A differential is a set of gears that enables your vehicle's wheels to rotate at different speeds. A fixed axle supports only one speed of the wheels. When turning, the inside radius is smaller than the outside, causing a fixed axle to drag one wheel. A limited slip differential, or LSD, has a set of clutch plates that inhibit the free rotation of either wheel. These clutch plates enable each wheel to retain some power while cornering. Limited slip differentials require a certain amount of friction modifiers in the gear oil of the differential to operate properly.
Inspect the differential for a metal tag or model marking. Some manufacturers, such as Ford Motor Company, will mark the differential in some way that designates it as a limited slip differential. The Ford markings, for example, will have an "L" on the differential model number indicated limited slip. Consult your manufacturer for details on tag location and identification.
Read the manufacturer sticker on the driver's side door. Some manufacturers will specifically identify whether the model was shipped from the factory with a limited slip differential.
Decode the VIN number for your vehicle. VIN numbers may contain information that specify whether the vehicle was shipped from the manufacturer with a limited slip differential. Be sure the differential installed is the same one installed from the manufacturer.
Place the vehicle in "Park" if it is has an automatic transmission, or in first gear if it has a manual transmission.
Brace the two tires, with wheel chocks, on the axle you will not be inspecting. Jack the vehicle to lift the two tires--on the axle with the differential you are inspecting--off the ground.
Turn the tire on one of the lifted wheels slowly. Use your hand to turn the tire. If the differential is limited slip, the wheel will be difficult to turn. If the differential is an open differential--also known as a conventional differential--the wheel will turn freely.
Place the vehicle in neutral.
Turn the tire again. The tire should turn more freely on a limited slip. Also, the opposite tire will turn in the same direction. If your vehicle is equipped with an open differential, the wheel on the other side of the axle will turn in the opposite direction.
A phone call to a dealership service department usually will result in specific instructions on how to find limited slip markings, if they are available.