Mechanics

Brake Pads

Article describes how automotive brake pads work.

Brake pads are designed to absorb heat as they create friction against the brake rotor when the brake pedal is activated. These pads ride against either side of the rotor which are held in place by the brake caliper which is typically mounted to the spindle or backing plate. Hydraulic pressure is provided by the brake system via a brake master cylinder. When the brake system is activated the brake pads are forced against the brake rotor causing it to slow down, in turn slowing the motion of the car. Heat is created and dissipated through the pads and rotors. If a brake pad or rotor becomes overheated it can hinder the brake operation until cooled because no additional heat can be absorbed which is known as brake fade.

Brake pads are designed to withstand the amount of pressure provided by the master cylinder. While the backing plates of all brake pads are made of metal there are several different classifications of the brake composite, for example; organic, semi metallic and ceramic to name a few. The organic pad is used mainly for stock applications, the semi metallic is used for trucks and SUV's while the ceramic pad is used for extended life applications. Each of these pads possess individual wear and usage characteristics, for example; organic pads are the most forgiving pad when it comes to brake rotor wear, and tend to make less brake noise such as squeaking.

Semi metallic pads tend to be more abusive to the rotors but can take more heat then organic pads before brake fade occurs. Ceramic pads are the hardest pad of the group and can wear out the rotors over the life of the brake pad. Ceramic pads can also be associated with brake pad producing noises like squeaking, grumbling and other undesirable characteristics. The advantage of the ceramic pads is the lifespan of the brake pad set is about 20% longer than a regular brake pad. Every brake pad manufacturer has their own mixture of composite material that can vary in cost and quality. This material is bonded or riveted to the metal backing plate that is fitted into the brake caliper.

Front Brake Pads
Front Brake Pads (appearance will vary)

When servicing or replacing brake pads it is advised to wear a breathing mask over your nose and mouth to avoid inhaling brake dust particles. It is also advisable to wear gloves to avoid skin irritation. These dust particles have been known to cause health problems when exposed to them for an extended amount of time. When replacing brake pad always match the old brake pads to the new brake pads. The backing plate of the brake pad should be identical to the old brake pads, except for the missing brake pad composite material. Some brake pads are fitted with anti rattle clips. These clips are design to allow the brake pads to move freely within the caliper mount.

If these clips are not included with the brake pad set transfer the old clips to the new brake pads set. Do not discard the anti rattle clips this will result in the brake pad having excessive clearance which will create a pop or click sound when the brakes are applied. Some brake pad design will include a screamer style of wear indicator. This minimum thickness indicator was created to make a "chirping or screaming noise" when the brakes are in the "idle" position or when the brakes are applied. In an effort to help keep the brake pad in place manufacturers have designed "built in" clips that hold the pad to the inside and outside of the caliper. The inboard pad clip fits inside the caliper piston while the outboard pad clip attaches to the outer part of the caliper. These clips hold the brake pads into the brake caliper.

Squeaking or Grumbling Brakes

Brake squeak is one of the most common problems that can occur when the brakes are in operation. The brake squeaking noise is caused by ultra small vibrations that develop into an audible frequency. There are a number of reasons brakes can produce this noise. The most common cause of brake squeak is cheap or inferior brake pads and rotors which are made using sub-par material and below average manufacturing techniques.

These brake components tend to wear out more rapidly with below average performance characteristics. There is additional steps you can take to help insure quiet brake operation. When installing new brake pads use brake pad shims. These shims act as a shock absorber to dampen brake vibration which will help stop brake squeak. Heat can affect brake pads in a negative way, if the brake pad has been over heated it can cause the composite material to become crystallized, when crystallization occurs the brake pad becomes harder.

If a brake pad is hardened it can cause brake squeak. Once the condition has occurred replacement is required. When replacing brake pads a brake rotor replacement or re-machine is needed.

When a brake pad is used it will develop an un-even surface across the face of the brake rotor. If new brake pads are installed onto a worn brake rotor it can cause weak brake operation and squeaking. This can cause the brake pedal or steering wheel to pulse when the brakes are in operation.

More Information Visit - Brake pad replacement

AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


COMMENTS TO THIS ARTICLE


Please use our question form if you have a specific question about your car as we are not able to give you a full answer on this page.



Article first published (Updated 2014-04-11)