Parking & Stopping

Study questions with answers

9 sample Parking & Stopping questions with the correct answer, a short explanation, and the official handbook reference. Read through them, then take the quiz above.

1. 1. When you pull on an s-cam slack adjuster by hand, about how much movement suggests it needs adjustment?

   Correct answer: More than roughly one inch where the push rod attaches

   If a slack adjuster shifts more than about an inch at the push-rod connection, it likely needs adjustment; poorly adjusted brakes are the fault inspectors most often write up at the roadside.

   Source: Missouri Commercial Driver License Manual, Section 5 (Air Brakes) - 5.3.2 Walk-around Inspection

2. 2. How do you check that the parking brake will hold?

   Correct answer: Set the parking brake and gently try to pull forward in a low gear

   With the vehicle stopped, set the parking brake and, in a low gear, tug lightly forward to confirm it holds the rig.

   Source: Missouri Commercial Driver License Manual, Section 5 (Air Brakes) - 5.3.3 Final Air Brake Check

3. 3. How large a crack in a brake drum is unacceptable during inspection?

   Correct answer: A crack running more than half the width of the friction area

   A drum crack that extends beyond half of the friction surface's width is unacceptable; linings must also stay secure, free of oil or grease, and not worn too thin.

   Source: Missouri Commercial Driver License Manual, Section 5 (Air Brakes) - 5.3.2 Walk-around Inspection

4. 4. How often must you empty air tanks fitted with manually operated drain valves?

   Correct answer: At the end of each day you drive

   Tanks with manual drains have to be emptied yourself at the close of every driving day.

   Source: Missouri Commercial Driver License Manual, Section 5 (Air Brakes) - 5.1.4 Air Tank Drains

5. 5. When should you skip setting the parking brakes and use wheel chocks instead?

   Correct answer: When the brakes are very hot from a grade or very wet in freezing weather

   Very hot brakes can be damaged and very wet brakes can freeze, so in those cases hold the vehicle with chocks and let the brakes cool or dry first.

   Source: Missouri Commercial Driver License Manual, Section 5 (Air Brakes) - 5.4.8 Parking Brakes

6. 6. On newer vehicles, how do you set the parking (spring) brakes?

   Correct answer: Pull the yellow, diamond-shaped knob outward

   Newer air brake vehicles use a yellow, diamond-shaped push-pull control; pulling it out sets the parking brakes and pushing it in releases them.

   Source: Missouri Commercial Driver License Manual, Section 5 (Air Brakes) - 5.1.15 Parking Brake Controls

7. 7. If a system includes an alcohol evaporator, can you skip draining the tanks?

   Correct answer: No, daily draining is still needed to clear out water and oil

   Even with an alcohol evaporator you still must empty the tanks each day to remove moisture and oil, except on systems fitted with automatic drain valves.

   Source: Missouri Commercial Driver License Manual, Section 5 (Air Brakes) - 5.1.5 Alcohol Evaporator

8. 8. Why should you avoid pressing the foot brake while the spring brakes are already applied?

   Correct answer: The combined force of the springs and air pressure could damage the brakes

   Adding air pressure on top of the spring force can damage the brakes, so it is best never to press the pedal while the spring brakes are set.

   Source: Missouri Commercial Driver License Manual, Section 5 (Air Brakes) - 5.1.15 Parking Brake Controls

9. 9. Why is draining the air tanks important?

   Correct answer: Water and oil collect inside and, if frozen, can cause the brakes to fail

   Compressed air carries water and oil that gather at the bottom of the tank; in cold weather the water can freeze and lead to brake failure, so the tanks must be drained.

   Source: Missouri Commercial Driver License Manual, Section 5 (Air Brakes) - 5.1.4 Air Tank Drains