A preselector or self-changing gearbox is a type of manual gearbox (US: transmission) used on a variety of vehicles, most commonly in the 1930s. The defining characteristic of a preselector gearbox is that the manual shift lever is used to "pre-select" the next gear to be used, then a separate control (a foot pedal) is used to engage this in one single operation, without needing to work a manual clutch.

Most pre-selector transmissions avoid a driver-controlled clutch entirely, some use one solely for starting off.

Preselector gearboxes are not automatic gearbox

Automatic transmission

An automatic transmission is one type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually...

es, although they may have internal similarities.