Shifting Gears in a Semi Truck

Shifting gears smoothly in a semi requires practice.

Most semi-trailers are equipped with multispeed manual transmissions. The selection of stock transmissions includes 10, 13 and 18 speeds. Driver preference and the type of hauling the truck is used for usually determines the type of transmission installed in the truck. The reason for the higher number of gears is the narrow efficient operating speed of a diesel engine. A diesel produces maximum torque at about 1,000 rpm and looses efficiency at around 1,500 rpm. Shifting gears keeps a driver busy while getting up to highway speed and slowing down again.

Things You'll Need

• Semi-trailer with a manual transmission
• Commercial driver's license, or learner's permit and a licensed driver

Instructions

1. Start the engine and allow the air pressure to build up to operating levels before releasing the parking brakes. Warning buzzers in the cab tell you when you have low pressure. The air gauges on the dashboard indicate the amount of pressure in the system.

2. Depress the brake with your right foot and release the parking brakes by depressing the knobs on the dashboard.

3. Depress the clutch all the way to the floorboard. This will engage the clutch brake and stop the transmission, allowing you to shift into first gear without grinding gears.

4. Place the gear-shifting lever into first. Slowly release the clutch. Increase your speed slowly until the tachometer reaches 1,500 rpm.

5. Depress the clutch pedal halfway to the floorboard and pull the shifting lever out of gear. Release the clutch pedal.

6. Depress the clutch pedal halfway to the floor again and place the shifting lever in second. Release the clutch pedal. Pressing and releasing the clutch twice during the shifting operation is known as double-clutching and is necessary due to the fact that large-truck transmissions do not have synchronized gearing like what you find in cars or pickups.

7. Continue accelerating and shifting in the same manner each time the tachometer reaches 1,500 rpm. When you reach fourth gear, lift the range-selector switch on the front of the shifting lever. This will put the transmission in high range, and the shifting pattern will be repeated. With the selection lever in high range, the position for first gear becomes fifth, second is sixth and so on.

8. Reduce speed and gears by slowing the truck until the tachometer reaches 1,000 rpm. Depress the clutch halfway to the floorboard, depress the accelerator pedal to raise the rpm to 1,500, depress the clutch halfway again and move the shifting lever to the next lower gear. When you reach fifth gear, move the range-selection switch to the low range by pressing it down before shifting to fourth gear.

Tips & Warnings

• These instructions are for a 10-speed transmission. Shifting patterns will differ with transmission manufacturers and the number of gears available. The shifting pattern for your transmission will be located on the dashboard or on top of the shifting lever's knob.

• Shifting smoothly and consistently requires many hours of practice.

• Always have an experienced driver in the cab while you learn how to operate a semi-trailer.

References

• Expedite Now: Transmissions 101
• Public Works Online: Shifting Gears
• Heavy Duty Trucking: Progressive Shifting
• You Tube: How to Drive a Big Rig