What are Brake Linings?
Brake linings are a friction material which help control movement of a vehicle. Brakes use friction to transmit force to a moving part of a vehicle (usually the wheels) to slow or stop it completely. Among the components of a braking system are brake pads, or brake shoes, which consist of a brake lining bonded to a metal backing. When the brake is engaged, the pad or shoe is pressed against a metal disc or drum attached to the wheel, causing it to slow or stop. The forward motion of the wheel is converted into heat, subjecting the brake linings to high temperatures. Because of this, brake linings have customarily been made with asbestos.
Most vehicles employ multiple sets of brake pads and one or more clutches. Brake pads and shoes are typically sold in pairs.
Who Works with Brake Linings?
Automotive mechanics remove and replace worn linings or even resurface linings on a daily basis. Many car owners, especially of older or vintage cars, may do this work themselves, and may have a friend or family member assist them.
Assembly-line workers may install brakes in new vehicles. Auto parts manufacturers may assemble new brakes, or reline old pads and shoes. Operators of heavy machinery who do their own maintenance may also replace old linings. Junkyard operators may also handle friction materials.
Where are Brake Linings Found?
Most motor vehicles, from cars to trains, have brakes, and usually more than one set. Asbestos-containing brake linings are generally found in passenger cars, light- and heavy-duty trucks, motorcycles, buses and heavy machinery such as cranes, tractors and locomotives.
Most passenger vehicles have disc brakes on the front wheels, drum brakes on the rear wheels. Each set of brakes requires linings. Larger vehicles, such as trucks and buses, require heavy-duty brake linings. Some heavy machinery may have multiple sets of brakes. For example, a crane may have brakes on the wheels or crawlers which move it forward, brakes to control the rotation of the cab, and brakes to control the boom, or arm, of the crane.
How Does Brake Lining Asbestos Exposure Occur?
When brakes are engaged, they are subject to high temperatures as the motion of the wheels is converted to heat energy. They also experience some gradual wear from contact with these moving metal parts. In order for brakes to function properly, the brake linings must be replaced or renewed periodically.
Auto mechanics may be exposed to asbestos dust in several ways. In a typical brake repair job, accumulated brake dust must be cleaned away before the old pads or shoes are removed. This is often done with a small brush, or with a blast of compressed air. Either method may cause asbestos particles to become airborne. If the old brake linings are still thick enough to be effective, the mechanic may use a bench grinder to restore the surface, or deglaze the linings of oil and dirt. When installing new brake pads or shoes, the mechanic may grind the surface to speed up the "breaking in" process, bevel the edges with a grinding wheel to reduce noise, and drill or punch holes for rivets. Some manufacturers also recommended scoring the center of the pad with a hacksaw. Any of these tasks could release asbestos particles.
Common Diseases Associated with Asbestos Exposure
The strong link between asbestos exposure and pulmonary disease did not become commonly known until the mid-1970's. Workers who have handled asbestos-containing friction materials and other workers or supervisory personnel working in the general vicinity, may have inhaled airborne asbestos fibers while at work, putting them at significant risk for developing one of these diseases: pleural mesothelioma, peritoneal mesothelioma, pericardial mesothelioma, asbestos cancer and asbestosis. In addition, workers often brought their work clothes home for laundering, bringing asbestos fibers home which also put their family members, especially women at risk for developing one of the above diseases. A disease like mesothelioma has a long latency period which means it can develop slowly, sometimes taking 30 or 40 years following initial asbestos exposure to appear. The mesothelioma prognosis for those diagnosed with the disease is generally not favorable as at this time there is no known mesothelioma cure.
Brake Linings Containing Asbestos
The following partial list of brake linings were known to contain asbestos:
|Product Name||Start Year||End Year|
|Abex Corporation Brake Linings||1926||1987|
|Anchor Packing Brake Linings||1908||1984|
|Bendix Brake Linings||1939|
|Borg-Warner Brake Linings||1971||1975|
|Chrysler Brake Linings|
|Dana Corporation Brake Linings|
|Ferodo "FZ" Brake Lining||1923||1998|
|Ferodo Bonded Asbestos Brake Linings||1923||1998|
|Ford Motor Brake Linings||1909|
|General Motors Brake Linings||1920|
|Johns Manville Custom Four Star Brake Linings||1972|
|Johns Manville WK Brake Linings||1972|
|Raymark Brake Linings|