The braking system in large commercial trucks and trailers is similar to that of a passenger automobile. One major difference is that compressed air is used instead of brake fluid to cause the brake shoes to make contact against the inside of the drum.
As depicted at left, brake drums in large trucks are much greater in size than in automobiles. The shoes and linings are also much bigger on trucks. Because asbestos was utilized in brake linings well into the 1990's, the larger the brake lining the more asbestos is used and released.