Shims

[Grandpa]

Alright, anyone know the purpose of the shims on the brake pads and are they really necessary?

[amf1932]

Alright, anyone know the purpose of the shims on the brake pads and are they really necessary?

The purpose of shims is to prevent the brakes from squealing. They are actually called, anti-squeal shims.

They were put in there for a good reason....so why not use them? :)

[Grandpa]

Well, I replaced my rotors & brake pads, but was missing shims on the front pads.... can i just spray some of that anti-squel stuff instead of buying a new shim>

[amf1932]

Well, I replaced my rotors & brake pads, but was missing shims on the front pads.... can i just spray some of that anti-squel stuff instead of buying a new shim>

If you have no squeal problems then leave it alone.

The cause of brake "squeal" is counter-intuitive. Brake squeal is not caused explicitly by the contact of the pad and the rotor. Rather, brake squeal is caused by micro-vibrations in the pad as a result of extremely high-frequency "catching and slipping" of the pad against the rotor. Application of brake anti-squeal paste or spray is similarly counter-intuitive. I'm not exactly certain how these magical products prevent these vibrations, but they do. The trick is to apply the anti-squeal product to the back of the new pads (the clip side, not the pad material side).

[CUMan]

I think there is considerable variability in brake squeal from one vehicle to another. Perhaps it is the design of the rotor-caliper assembly that plays a big role. The pad compound may also be a factor.

Some of the noisiest brakes I ever encountered were on a 1987 Acura Legend I owned. I replaced the front pads with Acura pads, reused the shims, and did not use anti-squeal material. The sound these brakes made would wake the dead. I redid the assembly using the anti-squeal stuff, and all the noise stopped.

Several months ago, I helped my son replace the front pads on his 2002 Ford Ranger pick-up. The shims were glued to the old pads, and we bent them trying to remove them. We installed the new pads without shims, put anti-squeal on the back of the pads, and hoped for the best. He has absolutely no noise when braking.

I have always used anti-squeal material since the Acura episode. Over the years, I have replaced the brake pads numerous times on my two Lexus vehicles and have always reused the shims. I have never had any brake squeal. Is this noiseless operation due to the presence of the shims or the use of anti-squeal compound? I don't know.