What Does a Limited-Slip Additive Do?

You see them on the shelves of your local auto parts stores, but what does a limited-slip additive do?

Limited-slip differentials commonly use clutches to transmit torque between wheels. When both wheels have ample traction, the clutch plates bind together tightly, but smoothly slip enough to allow chatter-free turning.

When one wheel spins on a patch of ice or mud, however, additional power is sent to the other wheel through the clutch pack. This is where the gear lubricant’s frictional properties play an important role in performance and wear.

Clutch chatter

Differential manufacturers use different spring pressures and clutch discs made with different materials and surface areas. Additionally, spring tension and clutch-friction properties change with age and wear, while the frictional requirements of the gear lubricant can vary.

If the frictional properties are not correct, abnormal clutch engagement and disengagement – called chatter – can occur.

Chatter occurs when the clutches repeatedly alternate between slipping and sticking instead of smoothly slipping. It not only generates annoying noise and vibration, it causes premature wear.

What does a limited-slip additive do?

Instead of formulating multiple gear lubes of the same viscosity, but different frictional properties, to address occasional chatter in limited-slip differentials, gear-lube friction-modifier additives can be used to alter the fluid’s original frictional properties and eliminate chatter.

Should I use a friction-modifier additive with AMSOIL synthetic gear lube?

AMSOIL synthetic gear lubes are limited-slip capable and do not typically require an additional friction-modifier additive.

However, depending on the differential’s friction material and degree of clutch wear, chatter can still sometimes occur. The addition of AMSOIL Slip Lock will eliminate chatter in mechanically sound differentials.

AMSOIL SEVERE GEAR® Synthetic Gear Lube

SEVERE GEAR Synthetic Gear Lube excels in protecting gears and bearings from the rigors of severe-service operation. By design, it resists breakdown from high heat, preventing acid-caused viscosity changes and loss of gear protection. Its wax-free construction also improves cold-flow properties, improving fuel economy and cold-weather performance.

AMSOIL Slip Lock

Slip Lock is formulated with advanced friction modifiers and is designed to eliminate gear-housing chatter in cars, trucks and SUVs equipped with clutch-type limited-slip differentials. It is formulated for use with both synthetic and petroleum gear lubricants and safely replaces manufacturer-recommended friction modifiers. Its convenient squeeze-tube packaging provides quick and easy application to the gear housing.

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