Gear and Diff Oils
AMSOIL synthetic gear and differential oils provide outstanding protection for gears, bearings and other heavily loaded driveline components. Advanced synthetic formulations help reduce wear, resist extreme pressure and maintain dependable lubrication across severe temperatures and demanding operating conditions.
Browse the AMSOIL gear and differential oil range below for lubricants suited to differentials, manual gearboxes, transfer cases, final drives and other automotive, commercial and equipment applications.
Choosing the Right Gear and Differential Oil
Gearboxes and differentials rely on specialised lubricants to protect gears, bearings and other heavily loaded components. Unlike engine oil, gear oil must withstand intense pressure where gear teeth contact while maintaining a protective lubricant film under high loads, shock loading and changing operating temperatures.
AMSOIL offers synthetic gear lubricants for automotive differentials, manual transmissions, transaxles and other geared applications. Choosing the correct product requires more than matching viscosity alone — the lubricant must also provide the performance specification and friction characteristics required by the particular gearbox or differential.
Gear Oil Viscosity
Gear oils are commonly identified by SAE viscosity grades such as 75W-85, 75W-90, 75W-110, 75W-140 and 80W-90. These grades describe the lubricant's viscosity characteristics, but they do not tell you whether the oil is suitable for a particular differential or transmission.
Always consider both the required viscosity and the lubricant specification. Two 75W-90 gear oils can be designed for very different applications despite carrying the same viscosity grade.
API GL-4 vs GL-5
API GL-4 and GL-5 describe different gear-lubricant performance requirements and should not be treated as a simple progression where GL-5 automatically replaces GL-4.
GL-5 gear oils are commonly specified for hypoid differentials, where sliding gear contact and high loads require substantial extreme-pressure protection. AMSOIL SEVERE GEAR synthetic lubricants are designed for these demanding applications.
GL-4 gear oils are commonly specified for certain manual transmissions and transaxles, where the lubricant must protect gears while also providing appropriate synchroniser performance and shift characteristics.
AMSOIL 75W-90 Manual Transmission & Transaxle Gear Lube (MTG) is the dedicated API GL-4 gear lubricant in the AMSOIL range. If an application specifically requires a 75W-90 GL-4 lubricant, MTG should be considered rather than substituting a GL-5 differential oil solely because it has the same viscosity grade.
For a more detailed explanation of why these classifications are not interchangeable, read our guide to API GL-4 and GL-5 gear oils.
Manual Transmissions and Differentials Are Different
A manual transmission and a differential may both use a lubricant described as “gear oil”, but the operating requirements can be substantially different. Differentials containing hypoid gears place extremely high loads on the lubricant and typically require strong extreme-pressure performance, while a synchronised manual transmission must also allow its synchronisers to engage correctly and provide acceptable shift quality.
For this reason, a high-performance differential oil should not automatically be substituted into a manual transmission simply because the viscosity is the same. Where a transmission specifies a GL-4 gear lubricant, use a product designed to satisfy those requirements.
Limited-Slip Differentials
Some limited-slip differentials have additional friction requirements to allow their clutch packs to operate smoothly. Depending on the differential and lubricant being used, a limited-slip friction modifier may be required to address chatter or engagement characteristics.
Always check the vehicle or differential manufacturer's requirements before adding a friction modifier. More additive is not necessarily better, and it should only be used where required by the application.
Severe Service, Towing and Performance Applications
Differentials used for towing, four-wheel driving, motorsport, heavy loads and other severe applications can experience substantial heat and pressure. Synthetic gear lubricants provide excellent resistance to oxidation and viscosity breakdown while maintaining a strong protective film between heavily loaded gear surfaces.
AMSOIL SEVERE GEAR products are available in multiple viscosity grades for applications ranging from modern passenger vehicles through to four-wheel drives, towing vehicles, competition vehicles and heavy equipment.
Find the Correct Gear Oil
Check the required SAE viscosity, API classification and any manufacturer-specific lubricant requirements before selecting a gear or differential oil. Use the AMSOIL Vehicle Product Finder to identify recommended transmission and differential lubricants for your vehicle.
