Examkin

Question

Difficulty: MediumMountain Driving and Steep Downgrades

You have selected the proper low gear and established a safe speed of 30 mph30\text{ mph} before starting down a steep mountain downgrade. As gravity accelerates the truck to 30 mph30\text{ mph} on the slope, how should you apply the service brakes to manage your speed without overheating the brake drums?

  1. A
    Apply the brakes lightly and continuously down the entire grade to hold the speed steadily at 30 mph30\text{ mph}.
  2. Apply the brakes firmly enough to feel a definite slowdown until speed reaches 25 mph25\text{ mph}, then release the brakes completely.Answer
  3. C
    Shift the transmission into neutral and engage maximum retarder braking to keep vehicle speed below 25 mph25\text{ mph}.
  4. D
    Pump the brake pedal rapidly with light, quick taps whenever the speed climbs 5 mph5\text{ mph} above the safe speed.

Answer

Apply the brakes firmly enough to feel a definite slowdown until speed reaches 25 mph25\text{ mph}, then release the brakes completely.
The proper snub braking technique requires applying the brakes firmly enough to feel a definite slowdown until vehicle speed drops to 5 mph5\text{ mph} below the designated safe speed (from 30 mph30\text{ mph} down to 25 mph25\text{ mph}), followed by a complete release of the pedal to allow the brakes to cool while speed slowly rebuilds.

Step-by-Step Solution

1
Determine the speed reduction target for snub braking
Target speed is 5 mph5\text{ mph} below the established safe speed of 30 mph30\text{ mph}, which equals 25 mph25\text{ mph}.
The commercial motor vehicle manual mandates slowing down to 5 mph5\text{ mph} below safe speed during each braking cycle.
2
Apply moderate to firm brake pressure
The vehicle decelerates smoothly from 30 mph30\text{ mph} to 25 mph25\text{ mph} over approximately 3 seconds.
Firm application generates effective friction to reduce vehicle speed quickly without prolonging contact time.
3
Release the service brakes completely once the vehicle slows to 25 mph25\text{ mph}
Brake shoes retract from the drums, restoring cooling airflow while gravity slowly rebuilds speed.
Releasing the brakes allows heat to dissipate into the atmosphere until speed rises back to 30 mph30\text{ mph}, at which point the cycle is repeated.

Key Concept

Snub braking technique and thermal brake fade prevention on mountain downgrades
Estimated Time:1m 0s
Rate this question

Topics

Mountain Driving and Steep Downgrades

More questions from this topic