A gearbox is a mechanical device that uses gears and shaft assemblies to provide speed and torque from a power source (like an electric motor) to another machine. Gearboxes are designed in many different configurations for many different purposes. Gearbox repair is required when something in a gearbox breaks or wears out. Gearbox repair can be something as simple as changing bearings and flushing out oil. Another example of gearbox repair would be gear replacement and machine work, sometimes to gear shafts or even the gearbox case.