If your vehicle has four wheel drive, you most likely have a transfer case. Vehicles with both a front and a rear differential utilize a transfer case mated to the transmission.

The main purpose of the transfer case is the division of power between the two axles. Most 4x4s have a two-wheel drive setting which is used on road. Others have a full time four wheel drive transfer case that acts as a differential; sending power to the axle that needs it.

A transfer case contains many gears and moving parts. Transfer case fluid needs to be changed at manufacturer recommended intervals. Service intervals can range from 12,000 to 100,000 miles.