As you hit the road this summer, it’s important that your vehicles are ready for safe and reliable operation. While many of the safety systems in your car or truck don’t require any regular maintenance, an exception is the brake system.
Since the very earliest motor vehicles in the late 19th century, friction brakes have been used to slow down and stop vehicles. Today, modern vehicles utilize the braking system for much more, including functions such traction and stability control, adaptive cruise control and collision mitigation systems.
A moving object such as a car has kinetic energy, and the brake system uses friction that converts that kinetic energy into heat. Every time the brakes are used they heat up, causing brake pad linings to wear down little by little.
It’s particularly important to make sure your brakes are in tip-top condition if you plan to do any towing or any driving in the mountains. A vehicle’s kinetic energy is proportional to its weight, so the extra weight of a trailer means the brakes much work much harder. Similarly, driving down mountain roads or other steep grades means the brakes have to work against gravity as well.
Automotive brakes consist of three main parts – the disc or drum braking surface, the linings and the hydraulic apply system. The linings have a friction material designed to wear off that is riveted or glued to a solid metal backing (together, the lining material and metal backing are commonly called brake “pads”). The apply system clamps these linings against the steel or iron disc or drum when the brake pedal is applied, slowing the vehicle.
Over time, the linings will eventually wear down and require replacement. Depending on the driver’s style, the brake linings will generally last anywhere from 10,000 to 50,000 miles. As the linings wear, the metal surface of the discs or drums can also be worn down. The brake linings typically have a little metal clip that will rub against the brake surface when the linings wear to the point that they need to be replaced. When this happens they will squeal, providing an indicator that service is required.
Every 5,000 to 10,000 miles when the tires are being rotated, the brakes should be inspected while the wheels are off the vehicle. The brake linings should be wearing relatively evenly. If the lining material is heavily tapered, it can reduce the effectiveness of the brakes and cause extended brake pedal travel. In this case the pads should be replaced as soon as possible. If the linings have become too thin, they can become completely worn away and leave the metal backing plates rubbing directly on the rotors/drums. This, too, can cause extended stopping distances, as well as loud squealing when the brake pedal is pressed.
The surface of the linings that presses against the drum or rotor should have a relatively smooth but dull appearance. If the lining has consistently overheated it can take on a shiny, glazed look which indicates reduced friction and longer braking.
In addition to the linings, the rotors or drums should be inspected. Brakes can overheat, which can cause damage to the metal, and rotor/drum surfaces can become warped or develop hard spots from the heating and cooling. This can cause a pulsation in the brake pedal and knock back the linings so they don’t work as well. The rotor surface can also become grooved if stones or sand becomes jammed between the lining and the rotor while driving on dirt or gravel roads.
If the rotor surface is thick enough, superficial damage can removed and warped or grooved surfaces can be machined smooth. If the rotor gets too thin or is too badly damaged, it will need to be replaced.
If the brake pedal feels mushy when pressed, but firms up when pumped a couple of times, it is a sign that there is air in the hydraulic lines. Unlike brake fluid, air is compressible and won’t transmit the force a driver applies to the pedal to the brakes at the wheels. If there is air in the brake lines, the system will need to be bled and refilled with more fluid for the brakes to work properly. Brake lines can also deteriorate over time and should be regularly inspected, especially where they may run underneath a vehicle and be exposed to road salt and other corrosives.
Modern cars and trucks depend on good brakes more than ever for performance and safety. Before you head out on a summer road trip, have your dealer’s factory-trained technicians inspect your vehicle’s braking system to make sure it is fully operational and up to whatever conditions you may encounter.