Quick answer
Many gear oils marketed as “LS” or “limited slip” already include friction modifiers, designed to quiet LSD clutches. If yours isn’t labeled LS, you can add a separate additive. However, adding friction modifier to a gear oil that already has it can lead to excess slip, so check labels first.
Detailed answer
Friction modifier is integral to how LSDs operate, letting plates slip just enough in low-load scenarios. Some gear oils come with this additive pre-blended, usually marked “LS” or “Limited Slip.” Others are standard gear oils without LSD additive, requiring a separate friction modifier product. How do you know which is which? Check the bottle or product specs.
When Gear Oil Includes Modifier
– LS-labeled gear oils: Typically have enough additive for many factory LSDs.
– Potential Topping Up: In certain finicky LSD units or performance differentials, you might still add an extra ounce or two if mild chatter remains.
When Gear Oil Lacks Modifier
– Standard gear oil: No LSD additive, so LSD-equipped vehicles would experience chatter unless you add friction modifier separately.
Risks of Double-Dipping
Pouring an additional friction modifier into gear oil that already has it could overshoot the sweet spot, leading to LSD slip.
Advice
1. Read labels or brand data sheets.
2. If it says “Limited Slip” or “LS,” start with just that oil. Test for chatter.
3. Add extra only if needed.
Conclusion
Modern gear oils often incorporate friction modifiers right out of the bottle for LSD compatibility. If your LSD chatters, you can add more. If your diff is open or your manual warns against LSD additive, avoid it. The key is matching your gear oil’s friction properties to your differential’s needs, ensuring chatter-free operation without losing traction lock.
