When I first opened my auto repair business many years ago, I had a good friend and customer who owned a 1970 Ford Bronco. Since money was no object when it came to repairs or maintenance, I used only premium-grade replacement parts. So, when the original front brake shoes needed replacement, I ordered the “best” quality along with wheel cylinder kits and other hardware items needed to restore his prized possession to like-new status.
Better Or Best?
Of course, my first-call jobber didn’t have the “best” shoes in stock that day, so I called another jobber who claimed to have the “best” in stock. Upon taking delivery, I noticed that my second-call jobber’s “best” sold for much less that the first-call jobber’s “best.” Although I questioned that his brake shoes were his “best,” the second-call jobber insisted that these were indeed his “best” quality brake shoe.
After replacing the linings, I immediately noticed a greatly increased pedal effort during the initial test drive. After seating and readjusting the brakes, I attempted a panic stop. The second-call jobber’s linings would barely slow the Ford Bronco, let alone make the tires squeal. While these brake shoes might have passed muster on a Bronco equipped with power brakes, their performance was completely unacceptable on a Bronco equipped with manual brakes. In any case, I had to re-do the brake job out of my own pocket to make the Ford Bronco stop as it should.
Brake Friction Characteristics
Although the above story is technically dated, it vividly illustrates that not all brake friction is created equal. Whether drum or disc, attempting to cut costs by installing brake friction that doesn’t meet original equipment (OE) requirements generally produces less-than-desired results.
Generally speaking, any premium or “best” brake friction provides the greatest stopping power and longevity while producing a minimum level of noise and dust. For this reason, most premium brake pads are ceramic formulations, which are designed to provide the best overall performance characteristics for the average passenger car application. Ceramic brake pads generally use copper fibers to bond the brake friction compound together.
Because they don’t create large volumes of corrosive brake dust, ceramic (sometimes called NAO-ceramic) brake pads became popular during the 1990s when bright alloy spoked wheels became standard equipment on many vehicles. In addition, most ceramic formulations produce a high coefficient of friction over a broad range of operating temperatures, generate less noise than semi-metallic brake linings, are fade-resistant, and reduce brake rotor wear.
The semi-metallic or “better” brake friction uses steel wool to bond the brake friction compound together. The steel wool greatly increases the ability of the brake pad to transfer heat away from the brake rotor, which allows semi-metallic friction to operate at much higher operating temperatures without producing brake fade. Since about 80 percent of the braking power is concentrated on the front brakes many front-wheel drive (FWD) vehicles, semi-metallic friction became popular during the early 1980s to increase brake performance. On the downside, semi-metallic friction generally increases noise, brake dust, and rotor wear. Semi-metallic friction also tends to require higher initial pedal pressures when the brakes are cold. But, even today, semi-metallic still provides optimum brake performance in heavy-duty applications experiencing higher than normal operating temperatures.
The non-asbestos organic (NAO) or “good” brake lining was created to replace asbestos-based brake friction. While in many brake friction lines, NAO is considered a “good” rather than “better” or “best” lining, NAO is also used in many Original Equipment (OE) applications because it generally provides smoother application and more even side-to-side braking than do other formulations.
In passing, I’ll mention that the “edge codes” printed on the side of new brake lining generally indicate the lining’s cold and hot performance characteristics. Because edge codes are a general, rather than specific, indicator of overall brake friction performance, I’ll just say that a more detailed discussion of edge codes can be found by typing “brake edge codes” into your Internet search engine.
When discussing any type of modern brake friction, remember that, in the real world, modern brake friction manufacturers are constantly inventing new friction formulations designed for specific applications and operating conditions. Because conventional performance ratings don’t always describe the overall characteristics of modern brake friction, it’s always best to follow your brake friction manufacturer’s recommendations for specific applications.
Since auto manufacturers spend a tremendous amount of time and money to make their brakes operate as efficiently as possible, it’s important to follow a few rules for selling brake friction. For example, it’s important to never sell half-sets or transfer brake friction from one carton to another. Mixing pads or shoes creates an automatic warranty situation for your installer if the friction coefficient of individual linings differs enough to cause a brake pull complaint.
Similarly, it’s important to sell only the OE-equivalent linings front and rear, especially on front-wheel drive vehicles. On older FWD vehicles without anti-lock braking systems, many auto manufacturers actually reduce the potential for rear-wheel brake lock-up on slick roads or during panic stops by reducing the coefficient of friction in the brake lining compound. Similarly, mixing linings with different friction coefficients on rear wheel-drive (RWD) vehicles might also cause premature ABS activation or a rear wheel lock-up complaint on slick roads or graveled road surfaces.
It’s also important to make sure that the design of the replacement brake rotor meets OE specifications. An economy brake rotor will often increase brake noise because it uses a non-OE specification cast iron and it might tend to run hotter because it has less cooling fins and because those fins might not be shaped to provide maximum air circulation. In contrast, a premium rotor will appear and perform identically to the OE version.
Harsh brake grinding and squealing noises usually occur because the brake pad vibrates against the brake rotor as the brakes are applied. To minimize pad vibration, it’s important to replace the original equipment-style brake shims and locating grommets. Most premium brake pads are manufactured with the shims attached and, if required, include new grommets and brake caliper lubricant. Many economy pads require that those parts be purchased separately or reused.
Using the correct brake friction is also important because fast ratio, high-performance steering systems tend to transmit brake pad vibrations to the steering wheel. And, because modern vehicle stability control systems actually use the brakes to help steer the vehicle out of emergency situations, it’s important to install brake friction that minimizes brake pad and rotor vibration.
Brake pad vibration can also be created by improperly resurfaced brake rotors. The rotor should be turned as smoothly as possible without chatter marks. The rotor surface should also be non-directional, which means that the “phonograph” grooves left by the brake lathe are cross-hatched with a sanding disc especially designed for this purpose. Last, the brake rotor should be thoroughly scrubbed in soap and water to remove the microscopic bits of cast iron before they imbed into the surface of the new brake pads.
Last and most important, all brake friction must be clean when installed. Greasy handprints on brake friction can be avoided by using shop rags to keep the hands clean. Any residual contamination should be removed with brake and parts cleaner. When inspecting brake friction, it’s also important to replace sticking calipers, leaking wheel cylinders, and seeping axle oil seals. In most cases, it’s far more cost-effective to routinely replace these components than to wait for them to fail at a future date.