Advanced Technical Information

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Binder – 4 --- Chassis

Brake Squeal
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Understanding and addressing brake squeal complaints
Disc brake squeal is the most common brake noise complaint received from customers. This bulletin
will help you understand what disc brake squeal is, and how to address it.
Remember that brake squeal is a normal result of different factors acting on the brake system and
does not constitute a defect.
Porsche Brake systems are high performance brake systems engineered to perform on Porsche vehicles. Due to the stresses to which Porsche vehicles are oftentimes subjected, Porsche vehicles sent
in for brake service may exhibit exceptional wear at earlier than expected times compared to wear
found typically on other vehicles. All of the conditions described below are the result of normal brake
system wear and are therefore not warrantable.
The Owner’s Manual states: (Driving and Driving Safety section)
Brake pads and brake discs
Wear on the brake pads and brake discs depend to a great extent on the driving style and the conditions of use and therefore cannot be expressed in actual miles on the road. The high-performance
brake system is designed for optimal braking effect at all speeds and temperatures. Certain speeds,
braking forces and ambient conditions (such as temperature and humidity) therefore might cause the
brakes to squeal.

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Component Inspection Guidelines
Fluid
• Fluid replacement is recommended every two years in the workshop manual.
o WM 470855 Changing the brake fluid.
o There is also a section in the Owner Maintenance booklet dedicated to recording the brake
flushes every 2 years.
• Moisture in the fluid is heavier than the fluid, and accumulates in the calipers. Moisture affects the viscosity of the fluid and its ability to lubricate.
• The right rear caliper is the farthest from the reservoir and may be affected more than the other
calipers.
• This is due to the larger volume of fluid in that circuit and therefore a larger amount of moisture can
settle in that caliper.
• If squeal is occurring on one wheel in particular, fluid condition is likely to be a part of the problem.
Countermeasure: Flushing the fluid is necessary to get rid of the moisture accumulation.
Tip: Warming the fluid by driving and braking before flushing it, can help get a more thorough flush of
the fluid.
Brake Pads
• Glazed surface
• Dust buildup at edges
Countermeasure: Sanding the pad and chamfering the edges.
• Wear at contact points with caliper and hardware
• Correct shims / dampers; look for wear at contact points with pistons and edges of pad.
Countermeasure: Lubricating contact points with optimol grease and insuring proper fit of
shims/dampers.

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Rotors
• Glazed surface
• Lips develop at outer and inner edges of pad contact area

• Corrosion
• Contamination by sprays, fluids, road salt, grime, and small particles becoming embedded between
the pad and rotor.

Countermeasure: Sanding the rotor to create a non-directional finish, remove corrosion and
reduce/remove the lip around the edges.
Glazed pads and rotors are the fingerprint of the normal, light footed, slow speed brake squeal.
Replacement of the pads and rotors with the same pads and rotors that are already on the vehicle, will
not fix the situation. As soon as the new parts are subjected to the same conditions, the squeal will
return.
Deglazing the pads and rotors needs to be done so the noise will be gone for as long as possible.
A brake rotor hone can be used to get a non-directional finish on the rotor.

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Calipers
• Pins – movement between pad and caliper

Countermeasure: Lubricating contact points with optimol grease and insuring proper fit of components
will quiet the contact points.
• Tension spring – Movement between spring and pads will vary as spring tension varies. The witness
marks will reflect this. Replacing the spring and hardware will restore proper tension on the pads.

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• Caliper pistons – Wear marks from movement of pad against piston. This is an indication of pressure
distribution from the piston to the pad. Brake squeal is affected by pressure distribution.

• Inspect pistons to see if there are any that may not be returning completely. Moisture in the fluid can
have an effect on this.
• Exercising the caliper pistons can restore the movement of the piston to normal operation.
Exercising Brake Caliper Pistons
• Remove brake caliper
• Remove pads and hardware

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• Have the following parts on hand:
• Caliper paste 000.043.117.00

• Optimoly paste 000.043.020.00 (the 100g tube should last through several repairs)
• New hardware kit
• New dust seals

• Clean brake caliper so that there are no contaminants present when the dust seals are removed.

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• Remove dust seals from the caliper pistons

• Extend the pistons against a block of wood to keep them from coming out of the caliper. (It may be
necessary to retract and extend the pistons several times to free up the movement)
• Apply brake caliper paste to the piston and install new dust seals on the pistons
• Retract the pistons and seat the dust seals
• Install pads and new hardware
• Install caliper on vehicle
• Flush brake fluid
• Test drive the vehicle.

In cases where additional help is needed please file a TLAR and contact your FTM.

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What is Disc Brake Squeal?
Disc brake squeal is a noise that is the result of friction
induced minute vibrations. As the pad travels over the surface of the rotor, minute vibrations are produced, just like a
record player.

The noise (squeal) produced by the vibrations are radiated out by the rotor (the rotor is acting like a
speaker).

The condition producing the minute vibrations is called a “stick-slip”
condition. A common stick-slip noise is a squeaky door hinge. Unlike
a squeaky door hinge, we cannot lubricate the contact surfaces to
fix the problem.

This stick-slip condition is the result of light footed braking. When pads and rotors are seated, or bedded in, material transfer from the pad to the rotor establishes a working coefficient of friction between
the two surfaces. Light footed braking abrades this material transfer, and smooths the rotor & pad
surfaces. The conditions for stick-slip are now optimized.
The squeal that we are familiar with occurs in the transition between stick and slip. Light footed braking at low speed is the optimal time for this to occur. The squeal will not occur if the brake sticks
more or if the brake slips more. We don’t want it to slip though.

Frequency

Velocity
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Some clear indications that a normal brake squeal from the conditions described above are:
• When the squeal occurs, applying more brake pressure makes it go away.
• The rotor has a polished mirror like finish on it.
• The pads have a smooth surface finish, like a glaze.

Other Contributing Factors
There are other factors that contribute to brake squeal as well. All components (even the bolts) have
what are called “bending and twisting modes”. As force is applied to a component (as it is excited) it
will bend and twist in different ways. The bending and twisting modes change as brake pressure
changes.
The amount of bending and twisting is not visible to the naked eye. It is a normal characteristic of all
components that can be determined through Frequency Response testing.
This is one of the reasons why proper torque on fasteners is critical. Other factors would include things
such as component temperature, mass, geometry, insulation, and lubrication. Weather and driving conditions are also major factors.

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Countermeasure Limitations

Brake squeal can fall into a very wide frequency range. The range is divided into three groups.
1. Low Range 1 - 3 KHz
2. Mid-Range 3 – 6 KHz
3. High Range 6 – 20 KHz
The frequency of the noise will determine what countermeasure to use in an effort to quiet the
noise. Some common countermeasures are listed below.
• Pad Chamfers
• Various slot configurations in the pad
• Pad slippers
• Shims of various types
• Tuned mass dampers
• Fixed calipers
Countermeasures are limited on a given brake system due to limitations with space and
performance. Testing must be performed to determine if a countermeasure is effective without
deteriorating performance.
The Society of Automotive Engineers published an engineering text on the subject of brake
squeal. This is a quote from that text.
“However, disc brake squeal remains an elusive problem, and there is not yet a method to
completely suppress it.”

(Disc brake squeal: mechanism, analysis, evaluation, and reduction/prevention /
[edited by] Frank Chen, Chin An Tan, and Ronald L.Quaglia. SAE)
What can we do?
1. We can assure the customer that we will perform a test drive to verify the concern.
2. We can perform a thorough visual inspection of the brakes to see if any abnormalities exist and
repair them.

Dealership
Distribution
Routing

Service Manager _______ Shop Foreman

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Service Technician

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_______

_______

_______

Asst. Manager

_______

Service Technical

_______

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_______ Warranty Admin.

Dr. Ing. h.c. F. Porsche AG is the owner of numerous trademarks, both registered and unregistered, including without limitation the Porsche Crest®, Porsche®, Boxster®, Carrera®, Cayenne®,
Cayman®, Macan®, Panamera®, Speedster®, Spyder®, 918 Spyder®, Tiptronic®, VarioCam®, PCM®, PDK®, 911®, RS®, 4S®, FOUR, UNCOMPROMISED®, and the model numbers andthe
distinctive shapes of the Porsche automobiles such as, the federally registered 911 and Boxster automobiles. The third party trademarks contained herein are the properties of their respective owners.
Porsche Cars North America, Inc. believes the specifications to be correct at the time of printing. Specifications, performance standards, standard equipment, options, and otherelements shown are
subject to change without notice. Some options may be unavailable when a car is built. Some vehicles may be shown with non-U.S. equipment. The information contained herein is for internal authorized
Porsche dealer use only and cannot be copied or distributed. Porsche recommends seat belt usage and observance of traffic laws at all times.

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