Among the small pieces in a brake hardware kit is a springy clip called the anti-rattle spring - and despite its size, it is often the difference between quiet brakes and an annoying clatter. Here is what it does and why it matters.
What it does
The anti-rattle spring is a light spring clip that puts constant tension on the brake pad, holding it firmly against the caliper or bracket so it cannot move around. Because the pad sits in the bracket with a little clearance to slide, that clearance would let it rattle over bumps - the spring takes up the slop and keeps it quiet. It is a core piece of the brake hardware kit.
Why brakes rattle without it
When the anti-rattle spring is missing, weak, or corroded, the pad is free to vibrate and you get a metallic rattle or buzz over bumps that often quiets when you brake - see brake pad rattle and gap noise. Reusing old, tired springs from the last brake job is a top cause of a fresh set of pads rattling.
Works with the other hardware
The anti-rattle spring works alongside abutment clips and shims - the clips give the pad a clean surface to slide on, the shims damp squeal, and the spring holds everything snug. Together they keep the brakes quiet and the pads wearing evenly.
Replace it with the pads
Like all brake hardware, the anti-rattle spring should be replaced with every pad change - most quality pad sets include new ones; see when to replace brake hardware. Fit fresh hardware with quality pads and the rattle stays gone.