Friction modifier for limited slip differentials?

by Alex

Expert answer:

Quick answer

Yes, limited-slip diffs often require a friction modifier to prevent clutch chatter in low-torque turns. It adjusts the slip characteristics so the plates move smoothly without constant binding. Many “LS” gear oils contain it, or you can add a separate bottle if your diff chatters. Always follow your LSD’s specs.

Detailed answer

A limited-slip differential (LSD) relies on friction in its clutch packs to lock both wheels under heavy load. But at low torque, like parking-lot maneuvers, excessive friction can cause chatter or binding. Friction modifiers solve this by lowering friction at lower torque levels, ensuring a smooth slip when you’re just rolling around corners.

How It Helps

– Chatter Elimination: LSD plates won’t grab abruptly, so you avoid that knocking or squealing.
– Preserved Locking: A good friction modifier only reduces friction enough for low-load slips. Under heavy acceleration, the LSD still engages to drive both wheels.

Application

Many gear oils labeled “LS” or “Limited Slip” already have friction modifiers included. If you choose a standard gear oil, you might need to add a small bottle of friction modifier to mimic that effect. Usually, it’s a few ounces, depending on the capacity.

Test

1. Drain & Fill: Put in the right weight gear oil and the recommended friction modifier.
2. Figure Eights: Drive in a tight circle in both directions. Listen for chatter.
3. Adjust: If chatter remains, add another half-ounce or so, then retest.

Too Much

Going overboard with additive can reduce the diff’s ability to lock, leading to one-wheel peel. That’s why most LSD specs mention a precise or approximate amount.

Interval

Over time, friction modifiers degrade. If chatter reappears, it might be time to swap out the fluid or replenish the additive.

Conclusion

For limited-slip diffs, friction modifiers are nearly always essential. They tune the friction sweet spot so the LSD remains quiet at low speed but still locks up under load. Check your owner’s manual or LSD kit instructions for the right gear oil mix. Done properly, you’ll have smooth cornering and the traction advantage LSDs provide, all without the dreaded chatter.

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