Transfer case
The transfer case transfers the power from the transmission to the front and rear axles by means of drive shafts. The transfer case synchronizes the rotation of the front and rear wheels so they turn at exactly the same speed. It usually contains two or more sets of gears. It has a 1:1 ratio drive (usually called high range) for normal city and highway use. Then it contains a low range gear for off-road use. A common low range gear ratios is 2.72:1. That means for every 2.72 rotations of the transmission output shaft, the transfer case will turn both driveshafts 1 rotation. The Jeep Wrangler Rubicon model uses a 4:1 low range gearing.