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Thread: So, you thought you knew everything about Brake Pads?

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    Default So, you thought you knew everything about Brake Pads?


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    It is often said that brake pad manufacture involves more art than science, but this is generally not true.

    In fact, with more than 2000 materials and substances that are available to brake pad manufacturers, a scientific approach to brake pad manufacture is a requirement and luck can therefore have no part in the formulation of brake pad friction materials. Thus, if you have ever wondered what ingredients, substances, and materials go into the making of modern, high-quality brake pads, this article will answer all the questions you have ever wanted to ask, starting with answering this question:


    Are Aftermarket Brake Pads just as good as OEM?

    As with everything else in life, you get what you pay for, but in the case of Bendix brake pads, your customers pay for brake pads that meet, and often exceed OEM specifications in terms of durability, reliability, and smooth, silent operation.

    In fact, Bendix brake pads include several proprietary technologies such as their Blue Titanium Stripe that eliminates bedding-in, and Stealth Advanced Technology that ensures the optimum pad/rotor contact area to prevent overheating and brake fade in applicable applications.

    Given the above, it is fair to say that Bendix ranks high among the aftermarket brake pad manufactures that meet, and often exceed OEM brake pad performance levels on a consistent basis, so yes, aftermarket brake pads often outperform OEM brake pads, provided you fit Bendix brake pads to your customers’ vehicles.

    So, what goes into a Brake Pad?

    While brake pad manufacturers never publish the exact formulations of their brake friction materials, and are in many jurisdictions not obligated to, this article can only provide an overview of the materials that are most commonly used in brake pad manufacture. Consider the chart below.


    This chart is the result of diligent research, and it that shows the average percentages of the main categories of materials that are most commonly included in the products of most reputable brake pad manufacturers. As stated elsewhere, brake pad manufactures have a list of more than 2000 substances they can use legally, but since limited space precludes listing all 2000 substances here we will cover only some of the most commonly used materials, and explain what functions these substances have in the overall formulation of brake pad friction materials, starting with-

    Binders


    • Fibre glass functions both as a binding agent and a structural material, and can comprise between 5% and 25% of the total volume of the friction material, depending on the application
    • Phenolic resins are most commonly derived from cashew nut shells, and functions as both binding agents and performance enhancers. These resins typically account for between 10% and 20% of the total friction material volume, depending on the application



    Abrasives


    • Mineral fillers derived from quartz or synthesised silicates are used as abrasives to enhance friction, and can account for between 5% and 35% of the total volume. Note that mineral fibres are typically not used in metallic brake pads
    • Oxides of various metals, typically iron oxide and aluminium oxide, function as both abrasives and fillers/binders in metallic and semi-metallic brake pads. Note that it is almost certain that even so-called “organic” brake pads will contain a small percentage of metallic oxides. Depending on the application, oxides of metal can account for up to 70% of the total volume of the friction material
    • Brass filings or chips are used to boost friction in wet conditions. Depending on the application, brass chips can account for up to 5% of the total volume of the friction material
    • Pure carbon fibre is used as both an abrasive and a binder in mostly racing brake pads, although minute quantities of carbon fibre is present in some performance oriented aftermarket brake pads, with the price of the brake pads being a somewhat reliable indicator of how much, or how little carbon fibre is present in the pads.



    Performance enhancers


    • Cashew resin derived from cashew nut shells is used to resist brake fade, and to reduce, if not eliminate brake squeal. Depending on the application, cashew resin can account for up to 20% of the total volume of the friction material
    • Carbon in various forms exists in most brake pads, and it is commonly used as both a cheap friction booster and/or a lubricant, depending on the application. Carbon can account for up to 30% of the total volume of the friction material
    • Metal sulphides such as copper sulphide, lead sulphide, or antimony sulphide are used to stabilise friction coefficients across a wide range of brake operating temperatures. Depending on the application and the particular sulphide(s) used, sulphides can account for up to about 30% of the total volume of the friction material
    • Calcium hydroxide (lime) is used as a rust inhibitor in both metallic and semi-metallic brake pads
    • “Friction powder” is a generic term that applies to proprietary blends of several (usually unspecified) compounds that all brake pad manufacturers use for a wide variety of purposes and functions. Typically, though, friction powder is used as a flame retardant, friction modifier, lubricant to reduce dust creation, and brake noises. There is no verifiable information available on the average friction powder content of high quality brake friction materials



    Fillers


    • Fillers such as barium sulphate, potassium titanate, common household steel wool, and rubber derived from recycled tyres are commonly used to bulk up the total volume of a friction material formulation. Although the filler content of brake pads vary widely, these substances are used mainly to increase the wear resistance of brake pads



    Structural enhancers


    • Mineral-based fibres that are spun from alumina, silica, calcia, magnesia, and vermiculite are commonly used to strengthen the overall structure of brake pads, although these fibres are also used to resist brake fade caused by high brake temperatures. Depending on the application, mineral fibres can account for between 10% and 20% of the total volume of the friction material, but note that mineral fibres are typically not used in metallic brake pads
    • Ceramic materials occur in an enormous variety, and provided that any given brake pad contains actual ceramic material and not common clay, the ceramic component of the pad can fulfil any of the functions any of the other substances listed here, and in some cases, a brake pad can consist of nothing but highly refined ceramic. However, the problem with ceramics is that many brake pad manufactures define the word “ceramic” very loosely, with the result that many semi-metallic and even some organic brake pads are labelled as “ceramic” when in fact, there is no, or very little ceramic materials present in the pads.
    • Copper is commonly used in ceramic brake pads in small percentages to prevent brake fade, but also as a lubricant to reduce brake noise. Note though that since the use of copper in brake friction material has been banned in some jurisdictions, copper may have been replaced in some friction material formulations by hexagonal boron nitride
    • Kevlar in various forms is used in some specialised applications as a friction booster, but there is no verifiable information available regarding other possible uses. Note though that very few, if any brake pad formulations contain more than about 3% Kevlar.


    At this point, astute readers will have noticed two things; the first being that the number of friction material ingredients listed above represents only a small fraction of the possible total, and the second being that the numbers listed above do not add up to 100%. The latter point is because no brake pad manufacturer will ever list complete lists of ingredients and percentages, but despite this, the items and numbers listed above cover the most ground, which brings us to-


    Which type of brake pad is the best?

    While there is no clear, unambiguous answer to this question, reputable brake pad manufacturers like Bendix produce brake pads for specific applications, each of which works better on the application it was designed for than on any other. However, there are five main categories of brake pads, and while choosing the best formulation within each category for a given application is not always easy, it helps to understand that there are few, if any purely metallic, ceramic, semi-metallic, or organic brake pads on the market anywhere in the world.

    Nonetheless, Bendix produces high quality brake pads in each of these main categories, but it must be understood that given the extensive list of requirements a particular friction material formulation must satisfy, it is common for brake pad manufacturers to mix and match the characteristics and ingredients of two or more categories of brake pads to obtain the best results in a particular application. In fact, it would be fair to say that brake pads should therefore really be marketed as “predominantly ceramic”, “mainly metallic”, “mostly semi-metallic”, or “largely organic”.

    Having said that though, below are some details of the chief characteristics and advantages of each of the four main brake pad categories-

    Metallic brake pads


    • Excellent wear resistance, which is their single biggest advantage over other types of brake pad
    • Outperforms most other types of brake pads at high brake temperatures



    The disadvantage of metallic brake pads is that they are often not compatible with brake rotors on some high-end applications, which could result in severe brake noise and/or rapid wear of both pads and rotors.

    Semi-metallic pads


    • These pads offer the best possible compromise between wear resistance, performance, and quiet operation
    • Most new vehicles are factory fitted with semi-metallic brake pads, even though they are more expensive than metallic pads and organic pads
    • Most high quality aftermarket brake pads produced by reputable manufacturers are of the semi-metallic variety



    While semi-metallic brake pads typically do not outperform competing types in any particular area, these pads offer satisfactory performance in all areas, which makes them a great choice for variable driving conditions, with the exception of track racing or other motor sport applications.

    Organic brake pads


    • Quiet and smooth operation, which is their single biggest advantage
    • Outperforms other types of brake pads at lower brake temperatures, which makes them an excellent choice for city-driving conditions



    The disadvantages of organic pads include the facts that they are not particularly hardwearing, and that due to their composition they overheat easily, which destroys their ability to withstand brake fade.

    Ceramic brake pads


    • Ceramic pads offer excellent performance in all the important areas; they outlast all other types of brake pads even under extreme operating conditions, they are quieter and produce less brake dust than all other types of brake pads, and they offer the best performance over the widest range of brake temperatures and operating conditions



    However, both pure ceramic and semi-metallic brake pads that contain significant amounts of ceramic are the most expensive categories of brake pads for all applications, which makes them unattractive options for customers on budgets.

    Film transfer brake pads

    These are specialised brake pads in which the formulation of the friction material is designed to transfer some of the friction material to the rotor in the form of a thin film. In practice, these pads do not act on the rotating rotor directly; instead, the thin coating of friction material that was deposited onto the rotor forms a barrier between the pad surface and the rotor surface, but since the film and the pad consist of the same material, braking action is greatly increased. This characteristic makes this type of pad an excellent choice for drivers who do a lot of towing, or who participate in motor sports that place high, if not extreme demands on brake components.

    However, the biggest disadvantages of film transfer pads are that very specific bedding-in procedures must be followed and that very high brake temperatures are required for the transfer of friction material to take place. As a practical matter though, since the required temperatures are seldom, if ever reached during normal driving, film transfer brake pads are not recommended for normal street use.

    Conclusion

    From the above, it should be obvious that there is no single “best” brake pad that will satisfy all the requirements of all applications under all possible operating conditions. Nonetheless, brake pads are life-and-limb components on any vehicle, and as such, it is incumbent on us as experienced technicians not only to learn as much about brake pads as we can, but also to be aware of both the characteristics and limitations of the various types of brake pads.


    More information about brake pads in general, and specific recommendations for various applications in particular, is available at

    To learn more about the Bendix Brakes range of products visit: www.bendix.com.au

    Follow Bendix on Facebook by clicking HERE.
    Last edited by motorculture; 1st November 2018 at 04:06 AM.
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