An air-braked truck has used some stored air during normal braking. Which component replenishes that supply?
Correct answer: The air compressor
The compressor pumps air into the reservoirs. Slack adjusters belong to the wheel-brake mechanism, while the stop-light switch signals braking to traffic behind.
Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-1, physical 72 > 5.1.1 Air Compressor ↗
A mechanic describes a device that tells the compressor when to resume pumping and when to stop adding air. Which device is being described?
Correct answer: The compressor governor
The governor responds to reservoir pressure and controls compressor pumping. The gauge displays pressure; the parking control performs a different job.
Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-1, physical 72 > 5.1.2 Air Compressor Governor ↗
If a truck's compressor stops working, what is the role of the air already held in the reservoirs?
Correct answer: It provides a limited reserve for brake applications
Stored air allows some brake applications even without new air from the compressor. It is a finite reserve, not permission to continue with a failed compressor.
Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-1, physical 72 > 5.1.3 Air Storage Tanks ↗
A truck has manually operated air-tank drains. Why does the manual direct the driver to drain them completely at the end of each driving day?
Correct answer: Water and oil collect there, and retained water can freeze
Water and compressor oil tend to collect at the bottom of air tanks. Removing them protects the system, including against water freezing in cold weather. This scenario is expressly about manual drains.
Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-1, physical 72 > 5.1.4 Air Tank Drains ↗
An older air-brake system has an alcohol evaporator and manually drained tanks. Does maintaining the evaporator eliminate the need for tank drainage?
Correct answer: No; water and oil still need to be drained
Where fitted, the evaporator helps reduce ice formation. It does not replace drainage of water and oil from tanks that lack automatic drain valves.
Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-2, physical 73 > 5.1.5 Alcohol Evaporator ↗
Air is escaping through the air system's safety relief valve. What should the driver recognize?
Correct answer: A pressure-system fault needs mechanical attention
The relief valve protects against excessive pressure. Its operation indicates a problem to have repaired, not a reason to defeat the protective valve.
Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-2, physical 73 > 5.1.6 Safety Valve ↗
A driver repeatedly presses and releases the air-brake pedal when no braking is needed. What can this do to the air supply?
Correct answer: Use air faster than the compressor can replace it
Each release exhausts some compressed air. Unnecessary cycling can deplete the reservoirs rather than replenish them.
Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-2, physical 73 > 5.1.7 The Brake Pedal ↗
On an S-cam drum brake, what does rotation of the S-cam accomplish during a brake application?
Correct answer: It spreads the shoes against the inside of the drum
The S-cam converts the linkage's movement into outward shoe movement against the drum. The question is about this brake design, not every type of air-operated brake.
Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-2, physical 73 > 5.1.8 Foundation Brakes > S-cam Brakes ↗
A driver wants to know how much pressure is available in the air reservoirs, not how hard the brakes are being applied. Which instrument provides that information?
Correct answer: The supply-pressure gauge or gauges
Supply gauges show reservoir pressure. An application gauge, where fitted, shows pressure being applied to the brakes instead.
Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-2, physical 73 > 5.1.9 Supply Pressure Gauges ↗
Under comparable conditions, a truck's application gauge shows that increasingly more pressure is needed to hold the same speed. What does that suggest?
Correct answer: Possible brake fade, poor adjustment, or a leak
Increasing application pressure for the same result is a warning sign. The manual lists fade as well as adjustment, leakage, and mechanical problems, so the gauge alone does not identify one exclusive cause.
Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-3, physical 74 > 5.1.10 Application Pressure Gauge ↗
While a spring-brake-equipped truck is operating normally, what keeps the powerful parking-brake springs from applying the brakes?
Correct answer: Air pressure holds the springs back
Air pressure holds spring brakes released. Removing that pressure lets the springs apply the brakes mechanically.
Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-3, physical 74 > 5.1.14 Spring Brakes ↗
A spring-brake-equipped truck has badly out-of-adjustment wheel brakes. Why is it unsafe to rely on the spring brakes as a fully effective backup?
Correct answer: Their braking effectiveness also depends on proper adjustment
Spring brakes do not cure poor brake adjustment. The manual warns that both regular braking and emergency/parking braking can be impaired.
Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-3, physical 74 > 5.1.14 Spring Brakes ↗
