Transfer Case
A gearbox in four-wheel-drive or all-wheel-drive systems that splits power between the front and rear axles.
A transfer case is a specialized gearbox positioned behind the transmission in four-wheel-drive (4WD) and all-wheel-drive (AWD) vehicles. Its primary function is to receive rotational power from the transmission and split it between the front and rear drive axles via separate drive shafts.
In part-time 4WD vehicles, the transfer case allows the driver to select between 2WD (power to rear wheels only), 4WD High (power split equally for traction at speed), and 4WD Low (uses internal reduction gears to multiply torque for low-speed off-road crawling). In AWD systems, the transfer case typically features a center differential or viscous clutch to distribute power dynamically to the wheels with traction.
Transfer cases rely on a chain drive or gear set inside a metal housing, lubricated by specialized transfer case fluid. Regular fluid changes are necessary to prevent chain stretch, gear wear, and bearing failure.
Symptoms of a failing transfer case include difficulty shifting into or out of 4WD, fluid leaks from the seals, clicking or grinding noises from under the vehicle, and the vehicle popping out of 4WD. A damaged transfer case can lock up, disabling the vehicle drivetrain completely.