Four wheel drive gives me all four wheels driving doesn’t it? Well no is the simple answer, it only gives you two wheel drive; so how can this be.
In this section we will look at four wheel drive, its operation, and when it should be selected or deselected for differing driving conditions to prevent expensive damage to the system, and to uncover many of the myths associated with its operation. Many people think a 4WD is invincible of road, and on road in treacherous conditions such as ice and snow, no system is invincible but it needs understanding to exploit it to its full potential safely and efficiently, and without damaging it.

Motor vehicles all used to be front engined with rear wheel drive, this was the standard configuration except for a few mid engined vehicles and exotics, and these are called inline configurations. Most modern vehicles are now front wheel drive with the engine at the front, these are called transverse engine layouts. Many manufacturers claim transverse layouts offer more efficiency, this is a myth, it is only because they use less components and offer more profits for the manufacturer and nothing else.
The configuration of the vehicle is irrelevant as long as it gets drive to all four wheels somehow.

With inline configurations we have the engine under the bonnet, attached to this is the gearbox which is located between the front seats under the floor, from the gearbox the power is transmitted to the rear axle by a propeller shaft. Transverse configurations have the engine laid across the car with the gearbox on the end, a differential is bolted to the bottom or side of the gearbox and two drive shafts emerge to the front wheels.
Four wheel drive vehicles have an additional gearbox, this is called the transfer box, and this connects to the end of the gearbox on an inline configuration, and on the side of the gearbox on a transverse configuration.
The function of the transfer box, or case as it is commonly known is to provide an additional propeller shaft to the front axle on inline configurations, and a propeller shaft to the rear axle on a transverse configuration. Transfer cases also provide other functions, this is to provide low range gearing and neutral positions on true off roaders, other vehicles which do not have low range are often referred to as soft roaders as they only offer the four wheel drive function.
Low range is essentially another gear within the transfer case which reduces the output gear ratio by 1.9:1 to 2.7:1 depending upon the vehicle and reduction ratio gears selected for the vehicle by the manufacturer. Low range gearing offers the ratio of power and torque increase for a specific gear selected in the main gearbox at a matching engine speed when low range is selected. In simple terms this means that for example at 2000 RPM in a specific gear it increases the torque and power if low range is selected over high or normal range by the amount of the reduction gear.

If high range is selected and the engine is in a defined gear and producing 75 BHP, then exactly the same is done in low range at a 2.7:1 it will be providing 2.7 X 75 BHP which = 202.5 BHP to the driving wheels, it also multiplies the torque in the same way.

Although this is a very simplified determination it clearly demonstrates how the low range gearing multiplies power and torque to the driving wheels.

Power is then transmitted through the propeller shaft/s to the selected drive wheels, it maybe two or four wheels, through the axles; axles contain differentials, these are essentially a set of gears which allow wheels to turn independently under certain conditions. Differentials are necessary when a vehicle turns a corner as the inside wheel travels a lesser distance, the outside wheel travels a further distance, and the differential allows this to safely happen. If differentials were not fitted, the inside wheel would try to travel the same distance as the outer wheel, this would cause two problems, the vehicle would not steer correctly, and the inner wheel’s drive shaft would snap attempting to travel the same distance as the outer wheel.
As four wheel drive vehicles have two driven axles they contain a differential in each axle, it is important to remember this as it will crop up later.
When two axles are driven they will travel different distances when a vehicle corners, basically the front axle will travel a further distance than the rear axle as the rear axle follows a shorter line when the vehicle corners. Daihatsu systems fitted to the Fourtrak and Sportrak are fitted with these basic systems. Permanent four wheel drive vehicles such as Range Rover or vehicles with the option of either 2 or 4 wheel drive such as Mitsubishi Shogun’s compensate for this by adding a further differential between the front and rear propshafts, this is called a centre differential. Centre differentials work in exactly the same way as axle differentials, they allow the front and rear propshafts to turn at different speeds when the vehicle is cornering.

If you have a large model car or other vehicle you can show this if the model has operational steering, coat the wheels with different colour water based paints and turn the steering wheels on a piece of paper, push the car along, you will see the different lines the wheels take.

If differentials, or open differentials as they are known, were not fitted it would lead to a total disparity in the drive train, this is called “transmission wind up” and is where most novices or inexperienced drivers damage their vehicles. This is caused by using the four wheel drive system in inappropriate conditions, if the ground is muddy or slippery the excess travelling distance is taken out of the system in two ways, one being the axle differential. The other is for one wheel to slip slightly as the slippery ground conditions allow it to happen, this is called “hutching” and happens where fairly solid ground such as rocky surfaces are encountered, a momentary movement in the suspension removes the weight from one wheel which allows the excess power to be dispersed by hutching. If the same thing is done on a solid surface such as a tarmac road the tyres grip does not allow it to happen, this is what creates transmission wind up, and causes considerable transmission damage as it is not only the drive shaft’s which are strained to breaking point. The excess strain acts upon the wheel bearings, differential inner bearings, propeller shaft, transfer case, gearbox, and the vehicles clutch; so could cause damage in a number of components or accelerate their wear.

Having a neutral position in the transfer case is an important consideration for true working off road vehicles, this allows the main gearbox gears to be selected and a range of attachments to be connected to the transfer case, and these are controlled by the clutch. This allows these accessories to be driven by the engine and the input speed and direction to be controlled by selecting gears in the main gearbox, with the vehicle stationary.
In the case of Daihatsu it was predominantly the front winch which was driven through the transfer case, these attachments are connected through a separate clutch driven assembly which is called a power take off, or abbreviated to PTO. The winch operated by selecting or operating a separate manual clutch inside the vehicle which engaged the PTO into drive, the main gearbox used first gear to winch in and reverse gear to winch out, control was with the main clutch pedal. Soft roaders do not have the option of low range and a neutral position on the transfer case; so cannot have such engine driven attachments fitted.

Now we have an understanding of a transmission we now see we have answered our question of only having two wheel drive, but we have it in a choice of four different positions as the differentials are always shuffling power between the driving wheels. The only time we would get true four wheel drive is on a perfectly flat surface with all four wheels having equal traction and the vehicle travelling in a perfectly straight line, something which never happens on any surface with any vehicle. Conversely, a two wheel drive vehicle has only one wheel drive, but in a choice of two positions.

Daihatsu transmissions therefore consist of a standard engine, four or five speed conventional gearbox, a transmission case which allows the selection of two or four wheel drive, and the selection of low range gearing; or the neutral position for accessories.
Selecting four wheel drive manually merely moves a splined sleeve in the transmission case from the rear propeller shaft, it moves forwards to engage with a splined gear on the front propeller shaft, essentially making the two shafts one. This means the basic system has both axles turning at the same speed at all times with four wheel drive engaged, any turning of the steering means that the axle differentials work across the axle, but we have no compensation for the axles rotating at differing speed. Therefore we need to know when to engage four wheel drive, and WHEN NOT TO ENGAGE FOUR WHEEL DRIVE.

We have already worked out that four wheel drive should not be engaged on solid surfaces such as surfaced roads made of tarmac or concrete as we have no centre differential to compensate for speed differences between the axles. The axle differentials will work, but the wheels will not be able to “hutch” to disperse any surplus power if we use anywhere near the full steering lock to undertake manoeuvres such as three point turns or any other road condition which requires large steering angles.
Four wheel drive can be used on loose surfaces such as gravel, blinding, dirt, or any other surface which has any form of movement in it, we can always engage four wheel drive on muddy or grass surfaces. These surfaces offer enough slip for the four wheel drive system to naturally compensate through the differentials or hutching between the axles to disperse this excess power and wheel travel when the vehicle is turning on such surfaces.
Rocky or severe undulating surfaces can also have four wheel drive engaged as the constant suspension movement means one wheel will always have less traction then the rest. The combined action of the differentials and hutching means the wheel with the least traction will disperse this surplus movement or power through naturally and constantly changing suspension movement. There will always be one wheel which is momentarily not in contact with the ground for a brief period, or has less traction than the others, which is long enough to disperse the surplus power and movement to prevent transmission wind up.

Low range gearing can be engaged when more power or control are needed to suit ground conditions, this may be when traversing heavily mudded ground conditions, or when traversing undulating conditions where low speeds and total control are needed. Low range should always be used for ascending or descending steep hills, and the normal gearbox can be used in the normal way with low range engaged, this may be engaging 2nd or 3rd gear for hill climbing, or 1st gear for descending steep slopes.

Hubs are another issue, later models were fitted with automatic hubs, these replaced the earlier manual hubs, manual hubs require the driver to stop the vehicle to get out to manually engage them, and automatic hubs rely on relative motion and engage themselves.
(See section on automatic hubs for more detailed information)

Using automatic or manual hubs can be confusing for first time users, basically there are some simple rules:

With manual hubs you always engage them when you engage four wheel drive, then disengage them when you switch back to two wheel drive; never run with engaged when the vehicle is in two wheel drive. If the hubs remain engaged the axle is driving, in normal circumstances on many other vehicles it would not be a problem except for more vehicle drag, increased fuel consumption, and increased front tyre wear.
Daihatsu transfer cases are very durable and are machined with very tight internal tolerances, if the transmission has any play or wear in it, the rotating front axle can cause the front propeller shaft gears to catch the splined shaft. This actually leads to partial engagement of the four wheel drive system and to transmission wind up, and can cause considerable damage.

Automatic hubs require nothing except the front driveshafts or axle shafts to be turning as the turning motion in forwards or reverse operates against an internal spring which engages them. They do require disconnecting when the vehicle is reverted back to two wheel drive, to do this you need to switch back to four wheel drive and reverse the vehicle about 3 metres (10 feet) as this relieves any pressure on the engaging mechanism and centres them.

With basic systems you must always stop the vehicle to move from two wheel drive to four wheel drive, or from four wheel drive back to two wheel drive, or when you engage low range.

Never leave the transfer case in neutral, or engage the neutral position unless you are operating accessories from the PTO.