What is a brake pad shim?
A brake pad shim installs between the brake pad backing plate and the brake caliper piston on the inboard side and the brake pad backing plate and the outer caliper fingers on the outboard side. In simple terms, a noise-reduction shim “decouples” the brake pad’s steel backing plate from the caliper. A noise-reduction shim is made from a noise-dampening material and is designed to stop the transmission of vibration to the caliper. Shims also dampen the vibrations in the pad itself. provide a thermal barrier to ensure consistent temperature across the brake pad.
Single versus multiple layered noise reduction shims
A single layer noise-reduction shim is made from a soft metal that has a high degree of dampening ability. A multi-layer shim, on the other hand, often contains two thin outer metal plates and an inner elastomeric core, or an inner metal core with two outer sheets of noise dampening material. In some cases, the design of the inboard shim may be different than the outboard shim. In those cases, proper placement is critical to achieve maximum noise reduction.
Multi-layered shims are far more effective at noise reduction than single layer shims.
Brake Pad Shim attachment methods
Brake pad noise-reduction shims can be attached with adhesive, mechanical tabs and holes or be permanently riveted to the brake pad backing plate. The adhesive method isn’t designed to hold the shim in place over the life of the brake pad. Instead, the adhesive is used for first-time placement. Tabs and holes and rivets keep the shim in place over the life of the pad.
Pressure sensitive adhesive
Some noise reduction shims come separate from the brake pads and attach with pressure sensitive adhesive to the brake pad backing plate. The adhesive’s role is to secure the shim only during installation. Normal brake heat will degrade the pressure sensitive adhesive after a short period and the shim must stay in place due to its shape and placement in the caliper.
Tabs and holes
Other shim designs incorporate tabs or holes that mate to the brake pad’s backing plate to hold the shim in place.
Still other shims are designed to be permanently installed to the brake pad’s backing plate during pad manufacturing. This method ensures the shim will never migrate and also ensures the shim will never be reused.
Brake Pad Shims can’t be reused
Noise reduction shims, just like anti-rattle/abutment
clips should never be reused. Over their life, the shims lose their ability to reduce noise. Reusing old noise reduction shims will result in a brake job that produces noise, vibration and harshness (NVH).
© 2019 Rick MuscoplatPosted on by Rick Muscoplat