A locking differential or locker is a modified type of automotive differential. A locking differential provides increased traction compared to a standard differential.
A locking differential is designed to overcome the chief limitation of a standard differential. A standard differential will cease to transmit power to one wheel if the opposite wheel has little or no traction. This may occur if one wheel comes into contact with mud, snow, or ice, or if the wheel is somehow removed from contact with the road after encountering an obstacle or area of soft ground. In such a situation an open differential will continue to spin the wheel with little or no traction but will transmit no power to the wheel(s) that continue to have traction. This can result in the vehicle loosing control or becoming stuck.
A locking differential ensures that engine power is always transmitted to every wheel, regardless of traction conditions. A locking differential will automatically "unlock" when one wheel is required to spin faster than the other during cornering, but will never allow either wheel to spin slower than the speed of the axle as a whole.
Locking differentials are used in various applications:
Race cars often use locking differentials in order to maintain traction during high speed manuevers or when accelerating at extreme rates.
Some utility vehicles such as tow trucks, forklifts, tractors, and heavy equipment use locking differentials to maintain traction, especially when driving on soft, muddy, or uneven surfaces. Lockers are common in agricultural equipment and military trucks.
four wheel drive vehicles that drive off-road often use locking differentials to prevent from getting stuck when driving on loose, muddy, or rocky terrain. Locking differentials are considered essential equipment for serious off-road driving.
Locking differentials do have some disadvantages. Because they do not operate as smoothly as standard differentials, they are often responsible for increased tire wear. Some locking differentials are known for making a clicking or banging noise when locking and unlocking as the vehicle negotiates turns. This is annoying to many drivers. Also, some locking differentials can affect the ability of a vehicle to steer in some situations, especially when the locker is located in the front axle.
These disadvantages can be largely mitigated by proper maintenance and setup. Tire wear can be minimized by ensuring that the tires are properly sized and inflated. Steering difficulties can be mostly eliminated by selecting modern lockers which are better engineered than earlier versions which were notorious for steering difficulties.
limited slip differentials are considered a compromise between a standard differential and a locking differential.
There are various types of locking differentials. Most are Automatic Locking Differentials. This type of locker will automatically lock during normal driving but will "unlock" during cornering thereby maintaining differential action. The most famous automatic locker is the "Detroit Locker", though there are many other types available as well.
Other locking differentials are manually operated by the driver (or sometimes by electronic traction-control systems in some vehicles). These selectable lockers function as a traditional differential during normal operation. However, when "engaged" they lock up for maximum traction. The locking mechanism can be a mechanical shifter (OX Locker, etc.), an electronic device (Detroit Electrac, etc.), or pneumatic (ARB Air Locker). These selectible lockers have a distinct advantage in that the differential is only locked when needed. Thus, a vehicle equipped with a selectable locker suffers can drive normally on the street but can have the traction capability of a real locker when driving off-road. However, selectable lockers are expensive. As well, many drivers consider selectible lockers to be somewhat delicate or damage-prone due to the extra complexity of the selection mechanism and associated hardware, electrical wiring, and/or pneumatic components.
