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How to Combat Brake Noise Technical Bulletin:
How to Combat Brake Noise


Defining Brake Noise: Primary vs. Secondary

Primary Noise Audible and certainly irritating, occurs over a few seconds of time.
These noises include squealing and high pitch grinding. These noises typically occur
when you apply light / medium pressure to the pedal and/or at a medium rate of speed
(10 - 40mph). Primary brake noise is caused by vibration, and ALL brake systems vibrate.
Most of the time, the inherent vibration frequencies are either beyond audile ranges of the
human ear, or not loud enough. For most applications, the original equipment
manufacturer (O.E.M.) is forced to use noise suppression shims or gaskets.

[Note: If O.E.M.s designs were perfect, they wouldnt need noise suppression shims. They would
design the complete system (knuckle, caliper, rotor, pad, drum, shoe, wheel) so that any vibration
was absorbed and not cause noise. To do this it would take a significant amount of time and money
for every design. So, every O.E.M. has casa-by-case issues/problems with brake noise.]
These noise suppression countermeasures either move the vibration frequency (noise) out
of audible range, or deaden it all together (decrease the volume). For this discussion, we
will be focusing on what our customer complains about, the vibration that is heard, we call
brake NOISE.

Secondary Noise Occurs sporadically or during repeatable driving situations. Such as a
creak, clunk, or short grind when you first apply the pedal driving forward or backward.
These noises are sometimes other problems that have nothing to do with the brake system

Sources of.

Primary Noise High pitch squeal or grind.
1) Lot-Rot: A collection of rust on the rotors. Whats interesting about Lot Rot is
that the rust builds up where the pad isnt coveri ng the rotor. So, if you remove the
pads youll notice a clean area. Lot-Rot can occurs to any rotor. The classic
cases are when a vehicle sits for more than one (1) week. Lot-Rot is a typical
problem for OEMs because the vehicles are stationary for long periods after
manufacturing. Few cases of Lot-Rot occur after wet weather and the rotors have
drops of water on the surface. To countermeasure Lot-Rot an abbreviated
BURNISH is suggested. The worst case, which will cause vibrations & noise, is if
the vehicle is driven aggressively right out of the parking lot. The rust is then
bedded into the friction/rotor causing a change in surface hardness, decreasing
performance and causing primary noise.
NOISE (n.)
Vibration at a frequency and volume heard by the human ear.
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2) Glazing: Overheating or cooking the resins in the friction material. This destroys
the integrity of the friction composite, causing a hardened surface nearest the rotor.
The hardened surface then propagates the vibration causing noise. Glazing
typically occurs from improper burnish or overworking the pads. It can also occur
during repeated aggressive stops (highway traffic), or trailer towing in traffic and
down hills.
3) Friction contamination: Oil or grease contaminating the system causing loss of
friction grip and creating problems at other corners of the car. Example: A loss in
braking power in the left rear will require the front pads to do more work. In turn, the
front pads may glaze easier or excessively wear.
4) Bent/broken hardware: Pad mis-alignment can cause uneven pressure across the
brake pad, which will lead to chatter, uneven wear, and noise. Bent or broken clips,
springs, or shims, dont allow the parts the do the job they are designed to do.
Dust/splash shields can sometime become bent or misaligned, then causing what
sounds like brake noise, but is just the metal rubbing against the rotor or drum.
5) Inherent bad O.E.M. design: Both Chrysler and GM have published service
bulletins stating brake noise is normal during the burnish. This indicates that both
manufacturers have sensitive brake systems designs and are prone to primary
brake noise.

Secondary Noise Clunk, creak, or short grind.
1) Broken or wrong part application: Correct fitment is a must. If the parts are shifting
around in their mounted locations, secondary noise and possibly part failure may
occur.
2) Bad Installation: Again, fitment is important. If a guide or spring was install
backwards or bent in the process, sloppy fitment will be the cause of noise. Proper
guide lubrication will also eliminate any binding or sticking of the parts.
3) Non-brake system part failure: Parts such as suspension bushings, tie rods, ball
joints, or splash shields. If any of these parts are broken, worn, or bent, they could
be sources of noise in the wheel area.











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Combat Noise Checklist

q
Interview the Customer

Driving habits? Vehicle usage?

What are the problem symptoms? Performance, noise, pedal feel?

When and where does the problem occur?
q
Inspect Complete Vehicle

Previous repairs? Crash/Accident?

Broken suspension? Bushings? Splash shields?
q
Inspect Brake System

Brake fluid condition or color?

Even friction wear on the left or right side of car?

Condition of rotor/drum, O.E.M. spec? Blued? Cracked?

Current fitment of parts?
q
Service Bulletins

Refer to attached contact list.

www.inwoodauto.com
offers a few on our website.
q
Replace or Service Braking System Components


This includes the rotor, the brake drum, calipers, master cylinder and
wheel cylinders.

Check original equipment (O.E.) minimum thickness

Resurfacing is a MUST, if not new part. Best defense against brake
noise!

Non-directional finish and wash with soap and water.
q
Assembly of New / Serviced parts

Clean parts. Wire brush oxidation/rust & dirt build -up.

Lubricate all contact points. Pad guides, caliper guides, spring ends,
pivot points.

Install all hardware. New springs, guides, and clips.
q
Test Drive & Burnish the New Friction
§
Twenty (20) seconds between each stop.
§
Distance should be twice (2x) as the normal braking distance.
§
Ten (10) stops from twenty-five (25) m.p.h.
§
Five (5) stops from forty (40) m.p.h.
§
Two (2) moderate decelerations from sixty (60) to forty (40) m.p.h.
§
Steps to completed by vehicle owner:

Five (5) stops from thirty-five (35) m.p.h.

Five (5) gentle decelerations from sixty (60) to zero (0) m.p.h. .
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Possible Technical Service Bulletin Sources

Acura
800-382-2238, 2
BMW
Contact Dealership

Buick
Contact Dealership

Cadillac
800-333-4CAD
Chevrolet
800-950-2438
Daimler-Chrysler 800-992-1997 or 800-426-6451
Dodge
800-439-7694
Ford Motor Co. 800-392-3673
G.M.C. Truck
800-GMC-TRUCK
Honda
800-999-1009
Hyundai
800-633-5151

Infiniti/Nissan
800-826-6500

Isuzu
Contact Dealership
Jeep
Daimler-Chrysler
Kia
Contact Dealership
Land Rover
Contact Dealership
Lexus
Contact Dealership
Lincoln
800-521-4140
Mazda
Contact Dealership

Mercedes-Benz 800-FOR-MERCEDES

Mercury
800-446-8888

Pontiac
Contact Dealership
Porsche
Contact Dealership
Saab
Contact Dealership
Saturn
Contact Dealership
Subaru
866-428-2278
Toyota
800-331-4331, 3, 3
Volkswagen
800-544-8021 www.vw.ddsltd.com

Volvo
800-258-6586
www.volvotechinfo.com


All information was taken from various magazines (i.e. Motor Trend, Car & Driver, Automobile).