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Question

Difficulty: MediumBrake Failure

When a commercial motor vehicle experiences complete service brake failure, the parking brake may be used to assist in stopping the vehicle, provided the driver applies it carefully to avoid locking the drive wheels and causing a skid.

Answer: Answer

Answer

True
The statement is true because the parking brake serves as an independent secondary stopping mechanism when the primary service brakes fail completely. However, because parking brakes apply force without anti-lock modulation, drivers must apply them carefully to prevent drive-wheel lockup and dangerous skidding.

Step-by-Step Solution

1
Analyze the operational role of the parking brake system during complete service brake loss.
Identify that the parking brake (spring brakes or mechanical linkage) operates independently of the service brake circuit and can provide deceleration force.
Commercial vehicles require a secondary braking system capable of bringing the vehicle to a stop when service brakes fail.
2
Evaluate the directional control and traction risks associated with parking brake application at roadway speeds.
Recognize that applying the parking brake too abruptly can exceed tire adhesion and lock the drive axle wheels.
Locked drive wheels lose lateral stability, leading directly to drive-wheel skids or jackknifing.
3
Synthesize the procedure to verify the validity of the statement.
Confirm that using the parking brake with caution is the proper emergency procedure during total service brake failure.
This procedure achieves emergency deceleration while preserving vehicle steering and directional stability.

Key Concept

Emergency stopping using the parking brake and skid prevention during total brake failure
Estimated Time:1m 0s
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Topics

Brake Failure

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