how to check disk brakes

Disc Braking System Inspection and Evaluation

Components of a Disc Brake System

  • Rotor (Disc): The rotating component against which the brake pads apply friction.
  • Caliper: Houses the brake pads and pistons, and applies hydraulic pressure to clamp the pads against the rotor.
  • Brake Pads: Friction material that contacts the rotor to slow or stop the vehicle.
  • Brake Lines: Hoses or pipes that carry brake fluid from the master cylinder to the calipers.
  • Brake Fluid: Hydraulic fluid that transmits pressure from the master cylinder to the calipers.

Rotor Assessment

Visual Examination

Scrutinize the rotor surface for signs of damage such as:

  • Scoring or grooves: Indicates wear or presence of debris.
  • Cracks: A critical safety concern requiring immediate replacement.
  • Rust: Surface rust is normal but excessive rust indicates lack of use or corrosion.
  • Bluing: Evidence of overheating, potentially compromising the rotor's integrity.

Rotor Thickness Measurement

Use a micrometer to measure rotor thickness at various points. Compare measurements to the manufacturer's minimum thickness specification. Rotors below this thickness must be replaced.

Rotor Runout (Lateral Deviation)

Employ a dial indicator to measure rotor runout. Excessive runout can cause brake pulsation and uneven pad wear. May require resurfacing or replacement.

Brake Pad Evaluation

Friction Material Thickness

Determine the remaining thickness of the friction material on each brake pad. Compare to the manufacturer's recommended minimum thickness. Pads worn below the minimum must be replaced.

Pad Condition

Assess the brake pads for:

  • Uneven wear: Indicates potential caliper or rotor issues.
  • Cracking or crumbling: Compromises the pad's ability to function effectively.
  • Glazing: Hard, shiny surface reduces friction.
  • Contamination: Oil, grease, or other contaminants reduce braking performance.

Caliper Examination

Visual Inspection

Examine the caliper for:

  • Leaks: Indicates a seal failure requiring repair or replacement.
  • Corrosion: Can affect caliper function and piston movement.
  • Damage: Cracks or other physical damage can compromise the caliper's structural integrity.

Piston Movement

Verify that the caliper pistons move freely. Sticking pistons can cause uneven pad wear and reduced braking performance.

Slide Pins (if applicable)

Ensure that slide pins are clean, lubricated, and move freely within the caliper bracket.

Brake Line Inspection

Visual Assessment

Inspect brake lines for:

  • Cracks or abrasions: Can lead to leaks or line failure.
  • Bulges: Indicate weakening of the line.
  • Corrosion: Can weaken the line and lead to leaks.
  • Leaks: Visible fluid indicates a break in the line or a loose connection.

Brake Fluid Assessment

Fluid Level

Confirm the brake fluid reservoir is filled to the appropriate level.

Fluid Condition

Observe the brake fluid's color and clarity. Dark or contaminated fluid should be flushed and replaced. Test the fluid for moisture content using a brake fluid tester. Excessive moisture can lead to corrosion and reduced braking performance.