Rick's Free Auto Repair Advice

Transfer layer

Transfer layer — brake pads

There are two types of brake pad friction materials; abrasive and adherent

Abrasive brake pad friction material

In simple terms, abrasive brake pads act like sandpaper and the rotor acts as the wood. 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.

Adherent brake pad friction material and the transfer layer

Adherent brake pads operate differently. When first installed, the technician drives the vehicle and makes multiple smooth brake applications to wipe a thin layer 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 the braking process the brake pad presses against the transfer layer, creating friction. This an important distinction between abrasive and adherent brake pads. 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, changes the transfer layer on a molecular basis and 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.

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Posted on by Rick Muscoplat

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