NJ CDL Combination cheat sheet

Pre-trip inspection order for a tractor-trailer: left side and engine compartment, then coupling system, then right side, then lights and brakes; report any defect in writing before driving.

Fifth wheel inspection points: jaws closed fully around the kingpin, locking lever in the locked position and secured with a safety latch or pin, mounting bolts tight, no cracks in the plate, pivot pins secure.

Air/electrical coupling order: secure tractor, back under trailer until jaws lock, tug test twice, then connect air lines (emergency/red to emergency/supply, service/blue to service) and plug in electrical cord with enough slack for turns.

Trailer air line placement matters: crossing the lines or connecting to the wrong gladhand causes the trailer brakes to stay locked or release incorrectly; verify with the trailer brake test after coupling.

Raise the landing gear fully after coupling and before driving; confirm the trailer is supported by the fifth wheel, not the landing gear or the tractor frame.

Tug test procedure: after locking the fifth wheel, pull forward gently in low gear with the trailer brakes set; the tractor should not move if the coupling is secure.

Uncoupling sequence: park on firm level ground, chock wheels, lower landing gear to firm contact, disconnect air lines and electrical cord, then release the fifth wheel and pull forward slowly.

Trailer height check: the trailer should be slightly lower than the fifth wheel plate before backing under, so the plate lifts the trailer nose; too high causes over-ride and kingpin damage.

After coupling, check that the trailer apron clears the tractor frame and that the gap between tractor and trailer is even; uneven gaps suggest a bent or misaligned frame.

Off-tracking rule: the rear wheels of a combination vehicle follow a shorter path than the front wheels; the longer the wheelbase and the more axles, the greater the off-track, so swing wide before starting a turn.

Right turns: approach from the proper lane, move as far right as safe, then swing left slightly before turning; check the right mirror continuously for the trailer's rear wheels and any pedestrian entering the gap.

Left turns: keep the tractor close to the center line and allow for the trailer cutting the corner; do not swing wide to the right before a left turn.

Braking distance grows with weight and speed; a fully loaded combination needs substantially more stopping distance than a light one, so increase following distance to at least one second per 10 feet of vehicle length below 40 mph, plus one second above 40 mph.

Speed on curves: enter slower than the posted advisory speed if loaded or if the curve is downhill; centrifugal force acts on the highest center of gravity first, and a loaded trailer can roll over before the tractor loses grip.

Lane changes require checking both mirrors and blind spots; the trailer's rear quarter is invisible in the mirrors during a turn, so use a spotter or get out and look when space is tight.

Downhill grades: select a gear low enough to hold speed without heavy braking, use engine braking, and brake firmly enough to feel the trailer brakes engage; do not ride the brakes continuously.

Backing a combination vehicle: back toward the driver's side when possible, use a spotter, and correct steering early; a trailer responds opposite to the tractor steering direction, so small corrections prevent jackknife angles.

Tractor protection valve: closes automatically if trailer air lines separate or pressure drops too low, sealing the tractor's air supply and applying the trailer spring brakes; the trailer air supply valve (red) also controls this.

Dual air system: one circuit serves the tractor (primary) and one serves the trailer (secondary); a loss in either circuit triggers a low-pressure warning at about 60 psi and the spring brakes apply around 20-45 psi.

Static leak test: with the engine off and full pressure, release the parking brake and watch the gauge; loss should be no more than 3 psi in one minute for a single vehicle and no more than 4 psi for a combination.

Applied leak test: hold the brake pedal firmly for one minute with the engine off; pressure loss should not exceed 4 psi for a combination vehicle.

Low-pressure warning test: with the engine running, pump the brake pedal until the warning buzzer and light come on; this should occur before the gauge falls below 60 psi.

Spring brake test: with the engine off and pressure below 45 psi, the parking brake valve should pop out and the spring brakes should apply; the vehicle must not move when you try to pull away.

Trailer brake check: with the trailer air supply valve pushed in and the trailer charged, apply the hand valve or trailer brake lever to confirm the trailer brakes hold; release and verify the trailer rolls freely.

Brake adjustment: with the brakes released, measure pushrod travel against the limit for the chamber type; excessive travel means the slack adjuster needs adjustment or the chamber needs service.

Automatic slack adjusters do not eliminate the need to check pushrod travel; they only self-adjust during normal brake applications, and a broken or frozen adjuster will not correct itself.

Jackknife types: a drive-axle jackknife occurs when the tractor's drive wheels lock and the trailer pushes the tractor sideways; a trailer jackknife occurs when the trailer wheels lock and the trailer swings around the tractor.

Cause of most combination skids: excessive speed for conditions, hard braking, and abrupt steering; locked wheels lose directional control, so the vehicle goes where momentum carries it.

Anti-lock braking system (ABS) prevents wheel lock during hard braking; keep firm, steady pressure on the pedal and steer, and do not pump the brakes on an ABS-equipped vehicle.

If the trailer starts to swing, release the brakes to let the trailer wheels roll and regain grip, steer in the direction the trailer is moving, and avoid counter-steering sharply.

If the tractor drive wheels lock and the rig starts to jackknife, release the brake pedal to unlock the wheels, steer to keep the tractor aligned with the trailer, and reapply brakes gently once grip returns.

Recovery from a skid requires looking and steering where you want to go; slamming the brakes or overcorrecting usually worsens the skid, especially with a loaded trailer.

Hazard response: reduce speed before a curve, bridge, or construction zone; a combination vehicle needs more time to react, and the trailer's momentum can push the tractor off line if speed is cut abruptly.

Following distance: at highway speed, keep at least one second per 10 feet of vehicle length plus one second; a 65-foot rig at 55 mph needs about 7 seconds of space.

Roadside emergency: if a tire blows or the trailer brakes lock, hold the steering wheel firmly, ease off the accelerator, avoid hard braking, and pull off the road gradually with hazard lights on.

Compressor builds air pressure and is driven by the engine; the governor controls when the compressor loads and unloads, typically cutting out around 120-140 psi and cutting in around 100 psi.

Air dryer removes moisture and oil from the air supply; a failed dryer or saturated desiccant lets water reach the reservoirs, where it can freeze or corrode valves and cause brake failure.

Reservoirs store air for the tractor and trailer; drain them daily to remove moisture and check for oil or excessive water, which indicate compressor or dryer problems.

Safety valve on the reservoir protects against overpressure; it should open at about 150 psi, and a valve that discharges during normal operation indicates a governor or compressor fault.

The foot valve (treadle valve) applies the brakes; the hand valve (trailer brake valve) applies only the trailer brakes and is used for testing and for stopping in some situations.

The tractor protection valve and trailer air supply valve must be tested after coupling; a failure may leave the trailer without brakes or prevent the trailer brakes from releasing.

Slack adjusters transfer pushrod force to the brake shoes; check for a loose or broken adjuster, missing cotter pins, and proper pushrod travel at each wheel.

Brake chambers convert air pressure into mechanical force; a ruptured diaphragm or a cracked chamber causes weak or dragging brakes and must be repaired before driving.

Low air pressure warning: buzzer and light must activate before pressure falls below 60 psi; a vehicle that fails this test is out of service until repaired.

Kingpin inspection: check for cracks, wear, and a secure mounting to the trailer apron; a worn or damaged kingpin can let the trailer separate from the tractor under load.

Fifth wheel plate and jaws: the jaws must close around the kingpin with no gap, and the locking lever must be fully engaged with the safety latch in place; a partially closed jaw is a separation risk.

Gladhand seals: inspect the rubber seals for cracks or missing pieces; a bad seal leaks air and can keep the trailer brakes from releasing or cause the compressor to run constantly.

Air line routing: the emergency (red) line supplies the trailer and applies spring brakes when disconnected; the service (blue) line carries the application signal; reversed lines cause brake malfunction.

Electrical cord: check for cracked insulation, corroded pins, and a secure plug; a loose cord can cause trailer lights to fail or the ABS warning light to stay on.

Trailer frame and apron: look for cracks, bends, and loose mounting bolts; a cracked apron can let the kingpin pull out of the fifth wheel.

Landing gear: check for bent legs, missing shoes, and a working crank; landing gear must support the trailer when uncoupled and must be fully raised before driving.

Tire and wheel check on the trailer: look for cuts, bulges, and proper inflation, and confirm lug nuts are tight; trailer tire failure is a common cause of loss of control.

After coupling, perform a visual check that the fifth wheel jaws are closed and the locking lever is secured, then do a tug test with the trailer brakes set before connecting air lines.

Speed limit for combination vehicles is often lower than for passenger cars; obey posted truck speeds and reduce speed further for curves, rain, snow, and heavy loads.

Following distance rule: one second per 10 feet of vehicle length at speeds below 40 mph, plus one extra second above 40 mph; a 70-foot combination at 55 mph needs about 8 seconds.

Stopping distance grows with the square of speed; doubling speed roughly quadruples the distance needed to stop, so a rig that stops in 200 feet at 30 mph needs far more at 60 mph.

Space to the sides: combination vehicles need extra room in adjacent lanes because the trailer swings wide in turns and off-tracks on curves.

Space ahead at intersections: do not enter an intersection unless the entire rig can clear it; a long combination can block cross traffic and get trapped by a light change.

Passing: allow more time and distance because of the rig's length and slower acceleration; check mirrors before returning to the lane so the trailer clears the passed vehicle.

Downgrade speed: crest a hill at a speed that lets you hold the grade in a low gear; if brakes are needed continuously, the gear is too high and brake fade is likely.

Railroad crossings: slow down, look both ways, and do not stop on the tracks; a long combination needs extra time to clear the crossing.

Work zones: reduce speed early, increase following distance, and watch for narrowed lanes; the trailer's rear wheels track inside the tractor's path and can strike barriers.

Pre-trip air brake test sequence: build pressure to governor cut-out, check for leaks with the engine off, test the low-pressure warning, test the spring brakes, and test the trailer brakes.

Build-up rate: with the engine at operating rpm, pressure should rise from 85 to 100 psi within 45 seconds for a combination vehicle; slower build-up indicates a compressor or leak problem.

Governor cut-out and cut-in: the compressor should stop building at about 120-140 psi and restart around 100 psi; a narrow or shifting range suggests a governor fault.

Static leak test limits: no more than 3 psi loss in one minute for a single vehicle and 4 psi for a combination with the engine off and brakes released.

Applied leak test limit: no more than 4 psi loss in one minute with the brake pedal held down for a combination vehicle.

Low-pressure warning: the buzzer and light must come on before pressure drops below 60 psi; failure is an out-of-service condition.

Spring brake application: with pressure below 45 psi, the parking brake valve should pop out and the spring brakes should apply; the vehicle must not move when you try to pull away.

Trailer brake test: charge the trailer, apply the trailer hand valve, and confirm the trailer brakes hold; then release and confirm the trailer rolls freely.

Brake adjustment limit: pushrod travel must not exceed the limit for the chamber size; excessive travel means the brakes are out of adjustment and the vehicle is out of service until repaired.

Skids begin when tire traction is exceeded by braking, acceleration, or steering; on a combination vehicle, the trailer's mass makes any loss of traction harder to recover.

Drive-wheel skid: the tractor's drive wheels lock and the trailer pushes the tractor sideways; release the brake pedal to let the wheels roll and steer to align the tractor with the trailer.

Trailer skid: the trailer wheels lock and the trailer swings out; release the brakes, steer in the direction the trailer is moving, and reapply brakes gently once the trailer straightens.

Front-wheel skid: the steering axle loses grip and the vehicle goes straight regardless of steering input; release the brakes and steer where you want to go once grip returns.

ABS operation: hold firm, steady pressure and steer; the system pulses the brakes faster than the driver can, and pumping the pedal defeats the system.

Traction and stability control on newer tractors can help but do not replace safe speed; these systems have limits on ice and in sharp curves.

Recovery rule: look and steer where you want the vehicle to go, ease off the accelerator, and avoid hard braking until the tires regain grip.

Prevention: slow down before curves and wet or icy patches, increase following distance, and avoid abrupt steering or braking inputs with a loaded trailer.

Jackknife prevention: keep the trailer brakes and tractor brakes balanced, avoid hard braking on slick surfaces, and keep the tractor and trailer aligned when braking in a curve.

Tire blowout: hold the steering wheel firmly, ease off the accelerator, avoid hard braking, and let the vehicle slow gradually before pulling off the road with hazard lights on.

Brake failure: downshift to use engine braking, pump the brakes if the system is not ABS-equipped, use the parking brake gradually, and look for an escape route such as a runaway truck ramp.

Trailer breakaway: if the trailer separates, the tractor protection valve should seal the tractor's air supply and the trailer's spring brakes should apply; stop and secure the scene before attempting to recouple.

Fire: stop, shut off the engine, get everyone out and away, and call for help; do not open the hood or attempt to fight a large fire, and stay clear of fuel and cargo.

Hydroplaning: reduce speed, avoid hard braking, and steer gently; a combination vehicle can hydroplane at lower speeds than a car because of tire loading and trailer weight.

Crosswinds: reduce speed and keep a firm grip on the wheel; empty trailers and high-profile loads are pushed sideways, and the trailer can sway into adjacent lanes.

Fog and heavy rain: slow down, use low beams, increase following distance, and be ready to stop within the distance you can see.

Winter driving: brake earlier and gentler, avoid cruise control on slick roads, and watch for black ice on bridges and shaded curves.

Roadside stop: pull as far off the road as possible, set the parking brake, turn on hazard lights, place reflective triangles, and stay in the vehicle if traffic is close.

Before backing under a trailer, check that the trailer's kingpin is at the correct height, the fifth wheel is greased, and the trailer wheels are chocked.

Back under slowly and straight; the fifth wheel should lift the trailer nose slightly, and the jaws should close with an audible click.

Tug test: with the trailer brakes set, pull forward gently in low gear; the tractor should not move, confirming the jaws are locked around the kingpin.

Connect the emergency (red) line first, then the service (blue) line, then the electrical cord; verify the lines are not crossed and have enough slack for turns.

After connecting, charge the trailer and test the trailer brakes with the hand valve; the trailer should hold and then roll freely when released.

Raise the landing gear fully and secure the crank; a partially raised landing gear can strike the ground or a railroad crossing.

Uncoupling: park on firm level ground, chock the trailer wheels, lower the landing gear to firm contact, disconnect the air lines and electrical cord, then release the fifth wheel.

Pull forward slowly after releasing the fifth wheel; a trailer that moves or tips indicates the landing gear is not supporting it properly.

After uncoupling, cap the gladhands and secure the electrical cord to keep dirt and moisture out of the connections.

Emergency braking: apply firm, steady pressure and steer; on an ABS-equipped vehicle, do not pump the brakes, and keep pressure on until the vehicle stops.

Brake fade: caused by overheating from continuous braking on long downgrades; symptoms include a soft pedal and reduced stopping power, and recovery requires stopping to let the brakes cool.

Use engine braking on downgrades and apply the brakes firmly in short bursts rather than riding them; this lets the brakes cool between applications.

Trailer brakes should engage slightly before or with the tractor brakes; if the trailer pushes the tractor, the trailer brakes may be weak or out of adjustment.

Stopping distance on a combination is longer than on a single vehicle; at highway speed, the rig may need the length of a football field or more to stop.

When stopping on a hill, set the parking brake and chock the wheels; a combination vehicle can roll if the spring brakes are weak.

If the brakes fail, downshift, use the parking brake gradually, and look for an escape ramp or a safe runoff area; do not turn sharply at speed.

After any hard stop, check the brakes for overheating, air pressure recovery, and any dragging or smoke before continuing.

Report brake defects in writing and do not drive a vehicle with an out-of-service brake condition.

Emergency (red) gladhand supplies air to the trailer and charges the trailer reservoirs; disconnecting it causes the trailer spring brakes to apply.

Service (blue) gladhand carries the brake application signal from the tractor to the trailer; a leak here causes weak or delayed trailer braking.

Gladhand seals must be in place and free of cracks; a missing or damaged seal leaks air and can prevent the trailer brakes from releasing.

Crossed lines: connecting the red line to the blue gladhand can cause the trailer brakes to stay applied or release unexpectedly; verify after coupling.

Electrical cord: check for cracked insulation, bent or corroded pins, and a secure connection; a loose cord can cause trailer lights or ABS to fail.

Cord slack: leave enough slack for turns and articulation, but secure the cord so it does not drag or catch on the fifth wheel.

Trailer ABS light: a trailer ABS warning light that stays on after the ignition check indicates a fault; report it and have it repaired.

After coupling, check that the air lines are not kinked or resting on the fifth wheel or exhaust, where heat can damage them.

Drain the trailer reservoirs during the pre-trip inspection and check for moisture or oil, which indicate dryer or compressor problems.

Off-tracking: the rear wheels of a combination follow a path inside the front wheels; the longer the wheelbase, the greater the off-track, so swing wide before turning.

Right turn: approach from the proper lane, swing left slightly before turning, and watch the right mirror for the trailer's rear wheels and pedestrians.

Left turn: keep the tractor close to the center line and allow for the trailer cutting the corner; do not swing right before a left turn.

Curve speed: enter slower than the advisory speed if loaded or downhill; a loaded trailer can roll over before the tractor loses grip.

Centrifugal force increases with speed and is applied at the center of gravity; a high center of gravity, such as a loaded tanker, increases rollover risk.

Lane position in curves: stay centered and avoid braking hard in the curve; brake before the curve and accelerate gently through it.

Mirror use: check both mirrors before, during, and after a turn to confirm the trailer clears curbs, poles, and other vehicles.

Backing: back toward the driver's side when possible, use a spotter, and make small steering corrections; a trailer responds opposite to the tractor's steering direction.

Tight spaces: get out and look if unsure; a spotter or a walk-around prevents trailer damage and injury.

ABS prevents wheel lock during hard braking; the driver should hold firm, steady pressure and steer, and should not pump the pedal.

ABS does not shorten stopping distance on all surfaces; on gravel or loose snow, it may lengthen it slightly, but it preserves steering control.

Traction control reduces drive-wheel spin during acceleration; it helps on slick surfaces but does not replace reduced speed.

Stability control on newer tractors can detect and reduce rollover or jackknife risk, but it has limits on ice and in sharp curves.

ABS warning light: if the light stays on after the ignition check, the system has a fault; the vehicle still has normal brakes but loses ABS function.

Trailer ABS: a trailer ABS light that stays on indicates a fault; report it and have it repaired, since trailer wheel lock can cause a trailer jackknife.

Driver response to a skid: release the brakes, look and steer where you want to go, and reapply brakes gently once grip returns.

Jackknife recovery: release the brake pedal to unlock the drive wheels and steer to align the tractor with the trailer; do not counter-steer sharply.

Prevention: slow down before curves and slick patches, increase following distance, and avoid abrupt steering or braking with a loaded trailer.

Start with a walk-around: check lights, tires, wheels, and the coupling system before entering the cab.

Left side and engine compartment: check the engine oil, coolant, belts, hoses, and the left-side lights and tires.

Coupling system: check the fifth wheel jaws, locking lever, safety latch, mounting bolts, and the kingpin and apron for cracks.

Right side: check the right-side lights, tires, wheels, and the trailer frame and landing gear.

Air brake test: build pressure, check for leaks, test the low-pressure warning, test the spring brakes, and test the trailer brakes.

Lights: check headlights, turn signals, brake lights, clearance lights, and trailer lights, using a helper or a reflective surface.

In-cab checks: seat, seat belt, mirrors, steering, horn, wipers, and gauges, including the air pressure gauge.

Report any defect in writing and do not drive a vehicle with an out-of-service condition.

After coupling, do a tug test and a visual check of the fifth wheel jaws before connecting the air lines.

Build-up rate: with the engine at operating rpm, pressure should rise from 85 to 100 psi within 45 seconds for a combination vehicle.

Governor cut-out: the compressor should stop building at about 120-140 psi and restart around 100 psi.

Static leak test: with the engine off and brakes released, loss should be no more than 3 psi in one minute for a single vehicle and 4 psi for a combination.

Applied leak test: with the engine off and the brake pedal held down for one minute, loss should be no more than 4 psi for a combination vehicle.

Low-pressure warning: the buzzer and light must come on before pressure drops below 60 psi.

Spring brake test: with pressure below 45 psi, the parking brake valve should pop out and the spring brakes should apply.

Trailer brake test: charge the trailer, apply the trailer hand valve, and confirm the trailer brakes hold, then release and confirm the trailer rolls freely.

Safety valve: the reservoir safety valve should open at about 150 psi; a valve that discharges during normal operation indicates a governor or compressor fault.

Drain reservoirs daily and check for moisture or oil, which indicate dryer or compressor problems.

Following distance: one second per 10 feet of vehicle length below 40 mph, plus one extra second above 40 mph.

A 70-foot combination at 55 mph needs about 8 seconds of following distance; at 30 mph it needs about 7 seconds.

Stopping distance grows with the square of speed; doubling speed roughly quadruples the distance needed to stop.

Space to the sides: the trailer swings wide in turns and off-tracks on curves, so leave extra room in adjacent lanes.

Intersections: do not enter unless the entire rig can clear; a long combination can block cross traffic.

Passing: allow more time and distance, and check mirrors before returning to the lane so the trailer clears the passed vehicle.

Railroad crossings: slow down, look both ways, and do not stop on the tracks; a long combination needs extra time to clear.

Work zones: reduce speed early, increase following distance, and watch for narrowed lanes; the trailer's rear wheels track inside the tractor's path.

Downgrades: crest a hill at a speed that lets you hold the grade in a low gear; if brakes are needed continuously, the gear is too high.

Spring brakes apply automatically when air pressure drops below about 45 psi; they are held off by air pressure during normal operation.

The parking brake valve (yellow) controls the spring brakes; pushing it in charges the system and releases the brakes, and pulling it out applies them.

The trailer air supply valve (red) controls air to the trailer; pulling it out applies the trailer spring brakes and seals the tractor's air supply.

Tractor protection valve: closes automatically if trailer air lines separate or pressure drops too low, sealing the tractor's air supply and applying the trailer spring brakes.

Trailer spring brakes should apply when the trailer air lines are disconnected; test this during the pre-trip inspection.

Do not use the spring brakes for normal stopping; they are for parking and emergency use, and repeated use can damage the mechanism.

Before driving, confirm the spring brakes release fully; dragging spring brakes overheat and can cause a fire.

If the spring brakes will not release, check air pressure, the parking brake valve, and the trailer air supply valve before moving.

A vehicle with inoperative spring brakes is out of service until repaired.

Rollover risk increases with speed in curves and with a high center of gravity; a loaded tanker or a tall load rolls over at lower speeds than a flatbed.

Enter curves slower than the advisory speed if loaded or downhill; centrifugal force acts at the center of gravity and pushes the trailer outward.

Jackknife causes: hard braking on slick surfaces, excessive speed, and abrupt steering; locked drive wheels let the trailer push the tractor sideways.

Keep the tractor and trailer aligned when braking in a curve; hard braking with the wheels turned can start a jackknife.

Balance braking: trailer brakes should engage with or slightly before the tractor brakes; if the trailer pushes the tractor, the trailer brakes may be weak.

Load placement: keep the center of gravity low and centered, and secure the load so it does not shift in a curve.

Tire condition: uneven tire pressure or worn tires reduce grip and increase skid and rollover risk.

Stability control can help but has limits; it does not replace reduced speed in curves and on slick surfaces.

Recovery: release the brakes, steer to align the tractor with the trailer, and reapply brakes gently once grip returns.

Tire blowout: hold the wheel firmly, ease off the accelerator, avoid hard braking, and let the vehicle slow gradually before pulling off the road.

Brake failure: downshift to use engine braking, use the parking brake gradually, and look for an escape ramp or safe runoff area.

Trailer breakaway: the tractor protection valve should seal the tractor's air supply and the trailer's spring brakes should apply; stop and secure the scene before recoupling.

Fire: stop, shut off the engine, get everyone out and away, and call for help; do not open the hood or fight a large fire.

Hydroplaning: reduce speed, avoid hard braking, and steer gently; a combination vehicle can hydroplane at lower speeds than a car.

Crosswinds: reduce speed and keep a firm grip on the wheel; empty trailers and high-profile loads are pushed sideways.

Fog and heavy rain: slow down, use low beams, increase following distance, and be ready to stop within the distance you can see.

Winter driving: brake earlier and gentler, avoid cruise control on slick roads, and watch for black ice on bridges and shaded curves.

Roadside stop: pull as far off the road as possible, set the parking brake, turn on hazard lights, place reflective triangles, and stay in the vehicle if traffic is close.

Check the trailer frame and apron for cracks, bends, and loose mounting bolts; a cracked apron can let the kingpin pull out of the fifth wheel.

Landing gear: check for bent legs, missing shoes, and a working crank; landing gear must support the trailer when uncoupled and must be fully raised before driving.

Tires and wheels: look for cuts, bulges, and proper inflation, and confirm lug nuts are tight; trailer tire failure is a common cause of loss of control.

Lights: check clearance lights, turn signals, brake lights, and the trailer ABS light; a trailer ABS light that stays on indicates a fault.

Doors and cargo: confirm doors are closed and secured, and check that the load is balanced and secured so it does not shift in a curve.

Mud flaps and splash guards: check that they are secure and not rubbing on the tires.

Air lines and electrical cord: check for cracks, kinks, and secure connections, and confirm enough slack for turns.

Brakes: check pushrod travel, slack adjuster condition, and air chamber condition at each wheel.

Report any defect in writing and do not drive a vehicle with an out-of-service condition.

Speed limit for combination vehicles is often lower than for passenger cars; obey posted truck speeds and reduce speed further for curves, rain, snow, and heavy loads.

Downgrade control: select a gear low enough to hold speed without heavy braking, use engine braking, and brake firmly enough to feel the trailer brakes engage.

Brake fade: caused by overheating from continuous braking; symptoms include a soft pedal and reduced stopping power, and recovery requires stopping to let the brakes cool.

Crest a hill at a speed that lets you hold the grade in a low gear; if brakes are needed continuously, the gear is too high.

Uphill: downshift before the grade to keep engine rpm in the power band and avoid losing speed.

Curves: enter slower than the advisory speed if loaded or downhill; a loaded trailer can roll over before the tractor loses grip.

Following distance: one second per 10 feet of vehicle length below 40 mph, plus one extra second above 40 mph.

Stopping distance grows with the square of speed; doubling speed roughly quadruples the distance needed to stop.

After a long downgrade, check the brakes for overheating and air pressure recovery before continuing.

Fifth wheel jaws must close fully around the kingpin with no gap; a partially closed jaw is a separation risk.

Locking lever must be fully engaged with the safety latch or pin in place; a lever that can be moved by hand is not secure.

Mounting bolts: check that the fifth wheel is tight to the tractor frame and that no bolts are missing or loose.

Pivot pins: check that the fifth wheel pivot pins are secure and that the plate can tilt freely.

Kingpin: check for cracks, wear, and a secure mounting to the trailer apron; a worn or damaged kingpin can let the trailer separate.

Apron: check for cracks and bends around the kingpin; a cracked apron can let the kingpin pull out of the fifth wheel.

Tug test: with the trailer brakes set, pull forward gently in low gear; the tractor should not move if the coupling is secure.

After coupling, check that the trailer apron clears the tractor frame and that the gap between tractor and trailer is even.

Grease the fifth wheel plate and check that the jaws are lubricated; a dry plate causes steering resistance and wear.

Pushrod travel must not exceed the limit for the chamber size; excessive travel means the brakes are out of adjustment and the vehicle is out of service.

Measure pushrod travel with the brakes released and the air pressure at normal operating level.

Automatic slack adjusters self-adjust during normal brake applications but do not eliminate the need to check pushrod travel.

A broken or frozen slack adjuster will not correct itself; it must be repaired or replaced.

Check for a loose or broken adjuster, missing cotter pins, and proper pushrod travel at each wheel.

Brake chambers convert air pressure into mechanical force; a ruptured diaphragm or a cracked chamber causes weak or dragging brakes.

Dragging brakes overheat and can cause a fire; check for smoke, a hot wheel, or a brake that will not release.

After any brake work, perform the pre-trip air brake test before driving.

Report brake defects in writing and do not drive a vehicle with an out-of-service brake condition.

Back toward the driver's side when possible; it gives the best visibility and control.

Use a spotter when backing in a tight space; if you lose sight of the spotter, stop.

Make small steering corrections; a trailer responds opposite to the tractor's steering direction, so large inputs cause jackknife angles.

Get out and look if unsure; a walk-around prevents trailer damage and injury.

Check mirrors continuously and watch the trailer's rear quarter, which is invisible in the mirrors during a turn.

Use the trailer's rear wheels as a reference point for clearance on the inside of a turn.

Avoid backing across traffic or into a blind area; if you must, use a spotter and hazard lights.

After backing, confirm the trailer is straight and the air lines and cord are not kinked or caught.

In tight spaces, reduce speed and use the lowest gear; a combination vehicle has limited visibility and a long stopping distance.

Compressor builds air pressure and is driven by the engine; the governor controls when the compressor loads and unloads.

Air dryer removes moisture and oil from the air supply; a failed dryer lets water reach the reservoirs, where it can freeze or corrode valves.

Reservoirs store air for the tractor and trailer; drain them daily to remove moisture and check for oil or excessive water.

Safety valve on the reservoir protects against overpressure; it should open at about 150 psi.

Foot valve (treadle valve) applies the brakes; the hand valve (trailer brake valve) applies only the trailer brakes.

Tractor protection valve and trailer air supply valve must be tested after coupling; a failure may leave the trailer without brakes.

Low air pressure warning: buzzer and light must activate before pressure falls below 60 psi.

Spring brakes apply automatically when pressure drops below about 45 psi; they are held off by air pressure during normal operation.

Dual air system: one circuit serves the tractor and one serves the trailer; a loss in either circuit triggers the low-pressure warning and spring brakes.

Reduce speed at night so you can stop within the distance lit by your headlights; a combination vehicle needs more stopping distance than a car.

Use low beams in fog, rain, and snow; high beams reflect off the precipitation and reduce visibility.

Increase following distance in poor visibility; the trailer's lights and reflective tape help others see you, but they do not help you see ahead.

Check that all clearance lights, trailer lights, and reflective tape are clean and working before driving at night.

Watch for black ice on bridges and shaded curves; brake earlier and gentler in winter conditions.

Avoid cruise control on slick roads; it can cause a loss of control if the wheels slip.

Use hazard lights and reflective triangles if you must stop on the roadside; stay in the vehicle if traffic is close.

Clean mirrors, windows, and lights before driving; dirt and ice reduce visibility and hide other vehicles.

At dawn and dusk, visibility changes quickly; reduce speed and watch for animals and pedestrians.

Keep the center of gravity low and centered; a high or off-center load increases rollover risk in curves.

Secure the load so it does not shift in a curve or during braking; a shifting load can cause a jackknife or rollover.

Check axle weight limits and gross weight limits before loading; overloaded axles reduce braking and steering control.

Balance the load across the trailer axles; too much weight on the rear axles lightens the steering axle and reduces steering control.

Check tire pressure and tire condition after loading; underinflation increases heat and the risk of a blowout.

A loaded trailer needs more stopping distance than an empty one; increase following distance and reduce speed.

Load height affects clearance; check bridge and overpass heights before driving a tall load.

After loading, recheck the coupling system, air lines, and lights before driving.

Report any load shift or damage in writing and secure the load before continuing.

Low air pressure: the warning buzzer and light come on before 60 psi, and the spring brakes apply below about 45 psi; stop and find the leak.

Compressor failure: pressure will not build or will not hold; stop and do not drive until repaired.

Air line separation: the tractor protection valve seals the tractor's air supply and the trailer spring brakes apply; stop and secure the scene.

Brake fade: caused by overheating from continuous braking; symptoms include a soft pedal and reduced stopping power, and recovery requires stopping to let the brakes cool.

Dragging brakes: a brake that will not release overheats and can cause a fire; check for smoke, a hot wheel, or a brake that will not release.

If the brakes fail, downshift, use the parking brake gradually, and look for an escape ramp or safe runoff area.

After any brake work, perform the pre-trip air brake test before driving.

Report brake defects in writing and do not drive a vehicle with an out-of-service brake condition.

A vehicle with inoperative spring brakes is out of service until repaired.

Following distance: one second per 10 feet of vehicle length below 40 mph, plus one extra second above 40 mph.

A 70-foot combination at 55 mph needs about 8 seconds of following distance; at 30 mph it needs about 7 seconds.

Stopping distance grows with the square of speed; doubling speed roughly quadruples the distance needed to stop.

Perception and reaction time add distance before the brakes even engage; a tired or distracted driver needs more space.

A loaded trailer needs more stopping distance than an empty one; increase following distance and reduce speed.

Wet or icy roads reduce traction and increase stopping distance; slow down and increase following distance.

Brake fade on a long downgrade increases stopping distance; use engine braking and short, firm brake applications.

After any hard stop, check the brakes for overheating and air pressure recovery before continuing.

Report brake defects in writing and do not drive a vehicle with an out-of-service brake condition.

After connecting the air lines, charge the trailer and check that the trailer brakes release when the trailer air supply valve is pushed in.

Apply the trailer hand valve and confirm the trailer brakes hold; then release and confirm the trailer rolls freely.

Disconnect the emergency (red) line and confirm the trailer spring brakes apply; this tests the tractor protection valve and trailer spring brakes.

Check for air leaks at the gladhands and along the lines; a leak can prevent the trailer brakes from releasing or cause the compressor to run constantly.

Check that the lines are not crossed and have enough slack for turns; a kinked or short line can separate during a turn.

Check the electrical cord for cracked insulation, bent or corroded pins, and a secure connection.

Trailer ABS light: a light that stays on after the ignition check indicates a fault; report it and have it repaired.

After coupling, do a tug test and a visual check of the fifth wheel jaws before driving.

Report any defect in writing and do not drive a vehicle with an out-of-service condition.