The transfer case attaches to the transmission and connects to both the front and rear drives axles of a four-wheel-drive vehicle. A transfer case usually has several different operating modes, controlled by the driver.
The transfer case routes torque from the transmission to both the front and rear axles. Depending on the design, the transfer case may provide equal amounts of torque to the front and rear axles, or the transfer case may proportion torque to the front and rear axles based on the amount of traction or slippage at the wheels. Transfer cases usually have different modes and ranges of operation. Check your vehicle's owner's manual to acquaint yourself with the details of different driving modes.
The transfer case should be checked at every oil change to ensure that it has enough lubricant. It's also a good idea to check the owner's manual for your vehicle to find out the maintenance interval for the transfer case. Many transfer cases require periodic changes of oil or fluid to maintain peak performance; use the lubricant specified by the manufacturer. Although transfer cases are usually trouble-free, they can develop problems over time. Common problems may include: no four-wheel-drive operation, four-wheel-drive operation only in some modes, or the inability to switch modes. These problems do not necessarily mean that the transfer case itself is at fault. The problem may lie in the transfer case engagement controls, as many of today's vehicles use electric or vacuum controls to carry out driver's commands. If your vehicle shows signs of a transfer case problem, have the system evaluated by a qualified service technician.