CDL Air Brakes Test flashcards

The specific air pressure level (typically 60 psi or half of governor cut-out) at which the low air pressure warning light and buzzer must activate.

• Mandated by federal regulations for air brake systems.
• Provides critical warning to the driver before spring brakes engage.
• Ensures driver awareness of system air pressure loss.

Memory trick: Warning At Sixty, Safe and Swiftly.

The distance the pushrod moves out of the brake chamber when the service brakes are fully applied, used to check brake adjustment.

• Should be between 1/2 inch and 2 inches (depending on chamber size/type).
• Excessive stroke (over 2 inches) indicates brakes are out of adjustment.
• Automatic slack adjusters should maintain proper stroke.
• Manual slack adjusters require periodic adjustment.

Memory trick: Pushrod stroke, a measured poke, tells if your brakes are fit for the road.

The brake pedal valve controls the amount of air pressure sent to the service brake chambers, directly proportional to the pedal's depression, and allows for smooth application and release of brakes.

• Controls air flow to service brakes.
• Smooth operation and quick return are normal.
• No leaks or unusual sounds when functioning correctly.

Memory trick: Smooth Pedal, Safe Stop: Valve's Victory!

An internal or external air leak originating from the foot brake (treadle) valve, often heard as a continuous hiss from the pedal area, even when brakes are not applied.

• Can lead to loss of air pressure over time.
• Indicates a faulty or worn foot valve.
• Requires replacement or repair of the valve.
• Can affect service brake performance.

Memory trick: Pedal hisses, air escapes, the foot valve has some leaky scrapes.

A significant difference in pressure readings between the primary and secondary air tanks in a dual air brake system typically indicates a problem in the lower-pressure circuit.

• Dual systems have separate circuits for front and rear brakes.
• Pressure differences pinpoint issues to a specific circuit.
• Leaks are a common cause of pressure drops.

Memory trick: Dual tanks, separate paths, different pressures, one big problem.

An unintended escape of compressed air from the air brake system, often indicated by the air compressor cycling on and off more frequently than normal to compensate for the pressure loss.

• Leads to increased compressor workload.
• Causes faster-than-normal pressure drop.
• Requires immediate inspection and repair.

Memory trick: Cycling Compressor Cries 'Leak!'

This test checks for air leaks in the service brake system when the brakes are applied. The maximum allowable pressure drop for a single unit vehicle is 3 psi in one minute.

• Performed after full air system charge.
• Hold service brake for one minute.
• Maximum 3 psi drop for single unit.

Memory trick: Leaky brakes mean pressure drops, but how much is too much for your rig?

The recommended interval for manually draining moisture and contaminants from air brake system reservoirs.

• Performed at the end of each work day.
• Removes water and oil that can freeze or corrode.
• Essential for air brake system longevity and safety.

Memory trick: Drain daily, keep the brakes sprightly!

A test to check for air leaks in the service brake system of a combination vehicle by applying the foot brake for one minute and observing the pressure drop.

• Combination vehicle: Max 4 psi drop in 1 minute.
• Straight truck/bus: Max 3 psi drop in 1 minute.
• Performed after charging system and releasing parking brake.

Memory trick: Combination four, no leaks or more!

The maximum time allowed for the air compressor to build air pressure from a specified lower limit to a specified upper limit, indicating proper system function.

• Dual air system: 85 psi to 100 psi in 45 seconds.
• Single air system: 50 psi to 90 psi in 3 minutes.
• Ensures compressor and system integrity.

Memory trick: Fast Air Builds Quickly, Safety Prevails.

The air pressure threshold at which a vehicle's low air warning device must activate to alert the driver of critically low air pressure.

• Must activate at or above 60 psi.
• Typically between 55-75 psi.
• Warns before spring brakes apply (20-45 psi).
• Can be a light, buzzer, or 'wig-wag' flag.

Memory trick: Sixty psi, eyes on the sky, or wig-wag's nigh!

Spring brakes are a safety feature that applies the vehicle's brakes automatically when air pressure drops to a critical level or when the parking brake is engaged.

• Held 'off' by air pressure.
• Apply automatically when air pressure drops below 20-45 psi.
• Used for parking and emergency braking.
• Are powerful and can lock wheels.

Memory trick: Springs pop, air drops, brakes lock!

The unloader mechanism in an air compressor stops the compressor from building pressure once the air system reaches its maximum, allowing the compressor to 'rest' or pump air without resistance.

• Regulates air pressure build-up.
• Prevents compressor from over-pressurizing the system.
• Failure can lead to continuous compression and overheating.

Memory trick: Compressor too hot? Unloader stuck, no rest for the hard worker.

Inspection of the belt that drives the air compressor for signs of wear, damage, or improper tension.

• Belt drives the air compressor, essential for air pressure.
• Check for cracks, frays, glazing, or missing chunks.
• Check for proper tension (typically 1/2 to 3/4 inch play).
• A damaged belt must be replaced to prevent total air system failure.

Memory trick: Belt's health, system's wealth; a fray means danger, a quick death.

A test performed during a pre-trip inspection to check for leaks in the service brake system by applying full brakes and observing pressure drop.

• Engine off, parking brake off, full service brake applied.
• Pressure drop is measured over one minute.
• Different maximum drops for straight trucks vs. combination vehicles.

Memory trick: Combination's four, straight's two; that's the leak test rule for you!

An indication that the air compressor is cycling too often, often pointing to a problem in the air brake system.

• Commonly caused by a significant air leak in the system.
• Can also indicate a faulty governor or compressor issues.
• Leads to increased wear on compressor and dryer.
• Should be investigated promptly to prevent air loss.

Memory trick: Purge too fast? Air's leaking past!

Continuous purging of an air dryer, even at stable system pressure, indicates an issue with the purge valve or its control mechanism, causing constant air loss.

• Purge valve stuck open or leaking.
• Control line leak to the purge valve.
• Leads to excessive air consumption and compressor cycling.

Memory trick: Constant hiss? Purge valve amiss!

Spring brakes are designed to apply automatically when the air pressure in the system drops to a critically low level (usually between 20-45 psi) to ensure safety.

• Activated by a drop in air pressure.
• Prevents vehicle movement if air system fails.
• Failure to apply indicates a problem with the control valve or mechanics.

Memory trick: No air, no play, spring brakes save the day!

For a Type 30 brake chamber, the maximum allowable pushrod travel is 2 inches. Optimal adjustment aims for less travel, typically around 1 to 1.25 inches.

• Type 30 chamber: Max travel 2 inches.
• Excessive travel indicates maladjustment.
• Maladjustment reduces braking efficiency and increases stopping distance.

Memory trick: Pushrod's reach, know its limit, 2 inches for a Type 30, don't miss it!

Specific severe defects in brake drums, such as large cracks or significant distortion, render a vehicle immediately 'out-of-service' due to safety risks.

• Cracks exceeding specific length/width.
• Severe distortion or breakage.
• Vehicle unfit for operation until repaired.

Memory trick: Big crack on the drum? Out of service, safety's number one!

The air dryer removes moisture from the air system and expels it during its purge cycle, typically when the air compressor unloads.

• Removes water vapor from compressed air.
• Purge cycle expels collected moisture.
• Indicates proper operation if moisture is expelled.

Memory trick: Dryer purges water, that's its job, keeping air clean, no glop!

The parking brake (spring brakes) must be capable of holding the vehicle stationary on a grade. Failure to do so indicates a problem with the spring brake system.

• Uses spring force to apply brakes.
• Tested by attempting to drive against the brake.
• Failure to hold points to adjustment issues or worn components.

Memory trick: Parking brake on, still rolls? Inspect the springs, before it tolls!

Automatic slack adjusters should not require manual adjustment. If they do, it signals a deeper mechanical issue with the adjuster or the brake components it's connected to.

• Designed to self-adjust.
• Manual adjustment indicates a defect.
• Can be due to worn components like cam bushings or adjuster itself.

Memory trick: Auto-adjuster needs a hand? A deeper problem's in the land!

Frequent cycling of the air compressor, especially at full system pressure without heavy braking, is a strong indicator of an air leak within the brake system.

• Compressor works harder to maintain pressure.
• Leads to increased wear on compressor and engine.
• Requires thorough leak detection and repair.

Memory trick: Compressor's working hard, a hidden leak's its card!

This test checks for air leaks in the air brake system with the engine off and parking brake applied, without operating the service brakes.

• Engine off, parking brake applied.
• Fully charge air system.
• After initial stabilization, monitor pressure for one minute.
• Pressure drop should not exceed 2 psi for a single unit truck.

Memory trick: Static, parked, a 2 psi drop is all you're allowed to flop.

A properly functioning air dryer is crucial for preventing moisture and contaminants from entering and accumulating in the vehicle's air tanks, thereby protecting the entire air brake system.

• Located before air tanks.
• Removes moisture and contaminants.
• Failure leads to tank contamination.

Memory trick: Wet primary tank? Dryer's sick, not cleaning air, what a trick!

Contamination of brake linings by oil, grease, or brake fluid severely reduces friction and braking effectiveness, creating a significant safety hazard.

• Causes brake fade and increased stopping distances.
• Requires immediate replacement of affected linings.
• Often indicates a leak from seals, bearings, or brake chambers.

Memory trick: Grease or oil? Your brakes will spoil!

The brake pushrod stroke (distance the pushrod travels when brakes are applied) has maximum allowable limits for different brake chamber types. Exceeding this limit indicates an out-of-adjustment brake.

• Limits vary by chamber type (e.g., Type 30 long stroke: 2.0 inches).
• Longer stroke means brake is loose.
• Requires adjustment to tighten.

Memory trick: Long stroke, loose brake, adjust it tight, for safety's sake!

A test performed with the engine off and parking brake applied to check for air leaks in the primary air system of a straight truck or bus.

• Max 2 psi drop in 1 minute (after initial parking brake drop).
• Engine off, parking brake applied.
• Checks for leaks in lines, tanks, and components not under service brake pressure.
• For combination vehicles, this limit is also 3 psi.

Memory trick: Static truck, two psi luck!

When the low air pressure warning device activates despite the air pressure being at a safe operating level.

• Usually indicates an electrical fault in the warning system.
• Could be a faulty pressure switch or wiring issue.
• Verify actual pressure with a reliable gauge.

Memory trick: Full pressure, light's a fright? Electrical short, not air's plight!

Air lines must be free from damage, securely mounted, and properly routed to ensure the safe and efficient operation of the air brake system.

• No chafing, cuts, or kinks.
• Securely mounted to prevent rubbing.
• No bulges or signs of deterioration.

Memory trick: Lines are fine, no kinks, no grind!

In an air brake system, a spongy or soft brake pedal feel, when air pressure is normal, typically points to improperly adjusted slack adjusters or excessive free play in the brake linkage.

• Indicates excessive pushrod travel.
• Reduces braking effectiveness.
• Requires slack adjuster adjustment.

Memory trick: Soft pedal, pressure's fine? Slack adjusters out of line!

The procedure to verify the proper functioning and adjustment of automatic slack adjusters without manual intervention.

• Do NOT manually adjust automatic slack adjusters.
• Check by making multiple full brake applications.
• Observe pushrod travel; if excessive, adjuster is faulty.
• Air system must be fully charged for the check.

Memory trick: Auto-adjust? Full air, hard press, then assess!

The distance the pushrod moves out of the brake chamber when the service brakes are applied. Excessive travel indicates improper brake adjustment.

• Measured from the brake chamber to the slack adjuster.
• Indicates how much slack is in the brake system for that wheel.
• Different chambers have different maximum allowable travel, typically 1.5 to 2.5 inches.
• Exceeding maximum travel means the brake is out of adjustment and unsafe.

Memory trick: Pushrod's reach, if too far, puts your safety far afar.

Checking the brake drums for damage, wear, and proper function during a pre-trip inspection to ensure safe braking.

• Inspect for cracks, especially those extending to the edge.
• Check for severe scoring, grooving, or heat discoloration.
• Ensure drums are free from oil or grease contamination.

Memory trick: Cracks and gouges are danger's call, slight blue's okay, not a fall!

Critical air line defects involve structural compromise that can lead to sudden air loss, such as bulges, deep cuts, or leaks, requiring immediate repair.

• Bulges indicate internal failure.
• Deep cuts compromise integrity.
• Leaks cause pressure loss.
• Require immediate attention.

Memory trick: Bulge in the line? Danger sign! It's about to blow, don't you know!

This test checks for air leaks in the service brake system by applying the brakes and monitoring pressure loss.

• Engine off, parking brake off, wheels chocked.
• Fully charge air system.
• Apply service brake fully and hold for one minute.
• Pressure drop should not exceed 3 psi for a single unit truck.

Memory trick: Applied pressure leaks reveal system's integrity.

Slack adjusters must be within a specific range of travel to ensure brakes engage properly. Excessive travel indicates worn components or improper adjustment.

• Manual slack adjusters should not move more than 1 inch at the pushrod.
• Automatic slack adjusters should adjust themselves, but must be checked.
• Out-of-adjustment brakes are a major cause of accidents.

Memory trick: Loose slack means brakes are bad; stopping distance makes you sad!

This test checks for leaks in the service brake system by applying full brake pressure and observing the air pressure gauge for drops.

• Engine off, parking brake off, wheels chocked.
• Apply full service brake pressure.
• Observe air pressure gauge for drops within 1 minute.

Memory trick: Applied brakes, rapid drop? Leak detected, don't stop!

The correct tension ensures the air compressor operates efficiently without slipping or putting undue stress on components.

• Checked by pressing on the longest span of the belt.
• Should not exceed 3/4 inch of play.
• Too loose can cause slipping; too tight can damage bearings.

Memory trick: Belt's tight, not too much give, 3/4 inch to live!

When the low air warning light or buzzer activates, it signifies insufficient air pressure for safe braking. The immediate action is to build air pressure until the warning clears.

• Warning activates typically 55-75 psi.
• Indicates unsafe braking pressure.
• Start engine, build pressure immediately.

Memory trick: Low air warning, don't drive, build pressure high!

The pressure points at which the air compressor is activated (cut-in) and deactivated (cut-out) by the governor to maintain system air pressure.

• Cut-in: compressor starts, typically 100 psi.
• Cut-out: compressor stops, typically 125 psi.
• Ensures adequate air pressure for braking.

Memory trick: Hundred in, twenty-five out, that's what the air brakes are all about!

The smallest allowable thickness for a brake lining before it must be replaced to ensure safe and effective braking.

• Typically 1/4 inch for heavy-duty vehicles.
• Check for oil/grease contamination as well.
• Worn linings reduce braking power and can damage drums.

Memory trick: Quarter inch is the line, below that, your brakes aren't fine!

A pre-trip inspection step to verify that the spring-activated parking brake can effectively hold the vehicle stationary.

• Performed after building full air pressure.
• Vehicle in low gear, gently attempt to move.
• Should hold vehicle without any movement.

Memory trick: Parking brake's might, holds the truck tight!

A flexible rubber membrane inside the brake chamber that moves the pushrod when air pressure is applied, activating the brakes.

• Essential for converting air pressure to mechanical force.
• Any damage (bulges, tears) compromises braking.
• Must be intact for safe operation.

Memory trick: Bulge in the chamber, means danger's in amber!

Any unintended escape of compressed air from the air brake system, which can compromise braking efficiency.

• Can be caused by damaged hoses, loose fittings, or cracked components.
• Slow leaks are harder to detect than rapid ones.
• Use soapy water to find small leaks.

Memory trick: Fittings are fickle, small leaks trickle!

This test checks for air leaks in the air brake system of a combination vehicle with the engine off and parking brake applied (or released with chocks), without operating the service brakes.

• Engine off, parking brake applied (or released with chocks).
• Fully charge air system.
• After initial stabilization, monitor pressure for one minute.
• Pressure drop should not exceed 3 psi for a combination vehicle.

Memory trick: Combined and static, a 3 psi drop is not erratic; more, and it's problematic.

The process of opening drain valves on air tanks to remove accumulated moisture and oil from the compressed air system.

• Should be done daily, especially in cold weather.
• Prevents freezing, corrosion, and component damage.
• Some tanks have automatic drain valves.

Memory trick: Moisture's the menace, keep it out of your tanks, or your brakes will get thanks... for nothing!

The brake pushrod must be straight and smooth to ensure unimpeded movement within the brake chamber, allowing full braking force to be applied.

• Dents or bends can restrict travel.
• Restricted travel reduces braking effectiveness.
• Damaged pushrods require replacement.

Memory trick: Pushrod's straight, no bends, no fate!

The air pressure level at which the low air pressure warning light and/or buzzer must activate, indicating a critical drop in system pressure.

• Must activate at or above 60 psi for most commercial vehicles.
• Provides a visual and/or audible warning to the driver.
• Essential safety feature to prevent complete loss of braking.
• Testing this involves pumping the brakes down until the warning activates.

Memory trick: Sixty psi, a warning high, tells you trouble is nigh.

Key conditions to evaluate when inspecting brake drums to ensure safe and effective braking.

• Replace if cracked, severely scored, or heat-checked.
• Check for loose or missing mounting hardware.
• Normal wear (smooth, polished surface) is acceptable.
• Measure for exceeding maximum diameter.

Memory trick: Drum's good: smooth and clean, not cracked or mean!

This test checks for air leaks in the service brake system of a combination vehicle by applying the brakes and monitoring pressure loss.

• Engine off, parking brake off, wheels chocked.
• Fully charge air system.
• Apply service brake fully and hold for one minute.
• Pressure drop should not exceed 4 psi for a combination vehicle.

Memory trick: Combined, a 4 psi drop is fine; more means trouble down the line.

When an air compressor passes excessive oil, it indicates internal wear (e.g., piston rings) allowing engine oil to enter the air system, contaminating components.

• Evident as oil residue in drained air tanks.
• Contaminates air dryer, valves, and brake chambers.
• Requires compressor repair or replacement.

Memory trick: Oil in the tanks, compressor's got leaks!

Slow air pressure build-up, taking longer than specified times (e.g., 3 minutes from 85 to 100 psi), often indicates a worn air compressor or a significant air leak.

• Compressor efficiency is compromised.
• Can be caused by internal wear or a large leak.
• Requires diagnosis of compressor or leak source.

Memory trick: Pressure's slow to rise? Compressor's seen better skies!

Oil found in the air lines or tanks, particularly the discharge line, indicates the air compressor is allowing engine oil into the air system.

• Usually caused by worn piston rings, cylinders, or seals in the air compressor.
• Can lead to contamination of air dryer, valves, and other components.
• Reduces braking efficiency and can cause component failure.
• Requires repair or replacement of the air compressor.

Memory trick: Compressor's oily sweat means internal wear, a system threat.

A bent slack adjuster is a critical defect that prevents proper brake adjustment, leading to insufficient braking force and potential safety hazards.

• Prevents correct brake adjustment.
• Reduces effective braking force.
• Requires immediate repair/replacement.

Memory trick: Bent slack adjuster, brake's a goner, no adjustment, danger's on ya!

The amount of movement (pushrod travel) in an air brake's slack adjuster before the brake shoes contact the drum.

• Indicates brake adjustment status.
• Too much free play means brakes are out of adjustment.
• Proper range ensures efficient braking and prevents excessive chamber stroke.

Memory trick: Measure the slack, keep it tight, for safety's sake.

The technique for stopping an air-braked vehicle with ABS in an emergency, involving applying and holding full pressure on the brake pedal.

• Apply full, firm pedal pressure.
• Hold pedal down, do not pump.
• ABS automatically prevents wheel lock-up.
• Allows steering control during braking.

Memory trick: ABS: Stomp and Steer, no fear!

The procedure for safely securing a commercial vehicle with air brakes on a sloped surface, requiring the use of the parking brake and additional wheel chocks.

• Engage parking brake.
• Chock the wheels.
• Prevents accidental rolling.
• Crucial safety measure on grades.

Memory trick: On a grade, don't just brake, add chocks for safety's sake.

A braking technique for non-ABS air brake systems on slippery surfaces, involving full brake application until wheels lock, then immediate release and reapplication.

• Used to maximize braking force while regaining steering.
• Prevents prolonged wheel lock-up and skidding.
• Only for non-ABS vehicles on slippery surfaces.

Memory trick: No ABS? Stab the brake, then release, to keep control.