The air reservoir’s safety relief valve opens because system pressure is too high. What does this indicate?
Correct answer: A system problem needs attention by a mechanic.
The safety valve protects against excessive pressure. Its operation is a reason to find the fault, not disable the protection or assume the brakes are otherwise sound.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Safety valve discharge; physical PDF page 62 (printed 62); reviewed September 14, 2026. ↗
In normal air-brake operation, pressing the brake pedal farther generally does what?
Correct answer: Applies more air pressure to the service brakes.
The foot valve meters service-brake pressure according to pedal demand. It does not adjust the governor’s pressure setting.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Foot valve pressure; physical PDF page 63 (printed 63); reviewed September 14, 2026. ↗
When you release the air-brake pedal after a normal application, what happens to the air used for that application?
Correct answer: It is exhausted from the brake chambers.
Releasing the pedal vents the application air so the service brakes can release. New air must be supplied from the reservoirs for later applications.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Releasing the service pedal; physical PDF page 63 (printed 63); reviewed September 14, 2026. ↗
Why should you avoid pumping air brakes unnecessarily?
Correct answer: Repeated applications can use air faster than it is replenished.
Each application consumes air. Repeated unnecessary applications can reduce the available reserve, especially if the compressor cannot keep up.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Repeated unnecessary pumping; physical PDF page 63 (printed 63); reviewed September 14, 2026. ↗
What actually slows the wheel when a drum-type service brake applies?
Correct answer: Friction between the brake lining and the drum.
Air pressure operates the brake mechanism, but contact between lining and drum creates the friction that slows the wheel and produces heat.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Drum brake friction; physical PDF page 63 (printed 63); reviewed September 14, 2026. ↗
In an S-cam drum brake, what does rotation of the S-cam do?
Correct answer: Pushes the brake shoes outward against the drum.
The chamber’s pushrod and slack adjuster turn the camshaft. The S-shaped cam spreads the shoes against the inside of the drum. This describes S-cam brakes, not every air-brake design.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, S-cam action; physical PDF page 63 (printed 63); reviewed September 14, 2026. ↗
How are the stop lights commonly activated in the air-brake system described by the handbook?
Correct answer: Air pressure operates an electrical switch.
An air-operated electrical switch turns on the stop lights when the service brakes are applied. The warning system and parking control serve different purposes.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Brake-light switch; physical PDF page 63 (printed 63); reviewed September 14, 2026. ↗
Why can poor brake adjustment weaken both service braking and spring-brake holding on the same wheel?
Correct answer: Both rely on properly adjusted foundation-brake components.
The spring brake and service brake depend on the wheel’s brake mechanism. A spring application does not overcome improper foundation-brake adjustment.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Shared adjustment consequences; physical PDF page 64 (printed 64); reviewed September 14, 2026. ↗
On a vehicle with the standard yellow diamond-shaped parking-brake control, how do you apply the parking brakes?
Correct answer: Pull the control out.
The standard yellow diamond control is pulled to apply and pushed to release. Older or special equipment may use a different control, so know the vehicle before operation.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Parking control direction; physical PDF page 64 (printed 64); reviewed September 14, 2026. ↗
A bus is equipped with a modulating valve for spring brakes. What is that control designed to permit?
Correct answer: Gradual control of spring-brake application.
A modulating control can vary spring-brake application rather than providing only an on/off action. Operation and securing the control for parking depend on the vehicle’s instructions.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Modulating parking control; physical PDF page 64 (printed 64); reviewed September 14, 2026. ↗
Some buses have a separate reserve that can release the spring brakes in an emergency. What limitation matters?
Correct answer: The reserve permits only a limited number of releases.
An emergency-release reserve is finite and vehicle-specific. Its presence is not permission to continue passenger service with an unsafe braking system.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Emergency release reserve; physical PDF page 64 (printed 64); reviewed September 14, 2026. ↗
An older vehicle has a driver-operated front-brake limiting valve marked NORMAL and SLIPPERY. For normal stopping, which setting does the handbook specify?
Correct answer: NORMAL.
The handbook specifies NORMAL to preserve normal stopping power. This question concerns the older manually controlled limiter, not ABS or a modern automatic system.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Older front-brake limiter; physical PDF page 64 (printed 64); reviewed September 14, 2026. ↗
Before moving a vehicle with two service-air circuits, what should you check on the pressure gauges?
Correct answer: That both circuits have reached the required operating pressure.
The handbook says to allow both systems to build adequate pressure. One satisfactory reading does not establish that the other circuit is ready; follow the vehicle’s specified procedure.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Checking both circuits; physical PDF page 66 (printed 66); reviewed September 14, 2026. ↗
What should be inspected when the air compressor is belt-driven?
Correct answer: The belt’s condition and proper tension.
A worn, damaged or improperly tensioned drive belt can affect compressor operation. This check applies when the compressor uses a belt, not a gear drive.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Belt-driven compressor inspection; physical PDF page 66 (printed 66); reviewed September 14, 2026. ↗
An air hose is rubbing against a sharp metal edge. What should you recognize?
Correct answer: The rubbing can damage the hose and cause air loss.
Inspect hoses for cuts, rubbing and damage. A warning device can alert the driver to pressure loss but cannot prevent a damaged hose from leaking.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Damaged air hose; physical PDF page 67 (printed 67); reviewed September 14, 2026. ↗
Before releasing parking brakes for the handbook’s stationary applied-air-leak test, what is essential?
Correct answer: Secure the vehicle against rolling, including proper wheel chocks.
Some air-system checks require releasing the parking brakes. Establish proper rollaway protection first and follow the vehicle’s full inspection procedure.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Applied-leak test preparation; physical PDF page 67 (printed 67); reviewed September 14, 2026. ↗
For the handbook’s applied-air-leak check, when does the one-minute measurement begin?
Correct answer: After a full brake application and the initial gauge drop has stabilized.
The initial air used to apply the brakes is different from continued leakage. Hold the application and measure the drop for one minute after the initial change settles.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Applied-leak timing; physical PDF page 67 (printed 67); reviewed September 14, 2026. ↗
Why does the handbook’s engine-off low-air warning test keep the electrical power on?
Correct answer: So the electrical warning devices can operate as pressure is reduced.
The warning test requires electrical power for the warning circuit. The engine is off while pressure is reduced according to the safe inspection procedure.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Warning test electrical supply; physical PDF page 67 (printed 67); reviewed September 14, 2026. ↗
Why must a driver use the manufacturer’s specified pressure range when checking automatic spring-brake application?
Correct answer: The application pressure varies with the brake equipment.
The handbook gives a typical range, not one exact pressure for all systems. The brakes may apply with air still in the tanks; use the specified procedure and limits.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Automatic application pressure; physical PDF page 67 (printed 67); reviewed September 14, 2026. ↗
The handbook warns against applying parking brakes when they are very hot. What must a driver still ensure while following the cooling procedure?
Correct answer: The vehicle is securely prevented from rolling, including suitable chocks.
The hot-brake caution is not permission to leave a vehicle unsecured. Use a level location, appropriate chocks and the vehicle’s safe parking procedure while the brakes cool.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Hot-brake parking exception; physical PDF page 69 (printed 69); reviewed September 14, 2026. ↗
