Examkin

Question

Difficulty: HardSpeed on Curves and Downgrades

While operating a fully loaded combination vehicle down a steep 5-mile mountain grade, you have downshifted into the appropriate low gear and established a safe operating speed of 35 mph. What is the correct method for applying the service brakes to regulate speed and avoid brake fade throughout the descent?

  1. A
    Maintain continuous, light foot pressure on the service brake pedal throughout the entire downgrade to hold the road speed steadily at 35 mph.
  2. B
    Allow vehicle momentum to increase to 40 mph before downshifting one gear lower, then apply heavy continuous braking to force speed down to 25 mph.
  3. Apply the service brakes firmly to reduce speed to 30 mph, release the pedal completely until speed returns to 35 mph, and repeat this cycle.Answer
  4. D
    Rely exclusively on maximum auxiliary retarder settings while keeping the service brakes disengaged, regardless of gradual acceleration past 35 mph.

Answer

Apply the service brakes firmly to reduce speed to 30 mph, release the pedal completely until speed returns to 35 mph, and repeat this cycle.
The correct technique is snub braking: once the safe speed of 35 mph is reached, the driver applies the service brakes firmly to decelerate the vehicle to 5 mph below that speed (30 mph), then completely releases the pedal. This cycle repeats as gravity causes speed to build back up, giving the brake drums and linings essential cooling intervals and preventing thermal brake fade.

Step-by-Step Solution

1
Establish the safe maximum descent speed and match it to engine braking capability in the selected low gear.
The vehicle is held primarily by engine compression at the target safe speed of 35 mph.
Engine braking provides sustained retarding force without generating thermal stress in the wheel friction components.
2
When vehicle speed reaches the safe speed threshold of 35 mph, apply the service brakes with firm, even pressure for approximately three seconds until speed drops to 30 mph.
The vehicle decelerates by exactly 5 mph below the established safe speed.
Firm, brief brake application achieves rapid deceleration without extended friction contact.
3
Release the service brake pedal entirely once speed reaches 30 mph, allowing the vehicle to roll under engine retarding until speed climbs back to 35 mph.
Brake linings and drums cool down in the airflow while the cycle is repeated down the grade.
Releasing the brakes provides critical thermal recovery time, preventing drum expansion and brake fade.

Key Concept

Proper execution of snub braking on steep downgrades to prevent thermal brake fade
Estimated Time:1m 30s
Rate this question

Topics

Speed on Curves and Downgrades

More questions from this topic