CDL General Knowledge Test flashcards

Visual and olfactory indicators that a vehicle's brakes have been subjected to excessive heat, potentially compromising their performance and integrity.

• Blue or glazed appearance of brake drums/rotors.
• Strong, acrid, burnt smell.
• Can lead to brake fade and reduced stopping power.

Memory trick: Blue drums and burnt smell mean brake trouble's real!

To prevent blinding other drivers, commercial vehicle operators must dim their high beam headlights to low beams when an oncoming vehicle is within 500 feet or when following another vehicle within 200 feet.

• 500 feet for oncoming traffic.
• 200 feet for following traffic.
• Failure to dim can result in citations and cause accidents.
• Allows other drivers to maintain their night vision.

Memory trick: Five hundred oncoming, two hundred following, keep those beams low and flowing!

The technique of using engine braking in a low gear to control vehicle speed on long, steep downgrades, preserving the service brakes.

• Use engine braking
• Select low gear before descent
• Avoid brake fade

Memory trick: Gear Down, Slow Down, Stay Safe.

A safety system in air brake vehicles that alerts the driver when air tank pressure falls below a critical level, indicating a potential braking system failure.

• Activates with light and buzzer
• Warns of insufficient air for braking
• Mandated by federal regulations

Memory trick: Sixty psi means Serious problem.

Federal regulations require steer axle tires on commercial vehicles to have a minimum tread depth of 4/32 inch. This ensures adequate traction and safety.

• 4/32 inch is the minimum for steer axles.
• 2/32 inch is the minimum for all other tires.
• Insufficient tread depth leads to poor traction and increased risk of hydroplaning.

Memory trick: Before you roll, check every hole, especially the steer's tread, or you'll be dead!

Immediate actions a commercial driver must take to maintain control and safely stop the vehicle after a tire blowout on a front steering axle.

• Grip steering wheel firmly.
• Do NOT brake immediately.
• Maintain a straight path.
• Allow vehicle to slow naturally before pulling over.

Memory trick: Blowout? Hold tight, no brake, stay straight!

Steps taken after a minor accident (no injuries, operable vehicles) to ensure safety and prevent further incidents.

• Prioritize personal safety first.
• Move vehicles off the roadway if safe and possible.
• Set out warning devices.
• Exchange information and document the scene.

Memory trick: Safety first, then move, then report, then prove.

The specific legal requirements for commercial motor vehicles when approaching and crossing railroad tracks that lack active warning devices like flashing lights or gates.

• Mandatory stop required
• Specific stopping distance
• Look and listen carefully

Memory trick: Stop, Look, Listen, Live.

When passing another vehicle, especially in a commercial vehicle, ensure you have enough space to safely return to your lane without cutting off the passed vehicle. A common guideline is to see the passed vehicle's headlights in your rearview mirror.

• Check mirrors before, during, and after passing.
• Signal clearly before changing lanes.
• Accelerate to pass quickly but safely.
• Ensure ample space before returning to the right lane.

Memory trick: Headlights in the mirror, then you're clear!

The alternator generates electrical power to run the vehicle's electrical components and recharge the battery while the engine is operating.

• Charges the battery
• Powers electrical systems
• Engine must be running to operate

Memory trick: Alternators Always Activate for Amps.

Downshift to a lower gear before starting down a grade to utilize engine braking for speed control and prevent service brake overuse.

• Engine braking saves service brakes.
• Prevents brake fade due to overheating.
• Provides better control on steep descents.

Memory trick: Before the hill, downshift for the thrill... of control!

When starting a commercial vehicle with a manual transmission on icy surfaces, use a higher gear (e.g., 2nd or 3rd) and a very gentle clutch engagement with minimal throttle to reduce torque and prevent wheel spin.

• Higher gear reduces torque to wheels.
• Gentle clutch release prevents sudden power delivery.
• Minimal throttle avoids overpowering traction.
• This technique applies to both starting and upshifting on slippery surfaces.

Memory trick: On ice, go slow and high, or your wheels will just fly!

In the event of a total loss of air pressure in an air brake system, the spring brakes (emergency brakes) will engage automatically, bringing the vehicle to a stop. The driver's role is to control the vehicle during this stop.

• Spring brakes engage when air pressure drops (20-45 psi).
• Steer firmly to maintain control during the stop.
• Do not pump the brakes; this uses remaining air.
• Downshift to help slow the vehicle.

Memory trick: Air gone, spring brakes on, hold tight until it's done!

If a vehicle's wheels drop off the paved surface, the driver should grip the steering wheel firmly, ease off the accelerator, avoid hard braking, and gently steer back onto the road once speed is reduced and it's safe.

• Hold steering wheel firmly.
• Ease off accelerator; avoid hard braking.
• Slow down gradually.
• Steer gently back onto pavement when clear.

Memory trick: Off-road, don't be bold; slow and steady, that's the gold!

When driving in fog, use low beam headlights and, if available, fog lights. High beams should be avoided as they reflect off the fog and reduce visibility.

• Low beams aim lights down and forward.
• Fog lights are mounted low and aim light directly in front.
• High beams reflect off fog, causing glare.
• Reduce speed and increase following distance in fog.

Memory trick: When the fog is thick, low beams are the trick!

Immediate actions to take when a vehicle tire is severely overheating or has caught fire.

• Pull over immediately and safely.
• Do not spray water on an overheated tire – it can explode.
• If fire, use a fire extinguisher (Class A or B/C for tires).
• Evacuate if fire is uncontrollable or near fuel tanks.

Memory trick: Smoke and fire, pull over, admire (from a distance).

In hot weather, commercial vehicle drivers must pay close attention to the engine's cooling system, primarily by frequently monitoring the coolant temperature gauge, to prevent overheating.

• Engines work harder in heat.
• Coolant temperature gauge indicates overheating.
• Overheating can lead to engine damage or failure.
• Check coolant levels and radiator fins before trips.

Memory trick: Heat's a foe, watch the temp go!

Commercial drivers should avoid backing whenever possible due to inherent safety risks.

• Limited visibility is a major hazard.
• Reduced control and maneuverability.
• Increases risk of collisions with objects or pedestrians.

Memory trick: Backing is Bad, always Blind, always Dangerous.

Excessive play or 'slop' in a commercial vehicle's steering system, requiring constant corrections, is typically caused by worn components in the steering linkage, such as kingpins, tie rod ends, or steering gear.

• Indicates worn steering components.
• Reduces driver control and increases fatigue.
• Serious safety defect requiring immediate repair.
• Often detected during pre-trip inspection by checking steering wheel free play.

Memory trick: Loose steering, bad kingpin's fearing!

Specific tire conditions that render a commercial vehicle unsafe for operation and require immediate repair or replacement.

• Exposed cords are always a disqualifying condition.
• Tread separation indicates structural failure.
• Deep cuts or bulges can also disqualify.

Memory trick: CORD-S: Cords Out, Road Danger - Stop!

The technique of reducing speed before entering a curve and maintaining a controlled speed or gentle acceleration through it to prevent loss of traction.

• Brake before the curve
• Maintain steady speed in curve
• Avoid braking in the curve

Memory trick: Slow Before, Smooth Through, Safe You.

The minimum distance at which a driver must dim their high-beam headlights for oncoming vehicles or when following another vehicle.

• For oncoming vehicles: 500 feet.
• When following another vehicle: 200 feet (some states 300 feet).
• Prevents blinding other drivers and improves overall road safety.

Memory trick: 500 feet for oncoming brights, 200 feet for following lights.

Techniques for maintaining control of a commercial vehicle when exposed to strong winds blowing perpendicular to the direction of travel, which can push the vehicle sideways.

• Requires constant vigilance and steering correction.
• Trucks with high profiles are most affected.
• Reduce speed if winds are severe.
• Be aware of sudden gusts from openings (e.g., bridge ends).

Memory trick: Wind's a brute? Steer acute!

The practice of strategically placing a commercial vehicle within its lane to maximize visibility, manage space, and minimize blind spots relative to other road users.

• Center of the lane is generally safest.
• Provides buffer space on both sides.
• Aids in being seen by other vehicles.
• Reduces chances of being in another's blind spot.

Memory trick: Stay Centered, Stay Seen, Stay Safe!

The time it takes for the air compressor to build pressure from 85 psi to 100 psi (or 50-90 psi for older systems), which should be no more than 45 seconds for a dual air system.

• Tests compressor efficiency and system integrity.
• Excessive time indicates a problem.
• Critical safety check for air brake systems.

Memory trick: Eighty-five to hundred, in forty-five, quick as a thunder.

A critical safety procedure for commercial drivers to physically exit their vehicle and inspect the area around it before backing or maneuvering in tight spaces.

• Eliminates blind spots.
• Ensures clear path for backing.
• Prevents accidents with objects or people.
• Mandatory for safe CMV operation.

Memory trick: Before you back, G.O.A.L. will keep you on track!

An indicator light on the dashboard that illuminates when the Anti-lock Braking System (ABS) detects a fault, signaling that the ABS feature is not operational.

• Indicates ABS failure, not total brake failure.
• Regular brakes (service brakes) still function.
• Requires inspection and repair, but vehicle can be driven cautiously.

Memory trick: ABS light on, regular brakes still strong!

A critical situation in air-braked vehicles where a rapid loss of air pressure necessitates immediate and safe cessation of vehicle movement.

• Rapid pressure drop indicates major leak.
• Risk of total brake failure is high.
• Immediate safe stop is required.
• Do not pump brakes; it depletes air faster.

Memory trick: Pressure Drop? Pull Over, Stop!

To safely descend a long, steep grade, drivers should select a low gear before starting the descent and use a 'controlled braking' technique to manage speed.

• Use a gear that keeps engine RPMs high enough for effective engine braking.
• Apply brakes firmly for a few seconds, then release for a few seconds.
• This allows brakes to cool between applications, preventing fade.
• Never coast or ride the brakes continuously.

Memory trick: Gear low, brakes slow, don't let the heat show!

Commercial vehicles must often swing wide to the left before making a right turn to ensure the trailer clears the corner without hitting obstacles.

• Prevents 'cutting the corner'.
• Accounts for off-tracking of trailer wheels.
• Requires careful observation of surroundings.

Memory trick: Right turn, swing left, then turn right to miss the mess.

The procedure for regaining control of a commercial vehicle when the drive wheels lose traction and begin to slide sideways.

• Release the accelerator to reduce power to the skidding wheels.
• Counter-steer gently in the direction of the skid.
• Do not use the service brakes heavily or lock the wheels.
• Regain control, then adjust speed and direction.

Memory trick: Gas off, steer to the tail, then you'll prevail.

The maximum permissible free travel (play) for a manual slack adjuster's pushrod on an air brake system, indicating proper adjustment.

• Ensures effective braking
• Checked during pre-trip
• Excessive play reduces braking force

Memory trick: One Inch is the limit, don't ignore it.

For commercial vehicles without ABS, use controlled braking: apply firm pressure to the point of lock-up, then release slightly to prevent skidding, and reapply.

• Maximizes braking force without losing steering.
• Prevents wheel lock-up and skidding.
• Requires driver skill and practice.

Memory trick: No ABS? Press, Release, Control, then stop with a pole.

The pressure at which the air compressor stops pumping air into the air tanks, typically between 125-140 psi.

• Indicates proper air brake system function.
• Ensures sufficient air pressure for braking.
• A lower cut-out pressure needs immediate attention.

Memory trick: Compressor Cuts Out at 125, ready to drive.

A condition where one of the two independent air brake systems (primary or secondary) in a commercial vehicle loses significant air pressure.

• Each system operates half of the service brakes.
• Loss in one system still allows partial braking.
• Requires immediate and safe stop due to reduced braking capacity.

Memory trick: Dual System Down? STOP Now, Don't Clown Around!

For emergency stops with ABS, apply firm, steady pressure to the brake pedal. ABS will prevent wheel lock-up and allow steering.

• Do not pump the brakes with ABS.
• Maintain firm, steady pedal pressure.
• ABS helps maintain steering control.
• Expect pulsation or noise from pedal.

Memory trick: ABS is your friend, firm and steady to the end.

Brake linings must be replaced if their thickness is less than 1/4 inch at the thinnest point, or if contaminated with oil/grease.

• Minimum 1/4 inch thickness.
• Check at thinnest point.
• Contamination also requires replacement.
• Worn linings reduce braking power.

Memory trick: Quarter inch, that's the line, less than that, you're out of time.

A component in the air brake system that removes contaminants like moisture and oil from the compressed air.

• Protects air system components from corrosion and freezing.
• Typically includes a desiccant cartridge.
• Requires regular maintenance (draining or cartridge replacement).

Memory trick: Air System: Compress, Govern, Dry, Store, Brake!

A procedure to check for excessive air leaks in a commercial vehicle's air brake system, crucial for safe operation.

• Vehicle off, brakes applied.
• Pressure drop should not exceed specific limits (e.g., 3 psi in 1 minute for single units, 4 psi for combination units).
• Excessive drop indicates a leak needing repair.

Memory trick: Leaky Brakes = Frequent Compressor Calls

Visual examination of the brake drums for defects, wear, and damage that could impair braking performance.

• Look for cracks, heat spots, and excessive wear.
• Cracks over 1/2 inch are critical defects.
• Essential part of pre-trip and post-trip inspections.

Memory trick: Drum's Got Cracks? Time for New Tracks!

When the automatic or manual slack adjusters are not correctly set, leading to too much clearance between the brake shoes and drum.

• Causes excessive brake pedal travel.
• Reduces braking effectiveness.
• Can lead to brake fade.

Memory trick: Slack is too much, brakes don't touch.

Brake pedal free play refers to the distance the brake pedal can be depressed before the brakes begin to engage. Proper free play is essential for effective braking and prevents dragging.

• Maximum free play is about 1 inch.
• Excessive free play can indicate maladjustment.
• Too little free play can cause brakes to drag.

Memory trick: The brake pedal should have just enough 'wiggle room' – about one thumb's width – before it starts to work.

The air compressor generates and stores compressed air in the air tanks, which is essential for the operation of air brakes and other air-powered systems.

• Engine-driven.
• Typically builds pressure to 100-125 psi.
• Governed by the air governor.

Memory trick: No Pressure = Compressor's Distress Call

An air leak heard directly at a foundation brake component (like a brake chamber) when the service brakes are applied indicates a problem with the air line to that component or the diaphragm/seals within the brake chamber itself.

• Leaks when brakes are applied point to issues in the applied pressure path.
• Brake chamber diaphragms are common failure points for leaks.
• Air lines to chambers can also crack or become loose.

Memory trick: If the brake chamber 'hisses' when you push the pedal, it's sick where the air goes in or where it's stored inside.

Brakes that use strong springs to hold them in the 'on' position; air pressure is used to hold them 'off'.

• Apply automatically when air pressure drops too low.
• Used for parking and as an emergency brake.
• Release only when sufficient air pressure is built.

Memory trick: Low Air? Springs Say 'STOP!'

The air pressure at which the air governor signals the compressor to stop pumping air into the system.

• Typically 120-125 psi.
• Ensures system doesn't over-pressurize.
• Higher pressure indicates a faulty governor or safety valve.

Memory trick: Too Much Air? BOOM! Careful, My Dear!

A test performed with the engine off and parking brake released to check the integrity of the air brake system for leaks.

• Maximum allowable drop: 3 psi in one minute.
• Must be performed after full air pressure is built.
• Indicates system leaks if pressure drops too quickly.

Memory trick: Three is fine, five is a whine.

When foreign substances like grease, oil, or brake fluid get onto the brake lining material, impairing its friction properties.

• Causes significant loss of braking power.
• Can lead to uneven braking.
• Requires immediate replacement of contaminated parts.

Memory trick: Grease on the brake, a dangerous mistake.

The control that engages and releases the spring parking brakes in an air brake system.

• Pops out to engage (set) parking brake.
• Pushed in to release parking brake.
• Indicates air pressure is either removed from or supplied to the spring brakes.

Memory trick: Knob out, brakes are stout.

In a dual air brake system, if one air tank consistently shows lower pressure than the other while the compressor is working, it indicates a leak or restriction specifically within the low-pressure system (tank or supply lines).

• Dual systems have separate tanks for front and rear axles.
• Compressor supplies both tanks.
• Pressure difference points to an issue in the lower-pressure circuit.

Memory trick: If one 'lung' of the dual air system is deflating faster, it must have a hole or a pinched tube.

The low air pressure warning light and buzzer in an air brake system must deactivate when the air pressure rises to a safe operating level.

• Activates below 60 PSI
• Deactivates at or above 60 PSI
• Indicates insufficient pressure for safe braking

Memory trick: Sixty PSI is the safety key, warnings off, you're good to see.

Checking the distance the pushrod moves out of the brake chamber when the service brakes are applied, indicating slack adjuster adjustment.

• Should be less than 1 inch on most brake types.
• Excessive travel indicates maladjustment or wear.
• Part of pre-trip inspection.

Memory trick: Slack Adjuster: Just Right, Not Too Far, Not Too Close

The low air pressure warning system is factory-set to activate when air pressure falls below 60 psi and deactivate once pressure rises above this critical threshold. Discrepancies in these thresholds indicate a calibration issue.

• Warning activates below 60 psi.
• Warning deactivates above a safe operating pressure.
• Significant difference between activation and deactivation points suggests miscalibration.

Memory trick: The warning light and buzzer are like a picky alarm clock, they should turn off right when it's safe, not much later.

An indentation or 'dishing' on the diaphragm housing of an air brake chamber is usually a sign of external physical damage.

• Indicates external impact.
• Can compromise chamber integrity.
• Requires replacement for safety.

Memory trick: A dent on the chamber, from an impact, that's the danger.

A constant hiss from under the cab with engine off and parking brakes released, accompanied by a slow air pressure drop, often indicates a leak in the parking brake control valve.

• Located in/near the cab.
• Controls air to parking brakes.
• Leaks when parking brakes are released (air supplied).
• Causes slow system pressure loss.

Memory trick: Hiss from the cab, brakes released, parking valve is not at peace.

Improperly adjusted slack adjusters lead to excessive brake pedal travel, a 'spongy' feel, and reduced, inconsistent braking performance.

• Excessive pushrod travel.
• Brakes engage late.
• Reduced braking force.
• Increases risk of brake fade.

Memory trick: Slack too long, the pedal feels wrong.

For a single commercial vehicle, with the engine off and service brakes applied, air loss should not exceed 3 PSI in one minute.

• Engine off, parking brake released.
• Service brake applied and held.
• Maximum 3 PSI loss for single unit.
• Maximum 4 PSI loss for combination unit.

Memory trick: Three for single, four for combo, less than that, you're good to go.

The periodic release of accumulated moisture and contaminants from the air dryer to maintain air system cleanliness.

• Produces a distinct 'whoosh' sound.
• Occurs intermittently during normal operation.
• Essential for preventing water and oil buildup.

Memory trick: Whoosh! It's Just the Dryer, Don't Be a Cryer!

An air line with exposed fabric due to chafing is severely compromised and requires immediate replacement to prevent brake system failure.

• Indicates structural damage.
• Risk of sudden air loss.
• Vehicle must be taken out of service.
• No temporary repairs are safe.

Memory trick: Fabric showing, air line going, stop the truck, no more flowing.

If one air tank in a dual air brake system loses pressure faster than the other during a static test, the leak is likely in the components supplied by that tank.

• Primary tank supplies rear brakes.
• Secondary tank supplies front brakes.
• Rapid drop indicates a leak in its circuit.
• Focus investigation on relevant components.

Memory trick: Primary drops, rear brakes are the cause, check those lines without pause.