gearbox maintenance

A preselector gearbox is a type of manual transmission mostly used on passenger cars and racing cars in the 1930s, in buses from 1940-1960 and in armoured vehicles from the 1930s to the 1970s. The defining characteristic of a preselector gearbox is that the gear shift lever allowed the driver to "pre-select" the next gear, usually with the transmission remaining in the current gear until the driver pressed the "gear change pedal" at the desired time.
The design removed the need for the driver to master the timing of using a clutch pedal and shift lever in order to achieve a smooth shift in a non-synchromesh manual transmission. Most pre-selector transmissions avoid a driver-controlled clutch entirely. Some use one solely for starting from a standstill. Preselector gearboxes were most common prior to the widespread adoption of the automatic transmission, so they were considered in comparison to the "crash gearbox" type of manual transmission.
Preselector gearboxes were often marketed as "self-changing" gearboxes, however this is an inaccurate description as the driver is required to choose the gear (and often manually actuate the gear change). An automatic transmission is a true "self-changing gearbox" since it is able to change gears without any driver involvement.
There are several radically different mechanical designs of preselector gearbox. The best known is the Wilson design. Some gearboxes, such as the Cotal, shift gears immediately as the control is moved, without requiring the separate gear change pedal.

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