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Difficulty: MediumStopping and Braking Procedures

In a heavy vehicle lacking Anti-lock Braking System (ABS) capabilities, which operational distinction correctly separates the controlled braking technique from the stab braking technique?

  1. A
    Controlled braking requires repeatedly pumping the foot valve to take up slack adjuster pushrod travel, whereas stab braking requires continuous light pedal application.
  2. B
    Controlled braking eliminates total stopping distance by canceling air brake lag, whereas stab braking only reduces driver reaction distance.
  3. Controlled braking applies braking force as hard as possible without locking the wheels, whereas stab braking involves locking the wheels, releasing the pedal upon lockup, and reapplying when the wheels resume rolling.Answer
  4. D
    Controlled braking relies primarily on activating the driveline retarder on slippery pavement, whereas stab braking uses only the trailer hand valve to slow the vehicle.

Answer

Controlled braking applies braking force as hard as possible without locking the wheels, whereas stab braking involves locking the wheels, releasing the pedal upon lockup, and reapplying when the wheels resume rolling.
The correct response accurately defines both non-ABS emergency stopping procedures. Controlled braking entails applying maximum braking effort without locking the wheels so directional steering control is preserved throughout the stop. Stab braking involves applying maximum braking force until the wheels lock, immediately releasing the pedal until the wheels resume rolling, and then repeating the cycle.

Step-by-Step Solution

1
Define the controlled braking procedure for commercial vehicles without ABS.
Controlled braking consists of applying the brakes as hard as possible without locking the wheels while keeping steering wheel movements small.
Maintaining rolling wheel rotation preserves steering control and produces optimal deceleration.
2
Define the stab braking procedure for commercial vehicles without ABS.
Stab braking involves applying full braking pressure until the wheels lock up, immediately releasing the pedal, and reapplying the brakes as soon as the wheels begin rolling again.
Releasing the brake pedal allows locked wheels to roll and restore directional stability between braking cycles.
3
Identify the core operational difference between the two methods.
Controlled braking seeks continuous braking just short of lockup to retain steering, while stab braking deliberately accepts momentary wheel lockup followed by cyclical release and reapplication.
This functional distinction directly governs driver execution during non-ABS emergency stops.

Key Concept

Emergency braking techniques for non-ABS commercial vehicles (Controlled Braking vs. Stab Braking)
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Topics

Stopping and Braking Procedures

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