Missouri CDL Combination cheat sheet

Pintle hook coupling requires the locking jaw to close fully around the drawbar eye and the safety pin or latch to be engaged before moving.

Fifth wheel coupling is complete only when the locking jaws close around the kingpin shank, the release handle is in the locked position, and a tug test in low gear shows no movement.

Trailer air lines are color coded: blue is the service (control) line, red is the emergency (supply) line; crossed lines cause trailer brakes to stay applied or release unexpectedly.

After coupling, the landing gear must be fully raised and the crank handle secured; the electrical cord should have enough slack to turn without pulling apart but not drag on the ground.

Tractor protection valve: if trailer air lines separate, the valve seals the tractor's air supply and applies the trailer spring brakes automatically.

Bobtail proportioning valve reduces rear tractor brake force when no trailer is attached, because the lighter vehicle would otherwise skid under full braking.

Off-tracking: the rear wheels of a combination follow a shorter path than the front wheels, so a right turn requires swinging wide left first to keep the trailer off the curb.

Total stopping distance = perception distance + reaction distance + brake lag distance + effective braking distance; air brake lag adds roughly 0.4 second at 55 mph.

Inspection order: start at the driver's door, check lights and leaks around the front, then engine compartment, then walk the sides and rear, then in-cab items.

CDL air brake test sequence: with engine off and full pressure, release brakes and hold 1 minute - loss must not exceed 3 psi (single vehicle) or 4 psi (combination).

Applied leakage test: press and hold the brake pedal with engine off for 1 minute; loss must not exceed 4 psi, and the low-air warning must sound by 60 psi.

Compressor build rate: with engine at operating rpm, pressure must rise from 85 to 100 psi within 45 seconds for a combination vehicle.

Spring brake test: with pressure below 45 psi, the trailer spring brakes should apply; release the parking brake and pull against them to confirm they hold.

Tire defects that fail inspection: tread depth under 4/32 inch on steering tires, under 2/32 inch elsewhere, plus cuts, bulges, or exposed cord.

Slack adjuster check: push the rod by hand - movement over about 1 inch (25 mm) at the clevis means brakes need adjustment.

Coupling inspection includes checking the fifth wheel mounting bolts, the kingpin, the apron, and that the fifth wheel plate is greased.

Straight-line backing: use both mirrors, back at a walking pace, and correct with small steering inputs - steer toward the mirror where the trailer appears to drift.

Alley dock setup: pull past the dock far enough that the trailer axles clear the near corner, then turn toward the dock and straighten before backing.

Offset backing to the left: back straight, then steer right to move the trailer left, then steer left to straighten the tractor and trailer.

Parallel parking a combination: position the tractor alongside and slightly ahead of the space, back at an angle until the trailer is inside, then swing the tractor to straighten.

90-degree alley dock: pull past the space, turn wide so the trailer is at roughly 90 degrees to the dock, then back with continuous small corrections.

Go slowly and turn the wheel only while moving; turning the wheel while stopped (dry steering) strains the steering gear and gives no feedback.

Use the reference points set during practice (mirror-to-cone alignment) rather than guessing; get out and look (GOAL) if position is uncertain.

Turn radius: a combination needs more space than a single unit - complete turns wide and let the trailer track inside the path of the tractor.

Downshift before a downgrade and use the same gear going down that would be needed going up; do not coast in neutral or with the clutch in.

Speed on curves: reduce speed before entering, because a combination rolls over at a lower speed than a single vehicle and brakes in a curve can cause a jackknife.

Following distance for a loaded combination at 55 mph is at least 7 seconds; add 1 second for each 10 feet of vehicle length over 40 feet.

Railroad crossing procedure: stop within 15 to 50 feet of the nearest rail, look and listen, cross without shifting gears, and do not stop on the tracks.

Bridge formula limits axle weight based on the distance between axles; scale checks can put a legal-looking combination out of service for axle overload.

Skid recovery: stop braking, turn the steering wheel in the direction you want to go, and avoid hard braking until the vehicle straightens.

Right turns: swing wide enough to clear the curb, watch the trailer's right rear in the mirror, and check for vehicles that may pass on the right.

Lane changes require signaling, checking mirrors, and confirming the trailer has cleared the lane before moving over; blind spots on both sides are large.