A combination is a tractor or truck pulling one or more trailers. The Combination and Doubles/Triples tests ask how the units couple, why they roll over or jackknife, and what to inspect at the connection.
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combination vehicle
veículo combinado
A tractor or truck pulling one or more trailers.
Tractor-trailers, doubles, triples and a straight truck with a trailer are all combinations. They are heavier and longer, need more skill, and roll over more easily in quick turns.
Tested:what makes combinations different to drive and inspect, what happens when the air lines separate, and how to couple safely.
A trailer with no front axle that rests on the tractor's fifth wheel.
When uncoupled it stands on its landing gear. Drivers often just say trailer. Older trailers may have no spring brakes, so chock the wheels when parking.
Tested:questions cover coupling height, inspection, brakes on older trailers, and how trailers behave in skids and lane changes.
The greased plate on the tractor that locks onto the trailer's kingpin.
Its jaws close around the kingpin. The plate must be greased, or friction between tractor and trailer makes steering hard. Before coupling it should tilt down toward the rear with the jaws open.
Tested:why the plate is greased, what position it should be in before coupling, and what to check on it.
A fifth wheel that can move along the tractor frame to shift weight.
Locking pins hold it in place. On the walk-around check that the slide is undamaged, nothing is missing and the pins are locked. It must not sit so far forward that the cab or frame hits the trailer in turns.
kingpin
pino rei
The steel pin under the trailer nose that the fifth wheel grips.
Check it is not bent, broken or worn. When coupling, the jaws must close around the right part of the pin, and there must be no gap between trailer and fifth wheel.
Tested:which part of the kingpin the jaws should close around, how to verify the lock, and what to check in inspection.
Pins that lock a sliding fifth wheel or sliding tandem in place.
Some parts of a tractor or trailer can slide to a new spot. Locking pins hold them there. Every pin must be in place and locked before you drive.
landing gear
pés de apoio
Crank-down legs that hold up the front of an uncoupled semitrailer.
A trailer has no front wheels. When you drop it, the landing gear holds the nose up. You crank it down before uncoupling and all the way up before driving.
Tested:how far to raise the landing gear before driving, where to stop the tractor while inspecting it, and what to check.
Hooking a tractor to a trailer, or one trailer to another.
Coupling means hooking up. You back the fifth wheel under the trailer until the kingpin locks. Then you connect the air lines and electrical cord and check the lock by sight and by a gentle pull.
Tested:questions ask the order of coupling steps, what to inspect after locking, and how the safety latch and locking lever should look.
Separating a tractor from its trailer, or a trailer from its dolly.
Uncoupling means dropping the trailer. You lock the trailer brakes, lower the landing gear, disconnect the lines, unlock the fifth wheel and pull out slowly.
Tested:questions ask the first step before uncoupling, when to lower the landing gear, and where to stop the tractor while the trailer settles.
A trailer tandem that unlocks and slides along rails to shift weight.
The trailer's rear axles sit on a rail. Pull the release handle, and the axles slide forward or back. Moving them changes how much weight each axle carries.
Knowledge questions rarely name it; on the pre-trip inspection you must show the release arm is secured and the locking pins locked.
converter dolly
dolly
converter gear
A fifth-wheel axle unit that lets one trailer tow another.
A semitrailer has no front wheels. The dolly gives it some. You hook the dolly to the first trailer with a pintle hook, then back it under the second trailer.
Tested:how to couple and uncouple the dolly, what trailer height is right, and how an ABS-equipped dolly is marked.
A tractor pulling three trailers, each extra one on a converter dolly.
Triples means three trailers in a row. They are the longest and least stable combination you can drive, and the last trailer whips the most.
Tested:questions pair doubles and triples: how to couple the third trailer, what extra items to inspect, and how the extra length changes your driving.
A skid that folds the tractor and trailer toward each other.
Picture a pocket knife folding. When the trailer wheels lock and slide, the trailer swings around toward the cab. It can also start when the tractor's drive wheels lose grip.
Tested:what causes a jackknife, which trailers jackknife most easily, and what to do with the brakes when one starts.
A crash in which a truck or trailer tips onto its side.
A tall, heavy load raises the center of gravity. Turn too fast and the rig tips over. Keep cargo low and centered, and slow down before curves and ramps.
Tested:what share of driver deaths involve rollovers, which units of a rig roll first, and how loading and speed change the risk.
The cable that powers the trailer's lights and ABS from the tractor.
Drivers call it the pigtail because it coils. You plug it into the trailer socket and close the safety catch. When unhooked, hang it plug-down so water stays out.
Tested:how the electrical cord and air lines should be checked and secured so they cannot be damaged or catch on moving parts.
The service and emergency hoses carrying air from tractor to trailer brakes.
Every trailer gets two air hoses. The service line tells the trailer brakes how hard to apply. The emergency line fills the trailer tanks and sets the brakes if it breaks.
Tested:what each air line does, what happens when lines are crossed or torn apart, and how to inspect them.
A gentle pull against locked trailer brakes to prove the coupling locked.
After you back under the trailer, you lock the trailer brakes and ease the tractor forward in low gear. If the trailer holds you back, the lock is good. The manuals describe this step but do not use the name.
Not the same as:Not a medical or firearms term; in CDL use it is the pull check after coupling.
header board
painel frontal
headache rack
A strong front wall that stops cargo sliding forward into the cab.
Drivers call it a headache rack. In a hard stop or crash, cargo keeps moving. The header board takes that hit instead of you.
Tested:what a header board is for and what you should check about the front-end structure before a trip.
The axle whose wheels get engine power and push the vehicle forward.
The engine turns the drive axle through the drive shaft. On a tractor it is the rear axle or axles. How much weight rests on it decides how well it grips.
Tested:what goes wrong when too little weight sits on the drive axle, and what to inspect on it during the pre-trip.
