Safe Driving Practices

Study questions with answers

12 sample Safe Driving Practices questions with the correct answer, a short explanation, and the official handbook reference. Read through them, then take the quiz above.

1. 1. What job does an alcohol evaporator perform in some air brake systems?

   Correct answer: It adds alcohol to cut the chance of ice forming in valves and other parts

   The evaporator introduces alcohol into the air to help prevent ice from forming in brake valves and lines during cold weather.

   Source: Illinois CDL Study Guide — Section 5.1.5: Alcohol Evaporator

2. 2. How do you test the low air pressure warning during the final air brake check?

   Correct answer: With the engine off and power on, fan the pedal to lower pressure and confirm the signal comes on before 60 psi

   With enough pressure that the signal is off, shut the engine, turn the power on, and fan the pedal; the warning must activate before pressure drops under 60 psi.

   Source: Illinois CDL Study Guide — Section 5.3.3: Final Air Brake Check

3. 3. On a system with an alcohol evaporator but no automatic drains, what must still be done each cold-weather day?

   Correct answer: Drain the tanks to remove water and oil

   The evaporator does not remove water and oil, so manual daily tank draining is still required.

   Source: Illinois CDL Study Guide — Section 5.1.5: Alcohol Evaporator

4. 4. When you check the governor, at roughly what pressures should the compressor start and stop pumping?

   Correct answer: Start near 100 psi, stop near 125 psi

   The compressor should cut in around 100 psi and cut out around 125 psi; if it does not, the governor may need repair.

   Source: Illinois CDL Study Guide — Section 5.3.3: Final Air Brake Check

5. 5. Where would you look for the yellow ABS malfunction lamp on a trailer?

   Correct answer: On the trailer's left side, at a front or rear corner

   Tractors, trucks and buses show the lamp on the dash; on trailers the yellow ABS malfunction lamp is on the left side, at a front or rear corner.

   Source: Illinois CDL Study Guide — Section 5.1.16: Antilock Braking Systems

6. 6. When checking a manual S-cam slack adjuster, about how much movement at the push-rod point suggests it needs adjustment?

   Correct answer: More than roughly one inch

   A slack adjuster that moves more than roughly an inch at the push-rod connection probably needs adjusting.

   Source: Illinois CDL Study Guide — Section 5.3.2: Walk-around Inspection

7. 7. In an S-cam brake, turning the S-cam does what to the brake shoes?

   Correct answer: Forces them apart against the inside of the drum

   As the S-cam rotates it pushes the shoes apart so their linings press against the drum; a spring pulls them back when you release the pedal.

   Source: Illinois CDL Study Guide — Section 5.1.8: Foundation Brakes

8. 8. Pressing the brake pedal (the foot or treadle valve) down harder has what effect?

   Correct answer: It sends more air pressure to the brakes

   Pushing the pedal harder increases the air pressure applied; easing off reduces it and releases the brakes.

   Source: Illinois CDL Study Guide — Section 5.1.7: The Brake Pedal

9. 9. On a typical air-brake vehicle, a visible low-air warning must appear before pressure drops below what level?

   Correct answer: About 60 psi

   The required visible warning must activate before tank pressure falls under 60 psi, or half the cut-out pressure on older vehicles.

   Source: Illinois CDL Study Guide — Section 5.1.11: Low Air Pressure Warning

10. 10. Which foundation brake design is found on most vehicles with air brakes?

    Correct answer: The S-cam drum brake

    S-cam drum brakes are by far the most common foundation brakes; wedge and disc types are less common.

    Source: Illinois CDL Study Guide — Section 5.1.8: Foundation Brakes

11. 11. On some pre-1975 trucks, moving the front brake limiting control to the 'slippery' setting does what?

    Correct answer: Cuts the normal front brake air pressure roughly in half

    The 'slippery' setting halves the front brake air pressure; however, front-wheel braking actually helps in all conditions, so keep the control in 'normal'.

    Source: Illinois CDL Study Guide — Section 5.1.13: Front Brake Limiting Valve

12. 12. In a dual air system at operating rpm, air pressure should climb from 85 to 100 psi within about how long?

    Correct answer: About 45 seconds

    In a dual system at operating rpm, expect pressure to climb from 85 to 100 psi in about 45 seconds; larger-than-minimum tanks may take a little longer.

    Source: Illinois CDL Study Guide — Section 5.3.3: Final Air Brake Check