Why do most 18-wheelers have manual transmissions instead of automatic transmissions?
The reason semis have manual transmissions, is that they were more reliable and longer lasting than an automatic, which uses a lot of consumable parts that wear down easily and need to be replaced more often. This is purely a factor of maintenance cost, however, current technology has improved and automatics are now being used more widely for two reasons; the maintenance costs have declined and to encourage newer drivers the ease of learning to drive an 18-wheeler without having to learn the subtleties of shifting and double-clutching through 8-15 gears. The reason a manual on a semi requires double-clutching is also due to maintenance costs. They have no synchronizer gears, which are made from a malleable/soft material that easily wears out. To alleviate this, they are removed, which means the driver must manually synchronize engine and drivetrain speed by clutching once to change gears to nuetral and a second time to change to the next gear.
