NJ CDL Combination flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Off-tracking

The tendency of a combination vehicle's rear wheels to follow a path inside the front wheels during a turn. Longer wheelbases and more axles increase off-track, so swing wide before turning.

Tug test

After locking the fifth wheel, set the trailer brakes and pull forward gently in low gear. If the coupling is secure, the tractor should not move.

Fifth wheel jaws

The locking mechanism that grips the trailer kingpin. Jaws must close fully with no gap, and the locking lever must be secured with a safety latch before driving.

Landing gear

The retractable legs that support an uncoupled trailer. Lower them to firm contact before uncoupling, and raise them fully before driving.

Tractor protection valve

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

Static leak test

With the engine off and brakes released, watch the air gauge for one minute. Loss should not exceed 3 psi for a single vehicle or 4 psi for a combination.

Low-pressure warning

The buzzer and light that warn of dropping air pressure. They must activate before pressure falls below 60 psi; failure is an out-of-service condition.

Spring brakes

Brakes held off by air pressure and applied automatically when pressure drops below about 45 psi. They are for parking and emergency use, not normal stopping.

Trailer air supply valve

The red valve that controls air to the trailer. Pulling it out applies the trailer spring brakes and seals the tractor's air supply.

Applied leak test

With the engine off, hold the brake pedal firmly for one minute. Pressure loss should not exceed 4 psi for a combination vehicle.

Governor cut-out

The pressure at which the compressor stops building air, typically about 120 to 140 psi. It restarts building around 100 psi.

Air dryer

A device that removes moisture and oil from the air supply. A failed dryer lets water reach the reservoirs, where it can freeze or corrode valves.

Safety valve

A reservoir valve that opens at about 150 psi to prevent overpressure. A valve that discharges during normal operation indicates a governor or compressor fault.

Slack adjuster

The lever that transfers pushrod force to the brake shoes. Check for looseness, missing cotter pins, and proper pushrod travel at each wheel.

Drive-wheel jackknife

A skid in which 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 rig.

Trailer jackknife

A skid in which the trailer wheels lock and the trailer swings around the tractor. Release the brakes and steer in the direction the trailer is moving.

ABS operation

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

Following distance rule

Keep one second per 10 feet of vehicle length below 40 mph, plus one extra second above 40 mph. A 70-foot rig at 55 mph needs about 8 seconds.

Brake fade

Loss of stopping power caused by overheated brakes from continuous braking on a long downgrade. Symptoms include a soft pedal; stop and let the brakes cool.

Right turn procedure

Approach from the proper lane, swing left slightly before turning, and watch the right mirror for the trailer's rear wheels and pedestrians entering the gap.

Stopping distance

The distance needed to stop grows with the square of speed, so doubling speed roughly quadruples it. A loaded combination needs more distance than an empty one.

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 recoupling.

Tire blowout response

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.

Hydroplaning

Loss of tire contact with the road on standing water. Reduce speed, avoid hard braking, and steer gently; a combination can hydroplane at lower speeds than a car.

Kingpin

The pin on the trailer apron that locks into the fifth wheel jaws. Check for cracks, wear, and a secure mounting; a worn kingpin can let the trailer separate.

Gladhand seals

The rubber seals inside the air line couplers. Cracked or missing seals leak air and can prevent the trailer brakes from releasing.

Build-up rate

With the engine at operating rpm, air pressure should rise from 85 to 100 psi within 45 seconds for a combination vehicle. Slower build-up indicates a compressor or leak problem.

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.

Rollover risk

Rollover risk increases with speed in curves and with a high center of gravity. Enter curves slower than the advisory speed if loaded or downhill.

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.

Downshift for grades

Select a gear low enough to hold speed without heavy braking on a downgrade. If brakes are needed continuously, the gear is too high.

Backing a combination

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.