by Bob Brown
mockup image by Dominique LUZY from Fotolia.com
Posi-Track is an abbreviated generic term for the GM brand name “Positraction”. It is a type of limited slip differential. To understand how LSD or limited slip differentials work, you need to understand how a differential works and how it relates to torque. In basic terms, a differential takes power from your engine’s transmission output and transfers it to your wheels.
What is a spread?
The differential of a car is located in the middle of the axle. It is found on the rear axle of a rear-wheel drive car, the front axle of a front-wheel drive car, and on both axles for a 4-wheel or four-wheel drive car. As defined by the Merriam-Webster Dictionary, a differential is “a set of gears in the drivetrain that connects two axles or collinear axles (like those in the rear wheels of a car) and allows one axle to turn faster than the other. ”.
The spool differential locks both sides of the axle so that torque is equally distributed to both wheels at all times. This is useful in off-road and drag racing applications, but can cause the rear end to slide uncontrollably in high-speed turns on pavement.
An open differential allows the two wheels to rotate at different speeds relative to each other. When cornering or turning, the inner wheel has less distance to travel than the outer wheel. An open differential allows the outer wheel to rev more while preventing it from skidding or skidding. The downside to an open differential is that it will always transfer torque equally, so the wheel with the least resistance will slip and no more torque will be applied. This means that if one wheel is on ice or snow and the other on dry pavement, the spinning wheel will receive torque or “power” and the wheel on dry pavement will not get enough torque to propel it forward. In other words, “You’re stuck!”
Limited slip differential
The limited slip differential is perhaps the most versatile, as it performs well in a wide range of uses. A limited slip system uses clutches or springs between the two axle halves to apply torque equally, but still allows a “limited” amount of slip when cornering, turning, or accelerating in loose gravel, sand, mud, or snow. This type of differential system was rated by the major automobile companies. Some of the best known are GM’s PosiTraction, Ford’s Track-Loc, and American Motors Corporation’s Twin-Grip.
Types of limited slip differentials
There are two types of limited slip differentials: mechanical and viscous type. Mechanical limited slip differentials work by using a clutch system as discussed above or the more modern torque sensitive system. This type of system uses clutches instead of gears to adjust slip. Viscous-type limited-slip differentials work by using a thick, viscous fluid to provide strength and achieve the same type of clutch system properties. This is also a popular application for four-wheel drive vehicles, as it allows more “skidding” on dry pavement in high-speed turns.