When I learned to drive trucks in the 1980s, the school spent the first third of the program in the yard, teaching how to shift gears. Unlike automobile transmissions, trucks' standard transmissions must be double-clutched since they don't automatically match gear and vehicle speeds.
That's easy enough to do, until you get on a hill. Then vehicle speeds change more quickly, requiring faster reaction time. Get it right, and you keep control. Get it wrong and you could find yourself in neutral, unable to get back in a gear.
That could be the start of a runaway truck situation or a crash.
Accurate shifting isn't the only skill experienced drivers develop. Skilled drivers also learn when and how to work the clutch and throttle to creep forward in snarled traffic or back up gently to load or creep down into a pit. For drivers who earn their livelihood with snowplows, dump trucks, concrete mixers, and heavy haul rigs, coordinating three pedals with only two feet is demanding.
This century, however, is ushering in fully automated manual transmissions for trucks that promise to be more forgiving to inexperienced drivers and less exhausting for all drivers — by providing creep and hill control along with clutch-free shifting, at least as far as the driver is concerned.
THE TRANSMISSION EVOLUTION
Shortly after World War II, Allison Transmission Inc. adapted parent company General Motors' Hydramatic fully automatic transmissions for commercial truck duty. They were heavier and far more expensive than the manual transmissions they were designed to replace, and slippage in the torque converters affected fuel economy.
The problems have been minimized over the years with lock-up mechanisms, better engineering, and lighter weight materials. But Allison automatic transmissions still cost thousands more than standard transmissions.
During the 1990s, Eaton Corp. introduced computer control to standard truck transmissions to reduce driver fatigue. Research showed that long-haul drivers made more than 90% of their shifts between the top two gears, so the company applied automation to those gears and called the new transmission “Top-2.” It cut fatigue to help keep long-haul drivers alert, but was no help in city driving or stop-and-go operations.
To remedy this, Eaton introduced the AutoShift, which uses the computer to shift all gears. Meritor countered with the ZF-based Freedom Line that shifts a full synchromesh transmission by computer.
Although not recommended by transmission makers, many experienced drivers “float” the gears — shifting without using the clutch. This method is easier on a driver's left leg, especially with a stiff clutch. Drivers lift the throttle to reduce torque and then nudge the shift lever into neutral. They then adjust engine rpm to match vehicle speed in the next gear, and, at the instant when everything aligns, they nudge the lever into the next gear. Pros get it right ... almost all the time. When they don't, the gears grind and they go back to the clutch.