A limited slip differential is a device found in the drive axle of an automobile or truck that the axles and ring gear are mounted to. Used to engage both sides of the axle in the event of needed traction, the limited slip differential causes both drive tires to receive power, resulting in added traction. Unlike a locked, welded or spooled differential that has both sides of the axle meshed together constantly, the limited slip differential is made so that the drive axle will disengage one side while turning a corner. This prevents the wheels from binding and the tires from chirping as the outside tire fights to turn faster than the inside tire while the vehicle negotiates a sharp turn.
Used primarily as an option for work trucks and muscle and sports cars, the limited slip differential uses springs that push against clutch packs and apply pressure on the spider gears in a differential, causing both the left and right side drive axles to receive power from the engine. Once a slipping or spinning tire is detected by the differential, the clutches in the limited slip differential engage so that both tires will spin the same amount at the same speed. This is especially useful in muddy and snowy conditions when one drive tire wants to spin and allow the vehicle to become stuck.
In high-performance applications such as drag racing, the use of a limited slip differential allows the vehicle to accelerate quickly at the hit of the throttle instead of one tire spinning under the engine's power and going up in smoke. In the case of a work truck, the equal application of power to both sides of the drive axle creates a very powerful pulling machine that is able to move large and heavy payloads without breaking a drive axle. Trucks with an open or single-side differential will commonly break an axle, as the entire force of moving a heavy load is applied to only one side of the axle.
The lubricating oil in a limited slip differential requires the addition of a special additive in order to aid in the operation of the drive line clutches. Operating the limited slip differential without this additive will result in a sticking clutch pack that can hinder the proper operation of the drive line. Most vehicle manufacturers of the limited slip differential recommend changing the lubricating oil and the additive at specific intervals. Failure to do so will void most manufacturers' warranties.