Trucks and SUV's DO NOT have a limited slip differential (aka POSI, short for Positraction), they have a Locking differential and you DO NOT NEED any limited slip additives. They can actually cause problems.
You would think the dealer would know this.
¨ Optional Equipment (G80 Order Code) on all GM two-wheel and four-wheel drive light trucks and sport utilities.
Benefits
¨ Improved traction differentiates the vehicle relative to other rear wheel and four-wheel drive vehicles on the market.
¨ Maintenance free; requires no lube additives.
¨ Enhanced towing and off-road performance.
¨ Patented carbon friction disc technology enhances performance and durability while reducing warranty claims.
Principles of Operation
¨ Wheel speed difference (left to right) in excess of 100 RPM will cause a flyweight mechanism to open and catch a latching bracket.
¨ The stopped flyweight will trigger a self-energizing clutch system, which results in the cam plate ramping against a side gear.
¨ Ramping increases until both axles turn at the same speed (full lock), which prevents further wheel slip.
¨ At speeds above 20MPH, the latching bracket swings away from the governor and prevents lockup from occurring.
Technical Specifications
¨ Automatic locking takes place within a fraction of a second, so smoothly that it is unnoticed by the average driver.
¨ Unlocking occurs automatically, once the need for improved traction is gone, and is unnoticeable to the average driver.
¨ Compatible with anti-lock brake systems.
Also, owners have no idea why Limited slip differentials even use the additive. Its to control chatter, i.e. noise.
Chatter is essentially the build-up and release of energy between the differential clutch packs in a limited slip differential during operation. This phenomenon often occurs when torque is transferred between the clutches or when rotational speeds change. During the stick-slip phase, energy is built up to a point where contact between the clutch plates change between static friction (stick) and dynamic friction (slip), resulting in noticeable vibrations. It is this vibration that causes an audible chatter or ratcheting to be heard within the differential. While certainly an annoying characteristic, there is typically no mechanical damage occurring to the differential. It is most often noticed in parking lots or slow driving while turning where the outside wheel turns faster than the inside wheel.
In an effort to control this chatter, friction modifiers are often used. These additives result in a smoother transition between the two states of friction: static and dynamic. Static friction occurs when the clutches physically lock together, while dynamic friction occurs as the clutches are slipping, ergo Limited Slip Differential.
Locking differentials make noise when they engage, its the nature of the best. Average driver would likely not even notice but aggressive drivers will for sure.