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Question

Difficulty: MediumBraking Systems

During a brake inspection, a technician finds that the inboard brake pad on a floating caliper assembly is worn down to the metal backing plate, while the outboard pad has substantial friction material remaining. What is the most likely cause?

  1. A
    Air trapped within the hydraulic brake lines
  2. Corroded or seized caliper slide pinsAnswer
  3. C
    Weak or broken drum brake return springs
  4. D
    A leaking master cylinder secondary cup seal

Answer

Corroded or seized caliper slide pins
In a floating disc brake caliper, hydraulic pressure pushes the caliper piston directly against the inboard pad, while the reactive force slides the caliper housing along lubricated slide pins to clamp the outboard pad against the opposite side of the rotor. When the slide pins corrode or seize, the caliper body cannot move laterally. As a result, the inboard pad sustains all the clamping friction and wears down prematurely, while the outboard pad barely contacts the rotor and retains its thickness.

Step-by-Step Solution

1
Identify the mechanical operating principle of a floating (sliding) disc brake caliper.
In a floating caliper, the hydraulic piston directly pushes the inboard pad against the rotor, while reactive sliding movement along guide pins pulls the outer caliper frame to press the outboard pad.
Understanding floating caliper mechanics explains how clamping force is normally balanced between the inner and outer pads.
2
Analyze the effect of seized guide pins on clamping force distribution.
When the slide pins bind or corrode, the caliper cannot slide sideways. The piston continues to press the inboard pad against the rotor during braking, but minimal clamping force reaches the outboard pad.
This restriction isolates friction and heat to the inboard pad, causing severe accelerated wear on the inner pad alone.

Key Concept

Floating Caliper Operation and Slide Pin Function
Estimated Time:1m 0s
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Topics

Braking Systems

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