Automatics and AMTs

      Automatic transmissions are easier to drive than manuals. In certain jobs they also tend to pay for themselves in less maintenance and longer life for the engine and driveline. Fuel economy can be better because while the driver may get tired, the transmission never does and always shifts properly.
      There are several types:
      • Fully-automated, continuous power—A generic description of Allison automatics, which are related in principle to those on cars and light trucks but are much stronger and more complex. Allisons use hydraulic pumps, torque converters, gear packs and mechanical or electronic controls to transmit power. Power is continuous during operation.
      Allison's traditional family—the AT (for light-medium trucks), MT (for medium trucks) and HT (for heavy trucks) is being phased out in favor of the more modern, electronically controlled World series. This includes the 1000, 2000 and 2600 light and medium-duty models, the MD 3000 series, and the HD 4000 series. These use four, five or six speeds. When used, 5th and 6th are overdrive ratios.
      • Automated, interrupted power (also called automated mechanical)—Describes products with mechanical gearboxes that are shifted electro-mechanically. Electronic controls in the tranny and engine work together to select and change gears as conditions dictate. Engine power is interrupted during shifts.
      Automation can be full or partial, as with medium- and heavy duty products from Eaton Fuller, ZF Meritor and TTC. Some need a manual clutch for starting and stopping, and others have automated clutches (so are called "two-pedal" systems because there are only an accelerator and brake pedals).
      The simplest products automate only the top two gears, and help in highway trucks. These cost only a few hundred dollars more than a straight manual. By contrast, a heavy duty Allison might cost $12,000 to $15,000, and an automated mechanical transmission, or AMT, within a thousand or two of that.