Testing, Testing

The National Highway Traffic Safety Administration (NHTSA) of the U.S. Department of Transportation believes that using air brakes will result in fewer collisions in emergency situations than using drum brakes. The NHTSA states that reducing the minimum stopping distance required by 30 percent would result in a significant number of lives saved. These conclusions were formed following simulator tests conducted at the University of Iowa [source: National Transportation Safety Board].

Big Disc Brakes for Trucks

Some trucks have disc brakes instead of S-Cam brakes. Air pressure works on the brake chamber and the slack adjuster in the same way that it does in S-Cam brakes. However, a power screw replaces the S-Cam. The power screw is turned by t­he pressure on the brake chamber and the slack adjuster. Then the power screw grasps the disc or rotor between a caliper's brake lining pads.

The many benefits of air disc brakes include the following:

  • Compared to drum brakes, air disc brakes reduce stopping distances by almost 40 percent. Because pressure is continually applied, it's easier for the vehicle to come to a complete stop.
  • Air disc brakes almost completely stop brake fade.
  • Air disc brakes don't increase the wear of brake linings on a trailer or disc pads on a tractor.

Still, despite all of the advantages, change isn't always embraced by the masses. In the United States, no regulation demands the use of air disc brakes, which are viewed as a high-end item because they're about twice the cost of drum brakes. Currently, about 95 percent of the U.S. heavy-duty truck market relies on drum brakes. In Europe, more than 80 percent of commercial trucks already use air disc brakes. The complete shift to air disc brakes may require 10 to 15 years.

They say that a picture is worth a thousand words. Let's cruise to the next page to get a glimpse of a diagram of a truck's braking system.

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