Transmission Fluid and Gear Oil: The Complete Guide

Automatic, manual, CVT or dual-clutch transmission, front or rear differential: every part of your driveline depends on the right fluid, changed at the right time. Start here to understand how each system works, what fluid it needs and how to keep it shifting smoothly.

Automatic transmission fluid

• What is Transmission Fluid?
• What Does Transmission Fluid Do?
• Which Automatic Transmission Fluid Do I Need?
• What is the Best Transmission Fluid?
• How Often to Change Transmission Fluid (By Type)
• Why Change Transmission Fluid?
• Should I Change Fluid in a Filled-for-Life Transmission?
• Transmission Flush vs Fluid Change: Which is Better?
• Can I Use Transmission Fluid in Oil to Clean My Engine?
• Do Transmission Fluid Additives Work?
• How Does an Automatic Transmission Work?
• Common Fixes for a Transmission that Shifts Hard
• AMSOIL Tech Tips: Jerky Transmission
• Advanced Transmission Technology Requires Advanced Protection

CVT, dual-clutch and manual transmissions

• What Is a CVT? How a Continuously Variable Transmission Works
• How Does a Dual-Clutch Transmission (DCT) Work?
• AMSOIL 100% Synthetic DCT Fluid: Protect the Thrill
• Manual vs. Automatic Transmission Fluid: The Difference
• See How the CVT Transmission in Your ATV Works
• Testing a Turbo UTV Dual-Clutch Transmission

Gear oil and differentials

• Differential Fluid vs. Gear Oil vs. Gear Lube
• Limited-Slip Differential: How It Works and Which Gear Oil to Use
• How Often Should I Change Differential Fluid?
• GL-4 vs. GL-5 Gear Oil: What’s the Difference?
• What Is Hypoid Gear Oil? How It Compares to Regular Gear Oil
• How to Read a Gear Oil Viscosity Chart
• Gear Oil vs. Engine Oil: What’s The Difference?
• More Performance, Less Wear: Why Gear-Oil Compatibility Matters
• The New SEVERE GEAR Easy-Pack Makes Changing Gear Oil Easy
• Why Upgrade Your Differential Cover?
• Dissecting the Transfer Case
• Harley-Davidson Transmission Oil Change Instructions