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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
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 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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
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. ↗
