4 wheel drive vehicles are popular for their off-road capabilities, good road grip and handling safety on slippery roads. Their increased traction makes them a favourite to campers, who use 4 wheel drive vehicles to go up steep hills and to tow trailers. These advantages come with a bit of downside, though.
In contrast to two-wheel drive vehicles which have only one differential drive unit, 4-wheel drive vehicles have got two differential drive units one to each axle. These differentials draw power from a transfer case, to which they connect with shafts. The transfer case in turn draws power from the gears box, and is commonly located between the two axles. Its mode of switching, or lack thereof, is what determines whether a vehicle is part time or full time four-wheel drive. The two differentials and transfer case utilise gear wheels for their operation. Due to the higher number of transmission components in 4 wheel drive vehicles and the high performance motoring duties they are subjected to, they require greater maintenance attention to the drive train, with a focus on proper driving technique and lubrication.
Grating sounds emanating from any of the two differentials or the transfer case indicate damage to internal gears. The damage can be chipped teeth, or broken segments of the various moving components enclosed within these units. This breakage of gear teeth is not always spontaneous; it is usually a complication arising when even tinier metallic chippings get caught between adjacent counter-moving parts. A common cause for internal chipping and breakage within 4WD differentials and transfer cases is severe axle wind up. Replacing your transmission fluid on time prevents this damage by flushing out these metal particles. Continuing to use your car while it issues such sounds might completely jam the differential drive units immobilise your car.
Transmission wind-up is the unequal distribution of forces acting on the opposite ends of each axil on a 4wheel vehicle while it is turning. When taking corners, each wheel covers a dissimilar length of the road surface, so it must turn at a speed varying from all the rest. The resulting tension tends to twist the final transmission drive shafts, with the rest of the drive train receiving this tension. 2 wheel drive vehicles avoid axle wind up as rear axle tension dissipates through h the free rolling font wheels. Axle wind up leads to accelerated tyre wear and damage to drive train components. Extreme instances will stall vehicles. To avoid wind up, disengage 4-wheel drive on firm road surfaces. Reversing your vehicle or jacking up one side of the car will allow the tensioned wheels to spin, remedying the axle wind up.