In a sense, the gearbox is the intermediary between engine and wheels. Its job is to optimise the engine’s rotational speed to achieve the desired road speed. It does this by converting the rotational speed of the engine to the appropriate rate of wheel rotation by changing the ratio between the two as required. The purpose of the gearbox is to increase torque whilst reducing speed. You will find a gearbox in both a manual and an automatic car, but while the manual gearbox requires the driver to physically move a gear stick to select the gears, the automatic gearbox engages the gear itself when the engine speed changes. For the gearbox to work properly, the gear linkage must be completely aligned and in good working order. If your gear linkage is worn you may notice excessive play in your gear stick or you may even be unable to change gear at the right time. Other gearbox problems include crunching or stiffness. As a complicated part with a number of moving parts and connections, your gearbox and its linkages should be replaced when worn out.