What is the air compressor’s job in an air brake system?
Correct answer: Pump air into the storage tanks
The compressor supplies compressed air to the reservoirs used by the brake system.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.1 Air Compressor, printed page 5-1 (physical PDF page 79) ↗
At approximately what tank pressure does the governor normally cut out the air compressor?
Correct answer: 125 psi
The governor normally stops compressor loading near 125 psi, although manufacturer specifications may vary.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.2 Air Compressor Governor; 5.3.3 manufacturer specifications on printed 5-6, printed page 5-1 (physical PDF page 79) ↗
At approximately what pressure does the governor normally allow the compressor to cut in again?
Correct answer: 100 psi
The governor normally restarts compressor loading near 100 psi. Check the manufacturer specifications for the particular vehicle; the final air-brake check uses those specified pressures.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.2 Air Compressor Governor; 5.3.3 manufacturer specifications on printed 5-6, printed page 5-1 (physical PDF page 79) ↗
Why must moisture and oil be removed from air storage tanks?
Correct answer: Water can freeze and interfere with braking
Water and oil collect in the tanks; frozen water can obstruct the system and cause brake failure.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.4 Air Tank Drains, printed page 5-1 (physical PDF page 79) ↗
When should manually drained air tanks normally be emptied?
Correct answer: At the end of each driving day
Manual tank drains should be opened completely at the end of each day of driving.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.4 Air Tank Drains, printed page 5-1 (physical PDF page 79) ↗
What does the air-system safety valve protect against?
Correct answer: Excessive pressure
The valve protects the first tank and the rest of the system from overpressure and usually opens near 150 psi.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.6 Safety Valve, printed page 5-2 (physical PDF page 80) ↗
Why should a driver avoid unnecessary repeated brake-pedal applications?
Correct answer: Air use may exceed compressor output
Each release exhausts compressed air, so repeated applications may lower pressure to an unsafe level.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.7 The Brake Pedal, printed page 5-2 (physical PDF page 80) ↗
What can increasing application pressure needed to hold the same speed indicate?
Correct answer: The brakes may be fading
A rising application-pressure requirement can signal brake fade, poor adjustment, leaks, or mechanical trouble.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.10 Application Pressure Gauge (continued), printed page 5-3 (physical PDF page 81) ↗
In the Florida handbook section 5.3.3 low-pressure warning check, the warning must activate before pressure falls below what threshold?
Correct answer: 55 psi
Section 5.3.3 specifies that the warning must come on before pressure falls below 55 psi in the tank, or the lowest-pressure tank of a dual system. Some vehicles warn earlier. Stop safely when a low-air warning occurs; do not wait for spring brakes.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.3 Test Low Pressure Warning Signal, printed page 5-7 (physical PDF page 85) ↗
What holds spring brakes off while a vehicle is being driven normally?
Correct answer: Air pressure
Air pressure compresses the powerful springs; loss of pressure lets the springs apply the brakes.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.14 Spring Brakes, printed page 5-3 (physical PDF page 81) ↗
At what approximate pressure range do tractor and straight-truck spring brakes come fully on?
Correct answer: 20 to 45 psi
Spring brakes normally apply automatically as pressure falls into the 20-45 psi range.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.14 Spring Brakes, printed page 5-3 (physical PDF page 81) ↗
On a newer air-brake vehicle, how is the parking brake normally applied?
Correct answer: Pull out the yellow diamond-shaped control
Pulling out the yellow push-pull knob releases air from the spring brakes so they apply.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.15 Parking Brake Controls, printed page 5-3 (physical PDF page 81) ↗
Why should the foot brake not be pressed while spring brakes are already applied?
Correct answer: Combined spring and air forces may damage the brakes
Some systems can be damaged when air pressure adds to the force of applied spring brakes.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.15 Parking Brake Controls, Caution, printed page 5-3 (physical PDF page 81) ↗
If the ABS malfunction lamp stays on, what braking capability remains?
Correct answer: Normal braking remains, but ABS needs service
An ABS fault does not remove normal brakes; drive normally and arrange service promptly.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.4.2 Braking with Antilock Brakes, printed page 5-8 (physical PDF page 86) ↗
On a reachable S-cam slack adjuster, what manually pulled movement at the push-rod connection suggests a need for adjustment?
Correct answer: More than about one inch
With wheels chocked and parking brakes released, manually pulling a reachable S-cam slack adjuster more than about one inch at the push-rod connection signals trouble. This is not a universal applied push-rod stroke limit. Have faults repaired; routinely adjusting automatic adjusters is not a substitute for repair.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.2 Check Slack Adjusters on S-cam Brakes, printed page 5-6 (physical PDF page 84) ↗
During a one-minute applied leakage test, what is the maximum pressure drop for a single vehicle?
Correct answer: 3 psi
Secure the vehicle, charge the system, shut off the engine, and release the parking brakes. Fully apply the foot brake and let the initial pressure drop stabilize before timing one minute. A single vehicle must not then lose more than 3 psi.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.3 Test Air Leakage Rate (continued from printed 5-6), printed page 5-7 (physical PDF page 85) ↗
During a one-minute applied leakage test, what is the maximum drop for a two-vehicle air-brake combination?
Correct answer: 4 psi
With both vehicles air-braked, secure the combination, charge the system, shut off the engine, and release parking brakes. Fully apply the foot brake. After the initial drop stabilizes, loss must not exceed 4 psi in one minute.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.3 Test Air Leakage Rate (continued from printed 5-6), printed page 5-7 (physical PDF page 85) ↗
In the Florida section 5.3.3 static leakage check, what loss rate should a single vehicle stay below?
Correct answer: 2 psi in one minute
Secure the vehicle against rolling, fully charge the system, stop the engine and release the brakes. The chapter specifies a loss rate of less than 2 psi per minute for a single vehicle. This is the brakes-released test, not the applied test.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.3 Test Air Leakage Rate, brakes released, printed page 5-6 (physical PDF page 84) ↗
At operating engine rpm, what buildup does Florida section 5.3.3 specify for a typical dual air system?
Correct answer: 85 to 100 psi within 45 seconds
Check at operating rpm. The handbook allows longer buildup for vehicles with larger-than-minimum air tanks; consult the manufacturer specifications. Do not apply the older single-system idle-speed test to this dual system.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.3 Check Rate of Air Pressure Buildup, printed page 5-7 (physical PDF page 85) ↗
How should service brakes be checked after normal air pressure is restored?
Correct answer: Move forward slowly at about 5 mph and apply them firmly
A low-speed firm application can reveal pulling, unusual feel, or delayed stopping.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.3 Test Service Brakes, printed page 5-7 (physical PDF page 85) ↗
On a vehicle without ABS, what defines controlled braking during an emergency stop?
Correct answer: Brake as hard as possible without locking the wheels
For controlled braking, brake firmly without locking the wheels and keep steering movements small. If wheels lock or a larger steering correction is needed, release the brakes and reapply as soon as possible. This question concerns a vehicle without ABS.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.4.3 Emergency Stops, Controlled Braking, printed page 5-8 (physical PDF page 86) ↗
Which extra factor is part of total stopping distance for an air-brake vehicle?
Correct answer: Brake lag distance
Air needs time to reach the brakes, adding brake lag to perception, reaction, and braking distances.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.4.4 Stopping Distance, printed page 5-8 (physical PDF page 86) ↗
At 55 mph on dry pavement, approximately how much distance can air-brake lag add?
Correct answer: 32 feet
The handbook estimates about 32 feet of brake-lag distance at 55 mph.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.4.4 Stopping Distance, printed page 5-8 (physical PDF page 86) ↗
What is a primary cause of brake fade on a long downgrade?
Correct answer: Excessive service-brake use and heat
Overuse creates heat that reduces lining friction and expands drums, weakening braking.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.4.5 Brake Fading or Failure, printed page 5-9 (physical PDF page 87) ↗
What should a driver do when the low-air warning activates on the road?
Correct answer: Stop and park safely as soon as possible
A warning may indicate a leak; stop safely before pressure falls far enough for spring brakes to apply.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.4.7 Low Air Pressure, printed page 5-9 (physical PDF page 87) ↗
Before moving a vehicle with a dual air brake system, what should you confirm on both pressure gauges?
Correct answer: Both systems have reached at least 100 psi
The handbook instructs drivers to allow pressure to build to at least 100 psi in both systems before driving. Check both gauges rather than assuming one charged circuit means the other is ready.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.2 Dual Air Brake, printed page 5-5 (physical PDF page 83) ↗
One circuit of a dual air brake system loses pressure while you are driving. Why must you stop safely and obtain repairs?
Correct answer: The remaining circuit does not provide normal braking at all wheels
A failure in one circuit can leave part of the vehicle without working service brakes. Stopping distance increases, so bring the vehicle to a safe stop and have the system repaired before continuing.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.2 Dual Air Brake, printed page 5-5 (physical PDF page 83) ↗
What should you inspect on a belt-driven air compressor during the engine-compartment check?
Correct answer: Belt condition and tightness
A loose or damaged drive belt can prevent correct air supply. Section 5.3.1 calls for checking the belt condition and tightness.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.1 Check Air Compressor Drive Belt, printed page 5-6 (physical PDF page 84) ↗
An automatic slack adjuster repeatedly has excessive stroke. What is the appropriate response?
Correct answer: Have the underlying brake problem diagnosed and repaired
Excessive stroke with an automatic adjuster can indicate a mechanical problem. Routine manual adjustment can conceal the defect and is not a substitute for qualified repair following the manufacturer’s procedures.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.2 Automatic Slack Adjusters, printed page 5-6 (physical PDF page 84) ↗
After its normal startup check, an ABS warning lamp comes on while the vehicle is moving. What does this suggest?
Correct answer: A possible ABS malfunction that needs attention
An ABS malfunction lamp that remains on after the appropriate check or comes on during travel can indicate an ABS fault. Normal braking remains, but the fault needs service; follow the vehicle-specific lamp-check procedure.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.16 Antilock Braking Systems, printed page 5-4 (physical PDF page 82) ↗
Which benefit should you expect from ABS during hard braking?
Correct answer: Reduced wheel locking, helping you retain vehicle control
ABS helps prevent wheel lock during hard braking. It supports control but does not necessarily shorten stopping distance and does not replace careful speed or following-distance choices.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.16 Antilock Braking Systems, printed page 5-4 (physical PDF page 82) ↗
Brakes are very wet and temperatures are freezing. What parking precaution does the Florida air-brake chapter describe?
Correct answer: Use wheel chocks on a level surface instead of applying wet parking brakes
Very wet parking brakes may freeze in place. Secure the vehicle with wheel chocks on level ground; never leave it able to roll.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.4.8 Parking Brakes, printed page 5-9 (physical PDF page 87) ↗
During a brake inspection, you find oil or grease on a brake lining. How should this be treated?
Correct answer: As a brake defect that needs correction
Brake linings should not be loose or contaminated with oil or grease. Normal air pressure does not make a defective friction surface safe; the defect needs correction.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.2 Check Brake Drums (or Discs), Linings, and Hoses, printed page 5-6 (physical PDF page 84) ↗
An older truck has a manual front brake limiting valve marked NORMAL and SLIPPERY. Which setting normally preserves full front braking?
Correct answer: NORMAL
The manual limiting valve reduces front brake pressure in the SLIPPERY position and can reduce stopping ability. The handbook says to leave this type of control in NORMAL for normal stopping power.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.13 Front Brake Limiting Valve, printed page 5-3 (physical PDF page 81) ↗
What should you look for when inspecting the flexible air hoses connected to brake chambers?
Correct answer: Damage or wear caused by rubbing
Inspect brake hoses for damage and wear from rubbing. A hose problem can lead to air loss; do not dismiss it because pressure is currently normal or disconnect a pressurized line as a routine inspection step.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.2 Check Brake Drums (or Discs), Linings, and Hoses, printed page 5-6 (physical PDF page 84) ↗
Which three functions make up the air-brake system described in the handbook?
Correct answer: Service, parking, and emergency braking
The functions serve normal stops, parking, and brake-system failures.
Source: Florida Commercial Driver's License Manual, July 2022, Section 5 introduction, three braking systems, printed page 5-1 (physical PDF page 79) ↗
In normal service braking, pressing the pedal farther does what?
Correct answer: Sends greater application pressure to the brakes
Pedal force controls service-brake application pressure.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.7 The Brake Pedal, printed page 5-2 (physical PDF page 80) ↗
An air compressor has its own oil supply rather than engine lubrication. What should you check before driving?
Correct answer: Its oil level
A separately lubricated compressor needs its own oil check.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.1 Air Compressor, printed page 5-1 (physical PDF page 79) ↗
Does an alcohol evaporator eliminate the need to drain manually drained air tanks?
Correct answer: No, tank drainage is still required
The evaporator helps reduce freezing risk; it does not remove accumulated water and oil.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.5 Alcohol Evaporator, printed page 5-2 (physical PDF page 80) ↗
The air-system safety valve releases air. What does this indicate?
Correct answer: A fault requiring mechanical attention
The safety valve is a pressure safeguard, not the ordinary compressor control.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.6 Safety Valve, printed page 5-2 (physical PDF page 80) ↗
What does the S-cam force against the inside of the drum?
Correct answer: The brake shoes and linings
Contact between lining and drum creates the friction used to slow the wheel.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.8 Foundation Brakes, S-cam Brakes, printed page 5-2 (physical PDF page 80) ↗
In an air-operated disc brake, what is clamped between the lining pads?
Correct answer: The disc or rotor
Disc brakes produce braking friction at the rotor rather than inside a drum.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.8 Foundation Brakes, Disc Brakes, printed page 5-2 (physical PDF page 80) ↗
What does the supply-pressure gauge show?
Correct answer: Pressure available in the air tanks
Do not confuse stored air pressure with an application-pressure reading.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.9 Supply Pressure Gauges, printed page 5-2 (physical PDF page 80) ↗
How are following drivers warned when air service brakes are applied?
Correct answer: An air-pressure-operated electrical switch illuminates the brake lights
The brake-light switch communicates the braking action to traffic behind.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.12 Stop Light Switch, printed page 5-3 (physical PDF page 81) ↗
With a safe test area and seat belt fastened, how do you check whether the parking brake holds?
Correct answer: Set it and gently pull against it in a low gear
Use a gentle holding test rather than forceful acceleration.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.3 Test Parking Brake, printed page 5-7 (physical PDF page 85) ↗
In the Florida section 5.3.3 static leakage check, what loss rate should a combination stay below with brakes released?
Correct answer: 3 psi in one minute
Secure the combination against rolling, fully charge the system, stop the engine and release the brakes. The chapter specifies less than 3 psi per minute; the applied combination limit of 4 psi is a different test.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.3.3 Test Air Leakage Rate, brakes released, printed page 5-6 (physical PDF page 84) ↗
A bus has a separate emergency air supply for releasing its spring brakes. Why must an emergency move be planned carefully?
Correct answer: The reserve may release the brakes only a few times
The separate reservoir is a limited emergency supply. Repeated releases may exhaust it and leave the bus stopped in a dangerous location.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.15 Dual Parking Control Valves, printed page 5-4 (physical PDF page 82) ↗
Why may an automatic air-tank drain have an electric heater?
Correct answer: To help prevent the drain from freezing
An electric heating device helps prevent the automatic drain from freezing in cold weather.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.1.4 Air Tank Drains, printed page 5-1 (physical PDF page 79) ↗
You have selected the proper low gear and a safe descent speed of 40 mph. Under the handbook’s snub-braking method, when do you release the service brakes?
Correct answer: After slowing to about 35 mph
The method reduces speed about 5 mph below the safe speed, then releases the brakes while engine braking continues.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.4.6 Proper Braking Technique, printed page 5-9 (physical PDF page 87) ↗
Why can some poorly adjusted brakes cause the other brakes to overheat?
Correct answer: The other brakes must do more than their share of the work
All brakes must contribute properly; imbalance increases the load on the working brakes.
Source: Florida Commercial Driver's License Manual, July 2022, section 5.4.5 Brake Fading or Failure, printed page 5-9 (physical PDF page 87) ↗
