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. ↗
What supplies compressed air to the brake reservoirs while the engine is running?
Correct answer: The air compressor
The engine-driven compressor supplies air to the storage tanks. The other parts do not replenish the air supply.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.1, 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. ↗
Why can properly charged air brakes still make several applications after the compressor stops?
Correct answer: The reservoirs hold a reserve of compressed air
Air already stored in the reservoirs permits a limited number of brake uses. It is a reserve, not permission to keep driving with a failed compressor.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.3, 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. ↗
Your truck has manually operated air-tank drains, not automatic drains. When does the guide tell you to drain the tanks?
Correct answer: At the end of each day of driving
Manual drains must be operated at the end of each driving day to remove collected water and oil. Follow the equipment's safe draining procedure.
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. ↗
The brake-system safety relief valve begins releasing air. How should you treat this?
Correct answer: As a fault that needs a mechanic's attention
The relief valve protects the system against excessive pressure. Air release from it indicates a problem; do not block this safety device.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.6, 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. ↗
In an S-cam drum brake, what does the turning cam make the brake shoes do?
Correct answer: Move outward against the inside of the drum
The S-shaped cam spreads the shoes against the drum's inner surface. Friction at that contact slows the wheel.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.8, 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 a truck equipped with an application pressure gauge, what does its reading describe?
Correct answer: Air pressure being applied to the brakes
An application gauge shows the pressure used for a brake application. It is different from a supply gauge that indicates reservoir pressure.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.10, 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. ↗
What normally holds a truck's spring brakes released while it is being driven?
Correct answer: Air pressure opposing the powerful springs
Air holds the spring mechanism back during normal driving. Removing that air allows the springs to apply the brakes.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.14, 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. ↗
Why does the guide warn against pressing the foot brake with the spring brakes already applied?
Correct answer: Combined spring and air forces can damage the brakes
Not every system prevents the forces from compounding, and protective features can fail. Avoid the habit of applying the foot brake against already-applied spring brakes.
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. ↗
A bus has a separate air reserve for briefly releasing applied spring brakes in an emergency. Why must any movement be planned carefully?
Correct answer: The reserve permits only a limited number of releases
The separate tank is a limited emergency resource. Repeated releases can exhaust it and leave the vehicle stopped in an unsafe location.
Source: Washington Commercial Driver Guide, N/10/20; section 5.1.15, physical PDF 82, printed 5-4. ↗
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. ↗
Before driving a dual-air-system vehicle, one gauge is above 100 psi and the other is still at 75 psi. What does the guide's minimum-pressure check require?
Correct answer: Wait for both systems to build to at least 100 psi
The guide calls for at least 100 psi in both the primary and secondary systems before driving. A healthy reading on one side does not establish adequate pressure on the other.
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. ↗
The air compressor is belt-driven. Which belt condition belongs in the engine-compartment inspection?
Correct answer: Its physical condition and proper tightness
A belt-driven compressor needs a sound, properly tensioned belt. Damage or poor tension can prevent reliable air supply.
Source: Washington Commercial Driver Guide, N/10/20; section 5.3.1, physical PDF 84, printed 5-6. ↗
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. ↗
An automatic slack adjuster repeatedly goes out of adjustment. Which response addresses the underlying problem?
Correct answer: Have the cause diagnosed and repaired by qualified personnel
Repeated manual adjustment can mask a mechanical problem without fixing it. The guide warns against relying on it as a routine repair and calls for proper diagnosis.
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. ↗
An air-brake hose is frayed where it rubs against a bracket. How should the condition be judged during inspection?
Correct answer: It is damage that must be addressed, not normal wear to ignore
The updated inspection supplement calls for checking cracked, worn or frayed lines, leaks, and secure fittings. Do not wait for a damaged hose to fail.
Source: Washington Commercial Driver Guide Supplement, September 9, 2022; 11M.5.2, physical PDF 10, printed 11M-7. ↗
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. ↗
For the updated Washington air-brake inspection test, which cutoff pressure should you identify?
Correct answer: The specified cutoff for the vehicle being tested
The supplement gives an approximate 120-140 psi range while requiring identification of the vehicle's cutoff and manufacturer specifications. A generic number alone is not enough.
Source: Washington Commercial Driver Guide Supplement, September 9, 2022; 11M.1.2, item 1, physical PDF 6, printed 11M-3. ↗
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. ↗
In a correctly set-up applied-air test on a single truck, pressure falls 4 psi during the minute after stabilization. What does that show?
Correct answer: The loss exceeds the supplement's 3 psi single-vehicle limit
The updated test checks for loss greater than 3 psi in one minute on a single vehicle. A 4 psi timed loss is excessive and needs correction before driving.
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. ↗
During the timed applied-air leakage check, what should you do with the foot brake?
Correct answer: Keep it fully applied for the one-minute check
The applied leakage test holds the foot brake after the gauge stabilizes. Repeated applications consume air and are used for a different part of the inspection.
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. ↗
Which low-air warning instruction appears in Washington's September 2022 skills supplement?
Correct answer: Activation before pressure falls below 55 psi, or at the manufacturer's specified level
The updated skills supplement states before below 55 psi or the manufacturer's specified level and makes the applicant responsible for knowing that specification. Main-guide section 5 uses 60 psi; do not treat these differently scoped instructions as one universal legal setting.
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. ↗
The manufacturer's design says a test vehicle's valves do not pop out during the emergency-brake check. What evidence does the supplement tell you to identify instead?
Correct answer: The sound of air discharging as the parking or emergency brakes apply
For a design without pop-out valves, the supplement says to listen for the discharge indicating brake application and explain the manufacturer's procedure. Valve movement is not universal.
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. ↗
For a dual system with standard minimum-size tanks, what buildup benchmark does the guide give at operating engine speed?
Correct answer: From 85 to 100 psi within 45 seconds
The guide uses 85-100 psi within 45 seconds for this dual-system check. Larger-than-minimum reservoirs can need longer; consult the manufacturer's specifications for that equipment.
Source: Washington Commercial Driver Guide, N/10/20; section 5.3.3, physical PDF 85, printed 5-7. ↗
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. ↗
During the separate tractor parking-brake check, which condition lets you check that brake without the trailer parking brakes masking a fault?
Correct answer: Tractor parking brake applied, trailer brakes released, then gently pull forward
The supplement separates the tractor and trailer holding checks. With the tractor parking brake applied and trailer brakes released, remove the foot from the service brake and gently test its hold in a safe test area.
Source: Washington Commercial Driver Guide Supplement, September 9, 2022; 11M.1.1, Parking and Trailer Brake Check, physical PDF 5, printed 11M-2. ↗
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. ↗
In the supplement's low-speed service-brake check, the vehicle pulls sharply left when stopping from about 5 mph. What does that suggest?
Correct answer: The brakes may not be operating correctly
The check looks for a proper stop without pulling to either side. A pull or poor stopping response is evidence of a possible brake problem.
Source: Washington Commercial Driver Guide Supplement, September 9, 2022; 11M.1.1, Service 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. ↗
How can excessive drum heating contribute to brake fade?
Correct answer: Expansion makes the shoes travel farther and reduces effective contact force
Overheating can expand drums and change the lining's friction characteristics. Continued brake overuse can leave the vehicle unable to slow adequately.
Source: Washington Commercial Driver Guide, N/10/20; section 5.4.5, physical PDF 87, printed 5-9. ↗
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. ↗
Your low-air warning comes on during a trip. Why should you stop safely before the spring brakes apply by themselves?
Correct answer: You still have more control while air remains for the foot brakes
A safe stop while service braking is still available is preferable to waiting for an abrupt automatic spring-brake application. Investigate and correct the air problem.
Source: Washington Commercial Driver Guide, N/10/20; section 5.4.7, 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. ↗
After a steep descent, the brakes are very hot. What does the guide recommend for securing the vehicle while they cool?
Correct answer: Use wheel chocks on a level surface before applying the parking brakes later
The guide cautions against applying parking brakes while they are very hot. Use chocks on level ground to hold the vehicle and let the brakes cool before applying them.
Source: Washington Commercial Driver Guide, N/10/20; section 5.4.8, 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. ↗
You will leave a truck unattended for only a minute. What still has to be done to prevent it rolling away?
Correct answer: Secure it with the parking brakes or wheel chocks as appropriate
A short absence does not remove the rollaway risk. The guide says never to leave the vehicle unattended without parking brakes or chocking; hot or wet-freezing brake exceptions still require secure chocking.
Source: Washington Commercial Driver Guide, N/10/20; section 5.4.8, physical PDF 88, printed 5-10. ↗
