Friction material deposits are a common cause of steering wheel vibration during braking. This type of brake shudder occurs when the brake pads intermittently grab and release against uneven deposits on the brake rotor surface.
The condition is often mistaken for disc thickness variation (DTV) or what is commonly referred to as a “warped rotor.” While DTV can also cause brake vibration, friction material deposits are a separate issue with a different cause.
Brake Pad Material Transfer
Brake pad material transfer is a normal and important part of modern braking. A consistent transfer layer helps the brake pad and rotor work together effectively.
Problems occur when this layer becomes uneven in thickness.
Uneven deposits can create alternating levels of brake torque at different points around the rotor. As the brake pad passes over these areas, braking force changes repeatedly. This can cause the steering wheel to vibrate, sometimes severely in extreme cases.
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How Do Friction Material Deposits Occur?
The most common cause of uneven friction material deposits is an unsuitable combination of brake pad and rotor for the vehicle, driving conditions or intended application.
All brake pad materials have a maximum operating temperature. When this temperature is exceeded, the friction material can begin to break down. Instead of producing the fine dust normally associated with brake wear, the pad may release larger amounts of softened or decomposed material.
For example, a typical commuter-style NAO, or Non-Asbestos Organic, brake pad is designed for low to medium braking torque and low to moderate operating temperatures.
If a slotted or cross-drilled brake rotor is then fitted for an application involving increased braking demands, heavier vehicle loads or repeated high-temperature braking, the brake system may operate at higher temperatures.
When the pad material exceeds its intended temperature range, the slots or cross-drilled holes can remove softened material from the pad and transfer it unevenly onto the rotor surface.
In many cases, deposits will be visible immediately after a slot or cross-drilled hole.
Match the Brake Components to the Application
The best solution is to match the brake pad and rotor to the vehicle and its intended use:
- General-purpose brake pads with plain-face rotors for everyday driving
- Performance brake pads with slotted or cross-drilled rotors for applications that demand increased braking performance
- Heavy-duty brake pads and rotors for vehicles carrying additional weight or used for towing
With so many friction materials available, it can be difficult to distinguish genuine performance benefits from marketing claims.
Brake components should be selected based on the:
- Vehicle
- Vehicle load
- Driving conditions
- Frequency of heavy braking
- Intended use
Can Friction Material Deposits Be Removed?
If identified early, friction material deposits may be rectified.
Light deposits can sometimes be removed by fitting a more suitable brake pad material and driving normally over several days. As the new pad beds to the rotor, it may gradually remove the uneven transfer layer.
Heavier deposits may require the rotor surface to be lightly treated with suitable abrasive paper or professionally resurfaced using a brake lathe. Any resurfacing must be carried out within the brake rotor manufacturer’s minimum thickness specifications.
In severe cases, friction material deposits can create concentrated heat spots within the rotor. These heat spots may permanently alter the rotor’s metallurgy and contribute to ongoing vibration or uneven braking.
Once this occurs, the affected brake rotors cannot be restored through normal cleaning or resurfacing and must be replaced.
Preventing Friction Material Deposits
For the best results, always ensure the brake pad and rotor combination is suitable for the vehicle and its intended use.
Proper installation, correct wheel lug nut torque and an appropriate brake pad break-in procedure are also essential for achieving consistent brake performance.
If you experience steering wheel vibration or brake shudder, have the complete brake system inspected by a qualified technician.