How do transfer cases work in 4WD and AWD vehicles?

Transfer cases distribute power from the transmission to front and rear axles in 4WD/AWD systems. Part-time 4WD transfer cases typically have 2WD, 4H, and 4L modes with no center differential (for off-road only). Full-time AWD transfer cases include a center differential for on-road use. Modern electronic transfer cases use clutch packs to vary front/rear torque split dynamically. Components include input shaft, chain or gear drive, range gears for low range, and output shafts to each axle.