Rick's Free Auto Repair Advice

Adherent versus abrasive brake pads

Adherent versus abrasive brake pads

Brake pads use either adherent or abrasive friction material

But no brake pad is 100% abrasive or adherent. Abrasive brake pads contain some lubricant additives and have some adherent qualities. Adherent brake pads contain some abrasive components.

Abrasive brake pad friction material explained

In simple terms, abrasive brake pads create stopping power by grinding away at the rotor. The brake pad acts like sandpaper and the rotor is the wood in this analogy.

It’s this mechanical rubbing of an abrasive material against the metal rotor that converts kinetic energy into heat that stops the vehicle. Abrasive pads wear away the rotor surface much faster than it wears out the brake pads.

The most common “abrasive” brake pads are semi-metallic. Due to their construction, hardness and abrasiveness, they provide the best stopping power of all brake pad types. That’s why they’re used on heavy SUV, light trucks and larger trucks.

Adherent brake pad friction material uses a transfer layer

Adherent brake pads operate differently. During the break-in or ‘bedding” operation,  the technician or owner drives the vehicle and makes multiple smooth brake applications to wipe a thin film of brake pad friction material into the pores of the rotor face. The thin film of brake pad material that adheres to the rotor face is called the transfer layer.

During all future braking the brake pad presses against the transfer layer, creating friction. In adherent braking, kinetic energy is converted into heat by pressing the brake pad against the transfer layer.

The heat breaks the transfer layer bond to the rotor, changing the transfer layer on a molecular basis. The brake pad then replaces the damaged transfer layer with a new layer of material from the brake pad. The process of damaging and replacing the transfer layer happens multiple times during braking.

Because the brake pads are always depositing a new transfer layer onto the rotor, the pads wear faster in this system than the brake rotor.

The most common adherent brake pads are non-asbestos organic (NAO) and ceramic.

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Posted on by Rick Muscoplat


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