Are brake pad shims necessary? The real truth

Learn what brake pad shims do and why they’re necessary

DIYers often reuse old brake pad shims or toss the old ones and complete the job without any shims. Then complain about noise shortly after installing new brake pads. That’s foolish. The brake shims play an important part in reducing brake noise and reusuing old brake shims isn’t smart.

The job of brake pad shims

All brakes vibrate when the brake pads rub against the rotor. If you think of the brake pad like a stylus and the rotor as an LP record, you can see how the pads “play” the wear grooves on the rotor. Modern brake pad shims are multi-layered with a thin rubber membrane between the two shim panels. The rubber dampens the vibrations, preventing the vibrations transferring from the pad’s backing plate to the caliper piston or “fingers.”

Noise reduction shims wear out

As mentioned above, brake pad shims are more than a sheet of metal. The high quality units are multi-layer designs with a rubber layer that deteriorates with heat and age.

That’s why it never pays to reuse old shims. If the shims don’t have a rubber layer, the shop manual usually recommends applying a light coat of molybdenum grease between the pad’s backing plate and the shim. Molybdenum grease dampens the vibrations.

In addition to dampening vibrations, the shims also act as a thermal barrier, preventing heat from flowing to the caliper face and piston. That provides constant temperature to the pad, resulting in more consistent braking.

If your new pads don’t come with them, BUY a new set. Then you’ll have a top quality brake job.

©, 2016 Rick Muscoplat

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