A transfer case is a device used to split torque between the front and rear axles of a four-wheel drive vehicle. The transfer case also includes a low range gear set that can be engaged to provide additional traction when driving over rough or slippery surfaces.
Most modern four-wheel drive vehicles are equipped with permanent all-wheel drive systems that do not require the driver to engage or disengage the transfer case. However, some older four-wheel drive vehicles may have manually operatedtransfer cases that must be engaged by the driver when additional traction is needed.