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?
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Ensure the tractor and trailer are on level ground and properly aligned.- What does the king pin do?
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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?
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Check that it is clean, free of grease, and properly adjusted.- What is the tractor protection valve?
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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?
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Ensure the fifth wheel jaws are locked around the king pin and safety chains are attached.- What is rearward amplification?
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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?
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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?
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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?
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The trailer's rear end swings out away from the direction of the turn.- What is the purpose of a slack adjuster?
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It maintains proper clearance between the brake shoes and brake drum during braking.- What is a spring brake?
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A spring-applied, air-release brake that automatically engages if air pressure is lost.- What is the correct first step when uncoupling a trailer?
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Lower the trailer jack to support it.- What is brake fade?
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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?
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Typically between 100 and 125 PSI.- When should tire pressure be checked on a combination vehicle?
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Every day as part of the pre-trip inspection and when the tires are cold.
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