Your compressor has its own oil supply rather than sharing engine lubrication. What additional maintenance check is needed?
Correct answer: Check that compressor’s oil level.
Some compressors have a separate oil supply. An acceptable engine oil level does not establish that a separately lubricated compressor has enough oil.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Separate compressor lubrication; physical PDF page 62 (printed 62); reviewed September 14, 2026. ↗
Why can an air-braked vehicle still have several brake applications available after the compressor stops pumping?
Correct answer: The reservoirs hold a supply of compressed air.
Reservoirs store braking air. That reserve is limited: it does not make continued driving with a failed air supply safe.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Stored-air reserve; physical PDF page 62 (printed 62); reviewed September 14, 2026. ↗
A truck has an alcohol evaporator for its air system. How should it be treated?
Correct answer: Maintain it as specified; it does not eliminate tank-drain checks.
An alcohol evaporator is fitted only on some systems. Follow the equipment’s instructions and continue required moisture-management checks; do not improvise additives for other systems.
Source: Colorado Commercial Driver License Manual (06/15/23), Section 5, Alcohol evaporator equipment; physical PDF page 62 (printed 62); reviewed September 14, 2026. ↗
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. ↗
