Brake Pad Shims
Thin metal or rubber plates attached to the back of brake pads to dampen vibrations and reduce brake noise.
Brake pad shims are thin backing plates made of metal, rubber, or a composite material that attach to the back of the brake pads, positioning them between the pad and the caliper piston or caliper frame. Shims are designed to absorb and dampen the microscopic vibrations and harmonics generated when the brake pads press against the spinning rotor.
These high-frequency vibrations are what cause the high-pitched squealing noise often associated with braking. Many premium brake pads come with pre-installed shims. If shims are missing, damaged, or installed without brake lubricant, the brakes are likely to squeal loudly even if the pads are new.
During a brake pad replacement, mechanics inspect the shims and apply a specialized high-temperature brake grease to the back of the pad/shim interface to ensure quiet operation.