What is it?

4x4, or four-wheel drive, is a drive-train that delivers power to all four wheels at once. If you drive a vehicle with four-wheel drive, you know that you put it through a lot. Vehicles with 4x4 go off-road onto rough terrain and tow big loads-they need regular maintenance to make sure they can keep doing their work as efficiently as possible.

What does it do?

Differentials allow the front and rear axles to turn the wheels at different speeds, which prevents slipping and wheel hopping when going around curves.

Typical Wear and Tear

Vehicles with four-wheel drive usually have a transfer case, which uses drive shafts to transfer power from the transmission to the axles. The transfer case is one of several components you'll want to get maintenance for. The fluid in the transfer case needs to be drained and refilled with fresh oil every 30,000 to 50,000 miles.

• Mileage

• Driving habits

• Driving and road conditions

• Type of fluid

• Vehicle type

Symptoms

• Problems shifting gears

• Chatter or grinding noises

• Loss of acceleration power

• Transmission leaks