Why are some brake pads noisy?

Applying lubricant to brake pad to eliminate brake noise

Brake noises caused by brake pads can take many forms; with squealing, screeching, growling, or rumbling sounds being the most common. Regardless of the actual sound, though, brake noises are always annoying, but there are effective ways of silencing noisy brakes. Here is what you should know about brake noise-

When you are trying to silence noisy brakes, it is important to remember that all brake pads always vibrate during braking. However, in fully functional brake systems, the brake pads vibrate at frequencies that are too high for human hearing to detect, which explains why we do not hear the brakes every time we apply the brakes in our vehicles.

By way of contrast, we hear various brake noises when the pads vibrate at frequencies we can detect, with the sound we hear being a direct function of the frequencies at which the brake pads vibrate. Moreover, brake noises can occur under a variety of conditions, including low road speeds, high road speeds, moderate braking, or even severe braking, which can sometimes make it difficult to determine the exact cause of the audible vibrations.

Nonetheless, since vibration is the root cause of all brake noises, it is always helpful to be aware of the vibration mitigation strategies car and brake pad manufacturers employ to either prevent brake pads from vibrating at audible frequencies or to force brake pads to vibrate at frequencies we cannot hear. While these strategies have the same ultimate goal, which is to prevent bake pad noise, not all such strategies work equally well on all vehicles, meaning that what works on one vehicle, may not necessarily work on another make or model.

Below are some details of the most common brake noise mitigation strategies most car and brake pad manufacturers employ today-

Suspending the brake pads

This strategy involves inserting spring-loaded clips between the brake pads and the caliper to prevent direct contact between the brake pads and the brake calipers. The practical effect of using such clips is that vibrations cannot pass from the pads to the calipers, because the spring-loaded clips absorb or damp out the vibrations.

Directly absorbing vibrations

Since some caliper designs do not allow for the use of spring-loaded clips, some manufacturers insert multi-layered steel plates between the caliper piston(s) (and other parts of the calipers) and the brake pads’ steel backing plates.

In practice, these composite steel plates can have anything between three and six layers, but regardless of the number of plates or layers in any given application, it is worth pointing out that the layers are made of different materials, including stainless steel in different grades, spring steel in different grades, and mild steel in different thicknesses.

This strategy is highly effective in mitigating brake noises because each plate in the stack absorbs a different frequency or a range of frequencies that we can hear. This means that although a collection of steel plates do not prevent brake pads from vibrating during braking, the steel plates do absorb audible frequencies up to about 20 000kHz, which is about the upper limit of sound that most humans can hear.

It should be noted that most high-quality brake pads come with new noise-mitigating plates and clips included in the packaging, and failing to fit these parts onto the new brake pads could result in noisy brakes. Therefore, we strongly recommend that you always fit all parts that come included in the packaging to ensure the proper operation of the new brake pads.

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