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  • A preselector or self-changing gearbox is a type of manual gearbox 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 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 gearboxes, 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.

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