Coupling, handling, and inspection concepts for combination vehicles tested on the CDL Class A exam.
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- What is the first step in coupling a tractor to a trailer?
- Ensure the tractor and trailer are on level ground and properly aligned.
- What does the king pin do?
- It is the large pin that connects the trailer to the tractor's fifth wheel.
- What should you check on the fifth wheel before coupling?
- Check that it is clean, free of grease, and properly adjusted.
- What is the tractor protection valve?
- It closes automatically if the tractor's air pressure drops to prevent loss of tractor brakes.
- How do you verify that a trailer is fully coupled?
- Ensure the fifth wheel jaws are locked around the king pin and safety chains are attached.
- What is rearward amplification?
- The tendency of the rear end of a trailer to move more than the front when steering, especially in doubles.
- What causes jackknife accidents in combination vehicles?
- Braking too hard, turning sharply while braking, or skidding on slippery surfaces.
- What weight ratio should exist between a tractor and trailer for safe operation?
- The tractor's GVWR should be at least 50 percent of the trailer's GVWR.
- When backing a tractor-trailer combination, which end swings out first?
- The trailer's rear end swings out away from the direction of the turn.
- What is the purpose of a slack adjuster?
- It maintains proper clearance between the brake shoes and brake drum during braking.
- What is a spring brake?
- A spring-applied, air-release brake that automatically engages if air pressure is lost.
- What is the correct first step when uncoupling a trailer?
- Lower the trailer jack to support it.
- What is brake fade?
- The reduction in braking power that occurs when brakes overheat due to prolonged use.
- What is the proper air pressure range for tractor and trailer brake systems?
- Typically between 100 and 125 PSI.
- When should tire pressure be checked on a combination vehicle?
- Every day as part of the pre-trip inspection and when the tires are cold.