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Question

Difficulty: MediumBraking Systems

In a vehicle equipped with front disc and rear drum brakes, which hydraulic valve limits fluid pressure to the rear wheels during heavy braking to prevent premature lockup?

  1. A
    Metering valve
  2. B
    Pressure differential valve
  3. Proportioning valveAnswer
  4. D
    Residual pressure valve

Answer

Proportioning valve
The proportioning valve is engineered specifically to limit hydraulic line pressure delivered to the rear brakes under hard deceleration. As vehicle weight shifts forward onto the front suspension during heavy braking, the rear tires lose traction; the proportioning valve restricts rear line pressure to prevent rear-wheel lockup and directional skidding.

Step-by-Step Solution

1
Identify the vehicle braking dynamic during heavy stops
Dynamic weight transfers forward toward the front axle, significantly reducing traction on the lighter rear axle.
Because less normal force acts on the rear tires during rapid deceleration, the rear wheels require less hydraulic clamping force to avoid lockup.
2
Evaluate the specific hydraulic valve designed to control rear brake pressure
The proportioning valve reduces the rate of hydraulic pressure increase to the rear drum brakes once a predetermined line pressure threshold is reached.
This pressure modulation prevents the rear wheels from locking prematurely, maintaining vehicle stability and steering control.

Key Concept

Hydraulic Brake Proportioning and Directional Stability
Estimated Time:1m 0s
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Topics

Braking Systems

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