Which air-brake system does the foot pedal normally operate when you slow for traffic?
Correct answer: The service brake system
The service brakes provide normal braking through the foot pedal. Parking and emergency functions have different roles.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1, physical PDF 79, printed 5-1. ↗
Tank pressure falls to the compressor's specified cut-in point. What should the governor allow next?
Correct answer: The compressor to resume pumping air
The governor starts air pumping at cut-in and stops it at cut-out. Use the pressure specifications for the vehicle rather than assuming every system has identical settings.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.2, physical PDF 79, printed 5-1. ↗
Water has collected in a brake air tank before freezing weather. What is the main brake-system risk?
Correct answer: It can freeze and interfere with brake operation
Compressed air can carry water that collects in tanks. Frozen moisture can make brake components fail, which is why tank drainage matters.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.4, physical PDF 79, printed 5-1. ↗
A truck has an alcohol evaporator and manual air-tank drains. Does the evaporator eliminate the need for daily draining?
Correct answer: No; water and oil still need to be drained
An alcohol evaporator helps reduce freezing in the air system. It does not remove the daily drainage requirement for manually drained tanks.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.5, physical PDF 80, printed 5-2. ↗
Why should a driver avoid repeatedly pressing and releasing the air-brake pedal when it is unnecessary?
Correct answer: It can use stored air faster than it is replaced
Releasing the brakes exhausts air. Unnecessary repeated applications can deplete the supply faster than the compressor restores it.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.7, physical PDF 80, printed 5-2. ↗
You want to check the air available in the reservoirs, not the force of your current brake application. Which gauge provides that information?
Correct answer: The supply pressure gauge
Supply gauges show stored air pressure. A dual system has indications for both sides, sometimes through two needles in one gauge.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.9, physical PDF 80, printed 5-2. ↗
On the same descent, progressively more application pressure is needed to hold the same speed. What may this indicate?
Correct answer: The brakes are fading or have another defect
Needing more application pressure can indicate fading, poor adjustment, leaks or a mechanical problem. Address the developing braking problem rather than relying on ever-harder applications.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.10, physical PDF 81, printed 5-3. ↗
A truck has the usual yellow, diamond-shaped push-pull parking-brake knob. How is that control used to apply the parking brakes?
Correct answer: Pull the knob out
On this common control, pulling out applies the parking brakes and pushing in releases them. Older or different equipment can have other controls.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.15, physical PDF 81, printed 5-3. ↗
A vehicle has a spring-loaded modulating control for its spring brakes. What does this control allow?
Correct answer: Gradual application of the spring brakes
A modulating valve permits progressively stronger spring-brake application rather than only an on/off action. Its parking position must be secured as designed.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.15, physical PDF 81, printed 5-3. ↗
What is the key arrangement in a dual air-brake system?
Correct answer: Two separate air systems operated by one set of controls
Dual systems have separate tanks, hoses and lines, while the driver uses a common set of controls. Their separation limits the effect of one circuit losing pressure.
Source: Washington Commercial Driver Guide, N/10/20; section 5.2, physical PDF 83, printed 5-5. ↗
While driving a dual-air truck, the low-air warning activates for one circuit but the other gauge still looks normal. What should you do?
Correct answer: Stop safely and have the air-brake fault repaired
A very low circuit can leave some brakes operating inadequately and lengthen stopping distance. The remaining system is not a reason to continue the trip.
Source: Washington Commercial Driver Guide, N/10/20; section 5.2, physical PDF 83, printed 5-5. ↗
A driver says automatic slack adjusters mean brake adjustment never needs checking. Is that correct?
Correct answer: No; automatic adjusters must still be checked
Automatic adjustment does not eliminate inspection. Excessive stroke can indicate an adjuster, installation or foundation-brake problem.
Source: Washington Commercial Driver Guide, N/10/20; section 5.3.2, physical PDF 84, printed 5-6. ↗
Before releasing parking brakes for a hands-on S-cam slack-adjuster check, how should the vehicle be secured?
Correct answer: Park on level ground and chock the wheels
Releasing parking brakes can let a vehicle move. The guide specifies level ground and wheel chocks before this inspection; follow safe equipment procedures.
Source: Washington Commercial Driver Guide, N/10/20; section 5.3.2, physical PDF 84, printed 5-6. ↗
Accessible brake linings are coated with oil. Why is this unsafe?
Correct answer: The contamination can reduce braking friction
Oil and grease on braking surfaces can reduce their effectiveness and create a fire hazard. Contamination belongs in the inspection, not on the friction surfaces.
Source: Washington Commercial Driver Guide Supplement, September 9, 2022; 11M.5.2, physical PDF 10, printed 11M-7. ↗
During the updated applied-air leakage test, when does the one-minute observation begin?
Correct answer: After full foot-brake application and gauge stabilization
With the vehicle secured and the test set up correctly, fully apply the foot brake and let the gauge stabilize before timing the hold. The initial application drop is not the timed leakage reading.
Source: Washington Commercial Driver Guide Supplement, September 9, 2022; 11M.1.2, item 2, physical PDF 6, printed 11M-3. ↗
A tractor and air-braked trailer lose 5 psi in one minute during a correctly set-up, stabilized applied-air test. How does that compare with the stated limit?
Correct answer: It exceeds the 4 psi combination-vehicle limit
The updated test uses 4 psi in one minute for a combination vehicle. A 5 psi timed loss is too much; it is not acceptable merely because a trailer is attached.
Source: Washington Commercial Driver Guide Supplement, September 9, 2022; 11M.1.2, item 2, physical PDF 6, printed 11M-3. ↗
When testing the low-air warning after the engine is shut off, how should electrical power be set?
Correct answer: Keep the key or electrical power in the on position
The warning devices need electrical power for the test. The supplement calls for engine off, electrical power on, then applying and releasing the foot brake to lower pressure.
Source: Washington Commercial Driver Guide Supplement, September 9, 2022; 11M.1.2, item 3, physical PDF 6, printed 11M-3. ↗
For a test vehicle whose parking-brake valve is designed to pop out, what range does the updated supplement give for that emergency-brake check?
Correct answer: 20 to 45 psi, with the vehicle's specified level identified
The supplement gives a 20-45 psi pop-out range and also requires the manufacturer's level and procedure. Vehicles with other valve designs or backup systems need their specified checks.
Source: Washington Commercial Driver Guide Supplement, September 9, 2022; 11M.1.2, item 4, physical PDF 6, printed 11M-3. ↗
Your inspection-test vehicle has a backup air system that prevents the expected valve pop-out. What must you explain?
Correct answer: That the backup system is present and how its specified check works
The supplement specifically addresses backup systems and requires the applicant to explain why valves will not pop out and the appropriate manufacturer-specific procedure.
Source: Washington Commercial Driver Guide Supplement, September 9, 2022; 11M.1.2, item 4, physical PDF 6, printed 11M-3. ↗
Air pressure fails to build at the rate required for your truck's system. What should happen before driving?
Correct answer: Have the problem fixed so the system can build pressure properly
An inadequate buildup rate can let pressure become too low in service and force an emergency stop. The guide says not to drive until the problem is corrected.
Source: Washington Commercial Driver Guide, N/10/20; section 5.3.3, physical PDF 85, printed 5-7. ↗
For the separate trailer parking-brake check on a combination, which setup isolates the trailer's holding ability?
Correct answer: Tractor parking brake released and trailer parking brake applied
The trailer check releases the tractor parking brake, engages the trailer parking brake, removes the service-brake application and uses a gentle forward pull. Follow the complete safe inspection procedure.
Source: Washington Commercial Driver Guide Supplement, September 9, 2022; 11M.1.1, Parking and Trailer Brake Check, physical PDF 5, printed 11M-2. ↗
Compared with hydraulic brakes, which extra delay must be included when accounting for an air-braked vehicle's stopping distance?
Correct answer: The delay while air travels through the system to apply the brakes
Air-brake lag follows pedal application and precedes braking action. Total stopping distance includes perception, reaction, brake-lag and braking distances; it is not one fixed number for all trucks.
Source: Washington Commercial Driver Guide, N/10/20; section 5.4.4, physical PDF 86, printed 5-8. ↗
Why can one out-of-adjustment brake make other brakes overheat?
Correct answer: The other brakes must do more than their share of the work
Every brake needs to contribute its share. Poor adjustment reduces one brake's contribution, increasing heat and fade risk at the remaining brakes.
Source: Washington Commercial Driver Guide, N/10/20; section 5.4.5, physical PDF 87, printed 5-9. ↗
Why is waiting for automatic spring-brake application especially unsafe in a heavily loaded vehicle?
Correct answer: Spring brakes do not act on every axle, so stopping can take a long distance
The guide warns that spring brakes do not operate on all axles and a heavily loaded vehicle can take a long distance to stop. Stop safely on the service brakes before air becomes critically low.
Source: Washington Commercial Driver Guide, N/10/20; section 5.4.7, physical PDF 87, printed 5-9. ↗
Brakes are very wet and the temperature is freezing. What problem can applying the parking brakes cause?
Correct answer: They can freeze in the applied position
Wet applied brakes can freeze so the vehicle cannot move. The guide calls for securing the vehicle with wheel chocks on level ground and using the specified drying procedure, not leaving it unsecured.
Source: Washington Commercial Driver Guide, N/10/20; section 5.4.8, physical PDF 87, printed 5-9. ↗
