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
, although they may have internal similarities. A fully automatic gearbox is able to select the ratio used, with a preselector gearbox this remains the driver's decision.
There are several radically different mechanical designs of preselector gearbox. The best known is the Wilson
design. Some gearboxes, such as the Cotal
, shift gear immediately the control is moved, without requiring the separate pedal action. These are termed 'self-changing' gearboxes, but were considered under the same overall heading. In recent years, a similar role... Read More