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Question

Difficulty: MediumBrake Failure

When using the parking brake to slow a commercial vehicle during a total hydraulic service brake failure, the driver should hold the release mechanism in the released position while applying the brake to modulate braking force and prevent wheel lockup.

Answer: Answer

Answer

True, because holding the parking brake release control allows the driver to modulate braking pressure and avoid locking the wheels.
The statement is correct because the parking brake is mechanically independent of the hydraulic system and serves as an emergency stopping mechanism. Holding the release control prevents the ratchet from locking the brakes fully on, allowing the driver to modulate friction and stop safely without initiating a drive-wheel skid.

Step-by-Step Solution

1
Identify the functional independence of the parking brake system during hydraulic failure.
The parking brake operates via a dedicated mechanical linkage separate from the hydraulic fluid lines.
The mechanical parking brake remains operational even when hydraulic fluid pressure is completely lost.
2
Analyze the mechanical behavior of the parking brake lever or pedal ratchet.
Without holding the release control, the ratchet locks the brake in maximum friction application.
Sudden full mechanical application at highway speed eliminates wheel rotation and causes immediate tire skid.
3
Apply standard commercial driving emergency procedures for controlled deceleration.
Holding the release lever or button enables variable pressure application and instant release if skidding begins.
Modulating the brake application maintains vehicle stability, tire traction, and steering capability during an emergency stop.

Key Concept

Hydraulic brake failure emergency sequence and parking brake modulation
Estimated Time:1m 0s
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Topics

Brake Failure

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