A truck's air compressor has its own oil supply rather than sharing the engine's lubrication. The engine dipstick reads correctly. What additional check is needed before driving?
Correct answer: The compressor's own oil level must still be checked
The manual distinguishes compressors with a separate oil supply from those lubricated by the engine. A correct engine-oil reading does not verify the separate compressor supply.
Source: Georgia DDS Commercial Driver's Study Guide, 2023-2024 cover, retained PDF modified June 16, 2025; Section 5 > 5.1.1 - Air Compressor; printed 47, physical 47. Current DDS-linked edition reviewed September 13, 2026. ↗
During an air-system lesson, the instructor describes a device that responds to reservoir pressure and controls when the compressor loads and unloads. Which device performs that role?
Correct answer: The compressor governor
The governor controls whether the compressor pumps air into the reservoirs. A drain releases collected liquid or air; the treadle controls service-brake application; the slack adjuster is part of the wheel-brake linkage. Actual cut-in and cut-out settings depend on the vehicle.
Source: Georgia DDS Commercial Driver's Study Guide, 2023-2024 cover, retained PDF modified June 16, 2025; Section 5 > 5.1.2 - Air Compressor Governor; printed 47, physical 47. Current DDS-linked edition reviewed September 13, 2026. ↗
An air-braked truck's compressor stops supplying air. The reservoirs still contain pressure. What does that remaining pressure provide?
Correct answer: A limited reserve for brake applications, not permission to continue the trip
The reservoirs hold compressed air that can support several applications even if the compressor stops. That reserve is finite; it does not make a failed compressor safe to ignore.
Source: Georgia DDS Commercial Driver's Study Guide, 2023-2024 cover, retained PDF modified June 16, 2025; Section 5 > 5.1.3 - Air Storage Tanks; printed 47, physical 47. Current DDS-linked edition reviewed September 13, 2026. ↗
A vehicle has automatic air-tank drains with electric heaters. In freezing weather, what specific problem are those heaters intended to reduce?
Correct answer: Freezing of the automatic drain mechanism
The optional heaters help keep automatic tank drains from freezing. They do not prevent all moisture formation, remove every source of compressor oil, or guarantee that the entire air system cannot ice up.
Source: Georgia DDS Commercial Driver's Study Guide, 2023-2024 cover, retained PDF modified June 16, 2025; Section 5 > 5.1.4 - Air Tank Drains; printed 47, physical 47. Current DDS-linked edition reviewed September 13, 2026. ↗
An air-brake system is designed with an alcohol evaporator and manually drained reservoirs. A driver argues that the evaporator eliminates the need to drain the tanks. Is that sound?
Correct answer: No; the manual drainage remains necessary to remove collected water and oil
The evaporator can reduce icing risk in a system designed for it, but it does not replace manual reservoir drainage. This question does not instruct drivers to add alcohol to systems not designed for it or to disregard manufacturer instructions.
Source: Georgia DDS Commercial Driver's Study Guide, 2023-2024 cover, retained PDF modified June 16, 2025; Section 5 > 5.1.5 - Alcohol Evaporator; printed 47, physical 47. Current DDS-linked edition reviewed September 13, 2026. ↗
During a pre-trip check, the reservoir safety relief valve releases air. Which response fits the manual?
Correct answer: Have the air-system fault corrected by a mechanic before relying on the system
The safety valve protects against excessive pressure. Its releasing air indicates a fault requiring repair, not a reason to block it or change its setting.
Source: Georgia DDS Commercial Driver's Study Guide, 2023-2024 cover, retained PDF modified June 16, 2025; Section 5 > 5.1.6 - Safety Valve; printed 47, physical 47. Current DDS-linked edition reviewed September 13, 2026. ↗
A driver repeatedly presses and releases the air-brake pedal while waiting, although no brake application is needed. Why can this practice reduce the available reserve?
Correct answer: Each release exhausts some air, and repeated cycling can outpace the compressor
The air used in a brake application is exhausted when the brakes release. Unnecessary cycling can use air faster than the compressor replaces it. This is not an instruction to pump brakes during an ABS stop.
Source: Georgia DDS Commercial Driver's Study Guide, 2023-2024 cover, retained PDF modified June 16, 2025; Section 5 > 5.1.7 - The Brake Pedal; printed 47, physical 47. Current DDS-linked edition reviewed September 13, 2026. ↗
On the S-cam drum brake described in the manual, air pressure moves the brake-chamber pushrod. What happens next in the mechanical path toward applying the shoes?
Correct answer: The pushrod moves the slack adjuster, turning the camshaft and S-cam
The described S-cam linkage transfers pushrod movement through the slack adjuster and camshaft; the S-cam spreads the shoes against the drum. This identifies the linkage, not an adjustment procedure.
Source: Georgia DDS Commercial Driver's Study Guide, 2023-2024 cover, retained PDF modified June 16, 2025; Section 5 > 5.1.8 - Foundation Brakes / S-cam Brakes; Figure 5.2 on printed/physical 48; printed 47, physical 47. Current DDS-linked edition reviewed September 13, 2026. ↗
A training cutaway shows the brake-chamber pushrod forcing a wedge directly between the ends of two shoes. Which design does this illustrate?
Correct answer: A wedge drum brake
The wedge pushes the shoes apart against the drum. Wedge-brake chamber arrangements and adjustment designs vary; recognizing the mechanism does not authorize a driver to adjust it.
Source: Georgia DDS Commercial Driver's Study Guide, 2023-2024 cover, retained PDF modified June 16, 2025; Section 5 > 5.1.8 - Foundation Brakes / Wedge Brakes; printed 48, physical 48. Current DDS-linked edition reviewed September 13, 2026. ↗
A vehicle's wheel brake is an air-operated disc design, not a drum design. Which friction action should a trainee expect?
Correct answer: Pads clamp the disc or rotor between them
Disc brakes clamp a rotor with pads. Drum shoes act against the drum's inner surface. The exact air-disc actuator and adjustment arrangement must be learned from the specific vehicle; no universal power-screw layout is assumed.
Source: Georgia DDS Commercial Driver's Study Guide, 2023-2024 cover, retained PDF modified June 16, 2025; Section 5 > 5.1.8 - Foundation Brakes / Disc Brakes; printed 48, physical 48. Current DDS-linked edition reviewed September 13, 2026. ↗
A truck has both supply and application pressure gauges. The tanks remain normally charged, but progressively more application pressure is needed to hold the same speed. What should the driver conclude?
Correct answer: There may be fade, adjustment, leakage or another brake problem despite normal tank pressure
The optional application gauge measures pressure being applied to the brakes, not just stored supply. Rising demand can indicate fading or other faults; a normal reservoir reading does not rule them out.
Source: Georgia DDS Commercial Driver's Study Guide, 2023-2024 cover, retained PDF modified June 16, 2025; Section 5 > 5.1.9 - Supply Pressure Gauges; 5.1.10 - Application Pressure Gauge; printed 48, physical 48. Current DDS-linked edition reviewed September 13, 2026. ↗
On an older vehicle equipped with a manual-reset wig-wag warning, the flag will not remain out of view while system pressure is low. What is the appropriate interpretation?
Correct answer: Adequate pressure must be restored; forcing the warning out of view does not correct low air
The manual-reset flag cannot stay in its normal out-of-view position until pressure is sufficient. Do not defeat the warning or mistake resetting it for restoring air. No universal activation pressure is asserted.
Source: Georgia DDS Commercial Driver's Study Guide, 2023-2024 cover, retained PDF modified June 16, 2025; Section 5 > 5.1.11 - Low Air Pressure Warning / manual-reset wig wag; Figure 5.5 on printed/physical 50; printed 48, physical 48. Current DDS-linked edition reviewed September 13, 2026. ↗
