Will It Hurt if You Use a Friction Modifier in a Non -Limited Slip Axle?by Robert Bayly
A vehicle's rear differential sends power from the driveshaft to the axles. When cornering, the inside tire turns slower than the outside tire. The differential allows the tires to rotate at different speeds. There are three basic types of differentials – open, limited-slip and locking. They all work in different ways; one requires a friction modifier to be used in the differential.
An open differential is the standard – or entry level -- type. When turning, it allows the outside tire to turn faster than the inside tire. The drawback to an open differential is that when a tire loses traction, it will spin and the tire with traction will remain stationary. In other words, all the power gets sent to one tire. This is colloquially referred to as a “one-legged” differential. If you do a burnout with this type of differential, there will only be one patch of rubber on the pavement.
A locking differential uses gears to “lock” the two axles together for improved traction. The most famous locking differential is probably the “Detroit” Locker. Locking differentials are performance options for high-performance cars and four-wheel-drive vehicles. They physically lock the axles together so they both rotate at the same speed. Modern lockers are electronically or pneumatically controlled and don't require a friction modifier.
Limited-slip differentials are also a performance option and are more common than lockers. Limited-slip differentials “limit” the slip between the two axles with clutch packs. When one wheel begins to spin, the clutch packs are engaged and transfer power to the non-spinning wheel. These differentials require a friction modifier for the clutch packs.
Friction Modifier in Non-Limited-Slip Differential
All differentials use gears, bearings and shims. Limited-slip differentials have additional clutch packs. Since there is nothing in any differential that is not in a limited-slip differential, there should be no harm in using a friction modifier in a non-limited-slip differential, although there is no need for it. This is borne out by the fact that most popular modern synthetic gear oils already have friction modifiers in them.