Overview
The drum brake uses brake shoes that have friction material called linings attached to them.
This friction material was once made of asbestos but concerns about health problems associated with asbestos have led to increasing use of non-asbestos alternatives.
Linings can be riveted, or more often, bonded to the brake shoes.
The composition of the friction material affects brake operation. Linings which provide good braking with low pedal pressures tend to lose efficiency when they get hot. This means the stopping distance will be increased.
Linings which maintain a stable friction co-efficient over a wide temperature range, generally require higher pedal pressures to provide efficient braking. This may necessitate the use of a booster.
Background
Drum brake lining normally come under one of three categories based on the composition of materials used in their manufacture. In addition, it is also depends on the curing method undertaken.
The majority of brake linings sold today will have manufacturer's codes stenciled on the edge of the lining. This will identify its co-effiecient of friction as outlined in the manufacturer's specification. To ensure the maximum life and performance from brake linings, it is recommended that repairers only use good quality brake lining from reputable suppliers.
The brake lining surface, as well as being smooth to ensure maximum surface contact for better braking, it also conducts heat away to the cooling air thus help maintaining it retardation/stopping ability. By allowing the linings to radiate heat away it helps prevent brake fade by the linings becoming overheated and loosing it frictional qualities.
WARNING
Asbestos in brake components
Beware many older brake pads and linings were constructed with asbestos in the material. Asbestos fibers are a known health risk that can lead to lung diseases after many years of exposure. As the linings or pads worn down asbestos fibers were present and could easily be inhaled. Reputable manufacturers have ceased using asbestos in their linings. Most governments around the world have now legislated against the inclusion of asestos in new brake linings. It is virtually impossible to know if asbestos has been used. In this case, all brake lining servicing should be carried out as though there is asbestos in the material.
Cleaning methods can vary from using special vacuum cleaners to a washing method of remove the brake dust. As a matter of importances, NEVER USE AN AIR HOSE to blow dry dust off any brake component.
Source: CDX Global & Wikipedia - en.wikipedia.org
