Friction Materials
The lining material is the most important aspect of any braking system. They are variations in the composition and quality levels.
Previously, there were basically two types of friction material:
Under present government regulations, manufacturers are using a variety of different friction materials such as:
Often these materials differ in name only. However, there are very few restrictions on what you can put in friction material so you may find any number of different raw materials in friction material.
Use of Various Lining Compositions
Generally:
Therefore, all linings should contain the following characterists to be an optinum performer:
Overview
Disc brake pads consist of friction material bonded onto a steel backing plate. The backing plate has lugs that locate the pad in the correct position in relation to the disc.
Calipers are usually designed so that the condition of the pads can be checked easily once the wheel has been removed, and to allow the pads to be replaced with a minimum of disassembly.
Some pads have a groove cut into the friction surface. The depth of this groove is set so that when it can no longer be seen, the pad should be replaced.
Some pads have a wire in the friction material at the minimum wear thickness. When the pad wears to this minimum thickness, the wire touches the disc as the brakes are applied. A warning light then tells the driver the disc pads are due for replacement.
The composition of the friction material affects brake operation. Materials which provide good braking with low pedal pressures tend to lose efficiency when they get hot. This means the stopping distance will be increased.
Materials which maintain a stable friction co-efficient over a wide temperature range generally require higher pedal pressures to provide efficient braking.
Brake Pads
On the majority of automobiles built today have two disc brake pads on each caliper. Today’s preferred method of construction is a lining bonded to a metal backing plate. A disc brake pad is mounted in the caliper, one on each side of the rotor. Older disc brake linings used to be made primarily of asbestos because of its heat absorbing properties and quiet operation; however, due to health risks, asbestos has been banned by governments, so new materials are now being used they also must absorb and disperse enormous amount of heat generation. Brake pads are a consumable item that wears out with use and must be replaced periodically. There are many types and qualities of pads available. The differences have to do with:
It is important that worn disc brake pads be replaced before they cause extensive rotor damage. Some manufacturers have built-in wear sensors that notify you when the pads are worn.
In vehicles without wear sensors, the pads should be inspected visually at manufacturer’s specified intervals for both normal driving conditions and severe operating conditions.
There are three types of wear sensors. They are:
If a visual check of the pads must be made, there are a few guidelines to keep in mind. For example, disc brake pads that are bonded to the backing plate, the amount of friction material should equal the thickness of the backing plate. If the pads fail meet these specifications, replace them, It is recommended by brake component manufacturer’s that brake pads should be replace on both axles at the same time. In other words, replaced as matched sets.
Harder linings tend to last longer and stop better under heavy use but they may produce an irritating squeal when they are applied. If the lining wears down to the metal brake shoe, then you will have a "Metal-to-Metal" condition where the shoe rubs directly against the rotor causing severe damage and loss of braking efficiency. This noise will usually be heard when your foot is on the brake and disappear when you release the brake pedal. If you hear this noise, have your brakes checked as soon as possible.
Source: CDX Global & Wikipedia
