Heavy-duty truck transmissions can be classified as:

• Conventional

• Semiautomated

• Automated

• Fully automatic

Transmission gears, shafts, bearings, forks, and other internal components must perform for thousands of hours, hundreds of thousands of miles, year after year. It is not unusual for a truck transmission to run for a half million or even a million miles with little maintenance other than checking lubrication levels and observing drain intervals. A majority of heavy-duty trucks are equipped with standard transmissions (see Chapter 15) but the use of computer-controlled, semiautomated, automated, and fully automatic transmissions continues to increase. Depending on engine output, the intended application of the vehicle, and the terrain over which it must operate, the transmission might have from six to twenty forward gears.

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