MN CDL Combination cheat sheet

Pre-trip order for a tractor-trailer: coupling system, air lines and electrical cord, landing gear, lights and reflectors, brakes and air loss, tires, wheels and rims, then the rear of the trailer and the tractor engine compartment.

Fifth wheel jaws must close completely around the kingpin shank; a visual check of the closed jaws plus a firm pull test in low gear confirms the lock. A high-mounted release handle must be in the locked position.

Apron-to-fifth wheel gap: after coupling, no visible gap between the trailer apron and the fifth wheel top plate; a gap means the kingpin is riding on top of the jaws, not locked.

Tug test sequence: set the trailer parking brake, release the tractor spring brake, pull forward gently in a low gear against the trailer brakes, then check that the tractor did not move and the jaws stayed locked.

Trailer air lines: emergency (supply) line is typically red, service line is blue; the electrical cord is green on standard color coding. Crossed lines cause the trailer brakes to release or drag unpredictably.

Landing gear: fully raised after coupling, with the crank handle secured in its holder; the trailer frame must clear the tires and the ground with the gear retracted.

Uncoupling order: park on firm level ground, apply the trailer parking brake, lower the landing gear to the ground, disconnect the air and electrical lines and secure them, then release the fifth wheel jaws and pull the tractor clear slowly.

Air loss test on a combination: with a fully charged system, engine off and brakes released, leakage must stay within the vehicle's specified limit; a steady drop signals a leak that must be fixed before driving.

Slack adjuster check: with the brakes released and pushed by hand, the slack adjuster should not move more than about one inch at the push rod on a properly adjusted brake.

Off-tracking: the rear wheels of a tractor-trailer follow a shorter path than the front wheels, so a right turn requires swinging wide left first and watching the trailer's rear wheels in the right mirror.

Right-turn rule: approach in the lane closest to the right but keep the tractor far enough left that the trailer's right rear tires clear the curb; complete the turn into the far right lane, not a middle lane.

Left-turn rule: start from the rightmost lane or a designated turn lane, swing slightly right before turning to keep the trailer from cutting the corner over the centerline.

Lane changes: mirror checks plus a head check to the blind spot on the side you are moving toward; a combination vehicle has larger blind spots than a single unit, so signal early and move smoothly.

Backing rule: back toward the driver's side (left) whenever possible so the trailer appears in the left mirror; if a right-side back is unavoidable, use a spotter or get out and look.

Steering while backing: hold the bottom of the steering wheel and turn it the direction you want the trailer to go; correct small deviations early because a combination vehicle responds slowly.

Speed on curves: enter slower than the posted advisory speed if the load is high or the surface is wet; a high center of gravity raises rollover risk in a curve.

Following distance: at least one second per 10 feet of vehicle length below 40 mph, plus one additional second for speeds above 40 mph; a 60-foot combination at 55 mph needs about 7 seconds.

Build-up check: with the system charged and the engine at operating rpm, pressure should rise from about 85 to 100 psi within 45 seconds in a dual air system.

Static leak test: with a fully charged system, engine off, brakes released, loss should not exceed about 2 psi in one minute; with the brakes applied, loss should not exceed about 3 psi in one minute.

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

Tractor protection valve: closes automatically if trailer air lines separate, trapping tractor air so the tractor can still brake and stop; the trailer emergency line then applies the trailer spring brakes.

Trailer hand valve (spike): operates the trailer brakes only; it is for testing the trailer brakes and should not be used for normal stopping because it does not apply the tractor brakes.

Brake fade: repeated or prolonged braking overheats the drums and linings, so downshift to a lower gear before a long downgrade and use intermittent firm braking rather than light continuous pressure.

Parking on a grade: apply the parking brake, place the transmission in the lowest reverse or first gear, and use wheel chocks; spring brakes are the primary holding force, not air pressure.

Stab braking on long downgrades: apply the brakes firmly to slow to a safe speed, release fully to let them cool, and repeat; do not ride the brakes continuously.

Skid recovery: stop braking, keep both hands on the wheel, look and steer in the direction you want to go, and do not accelerate until the wheels regain traction and the vehicle is straight.

Rear-wheel skid: the trailer swings out; steer into the skid by turning the wheel toward the direction the rear is sliding, and release the brakes to let the wheels roll again.

Front-wheel skid: the steering feels light and the vehicle keeps going straight; release the brakes and let the front wheels roll until steering control returns.

Jackknife risk rises when the tractor drive wheels lock while the trailer keeps rolling; proper brake balance and avoiding hard braking on slick surfaces reduce this.

Hazard perception on a combination: scan 12 to 15 seconds ahead, watch for brake lights several vehicles ahead, and check mirrors every 5 to 8 seconds for overtaking traffic and trailer tracking.

Space cushion: leave room ahead and to the sides, avoid driving beside other vehicles in the tractor-trailer's blind spots, and allow extra distance when the trailer is lightly loaded and prone to bouncing.

Railroad crossings: never stop on the tracks; if the trailer must cross, ensure enough room on the far side for the entire combination before starting across.

Bridge and overpass clearance: know the loaded height of the combination, including any raised equipment, and check posted clearance signs before committing to the route.

Roadside emergency: pull as far off the roadway as possible, set out reflective triangles within 10 minutes, and place them at 10, 100, and 200 feet (or closer on a curve or hill).