Brake pad shims are the thin metal or rubber-coated layers attached to the back of a brake pad. They are easy to overlook, but they play a real role in keeping your brakes quiet. Here is what they do.
What shims do
Brake squeal is caused by high-frequency vibration between the pad, caliper, and rotor. A shim sits between the caliper piston and the pad backing plate and acts as a damper - it absorbs and interrupts that vibration before it becomes audible noise. Think of it as a noise-canceling layer for your brakes.
Types of shims
- Integrated shims: many quality pads come with a shim already bonded to the backing plate.
- Separate shims: some kits include loose shims you install between the piston and pad.
- Multi-layer shims: a metal-rubber-metal sandwich that damps especially well.
Shims vs hardware vs grease
Shims work alongside two other anti-noise measures: the hardware kit clips that locate the pad, and a thin film of brake grease at the contact points. Together they keep the pad from vibrating. Skip any one and you invite squeal - a big reason for noise after new pads.
Use fresh shims
Old shims can corrode, lose their damping rubber, or get bent. When you install new pads, use the fresh shims that come with them (or a new set) rather than reusing tired ones. It is a small detail that makes the difference between quiet brakes and an annoying squeal. Start with quality pads that include good shims.