The air-system safety relief valve is venting because pressure is excessive. How should the driver treat this finding?
Correct answer: As a fault requiring mechanical attention.
The relief valve protects against excessive pressure; it is not the normal pressure-regulating control. A venting safety valve requires investigation and repair, not disabling.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.1.6 — Safety Valve, physical PDF page 83 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
A driver repeatedly presses and releases the air-brake pedal for no reason while waiting to depart. What can happen?
Correct answer: Air may be used faster than the compressor replaces it.
Brake releases discharge air, and the compressor must replenish it. Unnecessary repeated applications can deplete the available supply.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.1.7 — The Brake Pedal, physical PDF page 83 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
In an S-cam drum brake, what is the purpose of the rotating cam at the wheel?
Correct answer: To press the brake shoes outward against the drum.
The S-cam translates linkage movement into shoe contact with the drum. Friction at that contact slows the wheel; the governor and reservoir have different jobs.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.1.8 — Foundation Brakes: S-cam, physical PDF page 83 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
One gauge shows reservoir pressure; an optional second type rises with pedal force. What does that second type indicate?
Correct answer: Pressure being applied to the brakes.
Supply pressure and application pressure are different measurements. An application gauge indicates the pressure used for braking, not the amount stored in the tanks.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.1.9–5.1.10 — Supply and Application Pressure Gauges (physical pages 83–84), physical PDF page 84 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
A truck has two air-brake circuits but one foot pedal. What does the dual arrangement provide?
Correct answer: Separate air supplies and circuits operated by common controls.
Dual systems separate the air circuits while sharing the driver's controls. Each circuit has its own supply and related components; both must be monitored.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.2 — Dual Air Brake, physical PDF page 86 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
Using the manual's minimum-pressure guidance for a dual system, one circuit has reached 110 psi but the other is still at 80 psi. Is the truck ready to move?
Correct answer: No; both circuits need at least 100 psi under that guidance.
The cited guidance requires at least 100 psi in both circuits before driving. A healthy reading in one circuit does not substitute for adequate pressure in the other.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.2 — Dual Air Brake: before driving, physical PDF page 86 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
During a trip, one air circuit loses pressure while the other remains charged. What is the appropriate response?
Correct answer: Stop safely and have the air-brake defect corrected.
A dual system may retain enough braking for a controlled stop, but the loss reduces braking capability. The remaining circuit is not permission to continue normal operation.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.2 — Dual Air Brake: system failure, physical PDF page 86 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
An automatic slack adjuster repeatedly shows excessive stroke. What does routinely tightening it by hand fail to address?
Correct answer: The underlying installation, adjuster or brake-component problem.
Repeated manual correction can conceal a defect instead of fixing it. Automatic adjusters still need inspection, and an out-of-adjustment condition needs qualified diagnosis.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.3.2 — During Step 2: automatic slack adjusters, physical PDF page 87 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
The truck's ABS lamp comes on during travel, but there is no separate loss of conventional braking. What does this indicate?
Correct answer: ABS assistance may be impaired even though regular brakes remain.
An ABS fault does not by itself mean total service-brake failure. Report the fault and obtain service promptly; do not interpret the lamp as normal ABS intervention.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.4.2 — Braking with Antilock Brakes, physical PDF page 89 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
A motorcoach with functioning ABS is making an urgent stop on a slippery road and the ABS begins cycling. How should the driver use the pedal?
Correct answer: Maintain the needed steady application and let ABS regulate pressure.
With functioning motorcoach ABS, repeatedly pumping the pedal interferes with the intended control. Maintain the appropriate application and let the system manage impending wheel lock.
Source: FMCSA Motorcoach Brake Systems and Safety Technologies, Important Points about ABS and Related Technologies; functioning motorcoach ABS pedal technique. ↗
Only the tractor has ABS, and the non-ABS trailer starts swinging during braking. What does the manual advise if it can be done safely?
Correct answer: Ease off the brakes enough to regain control.
ABS on the tractor does not guarantee that the trailer's wheels cannot lock. Monitor the whole combination and reduce braking as needed, when safe, to regain control.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.4.2 — Braking with Antilock Brakes: tractor-only ABS, physical PDF page 89 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
On a long descent, a driver keeps applying the service brakes until they become excessively hot. Why can braking weaken?
Correct answer: Heat can reduce friction and expand the brake drums.
Prolonged brake overuse can reduce effective friction and increase the movement needed to contact an expanded drum. More pedal force is not a reliable cure for overheating.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.4.5 — Brake Fading or Failure, physical PDF page 90 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
During the Kentucky handbook's static leak check, a safely chocked single truck has full air pressure, its engine off and parking brake released. Pressure falls 3 psi in one minute without a foot-brake application. How should that result be assessed?
Correct answer: It fails the handbook's below-2-psi guideline for a single vehicle.
The handbook gives less than 2 psi per minute for a single vehicle's static check. A 3-psi loss fails that guideline and requires correction before operation. The applied check uses a different limit; do not substitute it for the static check.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.3.3 — Step 7: Test Air Leakage Rate, physical PDF page 87 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
When checking the compressor governor on a truck, which pressure should be used to judge whether its cutoff is correct?
Correct answer: The cutoff specified by that vehicle's manufacturer.
The manual gives approximate governor values but directs the driver to the manufacturer's specifications. The safety-relief setting and low-air warning are different checks, not substitutes for the correct governor setting.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.3.3 — Step 7: Check Air Compressor Governor Cut-in and Cut-out Pressures, physical PDF page 87 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
A supervised applied-leak check begins with full air pressure, wheel chocks, and the parking brakes released. Which action prevents compressor output from concealing leakage while the foot brake is held?
Correct answer: Shut off the engine before the timed brake application.
The engine is shut off and the foot brake is fully applied and held for one minute. A running compressor could replace lost air and conceal leakage. Secure the vehicle with wheel chocks before releasing parking brakes, and follow qualified instruction and the applicable vehicle procedure.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.3.3 — Step 7: Test Air Leakage Rate (applied), physical PDF page 88 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
In the cited handbook's single-vehicle applied-leak example, a safely chocked air-braked truck loses 4 psi in one minute with the engine off and foot brake held. How does that compare with the stated limit?
Correct answer: It exceeds the 3-psi limit for that single vehicle.
The Kentucky handbook treats more than 3 psi in one minute as excessive for a single vehicle with the engine off and the service brake held. A 4-psi loss exceeds that limit. The combination-vehicle and static-check limits do not apply to this example.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.3.3 — Step 7: Test Air Leakage Rate (single vehicle, applied), physical PDF page 88 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
For the standard dual-system example in the Kentucky handbook, with the engine at the operating rpm specified for the check, what is the air-pressure buildup benchmark?
Correct answer: 85 to 100 psi within 45 seconds.
Section 5.3.3 gives 85 to 100 psi within 45 seconds at operating rpms for a dual system. Larger-than-minimum air tanks can take longer; consult the manufacturer's specifications. This is equipment-study guidance, not a verified current Kentucky skills-test scoring rule.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.3.3 — Step 7: Check Rate of Air Pressure Buildup, physical PDF page 88 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
The air system cannot build pressure at the rate specified for that truck. What is the appropriate decision?
Correct answer: Do not drive until the cause is corrected.
Inadequate buildup can leave too little air during operation. A departure check should identify and resolve the problem rather than relying on the compressor to catch up on the road.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.3.3 — Step 7: Check Rate of Air Pressure Buildup, physical PDF page 88 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
In the manual's low-speed service-brake check, a truck with normal air pressure pulls sharply to one side when braking from about 5 mph. What does that suggest?
Correct answer: The brakes may not be functioning correctly.
The low-speed check assesses stopping action and directional pull. Pulling to a side is a fault indication, not a satisfactory result.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.3.3 — Step 7: Test Service Brakes, physical PDF page 88 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
A truck has the familiar yellow, diamond-shaped push-pull parking-brake knob. Which action applies the parking brakes?
Correct answer: Pull the knob out.
On this control design, pulling applies the parking brakes and pushing releases them. Identify the actual controls on the vehicle; older systems may use other arrangements.
Source: Kentucky State Police, current-linked 2025 CDL Manual; section 5.1.15 — Parking Brake Controls, physical PDF page 84 (section 5 has a July 2017 footer). Equipment-study guidance, not a claim about current skills-test scoring; follow the vehicle specification and qualified instruction. ↗
