Pennsylvania CDL Combination flashcards

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

Fifth-wheel jaw check

After coupling, pull gently forward against set trailer brakes. If the jaws are locked, the trailer resists; if the jaw is open or high, the trailer slides and a gap opens.

Kingpin

The greased steel pin on the trailer apron that the fifth-wheel jaws lock around. A worn or damaged kingpin can let the trailer separate from the tractor.

Tug test

A post-coupling check: with trailer brakes set, pull the tractor slowly forward. Movement of the trailer or a widening gap means the coupling is not secure.

Landing gear

The retractable legs supporting an uncoupled trailer. Crank them down before uncoupling and fully up before moving, or they strike the road and damage the trailer.

Emergency air line

The supply line that charges the trailer air tank and releases the trailer spring brakes. Connect it before the service line; if it separates, the trailer brakes apply.

Service air line

The line that carries the driver's brake application signal to the trailer relay valve. It does not charge the trailer tank, so it is connected after the emergency line.

Tractor protection valve

A valve that closes automatically when the trailer lines separate, trapping the tractor's air so it can still stop. The red trailer air supply knob pops out.

Trailer air protection valve

A trailer-mounted valve that applies and holds the trailer spring brakes when supply pressure is lost, preventing a separated trailer from rolling free.

Glad hands

The couplers joining tractor and trailer air lines. They must be locked, sealed with good rubber gaskets, and free of leaks; a leaky coupling drains air pressure.

Off-tracking

The tendency of trailer rear wheels to cut inside the path of the front wheels. It is worst in tight turns and short wheelbases, so swing wide and check mirrors.

Swing wide

A turn technique for combinations: move out before a turn so the trailer's rear wheels clear the inside curb, then watch the trailer in the mirrors through the turn.

Rearward amplification

The tendency of the trailer's rear to swing farther than the tractor in quick lane changes, which can cause trailer rollover. Avoid abrupt steering at highway speed.

Combination brake test

With full pressure and parking brake released, hold the foot brake one minute. A drop over about 4 psi indicates an air leak that must be fixed before driving.

Static leak check

With the engine off and brakes released, watch the gauge for a slow drop over a minute; then apply the brake and check again. Leaks above the limit require repair.

Spring brakes

Air-released, spring-applied parking and emergency brakes on tractors and trailers. Loss of air pressure makes them apply automatically, stopping the vehicle.

Trailer hand valve

A lever that applies only the trailer brakes, used for testing trailer brake operation and for controlling a trailer in some low-speed situations. It is not a parking brake.

Bobtail braking

Driving a tractor without a trailer. The light rear axle locks easily under hard braking, so brake gently and allow longer stopping distance.

Coupling height check

Before backing under, confirm the trailer apron is at the right height: the fifth wheel should contact the trailer and lift it slightly, not strike the kingpin or pass beneath.

Back slowly to couple

Back under the trailer in a straight line at low speed with the tractor aligned. Misalignment can damage the kingpin or push the trailer sideways.

Uncoupling sequence

Park on level ground, set the parking brake, lower the landing gear to the ground, disconnect the air lines and electrical cord, then release the fifth-wheel jaws and pull out.

Electrical cord stowage

Plug the cord into the trailer receptacle and route it so it will not drag or snag. A dragging cord wears through and kills trailer lights, turn signals, and ABS power.

Trailer ABS light

The trailer ABS lamp should come on at start and go out above about 5 mph. A light that stays on means the trailer ABS is not working; brakes still function.

Pre-trip combination walk-around

Check coupling, air lines, electrical cord, landing gear, tires, lights, and mud flaps. A missed item in any one can cause separation, fire, or loss of control.

Wheel chocks

Blocks placed against trailer tires before uncoupling on any slope. They prevent the trailer from rolling when the tractor is pulled away and the brakes release.

Release lever

The fifth-wheel handle that opens the locking jaws. It must be fully in the locked position after coupling; a partly open lever lets the trailer separate.

Fifth-wheel grease

Lubricant on the fifth-wheel plate and kingpin. Dry or dirty surfaces cause the trailer to resist turning, and the tractor can push the trailer instead of steering it.

Trailer brake check

With the trailer connected and charged, apply the trailer hand valve or foot brake and have someone watch the trailer wheels; the brakes should apply and hold.

Air pressure build-up

The compressor should raise pressure from about 85 to 100 psi within a set time. Slow build-up means a leak or weak compressor and must be checked.

Low air warning

A buzzer and light must activate before pressure falls below about 60 psi, warning that spring brakes will soon apply automatically and stop the vehicle.

Governor cut-out

The pressure at which the compressor stops pumping, usually around 120 to 125 psi. A gauge that keeps climbing past this indicates a faulty governor or gauge.

Following distance

Combinations need at least one second per ten feet of vehicle length plus one second. A 60-foot rig at 55 mph needs about seven seconds behind the vehicle ahead.

Controlled braking

Brake early and progressively on downgrades and before curves, using engine braking to hold speed. Harsh braking on a combination invites jackknife and trailer swing.

Jackknife

A loss of control in which the tractor and trailer fold at the coupling, often from locking drive or trailer wheels on a slick surface. Steady, light braking helps prevent it.