ELDT Coupling and Uncoupling 2 — Questions and Answers
Question 1: Before backing under a trailer, where should the fifth wheel plate be positioned relative to the trailer's apron?
- Slightly lower than the trailer apron (Correct answer)
- Exactly level with the apron
- Higher than the trailer apron
- Tilted fully forward and locked
Correct answer: Slightly lower than the trailer apron
The fifth wheel should be low enough that the tractor lifts the trailer slightly as you back under it, ensuring the kingpin engages properly.
Question 2: What is the correct height for the trailer before backing the tractor under it?
- Low enough that the tractor frame will hit the trailer
- So the trailer is raised slightly when the tractor backs under (Correct answer)
- As high as the landing gear will allow
- Level with the tractor's cab roof
Correct answer: So the trailer is raised slightly when the tractor backs under
The trailer should be at a height where the tractor raises it slightly when backing under, guaranteeing solid kingpin contact.
Question 3: When testing the coupling by pulling forward gently against the locked kingpin, this is called a:
- Brake check
- Tug test (Correct answer)
- Roll test
- Air test
Correct answer: Tug test
The tug test involves gently pulling the tractor forward against the locked fifth wheel to confirm the kingpin is secured.
Question 4: Which color glad hand or line typically supplies the emergency (supply) air to the trailer?
- Blue
- Red (Correct answer)
- Green
- Yellow
Correct answer: Red
The red line/glad hand is the emergency supply line that charges the trailer air tanks and controls the spring brakes.
Question 5: What should you do with the tractor parking brake before crawling under to inspect the coupling?
- Release it so the truck can roll freely
- Apply it and chock the wheels if needed (Correct answer)
- Leave it in whatever position it was
- Apply only the trailer brake
Correct answer: Apply it and chock the wheels if needed
Always apply the parking brakes before going under the vehicle to prevent it from rolling and crushing you.
Question 6: After coupling, how much space should there be between the tractor frame and the bottom of the trailer?
- Several inches of gap
- No space at all (Correct answer)
- Enough for two hands to fit
- About one foot
Correct answer: No space at all
There should be no space between the fifth wheel and the trailer apron, as a gap means the coupling may be resting on the kingpin only.
Question 7: Where should the kingpin sit in relation to the fifth wheel locking jaws when properly coupled?
- In front of the open jaws
- Locked inside the closed jaws (Correct answer)
- Resting on top of the fifth wheel
- Behind the locking mechanism
Correct answer: Locked inside the closed jaws
A proper coupling has the kingpin fully seated and the locking jaws closed around it, which you verify by inspection.
ELDT Coupling and Uncoupling 2
Before backing under a trailer, where should the fifth wheel plate be positioned relative to the trailer's apron?