IN CDL Combination cheat sheet

Pre-trip inspection order for a tractor-trailer: coupling system, air lines and electrical cord, landing gear, lights and reflectors, tires, wheels and rims, brakes, suspension, then the tractor engine compartment and in-cab controls.

Fifth wheel jaws must be closed around the kingpin with the release handle in the locked (in) position; a pull test (tug test) with the trailer brakes set confirms the lock before driving.

Coupling sequence: inspect the fifth wheel and kingpin, back under the trailer squarely, lock the jaws, tug test, set the tractor parking brake, connect the air lines and electrical cord, raise the landing gear, then check the trailer brakes.

Uncoupling sequence: park on firm level ground, set the trailer parking brake, lower the landing gear to firm contact with the ground, disconnect the air lines and electrical cord, release the fifth wheel jaws, then pull the tractor slowly forward.

Air line routing rule: the emergency (supply) line is charged first and disconnected last; the service line is connected last and disconnected first, so the trailer stays braked if a line separates.

Landing gear must be fully raised and the crank handle secured before moving; crank handles left in the lowered position can strike the ground or a railroad crossing.

Trailer height and clearance: measure or verify the highest point of the load against posted clearances; low-clearance bridges and canopies are struck because drivers assume a standard trailer height.

Electrical cord and air lines must be supported so they do not drag, kink, or rub on the catwalk; chafed lines cause loss of trailer brakes or lights.

Off-tracking rule of thumb: the rear wheels of a trailer follow a shorter path than the front wheels, so a combination vehicle needs more space to complete a turn than a single-unit truck of the same length.

Right-turn procedure: swing wide to the left before turning right, but never into an opposing lane; check both mirrors throughout the turn because the trailer cuts the corner.

Left-turn procedure: approach from the right side of the lane or use a wider entry, and keep the trailer from drifting into the adjacent lane by watching the trailer wheels in the mirror.

Braking distance grows with weight and speed; a fully loaded combination vehicle needs substantially more stopping distance than an empty one, and speed must be reduced before entering a curve or downgrade.

Controlled braking on a long downgrade: select a gear low enough that the engine and retarder hold the speed, and use the brakes in short applications rather than continuous pressure that overheats the drums.

Following distance for a combination vehicle should be at least one second for each 10 feet of vehicle length at speeds below 40 mph, plus one additional second at higher speeds.

When backing a tractor-trailer, steer the trailer by turning the wheel the opposite way from the desired trailer direction; use a spotter and stop immediately if the trailer begins to jackknife.

Lane changes require checking both flat mirrors and the convex mirrors; the trailer's blind spot and the area directly behind the trailer are not visible from the cab.

Air pressure build-up check: with the engine running at a fast idle, pressure should rise from 85 to 100 psi within 45 seconds in a dual air system; slower build-up indicates a compressor or leak problem.

Static leak test: with the engine off and the system fully charged, release the parking brake and watch the gauge; a loss of more than 3 psi in one minute (single vehicle) or 4 psi (combination) indicates a leak requiring repair.

Applied leak test: with the brakes fully applied and the engine off, hold the pedal for one minute; a drop of more than 4 psi in a combination vehicle signals a leak.

Low-air warning: the warning buzzer and light must activate before pressure drops below 60 psi; the spring brakes should apply automatically when pressure falls into the 20-45 psi range.

Governor cut-out and cut-in: the compressor normally cuts out around 120-125 psi and cuts back in around 100 psi; pressures outside these ranges indicate a governor or compressor fault.

Tractor protection valve test: with the trailer supply line disconnected, the valve should close and the trailer spring brakes should set; if the trailer does not brake, the protection valve is faulty.

Slack adjuster check: with the brakes released, pull the slack adjuster by hand; more than about one inch of free play at the pushrod indicates the brakes need adjustment.

Parking brake test: with the spring brakes applied, attempt to move the vehicle in a low gear; the vehicle must not move, confirming the spring brakes hold the load.

A skid begins when the tires lose traction because of excessive speed for conditions, hard braking, abrupt steering, or a slippery surface; the correction is to remove the cause, not to add more input.

Drive-wheel skid: release the accelerator and steer in the direction the vehicle needs to go; do not apply the brakes until the wheels regain traction.

Steer-wheel skid: release the brakes to let the front wheels roll again, then steer toward the intended path; braking during a front-wheel skid makes it worse.

Trailer skid: release the brakes and accelerate slightly to pull the trailer straight; braking harder will worsen a trailer swing.

Anti-lock braking systems prevent wheel lock-up but do not shorten stopping distance on all surfaces; the driver must still brake firmly and steer around the hazard.

On ice and snow, reduce speed before the skid begins; once sliding, look and steer where you want to go rather than at the obstacle.

Brake fade from overheating reduces stopping power; if the pedal feels soft or the vehicle will not slow, downshift and use engine braking while the brakes cool.

Tire hydroplaning occurs when water lifts the tires off the pavement; ease off the accelerator and avoid hard braking until contact is regained.

A jackknife happens when the tractor and trailer fold toward each other; a rear (trailer) jackknife is usually caused by locking the trailer brakes on a slippery surface, and a front (tractor) jackknife by locking the tractor steer axle.

Prevention rule: brake early and gently on slippery roads, keep the trailer brakes and tractor brakes balanced, and avoid sudden steering while braking hard.

Recovery from a trailer jackknife: release the brakes, steer in the direction the tractor is sliding, and gently accelerate to straighten the combination.

Emergency stop procedure: brake firmly with both hands on the wheel, keep the vehicle straight, and steer only after the speed has dropped; swerving at speed risks a rollover.

Tire blowout handling: hold the wheel firmly, keep the vehicle straight, ease off the accelerator, and brake gently once control is regained; hard braking on a blown steer tire can pull the vehicle off the road.

Off-road recovery: slow down before leaving the pavement, keep two wheels on the shoulder if possible, and return to the road at a shallow angle after checking for traffic.

Runaway truck ramp use: aim for the ramp early, keep the vehicle straight, and expect a soft gravel bed that will stop the vehicle; do not brake hard on the ramp entrance.

Space cushion rule: maintain a following distance that allows a stop within the visible distance ahead, especially on downgrades and in poor visibility, to avoid panic braking that triggers a jackknife.