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Difficulty: HardBraking Systems and ABS

You are descending a long, steep hill and notice that your vehicle's footbrake is gradually becoming less effective, requiring significantly firmer pedal pressure to slow down. What is the primary cause of this problem, and what action should you take to prevent it?

  1. A
    The anti-lock braking system (ABS) computer temporarily limits hydraulic pressure to prevent skidding; you should rapidly pump the footbrake pedal to restore normal bite.
  2. The brake discs and pads overheat from continuous friction, reducing their stopping power; you should select a lower gear before descending to utilise engine braking.Answer
  3. C
    Excessive heat causes brake fluid to evaporate and disconnect the hydraulic servo; you should shift into neutral and coast so the discs can cool down in the airflow.
  4. D
    Moisture on the road surface has cooled the braking assembly below its operating temperature; you should firmly apply the parking brake while driving to generate heat.

Answer

The brake discs and pads overheat from continuous friction, reducing their stopping power; selecting a lower gear before descending enables engine braking to help control vehicle speed.
Prolonged and heavy use of the footbrake down steep gradients generates excessive heat between the brake pads and discs or drums. This thermal saturation causes 'brake fade', dramatically reducing frictional grip and making the vehicle much harder to stop. To prevent this, drivers should select a lower gear before descending so that engine compression helps control vehicle speed, keeping the friction brakes cool and effective.

Step-by-Step Solution

1
Diagnose the mechanical cause of reduced braking efficiency during a prolonged descent.
Repeated and continuous use of the footbrake generates intense thermal energy, causing brake pads and discs to overheat. This thermal saturation leads to 'brake fade', where friction drops sharply and the pedal feels hard but ineffective.
Recognising the symptoms of brake fade is essential for identifying when friction components are operating beyond their safe thermal limits.
2
Determine the proper driving technique to prevent thermal overload on braking components.
Selecting a lower gear prior to or during the descent engages engine braking, using engine compression to control road speed and taking the strain off the wheel brakes.
Engine braking provides continuous, heat-free speed retardation on gradients, preserving full friction braking capability for emergency stops.

Key Concept

Brake Fade and Engine Braking on Steep Gradients
Estimated Time:1m 30s
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Topics

Braking Systems and ABS

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