Motul Motyl Gear 75W-90 Gear Oil 1L

API GL‑5 contains significantly more Extreme Pressure (EP) additives designed for the heavy shear loads of hypoid gears in differentials and axles. However, these EP additives can be corrosive to yellow metals (like brass or bronze) used for synchronizer rings in many manual gearboxes. Unless your manual specifically calls for GL‑5, you should use GL‑4 in manual gearboxes to protect the synchros, and GL‑5 in differentials.

Gear and axle oils are often highly neglected, but they degrade over time due to intense mechanical shearing and condensation buildup. A general rule of thumb is to replace manual gearbox and differential fluids every 30,000 to 50,000 miles to flush out metallic wear particles and ensure smooth operation.

It depends entirely on the specification. Limited Slip Differentials (LSDs) contain internal clutch plates that require specialized “LS” friction modifiers to prevent harsh chattering when cornering. If your vehicle has an LSD, you must ensure the gear oil specifically states it is “LS” or “Limited Slip” compatible, or purchase an aftermarket LS additive to mix with the fluid.

In a manual gearbox, degraded fluid usually presents as stiff or “crunchy” gear shifts, especially when the vehicle is cold. For differentials and axles, the most common symptom of low or ruined oil is a persistent “whining” or “howling” noise coming from the rear or front wheels, which changes pitch with vehicle speed.