Tech Tip: Brake Friction Materials – Good, Better or Best? – UnderhoodService
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Tech Tip: Brake Friction Materials – Good, Better or Best?

One thing you can always count on with brakes: sooner or later the brake linings will wear out and have to be replaced. Every time the brakes are applied, the pads rub against the rotors and wear just a bit. After 40,000 to 60,000 miles, the front pads are usually worn down to minimum thickness specifications and need to be replaced. The rear pads or shoes typically last 20,000 to 30,000 miles longer, but they also eventually ….

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By Larry Carley
Technical Editor

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One thing you can always count on with brakes: sooner or later the brake linings will wear out and have to be replaced. Every time the brakes are applied, the pads rub against the rotors and wear just a bit. After 40,000 to 60,000 miles, the front pads are usually worn down to minimum thickness specifications and need to be replaced. The rear pads or shoes typically last 20,000 to 30,000 miles longer, but they also eventually wear out.

So when a customer’s vehicle needs new brake linings, what kind of linings do you recommend? The most expensive premium linings? Standard replacement linings? The least expensive economy grade linings? Or do you discuss what’s available, and which type of lining best suits your customer’s budget?

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Many aftermarket friction suppliers today offer a premium line, a standard line and, in many cases, an economy line of replacement brake linings. The least expensive brake linings are typically offered in a “value line,” and are targeted primarily at the retail, do-it-yourself market. Standard and premium grade linings, by comparison, are aimed primarily at DIYers and professional installers who want a better product and are willing to pay more. Most professional technicians won’t even consider an economy lining grade because they don’t want to risk a comeback if the customer isn’t satisfied with the way the brakes feel or perform.

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VALUE LININGS
Though brake suppliers insist their value grade linings are as “safe” as standard grade linings, don’t expect their life or stopping power to be on par with the more expensive linings. Value linings are exactly what the name implies: an inexpensive fix that is adequate for the job but not much more.
Value linings may serve the purpose for a vehicle that isn’t driven a lot, or is not subjected to hard use. Stop-and-go driving in heavy city traffic is hard on the brakes, but highway cruising hardly uses the brakes at all. So for a customer who’s relatively easy on his/her brakes, value linings may be an option if they’re on a tight budget.

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STANDARD REPLACEMENT LININGS
The next step up is “standard grade” or “OEM equivalent” replacement linings. Such linings generally offer similar braking performance and service life as the original equipment linings on the vehicle. The goal is to usually restore “like-new” feel and performance with friction materials that are identical or very similar to the OEM brake linings.

In recent years, though, the distinction between standard and premium-grade linings has blurred as brake manufacturers have introduced new friction materials and new pad designs. There’s been an ongoing effort to continually upgrade brake performance, noise control and pad life.

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A few years ago, the buzzwords “application specific” and “application engineered” were applied to many linings whose friction characteristics were customized to more closely match the performance characteristics of the OEM brakes on specific vehicle applications. Instead of having one or a few basic friction materials that could be used on a wide range of vehicle applications, friction formulas were tweaked to make linings much more vehicle specific.

One leading brake supplier told us they now use about 40 different friction compounds in its various product lines to achieve application-specific coverage. Another supplier said it currently has 25 different compounds in its line, and will be adding more as needed to keep pace with new models and changes at the OE level.

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The widespread use of anti-lock brake systems has also played a role in the development of more application-specific brake materials. The threshold at which the wheels start to lock up depends on vehicle weight, speed, traction and the coefficient of friction of the brake linings themselves.

Because ABS and stability control systems are calibrated to the friction characteristics of the OEM brake linings, aftermarket replacement linings should closely match the friction characteristics of the OEM linings — which, in most cases, require the use of application-specific materials. That’s one reason why a growing number of aftermarket brake suppliers now “certify” that their brake linings perform at the same level of performance as the OEM linings they replace.

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Speaking of performance, all OEM brake linings must meet government safety standards. The Department of Transportation standards require vehicles to stop within a certain distance, and the latest FMVSS135 rules require an even shorter stopping distance. Consequently, some OEMs have had to upgrade their brakes and go to more aggressive linings to meet these standards.

Yet there are no equivalent standards for aftermarket brake linings or any other aftermarket brake parts. The safest course of action for aftermarket brake suppliers, therefore, is to use friction materials that are the same or closely match the OEM brakes — and to voluntarily certify their compliance.

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Most premium-grade linings are now application specific, but so are many mid-range or standard-grade linings. What’s more, many brake suppliers have introduced new product lines specially designed for trucks, SUVs and import vehicles.

PREMIUM LININGS
Premium-grade linings are the best the aftermarket has to offer. They typically equal or exceed OEM performance in all categories: stopping power, feel, fade resistance, noise control and lining life. Some have “low dust” formulas that reduce the accumulation or visibility of dust on alloy wheels. Some have exotic ingredients such as ceramics instead of metallic fibers, while others have exotic coatings such as copper, titanium and other materials. Special coatings help seat the pads on the rotors, dampen noise and/or eliminate the need for special break-in procedures. Some are designed to give the same performance and feel as “Euro” formula linings on European makes like Audi, BMW, Mercedes-Benz and VW.

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The word “ceramics” is often associated with premium linings, and many ceramic brake linings are indeed higher priced, upgrade replacement linings. But ceramic formulas vary a great deal, and the ceramic linings from one brake supplier may be entirely different than those from another supplier in terms of braking effectiveness, heat dissipation, noise suppression and wear resistance. So just because a set of pads have the word “ceramic” on the box doesn’t necessarily make them a premium-grade product.

PREMIUM PAD FEATURES
Most premium pads incorporate such features as chamfers, slots and built-in shims to control noise and vibration. Chamfers and slots change the loading on the surface of the pads and the frequency at which they vibrate to reduce noise. Shims on the backs of the pads, or that are molded inside the pads, are also there to dampen vibration and noise. Some manufacturers also use a “layered” construction when they mold their pads with different friction materials sandwiched together to control noise and performance.

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Some premium pads are also “pre-burnished” to eliminate many of the problems that can occur if the pads are not properly broken in. When brake linings are manufactured, the resins that bind the ingredients together are not fully cured. When the linings are later installed on a vehicle, the heat produced by normal braking bakes the linings and cooks out the residual chemicals from the resins to improve the friction characteristics of the lining.

If the brakes get too hot before the linings are fully cured, it can “glaze” the linings, causing noise and braking problems. So, to eliminate the need for a break-in period, some brake suppliers are now adding an extra manufacturing step to fully heat-cure (burnish) the linings.

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