Illinois CDL Combination flashcards

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

Brake lag distance

The distance a combination travels while air pressure moves through the lines before the brakes apply, making air-braked tractor-trailers stop more slowly than hydraulic-braked vehicles.

Static leak test limit

With the engine off and brakes released, a combination's air pressure should drop no more than 4 psi in one minute; a larger drop indicates a leak.

Applied leak test limit

With the engine off and brakes fully applied, a combination's air pressure should drop no more than 6 psi in one minute; a larger drop means the system needs repair.

Low-air warning threshold

The low-air warning must activate before pressure falls below 60 psi, and the spring brakes should apply automatically at roughly 20-45 psi.

Tractor protection valve

A valve that pops out at about 20-45 psi to protect tractor air pressure if a trailer line breaks, causing the trailer brakes to apply.

Slack adjuster limit

Pull each brake chamber pushrod by hand; movement of about 1 inch or less is normal, while 2 inches or more means the brakes are out of adjustment.

Fifth wheel inspection

Before coupling, check that the jaws are open, the locking mechanism is free, the mounting bolts are tight, and the fifth wheel is greased and tilted rearward.

Tug test

After coupling, pull forward gently in a low gear with the trailer brakes set; if the trailer does not move, the kingpin is locked in the fifth wheel.

Glad hand colors

The emergency or supply line is red and the service line is blue; connect each to its matching glad hand and open the shut-off valves before driving.

Uncoupling sequence

Park on level ground, set the brakes, lower the landing gear, disconnect the air and electrical lines, release the fifth wheel jaws, then pull forward slowly.

Landing gear check

Confirm the landing gear is fully raised, the crank handle is secured, and the support frame is not cracked or bent before driving the combination.

Kingpin inspection

Check the kingpin for bends, cracks, and wear, and confirm the trailer apron is not damaged; a worn kingpin can fail to lock in the fifth wheel.

Trailer light check

With a helper or by walking around, test headlights, turn signals, four-way flashers, brake lights, clearance lights, and trailer marker lights before departure.

Air line inspection

Check the service and emergency air lines for cracks, cuts, and wear, and ensure the glad hand seals are good and the electrical cord is not pinched.

Rollover threshold

A combination's higher center of gravity lowers the lateral acceleration it can handle, so a loaded tractor-trailer can overturn at speeds a passenger car handles easily.

Rearward amplification

The tendency of the last trailer in a multi-trailer combination to swing wider than the tractor during a quick lane change, increasing rollover risk.

Cargo center of gravity

A high, top-heavy load raises the combination's center of gravity and increases rollover risk; an unsecured load that shifts can cause loss of control.

Load distribution effects

Too much weight on the trailer axles can overload tires, while too much on the drive axles can lighten the steer axle and reduce steering traction.

Offtracking definition

The difference between the path of the front wheels and the rear wheels, which increases with wheelbase and with the number of trailers towed.

Right turn procedure

Swing wide to the left before turning without entering another lane, then check the right mirror throughout the turn to keep the trailer clear of the curb.

Lane change blind spots

A combination has large blind spots on both sides and directly behind the trailer, so signal, check mirrors, and turn your head before changing lanes.

Turn start point

Do not begin a turn until the tractor's front wheels reach the point where the turn starts; starting too early cuts the corner and the trailer strikes the curb.

Backing with a helper

Back only when necessary and with a helper outside the vehicle; agree on hand signals, use mirrors, and stop immediately if you lose sight of the helper.

Steering while backing

Turning the wheel right while backing swings the trailer's rear left, and turning left swings it right; make small corrections early.

Pull-up correction

When the trailer drifts off line while backing, stop, pull forward to straighten the combination, then resume backing instead of making large steering corrections.

Drive-wheel skid recovery

Release the accelerator and steer in the direction you want to go; do not brake until the wheels regain traction, then correct smoothly.

Trailer skid recovery

Release the brakes and steer the tractor in the direction the trailer is sliding to straighten the combination and stop the trailer swing.

Jackknife cause

A severe fold between tractor and trailer, usually caused by locking the drive wheels or braking hard on a slippery surface; release the brakes and steer to recover.

ABS emergency braking

Anti-lock braking systems prevent wheel lockup; keep firm, steady pressure on the brake pedal during an emergency stop and do not pump the brakes.

Railroad crossing clearance

Never stop on the tracks; wait until there is room on the far side before crossing, and confirm the trailer's rear wheels and landing gear will clear the rails.

Stuck on tracks response

If the vehicle stalls or gets stuck on the tracks, get everyone out immediately and move away, then call the railroad emergency number posted at the crossing.

Crossing approach speed

Approach every railroad crossing at a speed that lets you stop before the tracks, look and listen for trains, and never rely on the signals alone.