Examkin

Question

Difficulty: MediumBraking Systems

When the brake pedal is released, what component or mechanism pulls the disc brake caliper piston slightly back into its bore?

  1. A
    Coil return springs attached across the friction pads
  2. The elastic recovery of the square-cut O-ring sealAnswer
  3. C
    Engine vacuum routed through the power brake booster
  4. D
    Centrifugal force created by the rotating brake rotor

Answer

The elastic recovery of the square-cut O-ring seal
In a hydraulic disc brake caliper, the square-cut rubber seal deforms into a trapezoidal shape as fluid pressure drives the piston toward the rotor. When hydraulic pressure is vented upon releasing the brake pedal, the elasticity of the rubber seal pulls the piston back a fraction of an inch to maintain proper running clearance.

Step-by-Step Solution

1
Analyze how hydraulic pressure moves a disc brake caliper piston during brake application.
Pressurized brake fluid enters the caliper bore and pushes the piston outward, causing the square-cut rubber seal in the caliper groove to elastically distort in the direction of movement.
The square-cut seal provides a high-pressure fluid seal while simultaneously storing mechanical elastic energy.
2
Determine how the piston retracts once the brake pedal is released and line pressure vents back to the master cylinder.
The square-cut seal springs back to its original relaxed shape, pulling the piston back approximately 0.005 to 0.010 inches into the bore.
This slight retraction eliminates pad drag against the spinning rotor without requiring external mechanical return springs.

Key Concept

Disc brake caliper piston retraction through square-cut seal elastic deflection
Estimated Time:45s
Rate this question

Topics

Braking Systems

More questions from this topic