What Is a Transfer Case? Get the Facts

An essential part of four-wheel drive vehicles that many drivers overlook is the transfer case. If you drive a truck, SUV or any other vehicle that supports four-wheel drive, chances are it has a transfer case. You typically won't see it unless you crawl underneath your vehicle. Nonetheless, the transfer case will help to keep your vehicle on the road while ensuring that its four-wheel drive mode works as intended.

Overview of Transfer Cases

Transfer cases are designed to transfer the power from the engine to both the front wheels and the rear wheels in four-wheel drive vehicles. Four-wheel drive vehicles, of course, are capable of generating torque with all four wheels. Two-wheel drive vehicles can only generate torque with two wheels. In four-wheel drive vehicles, a transfer case is used to equally distribute the power produced by the engine to all four vehicles.

Only four-wheel drive vehicles have a transfer case. After all, the purpose of a transfer case is to distribute engine power to all four wheels. Two-wheel drive vehicles don't need a transfer case because only two of their wheels generate torque.

How Transfer Cases Work

There are different types of transfer cases, but most of them work in the same way. They serve as the heart of the drivetrain. When operating your vehicle in four-wheel drive, the transfer case will route engine power to all four wheels. It will ensure that each of your vehicle's four wheels receives an equal amount of power -- typically 25% engine power.

Your vehicle has a front differential and a rear differential. The transfer case will route power to these differentials. The differentials will then help to further distribute the engine power to the appropriate wheels. 

Transfer Case Maintenance

Transfer cases don't require much maintenance, but they should be inspected on a regular basis. Most transfer cases contain a lubricating oil. Known as transfer case fluid, it reduces friction to protect against premature wear and tear. Transfer cases are sealed, so the fluid shouldn't leak out of them. But leaks can and do occur. If your vehicle's transfer case has sprung a leak, it may succumb to damage, or it may overheat.

You can refer to your owner's manual for more information on when and how to get the transfer case inspected. With that said, most automakers recommend an inspection once every 30,000 miles. Regular inspections will allow you to catch small leaks and other minor problems before they snowball into bigger, more expensive problems.