The Ins and Outs of Brakes

Posted on June 1, 2001 by Denise Bibee

Page 1 of 2

Talk to any mechanic, and most likely they’ll tell you that brakes are what they see most often in terms of repairs. Understanding how brakes work and practicing proper maintenance will help you go the distance and avoid unplanned repairs.


Materials Make a Difference

Historically, asbestos was the brake material of choice. Asbestos provided good braking performance for low-to-medium temperature operating conditions. However, in the 1970s, disc brakes became more common. Because disc brakes generate more heat than brake drums, the heat generated by braking systems increased. In addition, front wheel drive applications, in which the front brake provides up to 80 percent of the stopping of the vehicle, brought about the need for alternatives to asbestos.


Since the federal government outlawed the use of asbestos on brake shoes, manufacturers have been using semi-metallic disc brakes. The high content of metal, 60 percent by weight, enables semi-metallic disc pads to maintain stopping power, even under high temperature conditions. However, the semi-metallic composition does pose some challenges. “One of the problems that we run into is that the manufacturers are always changing the composition,” says Vince Strang, service coordinator for Don Kott Lincoln-Mercury in Carson, Calif.


Strang explains that when the brake pads are made to last for a long duration, the result is an increase in brake noise. “When they try to soften them up to where they’re pretty quiet, then the pads don’t seem to last very long,” Strang says, adding that what he sees replaced the most are brake pads. “The pads and brake shoes just don’t last like they did 15 years ago, when they had asbestos in them,” he says.


Besides the load factor involved with limousines, there are often other modifications to the chassis, frame, drive train, etc. Combined with stop-and-go city driving, these factors have an impact on a vehicle’s braking system, both in terms of brake performance and wear life. Braking generates heat, and the harder the brakes have to work, the more heat that is generated. Constant high heat can result in poor performance and premature wear. To ensure that optimum braking power is available, the experts at Bendix Brakes recommend that limousines use brake pads that are specifically designed for severe duty operation.


Cause of Irregular Wear

In most cases, brakes are not going to wear evenly on both sides, and according to Strang, slightly different wear-and-tear is normal. He adds that independent repair shops will often advertise their “lifetime brakes.” “Anytime they get a vehicle back with worn-out brakes, they always use the excuse that it’s irregular wear, and they blame the manufacturer and say it’s a caliper problem,” Strang says.


He adds that often his mechanics will check out the vehicle, test the caliper and find that there’s no problem with it. “Often it’s the type of lining that they’re using,” Strang explains. However, if it’s a situation where the right front brake is worn and the left is in good condition, Strang says that most of the time the problem is then related to the caliper. “The piston is frozen, and it’s holding the brake on, causing it to wear down,” he says.


Another cause of irregular wear involves the driver. “Some people are what we call ‘left-footed brakers,’” Strang says. However, if the brake pedal pad shows extreme wear on the left side, rather than how it might normally wear when the driver is stopping with their left foot, this indicates that the driver likes to rest their left foot on the brake pedal. “Even though you feel like you’re not putting pressure on the pedal, sometimes that’s enough to actually activate those pads,” Strang says. The result is an irregularly-worn brake pad.

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