Asbestos in Drum Brakes and Other Friction Materials
The drum brake was the earliest type of automotive brake, dating back to approximately 1900. Unlike the disc brakes which have largely replaced them (in which a metal plate is seized between a pair of calipers, similar to bicycle brakes) a drum brake is circular, with linings on the inner surface. When the brake is applied, a hydraulic fluid is forced through tubes via a cylinder, causing brake shoes to expand against the inner lining of the drum.
Until the 1980s, asbestos was the primary ingredient in brake linings. When the Environmental Protection Agency and other federal protection organizations attempted to regulate asbestos use, brake manufacturers in the U.S. began switching to other materials. In the beginning however, vehicle owners found the non-asbestos materials to be unsatisfactory; later, the federal courts, bowing to industry pressure, overturned many bans on asbestos.
As public awareness has grown about the dangers of asbestos, market pressures have accomplished what legislation could not. However, many older vehicles equipped with drum brakes still contain asbestos – and while asbestos linings are not made in the U.S., there are several foreign companies that are thriving from the manufacture and marketing of asbestos brake linings and other friction products. These products continue to enter the United States. As recently as a decade ago, investigative reporting has revealed that dust samples from auto shops across the country still contain large amounts of asbestos fibers. The Occupational Safety and Health Administration and various state labor and industry agencies continue to advise auto service personnel to take proper precautions when working around automotive brakes.
Drum Brakes Products Containing Asbestos
The following partial list of drum brakes products were known to contain asbestos:
|Product Name||Start Year||End Year|
|General Motors Drum Brakes||1920||1975|
|Raymark "PGR" Drum Brake|
|Raymark "PGRX" Drum Brake|
|Raymark "PGTP" Drum Brake|
|Raymark Drum Brake|
|Raymark Raybestos Dynamold Drum Brake|
|Raymark Raymond RP Drum Brake|
|Raymark Raymond RR Drum Brake|
|Raymark Raymond RTP Drum Brake|
Hazards Associated with Drum Brake Products
Automotive repair technicians, brake workers, and anyone working in automotive repair facilities where brakes are worked on are at risk for inhaling asbestos from brake products containing this dangerous fiber. Shade-tree mechanics and people doing work on their own cars should be aware of the risk of asbestos dust from drum brake linings as well.
Professional and amateur musicians should also be alert to the presence of asbestos in brake drums, because old brake drums are often used as percussion instruments when an "industrial" sound is desired. As such improvised instruments may be used continuously for many years (as opposed to old drum brakes which are likely only worked on every few months at most), musicians should ensure that brake drums being used in this fashion do not contain asbestos linings.Sources
Bowker, Michael. Fatal Deception: The Untold Story of Asbestos (New York: Touchstone, 2003)
Schneider, Andrew and Carol Smith. "Nation's Mechanics At Risk From Asbestos." Seattle Post-Intelligencer, 16 November 2000.