Class 1 Commercial Driver Practice · Question
Spring (parking) brakes on a tractor-trailer will automatically apply when air pressure drops to about:
Spring brakes apply automatically as air pressure falls between roughly 20 and 45 psi, depending on the system.
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Question: Spring (parking) brakes on a tractor-trailer will automatically apply when air pressure drops to about:
Answer options: ✅ 20–45 psi
- 50–60 psi
- 70–85 psi
- 100 psi
Correct answer: 20–45 psi
Explanation: Spring brakes apply automatically as air pressure falls between roughly 20 and 45 psi, depending on the system.
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Question explanations
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