Vehicles

The Ins and Outs of Brakes

Denise Bibee
Posted on June 1, 2001

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.

Maintenance and Inspection

According to David Knecht, director of maintenance for Greene Classic Limousine in Atlanta, the master cylinder fluid level should be consistently checked and kept full. “If the master cylinder ever gets empty, air could get into the system and you could lose your brakes,” Knecht says. He advises inspecting the outside of the master cylinder for any leaks. Brakes and related components should be inspected once a year, or more frequently depending on your mileage.

 

Another factor with long-term negative consequences is moisture, whether it’s harsh winter weather or light spring rain. According to the manufacturers at Bendix Brakes, moisture can change the characteristics of the entire braking system. Most often, wet brakes will lose friction, making them slightly less effective at stopping. The good news is that when you are driving, the heat and friction from braking dries out some of the moisture that forms in the system before it does much damage. Your brakes will usually return to their normal performance after driving for a few miles in wet weather. However, if heavy rain occurs frequently in your area, it will eventually affect your vehicle’s overall braking performance.

 

To avoid brake damage, when you approach water that is hubcap deep, slow down your vehicle and gently ride the brakes. Riding the brakes creates heat from braking friction and dries some of the moisture before it does any harm. If your vehicle’s brakes are in water for a great length of time without being driven, problems can develop quickly. The braking system will collect moisture and damage can set in. Some parts can stick or bind, resulting in uneven wear or erratic pulling upon application. Other brake parts will slowly rust internally if exposed to excessive amounts of water. Additionally, brake cables could become non-functional. Make sure that the braking system receives a thorough inspection, cleaning and fluid flushing.

 

When It’s Time to Replace

How often brakes are replaced will often depend on the individual driver and the type of driving taking place. “I can take a vehicle and put three different drivers in it, and it will require brakes at three different intervals,” Strang says. “Since we are also a Chrysler dealer, I had a vehicle that Chrysler bought back. The customer had registered many complaints and gone through numerous sets of brakes.”

 

Strang arranged it so that he could take the car and use it himself. He had a new set of brakes installed on the vehicle and drove it regularly to see if he could exceed the previous owner’s mileage. “The customer was going through brakes every 6,000 miles,” Strang says. After continuous use, he put 15,000 miles on the car without the need for brake replacement. “In this case, it was just abuse – the way it was being driven,” he says. “In most cases, a driver that knows how to stop properly and isn’t doing ‘panic stops’ — they’re going to get probably 15,000 to 20,000 miles out of a set of brakes. Somebody who’s driving a vehicle very hard will be lucky if they get 9,000 miles or sometimes even less.”

 

Related Topics: braking systems, improving chauffeur driving style, maintenance tips, tires and wheels

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