How is the tractor-trailer connection initially tested after the kingpin locks?
Correct answer: Raise the landing gear slightly and pull gently against locked trailer brakes
A gentle pull against the locked trailer brakes is an initial coupling check, not complete proof. Secure the vehicle and also visually check that the fifth-wheel plates meet and the jaws are locked around the kingpin shank before driving.
Source: Texas DL-7C, March 2026, section 6, PDF page 98: Coupling security ↗
Where should the fifth-wheel locking jaws be after proper coupling?
Correct answer: Around the shank of the kingpin
A visual inspection must confirm the jaws fully encircle the kingpin shank with no gap between fifth-wheel plates.
Source: Texas DL-7C, March 2026, section 6, PDF page 98: Coupling inspection ↗
Before driving a coupled tractor-semitrailer, how far should the landing gear be raised?
Correct answer: Fully raised with the crank secured
Partly raised gear can strike tracks or road objects and must be fully stowed.
Source: Texas DL-7C, March 2026, section 6, PDF page 99: Landing gear ↗
Why should the tractor remain partly under the trailer during the first pull-forward step?
Correct answer: It can support the trailer if the landing gear collapses or sinks
Keeping the tractor frame under the trailer provides temporary support while the landing gear is checked.
Source: Texas DL-7C, March 2026, section 6, PDF page 99: Uncoupling ↗
On a combination equipped with a trailer hand valve, how are the trailer service brakes checked before normal operation?
Correct answer: Move slowly and apply the trailer hand valve to feel the brakes engage
At normal air pressure with parking brakes released, move slowly and apply the hand control if equipped. Feel the trailer brakes engage. Use the foot pedal during normal driving.
Source: Texas DL-7C, March 2026, section 6, PDF page 104: Brake testing ↗
You find dirt on a glad-hand coupling and its rubber seal before connecting a trailer. What should you do?
Correct answer: Clean the coupler and seal before making the connection
Clean couplers and seals before connecting them. The rubber seal prevents air from escaping, and keeping contamination out protects the air system.
Source: Texas DL-7C, March 2026, section 6, PDF page 95: Air-line connections ↗
After disconnecting a trailer, where should the tractor’s air-line couplers be attached if dummy couplers are provided?
Correct answer: To the dummy couplers to keep dirt and water out
Dummy or dead-end couplers protect unused air lines from water and dirt. Use them when the hoses are not connected to a trailer.
Source: Texas DL-7C, March 2026, section 6, PDF page 96: Unused air lines ↗
When you press the foot brake, what determines how much pressure the relay valves send from the trailer reservoirs to its brakes?
Correct answer: The pressure in the service line
Service-line pressure communicates the braking demand to the relay valves. The trailer’s own reservoirs supply the air sent to its brakes.
Source: Texas DL-7C, March 2026, section 6, PDF page 96: Trailer brake control ↗
A major trailer service-line leak may become obvious only when you apply the brakes. What can happen then?
Correct answer: Air pressure can fall rapidly and eventually apply the trailer emergency brakes
A service-line leak may not be apparent until braking pressurizes that line. The resulting air loss can rapidly lower tank pressure; at sufficiently low pressure, trailer emergency brakes can apply.
Source: Texas DL-7C, March 2026, section 6, PDF page 96: Service-line leaks ↗
A tractor-trailer has ABS on the trailer but not on the tractor. Which statement is correct?
Correct answer: Trailer ABS still helps, but the tractor can still lose control under braking
ABS on the trailer alone can reduce trailer swing, but it does not prevent tractor wheel lock or every jackknife. Monitor both units and use only the braking force needed to stop safely and retain control.
Source: Texas DL-7C, March 2026, section 6, PDF page 97: Partial ABS equipment ↗
Does an automatic drain eliminate the handbook’s advice to check trailer air tanks for accumulated moisture?
Correct answer: No; open the drains to check, because automatic drains remove most moisture, not necessarily all of it
The handbook says to drain each trailer air tank daily and still open drains to check tanks with automatic drains. Water and oil accumulation can interfere with correct brake operation.
Source: Texas DL-7C, March 2026, section 6, PDF page 96: Trailer reservoirs ↗
Before backing a tractor under a trailer, what must prevent the trailer from rolling?
Correct answer: Applied spring brakes or appropriate wheel chocks
Coupling forces can move an unsecured trailer. Check the area and its securement first.
Source: Texas DL-7C, March 2026, section 6, PDF page 98: Coupling and uncoupling ↗
Why should the tractor be straight in front of the trailer before coupling?
Correct answer: An angled approach can push the trailer sideways and damage its landing gear
Align the units rather than use the tractor to force the trailer sideways.
Source: Texas DL-7C, March 2026, section 6, PDF page 98: Coupling and uncoupling ↗
How should air lines be arranged before you finish backing under the trailer?
Correct answer: Supported clear of places where they could be crushed or caught
Line support must protect the connections during coupling and later movement.
Source: Texas DL-7C, March 2026, section 6, PDF page 98: Coupling and uncoupling ↗
What reverse gear and speed are appropriate for the final coupling movement?
Correct answer: Lowest reverse gear at a slow, controlled speed
Avoid striking the kingpin hard while completing the connection.
Source: Texas DL-7C, March 2026, section 6, PDF page 98: Coupling and uncoupling ↗
Before going underneath to inspect the coupling, how should you secure the tractor?
Correct answer: Parking brakes on, transmission neutral, engine off, and key with you
Prevent someone moving the rig while you inspect underneath.
Source: Texas DL-7C, March 2026, section 6, PDF page 98: Coupling and uncoupling ↗
You see a gap between the trailer’s upper plate and the fifth-wheel plate after coupling. What should you do?
Correct answer: Do not drive until the coupling problem is corrected
A gap can mean the kingpin is resting above the jaws rather than being correctly locked.
Source: Texas DL-7C, March 2026, section 6, PDF page 98: Coupling and uncoupling ↗
Besides checking the jaws around the kingpin, which locking parts need inspection?
Correct answer: The locking lever and its safety latch
Verify the complete locking mechanism rather than relying on a tug test alone.
Source: Texas DL-7C, March 2026, section 6, PDF page 98: Coupling and uncoupling ↗
Once the trailer’s weight rests on the tractor, which clearances must you check?
Correct answer: Tractor frame to landing gear and tractor tires to trailer nose
Turning or suspension movement must not cause contact between the units.
Source: Texas DL-7C, March 2026, section 6, PDF page 99: Coupling and uncoupling ↗
Before uncoupling a loaded trailer, what must you know about the parking surface?
Correct answer: It can support the trailer and landing gear
Landing gear can sink or collapse on an unsuitable surface.
Source: Texas DL-7C, March 2026, section 6, PDF page 99: Coupling and uncoupling ↗
