A differential is a gearbox located at the back of most vehicles that connects the driveshaft to the axles. The axle shafts transfer power from the differential to the wheels. The job of the differential is to allow each wheel to rotate at different speeds. This is necessary when turning corners, since the inner wheel needs to rotate faster than the outer wheel.
The amount of oil that a rear differential takes can vary depending on the make and model of your vehicle. Most rear differentials will take between 1 and 2 quarts of oil. Check your owner’s manual for specific information on what type and how much oil to use in your rear differential.