here's what i understand...forgot where i read this....sorry
Limited Slip Differential
A Limited Slip Differential (sometimes called positraction) is a modified or derived type of differential gear arrangement that allows for some difference in rotational velocity of the output shafts, but does not allow the difference in speed to increase beyond a preset amount. In a car or automobile, such limited slip differentials are sometimes used in place of a standard differential, where they convey certain dynamic advantages, at the expense of greater complexity.
The main advantage of an LSD is found by considering the case of a standard differential where one wheel has no contact with the ground at all. In such a case, the contacting wheel will remain stationary, and the non-contacting wheel will rotate at twice its intended velocity - the torque transmitted will be zero and the vehicle will remain stationary. In everyday use on typical roads, such a situation is very unlikely, and so a normal differential suffices. For more demanding use however, such as driving off-road, or for high performance vehicles, such a state of affairs is undesirable, and the LSD can be employed to deal with it. By limiting the velocity difference between a pair of driven wheels, useful torque can be transmitted as long as there is some friction available on at least one of the wheels.
Types
Two main types of LSD have been generally used - mechanical (geared or clutch-based) and fluid based (viscous). The latter is gaining ground especially in modern all-wheel drive vehicles, and generally requires less maintenance than the mechanical type.
Mechanical
In the mechanical clutch type, differential velocity is detected by some means, such as a centrifugal weighted rotor, and this applies a force to a clutch mechanism which links the two shaft together to a varying extent - the greater the differential velocity, the more force is applied. This forms a negative feedback loop which limits the slip to a preset degree. In some designs, the clutch is self-actuating. Often, small multi-plate clutches are used. One disadvantage of the mechanical type is that the limiting action tends to occur quite rapidly rather than gradually, and this in itself can create unsettling dynamic effects for the vehicle as a whole.
Another type of mechanical LSD is the geared torque-sensitive type. This arrangement uses planetary gears to "sense" torque on one shaft. The most famous version is the Torsen differential invented by Vernon Gleasman in 1958, then sold to Gleason Corporation, who started marketing it in 1982. But there are many other types available as well. Geared LSDs are less prone to wear than the clutch type, but their torque distribution characteristics can be less than ideal.
Viscous
The viscous type is generally simpler, and relies on the properties of a dilatant fluid - that is, one which thickens when subject to shear. Silicone-based oils are often used. Here, a chamber of fluid rotates with the normal motion of the output shafts, but a differential motion causes paddles or vanes to move through the fluid. The greater the speed of the vanes, the more resistance the fluid will put up to oppose this motion. In contrast to the mechanical type, the limiting action is much softer and more proportional to the slip, so for the average driver is generally much easier to cope with.
Viscous LSDs are less efficient than mechanical types, that is, they "lose" some power. However, they are less prone to breakdown as long as the fluid is changed regularly.
Locking Differential
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 maneuvers 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 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.
Kidding. Someone please enlighten me.
