A transmission is a mechanical device which uses a gear set—two or more gears working together—to change the speed, direction of rotation, or torque multiplication or reduction, in a machine.
Transmission internals for a 2009 Volkswagen Golf
Transmission for a Bristol Sycamore helicopter
16-speed tractor transmission (plus 8 reverse gears)
Mazda M5OD manual transmission (viewed from the engine side)
Automatic transmission
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An automatic transmission or automatic gearbox is a multi-speed transmission used in motor vehicles that does not require any input from the driver other than throttle position to change forward gears
Transmission (mechanical device)
…by the driver through a lever (the gear stick) that displaced gears and gear groups along their axes. Starting in 1939, cars using various types of automatic transmission became available in the US market. These vehicles used the engine's own power to change the effective gear ratio depending on the load so as to keep…
Cutaway view of a 2007 Toyota AA80E hydraulic automatic
Gear selector of a 1992 Ford Escort with automatic transmission
Cutaway view of a ZF 8HP transmission: torque converter on the left, planetary gearsets in the centre, control mechanisms at the bottom
Torque converter – cutaway view