from diesel engines but rather an understanding of them will not only prevent huge repair bills in the future but also enable you to get the long life that a diesel engine can deliver if treated correctly.
In 2000 owning a Mercedes 290 GDT, I experienced an engine failure which resulted in a huge learning curve for me. It happened on a trip through Johannesburg so I called Steven from Steve’s Auto Clinic. Having more experience with diesels than anyone else I knew, I felt confident I was in safe hands. To cut a long story short, a blocked air filter had caused an excessive exhaust gas temperature which caused turbo and injector damage. Two years later I purchased another used 290 GDT. I remember the famous quote, ‘Those who do not learn from history are condemned to repeat it’. I visited Steven and again I was on a learning curve. In just two years problems with damaged turbochargers in thousands of vehicles had spread from turbo failures to cylinder heads as well. I wanted to know why.
Steven uses an effective analogy. A new vehicle is like a healthy child, fit and energetic. The child’s body is like the vehicle’s engine. Once a child becomes a teenager some begin to smoke, drink or both. The body begins a path of deterioration and becomes diseased. By forty, the equivalent of forty-thousand kilometers, doctor says, “Stop smoking!”. So the smoking is stopped. Is the adult suddenly healthy because a bad habit is kicked? No. Damage has already been done.
A new vehicle drives energetically out of the showroom. In the case of a diesel engine it is often mishandled recklessly, like the teenager on a binge. Driving a turbo-diesel at full power for long periods, hauling heavy trailers up steep hills at full power, hour after hour of speeding down to the coast at 150 kph. That’s how to abuse a turbo-diesel. These engines are not designed to work this way and it damages them! So if you want your vehicle to perform these tasks, buy a petrol! Petrol car engines are more suitable than turbo-diesels for running at full power over long periods.
The advice on fitting exhaust gas temperature gauge early in the vehicle’s life cannot be over emphasized. Drivers inadvertently abusing the engine, driving it in a manner which over-stresses it will be warned by the gauge and buzzer. This is one of the problems with buying a used turbo-diesel. Fitting an EGT gauge after the vehicle has covered 50 000km is like a forty year old quitting smoking. The damage has been done. Not smoking at all is the most desirable: never abusing the engine because a gauge is telling you that you are. It’s a bit like a government health warning, but instead it reads, “RUNNING THE ENGINE LIKE THIS WILL SERIOUSLY DAMAGE YOUR WEALTH”.
Diesel engines are happiest when driven on or close to the revs that produce the highest torque. At higher revs, torque drops off and while power increases so does the temperature generated. The result is high fuel consumption and high engine temperatures. This is why above 140 kph most diesel engines will consume about as much fuel as a similar petrol vehicle. At this speed the petrol engine is happiest, revving high and burning its fuel efficiently, while a diesel is at high-stress, running hot and burning fuel inefficiently.
Things have much improved over the past couple of years. If you are contemplating a used turbo-diesel built before 2003 then what I have described here is most likely the case. Thankfully almost all diesel engines built today are equipped with sensors that will cut off fuel in the event of over-stress. This may mean that newer vehicles may not appear to perform as well as similar older versions, but this is not true: The newer engines are so much better at protecting themselves from abusive users.
So when considering a new or used vehicle, think about what kind of driver you are. If you are towing a heavy load, choose a petrol. If you want the economy of diesel, decide now that long stretches at high speeds are a thing of the past. If the vehicle is used, do a diagnostic test to see if damage has been done and if it’s new, fit an EGT gauge without delay and reset the diesel pump on an active dyna to limit the combustion temperatures before damage is done.
Turbo-charging a non turbo engine
Unlike a petrol engine a diesel engine is ideal for turbo-charging. Everything is already there: the compression ratios, the strengthened block, conrods and pistons. So it makes adding a turbo a simple matter of plumbing it in. Sounds too good to be true? Well is it, almost. The trouble is, not all diesels can cope with the added pressures caused by a turbo-charger when at full boost. One such engine is Toyota’s ubiquitous 4,2 six-cylinder 1HZ engine found in their Land Cruiser 70-series, among others. Among engines, this is the one renowned for being virtually indestructible, but the best way to bust this engine is to add a turbo-charger to it. This is why so many engine specialists have developed turbos for the 1HZ and found returning customers with unhappy faces. It is all because they all boasted that their’s produced the most power and those who were right, regretted it the most. The culprits are the pistons of the 1HZ. The crown of each piston is unusually thin, to save on weight, I suppose. The thin crown is soon blown apart by high boost pressures. The answer is low boost turbo-charging, or replace the pistons with heavier duty ones, which because they are not available off-the shelf, is very costly, and then add a normal boost turbo-charger. I have selected to try Steves Auto Clinics low-boost turbo-charging option for my own 1HZ powered Cruiser 105. (Any reports I have will be viewable on www.4xforum.com. Look under the ‘articles’ section)
So when considering adding a turbo to a normally-aspirated engine, beware of taking into consideration which conversion produces the most power, but instead look at the conservative approach that will tend to be the best, because it will likely mean that the developers have considered cooling and longevity more closely.
When travelling through remote or unpopulated areas; food, water, fuel, tools and camping equipment have to be carried. Therefore your vehicle should have a large enough loading capacity in terms of volume and weight. Water weighs one kilogram per liter and fuel almost as much. Heavy duty suspension should be fitted to those vehicles asked to carry loads close to their limits over rough ground. Heavy duty shock-absorbers will also assist.
When selecting a 4×4, it is worth asking how much weight can be carried on the roof. Unfortunately I have rarely seen this specification published in a sales brochure, because so often it is alarmingly low, so this information may be hard to find. The range of weight to be carried ranges from the lowest in vehicles such as old Range Rovers at about 50kgs, Land Rover Defender at 75kgs and up to 200kgs on a Mercedes G-Wagen and Nissan Patrol. (Specs not verified)
Loading any roof rack too well forward will cause overloading of both roof pillars and front springs. Structural failures from overloading show themselves in the form of cracks in the windscreen and fading shock absorbers. If you have a winch, bull bar, power steering and air conditioning fitted, your front springs may well be pushed beyond their design limits. Overloading a vehicle’s springs will quickly result in serious structural failures in rough terrain including chassis breakage.
Disc Vs drum brakes
All-wheel disc brakes are an advantage on and off-road. Apart from not being affected by water, like drums, they operate effectively in reverse. This is where the disadvantage comes, which can be significant off-road, when drum brakes are fitted on the rear wheels. Picture the following situation: A vehicle stalls while moving up a very steep climb. The vehicle must be secured before the clutch is depressed and the engine restarted or the reverse-stall manoeuvre performed. The foot brake and hand brake are used to hold the vehicle. With the drum brakes on the rear axle doing almost all the work, and with a stalled engine and no brake-boosting assisting the effort, it may be impossible to secure the vehicle with brakes alone. In this case the vehicle must be left in gear and rocks packed behind the wheels to assist the braking effort before the clutch can be depressed.
Although all drum brakes are less effective in reverse than discs, not all drum brakes are totally ineffectual in reverse. Generally speaking, the older the vehicle, the worse they perform.
After driving through deep water, water can become trapped in brake drums making them ineffective. Sand can also collect in drum brakes damaging the shoes.
Vehicle range and payload
A vehicle required to undertake journeys into unpopulated areas needs a good range to be effective. Because payload can be converted into range by carrying more fuel, either an economical engine or high fuel tank capacity and payload is required to give a vehicle a good range.
I suggest a range of no less than 1000 kms between fuel stops if you are planning to create a good expedition vehicle. Few standard vehicles will cover this distance without additional tanks or Jerrycans. Auxiliary fuel tanks are discussed in Chapter-3.
4×4 driving techniques
With many pickups and some stationwagons 4x4s, the spare wheel is carried under the load-bay. By fitting a rear-wheel carrier, like this one by IEF Engineering, a large fuel tank can now be put in its place, low down keeping the centre of gravity low.
One of the most useful auxiliary items for the vehicle that is going to drive off-road is the high-lift jack. It requires a suitable flat jacking surface on the vehicle for efficient use. Modern designs tend towards curved rounded body shapes and rounded bumpers. If you are purchasing a new vehicle and intend to take it off-road, ensure that the bumpers are adequate in both shape and strength for use as jacking points. If not, suitable adaptations can be made so that a high-lift can be used with the vehicle. These modifications are fitted by off-road vehicle fitment specialists.
Wheel rim size
The size of the wheel rims fitted to a vehicle has a significant effect on its off-road ability and suitability as an outback tourer. Many new 4x4s are delivered with 17, 18 or even 19-inch wheel rims. Low profile tyres found on large rims are a significant disadvantage off road, for three main reasons:
When dropping the tyre pressures to increase traction or flotation, with a low profile tyre, the percentage increase in footprint size gained by the reduction of tyre pressures is less, so much so that it can make almost no difference and the vehicle performs as if riding on tyres at normal pressures.
Secondly, low profile tyres are damaged more easily as are the rims.
Thirdly, in remote areas, tyres damage, which is one of the most common cause of a failure or disruption of a trip, can cause it to halt altogether because in these areas, replacement tyres larger that 16-inch are extremely difficult if not impossible to find. In this case, you could find yourself utterly stranded.
In my view, 16-Inch wheel rims seem to be the most ideal for an average 4×4. 17” is acceptable, but for the third point