7CDLFree CDL permit study for every state
Content preview, before public launch
Course › General Knowledge

Mountain driving and brake fade

General Knowledge4 minManual section 2.16

On hills, gravity controls a lot. Going up, gravity slows you down. Going down, gravity makes you go faster. A steeper grade, a longer grade or a heavier load all mean you need lower gears. Plan ahead: learn about long, steep grades on your route, and ask drivers who know them what speeds are safe.

Why brakes fade

You must go slowly enough that your brakes can hold you back without getting too hot. Hot brakes start to fade: you must press harder and harder to get the same stopping power. If you keep braking hard, they can fade until you cannot slow down or stop at all.

Brakes work by shoes or pads rubbing against drums or disks. This makes heat. Brakes are built to take a lot of heat, but they can fade or fail from too much heat when you use them too much instead of using engine braking.

Brake adjustment also affects fade. Every brake must do its share. Brakes out of adjustment stop working before the others. Then the good brakes overheat and fade, and you do not have enough braking left. Brakes can go out of adjustment quickly, especially with heavy use, and linings wear faster when hot. So check adjustment often.

Choose a safe speed

Your most important job is to pick a speed that is not too fast for:

  • The total weight of the vehicle and cargo.
  • The length of the grade.
  • The steepness of the grade.
  • Road conditions.
  • Weather.

If a speed limit or a Maximum Safe Speed sign is posted, never go faster than it shows. Also watch for and obey signs that give the length and steepness of the grade.

Use the braking effect of the engine as the main way to control speed. Engine braking is strongest when the engine is near governed rpm and the transmission is in a lower gear. Save your service brakes so you can slow or stop when road and traffic need it.

Pick the right gear before going down

Shift to a low gear before you start down the grade. Once you have picked up speed, it is too late to downshift. You will not be able to get into a lower gear, and you may not get into any gear — then you lose all engine braking.

Forcing an automatic transmission into a lower gear at high speed can damage it and also cause loss of all engine braking.

Old rule: older trucks were driven down a hill in the same gear they needed to climb it.

Modern trucks have low-friction parts, streamlined shapes and often stronger engines. They can climb in higher gears, and on the way down there is less friction and wind resistance to slow them. So drivers of modern trucks may need a lower gear going down than going up. Know what is right for your truck.

Proper braking on a downgrade

On a long or steep downgrade, the service brakes only supplement (add to) engine braking. Once you are in the right low gear, use snub braking:

  • Step 1: Apply the brakes just hard enough to feel a definite slowdown.
  • Step 2: When your speed is about 5 mph below your safe speed, release the brakes. This application should last about 3 seconds.
  • Step 3: When your speed rises back to your safe speed, repeat steps 1 and 2.

Example: your safe speed is 40 mph. Do not brake until you reach 40 mph. Then brake firmly enough to slow gradually to 35 mph, and release. Repeat as often as needed to the bottom of the grade.

Why: light, steady braking all the way down heats the brakes the whole time. Short firm applications give the brakes time to cool between uses.

Escape ramps

Many steep mountain downgrades have escape ramps. They stop runaway vehicles safely without hurting drivers or passengers. They use a long bed of loose, soft material (like gravel) to slow the vehicle, sometimes together with an upgrade.

Know where escape ramps are on your route. Signs show where they are. Escape ramps save lives, equipment and cargo.

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: 2.16

Official CDL handbook · Utah ↗StatesOur editorial approach

Put it into practice

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

Preparing your questions…

Review questions with answers

  1. When driving down a long, steep grade, the main way to control your speed should be:
    1. The service brakes
    2. The parking brake
    3. The braking effect of the engine
    4. Shifting to neutral
    Show answer
    The braking effect of the engine

    Engine braking is the principal way to control speed on a downgrade. Save the service brakes for when you must slow or stop.

  2. Brake fade means:
    1. You must press the brakes harder and harder to get the same stopping power
    2. The brakes lock up on ice
    3. The brake lights stop working
    4. The air pressure is too high
    Show answer
    You must press the brakes harder and harder to get the same stopping power

    Overheated brakes fade: they need more and more pedal pressure, and can fade until you cannot stop at all.

  3. Which is NOT one of the factors the manual lists for choosing a safe downhill speed?
    1. Total weight of vehicle and cargo
    2. Length of the grade
    3. Weather
    4. The color of the trailer
    Show answer
    The color of the trailer

    Safe speed depends on total weight, length and steepness of the grade, road conditions and weather.

  4. Engine braking is strongest when:
    1. The engine is idling in high gear
    2. The engine is near governed rpm and the transmission is in a low gear
    3. The clutch is pushed in
    4. The truck is in neutral
    Show answer
    The engine is near governed rpm and the transmission is in a low gear

    The braking effect of the engine is greatest near governed rpm in the lower gears.

  5. A sign shows "Maximum Safe Speed 35." Your truck is light and the road is dry. You should:
    1. Go up to 45 since you are light
    2. Go 5 mph over the sign
    3. Never go faster than 35
    4. Ignore it; it is for cars
    Show answer
    Never go faster than 35

    Never exceed a posted speed limit or Maximum Safe Speed sign.

  6. When should you shift into a low gear for a long downgrade?
    1. Before you start down the grade
    2. Halfway down
    3. When the brakes start to smell
    4. At the bottom
    Show answer
    Before you start down the grade

    Get into low gear before starting down. Once speed builds you may not be able to downshift at all.

  7. What can happen if you try to downshift after speed has built up on a downgrade?
    1. The engine will brake harder
    2. The ABS will take over
    3. The trailer brakes will apply
    4. You may not get into any gear and lose all engine braking
    Show answer
    You may not get into any gear and lose all engine braking

    You may be unable to shift down, or even get back into any gear, losing all engine braking.

  8. Compared with older trucks, drivers of modern trucks may need to go down a hill in:
    1. A higher gear than they used to climb it
    2. A lower gear than they used to climb it
    3. Neutral
    4. The same gear always
    Show answer
    A lower gear than they used to climb it

    Modern trucks have less friction and air drag and stronger engines, so a lower gear may be needed going down than going up.

  9. Forcing an automatic transmission into a lower gear at high speed can:
    1. Increase engine braking safely
    2. Cool the brakes
    3. Damage the transmission and cause loss of engine braking
    4. Turn on the ABS lamp
    Show answer
    Damage the transmission and cause loss of engine braking

    It can damage the transmission and lead to the loss of all engine braking.

  10. Brakes that are out of adjustment can cause fade because:
    1. They stop doing their share, so the other brakes overheat
    2. They grip harder than the others
    3. They make the ABS turn off
    4. They use more air
    Show answer
    They stop doing their share, so the other brakes overheat

    Out-of-adjustment brakes quit working first. The remaining brakes overheat and fade, leaving too little braking.

  11. Why must brake adjustment be checked often?
    1. Adjustment never changes, but inspectors ask
    2. Cold linings wear faster
    3. Only to pass the pre-trip test
    4. Brakes go out of adjustment quickly with heavy use, and hot linings wear faster
    Show answer
    Brakes go out of adjustment quickly with heavy use, and hot linings wear faster

    Brakes can lose adjustment quickly, especially when used a lot, and linings wear faster when hot.

  12. Your safe speed on a downgrade is 50 mph. Using the proper braking technique, you apply the brakes when you reach 50 mph and release them at about:
    1. 40 mph
    2. 45 mph
    3. 48 mph
    4. 30 mph
    Show answer
    45 mph

    Brake to about 5 mph below your safe speed, then release. Here that is about 45 mph.

  13. With the proper downhill braking technique, each brake application should last about:
    1. 1 second
    2. 10 seconds
    3. 3 seconds
    4. Until the bottom of the hill
    Show answer
    3 seconds

    Each firm application, from safe speed down about 5 mph, should last about 3 seconds.

  14. On a long downgrade, the service brakes should be used:
    1. Only as a supplement to engine braking
    2. As the main way to control speed
    3. Lightly and continuously all the way down
    4. Only after the truck passes the safe speed by 10 mph
    Show answer
    Only as a supplement to engine braking

    Brakes only supplement the engine's braking effect. Use firm, short applications once you are in the right low gear.

  15. Escape ramps stop runaway vehicles mainly by using:
    1. Steel cables across the road
    2. Water barriers
    3. A row of concrete posts
    4. A long bed of loose, soft material, sometimes with an upgrade
    Show answer
    A long bed of loose, soft material, sometimes with an upgrade

    Escape ramps use a long bed of loose, soft material such as gravel, sometimes combined with an uphill slope.

  16. Before driving a route with long, steep grades, a good driver should:
    1. Fill the fuel tanks to the top
    2. Get information about the grades and ask drivers who know them about safe speeds
    3. Lower the tire pressure
    4. Plan to use neutral on the downgrades
    Show answer
    Get information about the grades and ask drivers who know them about safe speeds

    Plan ahead: learn about steep grades on the route and talk to drivers familiar with them.

  17. On an upgrade, a heavier load or a steeper and longer hill means you will:
    1. Climb in higher gears
    2. Need less fuel
    3. Have to use lower gears
    4. Have to use the retarder
    Show answer
    Have to use lower gears

    The steeper or longer the grade, or the heavier the load, the more you must use lower gears to climb.