Drum & Disk Brakes

Parts of a Drum brake

Backing Plate

  • Provides a mounting point for shoes , springs, wheel cylinders inside the brake drum (holds everything together)

  • Keeps dirt and water off the brake parts

  • Bolted to the rear axle or spindle

Brake shoes

  • Metal shoe supports and holds the brake lining

Two ways of mounting brake lining

riveted and bonded

  • Primary shoe is the front brake shoe (shorter lining)

  • Secondary shoe is the rear brake shoe (longer lining)

Wheel cylinder

  • Filled with brake fluid

  • A cylinder that has two pistons

  • Exerts mechanical force to the shoes

  • Moves the shoes into contact with the drums

  • Wheel cylinder must be replaced or rebuilt if show signs of leakage

  • Rebuilding wheel cylinders is no longer common practice

Return Spring

  • Pulls shoes back to place after the wheel cylinder is applied

  • Hold-down springs

  • Holds the brake shoe against the backing

  • Star Wheel (brake shoe) Adjuster

  • Maintain the correct drum-to-lining clearance

Parts of a Disk brake

Rotors

  • Cast Iron

  • Vented or Solid type rotors

  • Hub and rotor design or rotor separate

  • Rotates with the wheel

  • Mounted between the two pads

Calipers

  • Attached to the steering knuckle

  • Contains one or more pistons (dual piston or single piston)

  • Floating caliper- caliper is free to move sideways on bushings and guide pins. Contains only one piston

  • Non-floating or fixed- caliper is in a fixed position and cannot move, has pistons on both sides of the rotor, both inboard and outboard halves.

  • Contains a bleeder screw which allows the system to be bled

Brake Pads

  • Types - non asbestos, semi-metallic, full-metallic, ceramic

  • Lining is either riveted or bonded

  • Lining contacts both sided of the rotor

  • Wear indicators purpose is to contact the rotor when pads are at there minimum

  • A high pitch squeal is heard as a reminder, to prevent rotor damage (scoring, gouging)

  • Special lubricants are required when servicing pads and calipers

  • Service sliders and bushing for maximum brake performance and longevity