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What do You Need to Know about Your 4WD Vehicle's Transfer Case?

by Emilia Latvala

A typical mechanically operated car or truck relies on an engine, gearbox and transmission to create and transfer power. While many cars will transfer this power to the road through either the front or rear wheels, some rely on four-wheel drive. In this case, the transmission system is a little more complex than it would be otherwise and needs a special type of component known as a "transfer case." What do you need to know about this equipment, and does it require any ongoing maintenance?

Using the Energy

While the engine creates the power and the gearbox selects the right rotational speed, a transmission system connects those rotating shafts to the road wheels. In front-wheel-drive vehicles, this is all relatively simple, as everything takes place in a confined area. With rear-wheel-drive vehicles, there is a lengthy prop shaft in between the back of the gearbox and the rear axle casing.

Splitting the Power Output

Four-wheel-drive cars need another component that can "split" the power provided by the gearbox whenever traction is required at both ends. This magic takes place within the transfer case and, depending on your make and model, can be simple or relatively sophisticated.

How Things Work

You'll find a series of chains, step shafts, gears, bearings and clutches within the transfer case. If the vehicle is designed to be rear-wheel-drive in normal format, the transfer case allows power to go straight through without intervention. If you encounter slippery going, then you can engage the transfer case by selecting the appropriate lever, or this may be done automatically in higher-end vehicles. This will engage certain gears that will also provide power through separate shafts to the front wheels. The ECU will typically manage how much power is directed to each axle to give you stability in these situations.


While the transfer case may not get much use if you tend to drive on sealed, clean roads most of the time, it is still a mechanical contraption. While it is carefully lubricated to deal with friction and temperature, the fluid will eventually wear out. Further, it may become contaminated as microscopic particles wear away from internal parts, compromising its efficiency.

Regular Attention

So make sure that you take your vehicle to a mechanic so that they can look at the transfer case as well as other components. They can take the service cover off the casing to inspect and repair the internal parts and can also replace the fluid if needed.

Contact an auto shop that offers 4WD servicing to learn more.