California CDL Combination Vehicles Test flashcards

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

Combination vehicle definition

A power unit towing one or more cargo units, such as a tractor pulling a semitrailer. The heaviest unit's GVWR or the towed unit's GVWR sets the required CDL class.

Tug test

After backing under a trailer, pull gently forward in low gear. If the tractor moves and the trailer stays put, the fifth wheel jaws are locked around the kingpin.

Off-tracking

The tendency of a combination vehicle's rear wheels to follow a shorter path than the front wheels in a turn. It requires swinging wide before turning to keep the trailer clear.

Trailer supply valve

The red push-pull knob that charges the trailer air system when pushed in. Pulling it out closes the supply line and applies the trailer emergency spring brakes.

Fifth wheel gap check

A visible gap between the tractor frame and the trailer apron after coupling means the kingpin is not locked in the jaws. Do not move the vehicle until it is corrected.

Landing gear inspection

Landing gear must be fully raised with the crank handle secured before driving. While parked uncoupled, it must rest on firm ground and support the trailer nose.

Tire tread minimums

At least 4/32 inch tread depth on front steer tires and 2/32 inch on all other tires. Measure with a gauge at several points around the tire.

Swing-out

The rear of a trailer swings outward opposite the direction of a turn. Check the outside mirror during tight turns so the trailer does not strike nearby objects.

Tractor protection valve

A valve that closes automatically when trailer air pressure falls to about 45 psi. It seals the tractor's air supply so the tractor retains braking ability.

Coupling order

Inspect the fifth wheel and kingpin, back under, tug-test, connect air lines and electrical cord, open the trailer supply valve, then raise the landing gear.

Uncoupling order

Park on firm level ground, set the parking brake, lower the landing gear, disconnect air and electrical lines, release the fifth wheel lock, then pull out slowly.

Following distance rule

Allow at least one second per 10 feet of vehicle length, plus one second for speeds above 40 mph. A 60-foot combination at 55 mph needs about seven seconds.

Low-air warning

A buzzer and light must activate before air pressure drops below 60 psi. Spring brakes must fully apply by roughly 20 to 45 psi as pressure continues to fall.

Static leak test

With the system charged, engine off, and brakes fully applied, a combination vehicle should lose no more than 4 psi in one minute. More indicates a leak.

Trailer hand valve

A control that applies only the trailer brakes, used to test trailer braking action. It must never be used for normal stopping because it can cause a jackknife.

Alley dock

A basic control skill requiring a straight-line backing maneuver into a simulated dock between barriers. Pull-ups are allowed but count as limited correction moves.

Kingpin

The pin mounted under the trailer nose that locks into the fifth wheel jaws. It carries the trailer's weight and keeps the trailer attached to the tractor.

Fifth wheel height error

If the fifth wheel is too high, the tractor strikes the trailer nose. If too low, the kingpin can ride over the fifth wheel and the coupling fails.

Pre-trip pass or fail

The CDL vehicle inspection is scored pass or fail. Missing a critical defect, such as a cracked brake drum or leaking air line, fails the inspection.

Downgrade gear selection

Choose a low gear before starting down a grade so engine braking holds a safe speed. Do not coast in neutral or rely on brakes alone.

Right turn technique

Approach wide, begin the turn later, and watch the trailer in the mirror. The trailer must clear the inside curb without striking it or nearby signs.

Dual air brake system

Two separate air circuits so a failure in one still leaves braking ability in the other. The low-air warning must work before 60 psi.

Supply pressure gauge

Shows the air pressure available in the system for braking. It is compared with the application gauge during brake tests to detect problems.

Application pressure gauge

Shows how much air pressure is being applied to the brake chambers. A rising reading without pedal input can indicate a leak or sticking valve.

Trailer breakaway

If the trailer separates from the tractor, the emergency line loses pressure and the trailer spring brakes apply automatically, stopping the trailer.

Air line slack

After coupling, air lines and the electrical cord need enough slack to allow turns and backing without kinking, rubbing, or contacting the catwalk.

Backing steering response

Turn the steering wheel left and the trailer's rear swings right. Correct early with small inputs and use a helper whenever possible.

Curve speed rule

Enter a curve at or below the posted advisory speed and avoid hard braking inside it. A combination rolls over at much lower speeds than a passenger car.

Engine compartment check

First step of the pre-trip: check oil, coolant, power steering fluid, belts, hoses, and the windshield washer. Look for leaks under the engine.

Light check

With a helper signaling, verify headlights, turn signals, four-way flashers, brake lights, clearance lights, and reflectors on both tractor and trailer.

Cargo securement check

Confirm tiedowns, straps, and chains are tight and rated for the load. Check that the load cannot shift, spill, or fall during normal driving.

Blind spot check

Before a lane change, check both mirrors and the area beside the trailer that mirrors do not cover. Confirm the trailer is fully in the new lane.