A transfer case is a small, heavy-duty gearbox that splits engine power between the front and rear wheels of a vehicle. In some cases, the transmission can send power to all four wheels. Transfer cases are found in many vehicles — from trucks, SUVs, and vans to cars with all-wheel drive (AWD). They're also used in off-road vehicles, like Jeeps and rock crawlers.
There are two basic types of transfer cases; manual (with a lever) and automatic. Manual transfer cases use a lever or button to engage or disengage different gears; automatic ones use an electric motor to shift gears…