Drive one (first gear)- paul-ryan.info
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The forward-drive clutch is engaged and the engine turns the first ring gear.

This causes the planet gears to drive the common sun gear in the opposite direction.

The second planet carrier is held by a brake band, so the planets drive the second ring gear and output shaft thus producing two reductions in the speed of the engine.

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How automatic gearboxes work

Most modern automatic gearboxes have a set of gears called a planetary or epicyclic gear train. ...