Final Drives and Gears The purpose of gears in a final drive is to provide speed reduction and generate torque. Gears are one of the critical components of your final drive, and they carry some its the heaviest loads and most intense forces. The gear teeth are where the actual loads get transferred as they push against each other. This requires a very hard surface that resists damage. If the entire gear were hardened all the way through, it would become too brittle to serve its purpose. Thats why a surface hardening process is used to just harden the surface of the gear while leaving the inside still ductile enough to be tough and not brittle. The surface treatment typically used on the type of gears found in final drives is called carburizing and is sometimes referred to as a case hardening process.