High-Performance Differentials, Axles, Drivelines

The main reason to have a limited-slip differential in your rear axle is to maximize traction on slippery surfaces, such as snow, ice, or mud, which can be exacerbated with an open differential. Another important reason is to help distribute the torque to the wheels from a high-performance engine and transmission combination. The limited-slip differential transfers torque to both wheels even if one wheel is spinning. This is a huge improvement over the traction-limited open differential. Limited-slip differentials also maximize acceleration of the vehicle.
DETERMINING LIMITED-SLIP VS. OPEN DIFFERENTIAL To determine whether your vehicle has a limited-slip or an open differential is one of the easiest driveline checks. The first step is to place the vehicle on a flat and level surface, block the front wheels, and raise the rear wheels off the ground with a jack. As always, practice safety first and place the vehicle on jack stands. Shift the transmission into neutral and make sure that the parking brake is released. Now just rotate one rear wheel in the forward direction and pay attention to the rotation direction of the other wheel. If it rotates in the same direction (forward), the rear end has a limited-slip differential. If the other wheel rotates in the reverse direction, then the rear end has an open differential. It is that simple. However, there is one exception: An extremely worn clutch-plate-style limited-slip differential may act like an open differential because the plates are so severely worn. So it's not a totally foolproof test. But this method works for most cases.