Brake
Noise and Squealing
by Austin Davis of TrustMyMechanic.com
Reader
Question: I just had my brakes replaced and they
are now squealing. My mechanic says this is normal,
why did I have to pay for normal brake squeal? Is he
just blowing me off?
Dear
concerned car owner,
This
unfortunately can happen more than you or I want it
to. A certain amount of high-pitched brake noise is
considered "normal" these days because of
the harder semi-metallic brake pads that are used on
cars now. In my experience, the smaller cars like Honda
and Toyota seem to have the most trouble with this.
Squeals heard the first few stops in the morning when
the brakes are cold and somewhat damp from dew, and
squeals that are heard the last few feet while coming
to a stop are usually nothing to worry about.
Semi-metallic
brakes are made of bits of metal shavings in place of
the asbestos material that has been banned by the U.S.
government. These semi-metallic brakes have great stopping
power and have a long wear life, but can cause a high-pitched
squeal that drives car owners crazy and frustrates mechanics
who can't get it to go away to please their customers.
When
are squeals not a problem?
Some brands of semi-metallic pads are inherently noisier
than others because of the ingredients used in the manufacture
of the friction material. Think of it this way, the
longer life pads or pads that claim to have more stopping
power usually contain more metallic material. Yes, they
will last longer and could enhance braking but the chance
of causing a squeal noise is very high. The squealing
noise that might be caused from use of these pads does
not affect braking performance and does not indicate
a brake problem.
Brake
squeal is caused by vibration between the brake pads,
rotors, and calipers. Having the brake rotors refinished
or trued (machining a small layer of the metal away
from the brake rotor to make it smooth and "true"
again) and a thin layer of a silicone compound placed
on the back of the brake pads are a great way to reduce
the squeal if the semi-metalic pads are the culprit
of the noise and not due to a worn out brake pad.
Why
does this squeal happen anyway?
The brake rotor is the round metal object that the brake
pads squeeze together like the white part of an Oreo
cookie. The rotor is metal and has a smooth slick finish,
and the brake pads are made of metal shavings and also
have a smooth somewhat slick finish. The more metallic
material found in the pad the greater the chance for
noise, and vise-versa.
The
other type of brake pad is called organic. There is
no metallic material used in this kind of brake pad.
Organic style brake pads can only be used on vehicles
that are specifically designed to use them. Improper
use of organic pads on a vehicle designed to use semi-metallic
can severely reduce stopping ability. Organic pads are
softer than semi metallic and usually do not have a
squeal problem. Unfortunately due to shorter life expectancy,
inability to stop larger vehicles, and the addition
of substances like asbestos in their construction, they
are not very widely used.
When
are squeals signaling a problem?
Sometimes brake squeals are an indication that maintenance
is required. Some common conditions that cause brake
noise are:
