The differential transfers torque from the drive shaft or transmission output to the differential?s drive axles. The spider gears and side gears allow the axles to turn at different rates, which is necessary when the car makes a turn. The outer wheel must turn faster than the inner wheel, creating a speed differential (which is how it got its name).
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 vehicles owners manual to acquaint yourself with the details of different driving modes.