The 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’s generated in the front prop shaft is transferred through the differential to the rear prop shaft.
The transfer box is part of the drivetrain on 4 x 4 and multi-axle vehicles and allows the driver to change between 4 x 4 and 2 x 2 wheel drive. It receives power from the transmission and uses either gears, hydraulics or in the case of some multi-axle vehicles, chain drive.
The transfer box is designed for both on-road and off-road driving. The transfer box can leak oil, which can be noticed either on the transfer box or from the handbrake drum, depending on the position of the leaking seal. This leaking of oil will cause a loss of power steering. Other signs of a failing transfer box include a whining noise when you accelerate and a tapping noise as you decelerate. These issues can be accompanied with, or separate to a loss of braking ability and a loss of gears.