Why do Brake Pads Fail?

Example of brake pad failure caused by severe overheating

High-quality brake pads seldom fail, but even OEM or OEM-equivalent brake pads can suffer induced failures. Put differently, this means that when high-quality brake pads fail, the cause(s) of the failure seldom involve defects in the brake pads themselves. There are many possible causes of induced brake pad failures, but let us look at the most common causes of such failures in some detail-

The use of unsuitable brake pads

All manufacturers of high-quality brake pads go to great lengths to ensure that their products produce reliable, consistent, and predictable braking forces under all reasonable operating conditions. However, as with so many other things in life, the proverbial devil lives in the details, and in this case, the details involve the meaning of the term “reasonable operating conditions”.

Let us put this into perspective by saying that a heavy 4WD truck that regularly tows heavy trailers at highway speeds places much greater demands on its brakes than a similar truck that carries maybe one adult on its daily commute to work and back in an urban environment. This is perhaps an extreme example, but it does illustrate the point that different vehicles have different braking requirements in different operating environments.

To address these differences, brake pad manufacturers continually develop new brake friction materials that produce braking forces to suit particular needs and requirements. For instance, most manufacturers produce specialised brake friction materials that can withstand the very high brake temperatures that a vehicle towing a heavy trailer generates without degrading any of the ingredients in the friction material.

Therefore, installing such specialised brake pads in a vehicle that spends its life on urban roads, and whose brakes never reach the temperatures that are required to make the brakes work optimally means that the brakes will never perform optimally simply because the brakes never get hot enough for the brakes to work as intended.

In such cases, the brake pads and brake rotors will simply polish each other to a mirror-like shine, which reduces the friction coefficient of the brake pads even further. This produces a condition known as “brake fade”, which simply means that whatever braking action the pads do produce, simply fades away during braking events.

While a condition such as that described above can be seen as a brake pad failure, the brake pads did not fail because they were deficient or defective in some way: the brake pads failed because they were installed in the wrong application.

Bedding in new brake pads incorrectly

ERxample of overheating brake pads

The process of bedding-in new brake pads is crucially important to ensure the proper operation of the new brake pads throughout their expected service lives, and especially so if the brake rotors are also new, as they should ideally be.

The image above illustrates the (almost certain) consequences of not bedding in new brake pads correctly. In this instance, an incorrect bedding-in procedure caused the brake pads and brake rotors to overheat severely, thereby effectively destroying both the new brake pads and brake rotors, which begs the question of how brake pads should be bedded in.

As a practical matter, the exact bedding process largely depends on the type of brake pad, but essentially, the process of bedding in new brake pads involves forcing the surfaces of the brake pads and brake rotors to conform to each other. More importantly, though, this process must allow for a gradual deposition of some of the brake pads’ friction material onto the surface of the brake rotors. While normal braking continually removes and replaces this film of the friction material on the brake rotors, the presence of such a film is essential for the efficient operation of organic and semi-metallic brake pads.

Thus, in general terms, bedding in new brake pads involves applying the brakes several times at low road speeds, but crucially, at intervals that are long enough to allow the brakes to cool down between brake applications. As stated elsewhere, the recommended number of brake applications and the intervals between them largely depend on the type of brake pad installed, so we highly recommend that you research the correct bedding-in procedure for the type and brand of brake pads you are planning on installing before you place the vehicle back into service.

Failing to get this critically important procedure right could not only destroy the new pads and rotors but also cause sudden and unexpected brake failure when you need the brakes to work as expected.

Abusing the brakes

Brake system abuse can take several forms, but perhaps the most common forms of brake abuse are a) towing trailers or carrying loads that exceed the vehicles’ towing or load capacity, and b) keeping the brakes engaged for extended periods when going downhill.

While it could be argued that brakes are supposed to get hot, brake temperatures that exceed the maximum thresholds recommended by brake pad manufacturers cause some ingredients in the friction material formulation to degrade, evaporate, or even separate out of the friction material matrix.

Although the degree of damage that severely overheated brake pads suffer depends on both the brake fiction material formulation and the degree of overheating, it is worth bearing in mind that all the ingredients in any friction material formulation depend on each other being present in an un-degraded state for the friction material to work as expected.

If the brake pads overheat to the point where say, some binding materials in the matrix evaporate, the friction material could become brittle, or delaminate from the steel backing plate, both of which conditions could potentially cause the brake pads to fail catastrophically. We could list other examples, but the point is that brake pads always suffer some form of damage or degradation when they overheat, although the type of damage or degree of degradation is not always visible or detectable just by looking at the brake pads.

Therefore, we strongly recommend that you replace both the brake pads and the brake rotors when you suspect that the brakes may have overheated to avoid a sudden and unexpected failure of the brakes to work as expected.

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