The transfer box is attached to the back of the main gearbox and controls high and low ratios to enable the vehicle to use double the amount of gears of a normal vehicle. Despite the large amount of gears, the 4 x 4 transfer box makes it easier to select the gears.
The 4 x 4 transfer box, as the name suggests, transfers power to the front prop shaft. This prop shaft is attached to the rear prop shaft with a differential connecting the two. The power that is generated in the front prop shaft is transferred through the differential to the rear prop shaft.
The 4 x 4 transfer box can leak oil, which can be noticed either on the 4 x 4 transfer box or from the handbrake drum, depending on the location of the leaking seal. This oil leak will cause a loss of power steering. Other signs of a failing transfer box include a whining noise as you accelerate or a tapping noise as you decelerate. These issues can be accompanied with a loss of gears and braking ability.