Missouri CDL Combination flashcards

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

Tug test

After coupling, release the parking brake, pull gently in low gear against the trailer brakes, and confirm the tractor does not move away from the trailer.

Kingpin

The vertical pin under the trailer nose that locks into the tractor's fifth wheel jaws. It carries the trailer's weight and transfers pulling force.

Fifth wheel jaws

The locking mechanism that closes around the kingpin. Coupling is complete only when the jaws are fully closed and the release handle is locked.

Blue service line

The air line that carries the driver's brake application signal to the trailer relay valve. It is the control line, not the supply line.

Red emergency line

The supply line that charges the trailer air tanks. If it separates, the trailer spring brakes apply automatically and the tractor protection valve seals.

Tractor protection valve

A valve that closes the tractor's air supply to the trailer when pressure drops too low or lines separate, keeping enough air to stop the tractor.

Bobtail proportioning valve

A valve that limits rear tractor braking force when no trailer is attached, preventing the lighter bobtail from locking its rear wheels.

Off-tracking

The tendency of a combination's rear wheels to follow a path inside the front wheels' path, making turns and lane changes require extra room.

Landing gear

The retractable support legs under the trailer nose. After coupling, they must be fully raised and the crank handle secured before driving.

Air brake lag

The delay between pressing the brake pedal and the trailer brakes applying, because air must travel through the lines. It lengthens stopping distance.

Static leak test

With the engine off and full pressure, release the brakes for one minute. Loss must not exceed 3 psi single or 4 psi combination.

Applied leak test

With the engine off, hold the brake pedal for one minute. Air loss must not exceed 4 psi, and the low-air warning must sound by 60 psi.

Compressor build rate

With the engine at operating rpm, pressure must rise from 85 to 100 psi within 45 seconds on a combination vehicle.

Spring brake test

With pressure below 45 psi, trailer spring brakes should apply. Release the parking brake and pull against them to confirm they hold.

Slack adjuster check

Push the brake rod by hand; movement of more than about one inch at the clevis means the brakes are out of adjustment and need service.

Steering tire tread

Front tires must have at least 4/32 inch tread depth. All other tires need at least 2/32 inch, and no tire may show cord or bulges.

Walk-around order

Start at the driver's door, check lights and leaks around the front, inspect the engine compartment, then walk the sides and rear before entering the cab.

Fifth wheel inspection

Check mounting bolts for tightness, the kingpin for wear, the apron for damage, and confirm the fifth wheel plate is properly greased.

Straight-line backing

Back slowly using both mirrors, correcting with small steering inputs toward the mirror where the trailer appears to drift.

Alley dock setup

Pull past the dock until trailer axles clear the near corner, turn toward the dock, straighten the unit, then back with small corrections.

Offset backing

Back straight, steer right to move the trailer left, then steer left to straighten tractor and trailer in the adjacent lane.

Parallel parking

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.

Dry steering

Turning the steering wheel while the vehicle is stopped. It strains the steering gear and gives no useful feedback, so turn only while moving.

GOAL

Get Out And Look. When backing position is uncertain, stop and check outside the vehicle rather than guessing with mirrors.

Reference points

Fixed mirror-to-cone alignments established during practice that tell the driver where the trailer is without leaving the cab.

Turn radius

The space a combination needs to complete a turn. It is larger than a single unit, and the trailer tracks inside the tractor's path.

Downgrade gear rule

Select the same gear going down a grade that would be needed going up, and do not coast in neutral or with the clutch depressed.

Curve speed rule

Reduce speed before entering a curve. A combination rolls over at lower speed than a single vehicle, and braking in a curve can cause a jackknife.

Following distance

At 55 mph a loaded combination needs at least 7 seconds. Add one second for each 10 feet of vehicle length over 40 feet.

Railroad crossing rule

Stop within 15 to 50 feet of the nearest rail, look and listen, cross without shifting gears, and never stop on the tracks.

Bridge formula

A federal limit on axle weight based on the distance between axles. A combination can look legal and still be overloaded on one axle.

Skid recovery

Stop braking, steer in the direction you want to go, and avoid hard braking until the vehicle straightens out.