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Shifting gears, automatic transmissions and retarders

General Knowledge4 minManual section 2.3

If you cannot get into the right gear while driving, you have less control. This lesson covers double clutching, when to shift up and down, the two special times to downshift, extra gear systems, automatic transmissions on grades, and retarders.

Double clutching: shifting up (2.3.1)

Most heavy vehicles with unsynchronized manual transmissions need double clutching to change gears. With a synchronized transmission, double clutching is not required.

Basic steps for shifting up:

  • 1. Release the accelerator, push in the clutch and shift to neutral, all at the same time.
  • 2. Release the clutch.
  • 3. Let the engine and gears slow down to the rpm needed for the next gear (this takes practice).
  • 4. Push in the clutch and shift to the higher gear at the same time.
  • 5. Release the clutch and press the accelerator at the same time.

If you stay in neutral too long, the next gear may be hard to get into. Do not force it. Go back to neutral, release the clutch, raise engine speed to match road speed, and try again.

Knowing when to shift up

There are two ways to know when to shift:

  • Engine speed (rpm). Learn your vehicle's operating rpm range from its driver's manual. Watch the tachometer and shift up as the needle reaches the top of that range. Some newer trucks use progressive shifting: the shift rpm gets higher as you move up through the gears.
  • Road speed (mph). Learn which speeds each gear is good for, then use the speedometer.

Over time, with either method, the sound of the engine can also tell you it is time to shift.

Shifting down, and the two special times to downshift

Basic steps for shifting down:

  • 1. Release the accelerator, push in the clutch and shift to neutral at the same time.
  • 2. Release the clutch.
  • 3. Press the accelerator to raise engine and gear speed to the rpm needed in the lower gear.
  • 4. Push in the clutch and shift to the lower gear at the same time.
  • 5. Release the clutch and press the accelerator at the same time.

Notice the difference: shifting up you let the rpm fall; shifting down you raise the rpm with the accelerator. Like upshifting, use the tachometer or speedometer to downshift at the right rpm or road speed.

Special time 1 — before starting down a hill. Slow down and shift down to a speed you can control without hard braking, or the brakes can overheat and lose power. Downshift before the hill starts. Choose a low enough gear — usually lower than the gear you would need to climb the same hill.

Special time 2 — before entering a curve. Slow to a safe speed and downshift before the curve. You can then use a little power through the curve, which makes the vehicle more stable, and you can speed up as soon as you leave the curve.

Extra gears and automatic transmissions (2.3.2–2.3.3)

Multi-speed rear axles and auxiliary transmissions give many vehicles extra gears. You usually control them with a selector knob or switch on the gearshift lever of the main transmission. Shift patterns differ a lot, so learn the right way for the vehicle you drive.

With an automatic transmission, you can select a low range to get more engine braking on downgrades. A low range stops the transmission from shifting up past the selected gear (unless the governor rpm is exceeded). Using this braking effect on downgrades is very important.

Retarders (2.3.4)

A retarder helps slow the vehicle so you use the service brakes less. It reduces brake wear and gives you another way to slow down.

  • There are four basic types: exhaust, engine, hydraulic and electric.
  • The driver can turn every retarder on or off. On some vehicles the retarding power can be adjusted.
  • When on, a retarder applies braking to the drive wheels only, whenever you let up on the accelerator all the way.
  • Retarders can be noisy, so know where their use is allowed.

Caution: when the drive wheels have poor traction, the retarder can make them skid. Turn the retarder off when the road is wet, icy or snow covered. A retarder does NOT prevent skids on slippery roads — it can cause them.

References and scope

The topic reference is listed below. Sources support verification; the lesson itself is here. The current content needs technical and language review before public launch.

Manual reference: 2.3

Official CDL handbook · Utah ↗StatesOur editorial approach

Put it into practice

Educational questions with explanations. The answer review also works without the interactive quiz.

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Review questions with answers

  1. Double clutching is needed on which type of transmission?
    1. Automatic
    2. Unsynchronized manual
    3. Synchronized manual
    4. Every transmission
    Show answer
    Unsynchronized manual

    Most heavy vehicles with unsynchronized manual transmissions require double clutching; synchronized ones do not.

  2. When upshifting with double clutching, after you shift to neutral and release the clutch, you should:
    1. Press the accelerator to raise rpm
    2. Shift straight into the next gear without the clutch
    3. Let the engine and gears slow down to the rpm needed for the next gear
    4. Apply the brakes
    Show answer
    Let the engine and gears slow down to the rpm needed for the next gear

    On an upshift, rpm must fall to match the higher gear.

  3. When downshifting with double clutching, while in neutral with the clutch released, you should:
    1. Press the accelerator to raise engine and gear speed to the lower gear's rpm
    2. Let the rpm drop to idle
    3. Push the brake pedal hard
    4. Turn off the engine
    Show answer
    Press the accelerator to raise engine and gear speed to the lower gear's rpm

    On a downshift, the lower gear needs higher rpm, so you speed up the engine in neutral.

  4. You stayed in neutral too long and cannot get into the next gear. What should you do?
    1. Force the shifter into gear
    2. Coast in neutral down the road
    3. Shift into the highest gear
    4. Return to neutral, release the clutch, match engine speed to road speed, and try again
    Show answer
    Return to neutral, release the clutch, match engine speed to road speed, and try again

    Do not force it; go back to neutral, match rpm to road speed and retry.

  5. A driver can tell when it is time to shift by watching:
    1. Fuel gauge and oil pressure
    2. Engine speed (rpm) and road speed (mph)
    3. Air pressure and engine temperature
    4. Time and distance
    Show answer
    Engine speed (rpm) and road speed (mph)

    Use the tachometer (rpm) or the speedometer (road speed).

  6. In a vehicle with “progressive” shifting:
    1. You never need to use the clutch
    2. The shift rpm stays the same in every gear
    3. You shift only by road speed
    4. The rpm at which you shift gets higher as you move up through the gears
    Show answer
    The rpm at which you shift gets higher as you move up through the gears

    With progressive shifting, the shift point rises as you go up the gears.

  7. Two situations call for downshifting ahead of time. Which are they?
    1. Before starting down a hill and before entering a curve
    2. After a curve and at the bottom of a hill
    3. When passing and when merging
    4. In heavy traffic and at night
    Show answer
    Before starting down a hill and before entering a curve

    Downshift before going down a hill and before entering a curve.

  8. Before going down a steep hill, the right gear is usually:
    1. The highest gear, to save fuel
    2. The same gear you would use on flat road
    3. Lower than the gear needed to climb the same hill
    4. Neutral, to coast
    Show answer
    Lower than the gear needed to climb the same hill

    Choose a gear low enough to control speed without hard braking — usually lower than the climbing gear.

  9. Why should you downshift before entering a curve?
    1. So you can brake harder in the curve
    2. So you can use some power through the curve for stability
    3. So the engine is quieter
    4. So you can coast through the curve
    Show answer
    So you can use some power through the curve for stability

    Being in the right gear lets you use some power in the curve, which helps stability, and speed up after it.

  10. Multi-speed rear axles and auxiliary transmissions are usually controlled by:
    1. A pedal next to the brake
    2. A lever under the seat
    3. The parking brake knob
    4. A selector knob or switch on the main gearshift lever
    Show answer
    A selector knob or switch on the main gearshift lever

    They are usually controlled by a selector knob or switch on the gearshift lever.

  11. With an automatic transmission, why select a low range on a downgrade?
    1. To get greater engine braking
    2. To save fuel
    3. To let the transmission shift up faster
    4. To keep the brakes cool by using them more
    Show answer
    To get greater engine braking

    A low range gives more engine braking and keeps the transmission from upshifting past that gear.

  12. Turning on a retarder helps prevent skids on wet or icy roads.
    1. True
    2. False
    Show answer
    False

    False. On poor traction a retarder can cause the drive wheels to skid; turn it off on wet, icy or snowy roads.

  13. A retarder that is turned on applies braking power to:
    1. All wheels
    2. The steering axle only
    3. The drive wheels only
    4. The trailer wheels only
    Show answer
    The drive wheels only

    Retarders brake the drive wheels only, whenever you fully release the accelerator.

  14. Which is NOT one of the four basic types of retarders?
    1. Pneumatic (air)
    2. Exhaust
    3. Hydraulic
    4. Electric
    Show answer
    Pneumatic (air)

    The four types are exhaust, engine, hydraulic and electric.

  15. When does a retarder that is switched on apply its braking power?
    1. Only when you press the brake pedal
    2. Only below 20 mph
    3. Only when the clutch is pushed in
    4. Whenever you let up on the accelerator all the way
    Show answer
    Whenever you let up on the accelerator all the way

    When on, the retarder works whenever the accelerator is fully released.

  16. Why should you know where retarder use is permitted?
    1. They use a lot of fuel
    2. They can be noisy
    3. They damage the road
    4. They need a special endorsement
    Show answer
    They can be noisy

    Some retarders are noisy, and some places restrict their use.