TransmissionAlthough the engine develops a substantial amount of power, it does so best at relatively high revolutions per minute (rpm). To handle all driving conditions, it is necessary to use gearing to change the ratio of engine rpm to vehicle speed. A manual transmission is simply a mechanism which contains several sets of gears in a compact assembly, each suited to a particular range of driving speeds, and a mechanism to allow the driver to change from one gear ratio to the next on the move as vehicle speed requirements change. For information on manual transmission maintenance and adjustments, see MANUAL TRANSMISSION AND CLUTCH. An automatic transmission has the same purpose, but uses hydraulic fluid under pressure in a complex network of passages, valves, and hydraulically operated control mechanisms to engage and disengage constantly meshed planetary gear sets. Hydraulic controls select the appropriate gear based on vehicle speed, engine load, throttle position, and gear shift position. For information on automatic transmission maintenance and adjustments, see AUTOMATIC TRANSMISSION. |
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