By Jim Marotta
I think we can all agree that the braking system is the most
important safety device on any vehicle. Since people place such a high value on their car's ability
to slow and stop, it is smart to pay attention when they complain about the
Let's review the five most common brake complaints and how
to resolve them.
Brake noise, or squealing, is the most obvious problem to
drivers. Unwanted movement of brake components causes the noise. What's the solution?
Keep brake components in place per factory specifications and properly prepare
surfaces during service.
According to Chuck Kennedy, Bendix Technical Training
Manager, "Today's brake systems are very sensitive to rust and corrosion and
should receive a thorough cleaning in preparation for fresh lubricant,
hardware, and friction material.
Residual rust or corrosion left in critical areas can begin to cause
brake issues almost immediately."
In addition to the normal inspections for binding,
corrosion, lack of lubrication, and worn or damaged components, clean the caliper
moving parts and retaining
hardware. Clean pin bores with a round wire brush and cleaner to remove old
lubricant and corrosion.
Caliper pins can cause binding. Clean
the caliper moving parts and retention hardware of dirt, corrosion and rust. Clean pin bores with a round wire brush and cleaner to remove old lubricant and
Pad abutments need to be clean and smooth, whether they are
part of the caliper bracket or steering knuckle. If there are notches or
grooves caused by pad movement, replace these parts. Damage like this can cause
excessive pad movement that leads to noise and vibration.
It may be counterintuitive to clean a new or freshly machined
rotor with soap, warm water, and a stiff brush, but this simple step removes fine,
metal particles from the surface and pores, which if left there, can embed in
the friction material, causing brake noise.
Clean, inspect and adjust rear
calipers or drum brake systems before the vehicle gets back on the road.
If there are grooves on the backing plate shoe support pads, replace the
backing plates. This prevents shoe chatter and improper brake shoe return,
which leads to grabbing and premature shoe failure.
Pulsation is another issue that is obvious to
the driver. Check for rotor lateral
runout and thickness variations that point to pulsation issues. Do not
forget to check the hubs. Hubs can be the culprit while the rotor shows the
Checking for rotor thickness variations will help diagnose pulsation issues.
Use a polishing pad to clean as much rust as possible from
the hub face and next to the studs. Leaving corrosion in these areas is one of
the top causes of pulsation.
An often overlooked area is the wheel hub mounting pad. If
there is rust or debris in this area, it can lead to rotor distortion and
pulsation just as easily as if debris were left on the hub.
Another common cause of pulsation is uneven tightness of
wheel lugs. Lighter components on today's vehicles can be easily distorted. Eliminate
this issue by lightly seating and then torquing wheels to specification in two
stages. On wheels with lug-centric hubs, rotate the wheel as the lugs are
seated to help keep the wheel centered on the hub.
What do you do if all else fails and there is still pulsation?
Check the tire and wheel assemblies for speed-dependent, loaded, radial force
variations. A tire or wheel rim out-of-round or imbalanced can cause a
pulsation similar to the pulsation caused by rotor problems.
When applying braking
force, small amounts of material gradually abrade from the brake pads. This
material, known as "brake dust," usually deposits on the braking
system and the surrounding wheel.
The proper friction material choice can affect dusting. Different brake pad formulations create
different amounts of dust, and some formulations, particularly metallic brake
pads, create more dust than others. Ceramic brake pads contain significantly
fewer metal particles, and therefore produce less abrasion of surrounding metal
Rob Backode, Director of Product Management for Bosch
Automotive Aftermarket Brake Components reports that "The number of complaints about
brake dust is far,
far fewer with more service shops installing ceramic-type brake pads."
Brake dust can be more than just a visual nuisance; it can badly damage the finish of most
wheels if not washed off. Removing brake dust can
eliminate other problems and avoid customer complaints.
Some technicians tape off the brake shoes to
prevent contamination during service.
4. Excessive Wear
Common complaints due to excessive wear are usually due to
lack of maintenance, hard driving style, or vehicle usage characteristics. Brakes
on one vehicle may last substantially longer if the owner drives it easy or
takes more highway trips. If the owner overloads the vehicle, makes short,
stop-and-go trips, or leaves one foot on the brake pedal while driving, the pads
will have more wear and failures from the abuse.
Common complaints due to excessive wear are usually due to lack of
maintenance, driving style, or the way the vehicle is being used.
Residual pressure trapped in the hydraulic system can lead
to excessive wear and premature failure of friction materials. Quickly determine
whether it is a mechanical or hydraulic issue by cracking a bleeder screw on a
caliper that shows drag. If fluid comes
out and the caliper releases, then a component is restricting fluid return to
the master cylinder reservoir. If no fluid escapes and the drag remains, then
it is a mechanical issue within the caliper or slides.
pressure trapped in the hydraulic system can cause excessive wear and premature
failure of friction materials and surfaces.
5. Stopping Performance
Stopping performance is crucial for today's high performance
vehicles and driving conditions. Poor performance can be related to a previous
brake job that was done improperly, failing components, vehicle overloading, or
installing the wrong type of friction material.
Proper inspection, preparation, and break-in are the best ways to
overcome these issues.
Pad burnishing or break-in is recommended by many original
vehicle manufacturers, but not all. When
recommended, a proper burnishing or break-in of the friction material
and rotor surface will enhance brake performance, reduce noise, and give the
best life possible for the pad materials installed. Burnishing works by mating
the two surfaces together to allow proper heat dissipation. It also transfers a
film from the friction material to the rotor surface that will enhance its
Old Concerns, New
While there are issues we no longer have to deal with on
today's vehicles thanks to technological advancements, some changes create new challenges. Improvements in materials such as rubber and composites lengthen
the service life of brake components. Modern, synthetic lubricants give more
protection, last longer, withstand higher temperatures, and are compatible with
improved in recent years, give more protection, last longer, sustain higher
temperatures, and the synthetic compounds are compatible for use with rubber
The smaller components and lighter weight of the brake
components and the vehicle itself drive many of the changes. Less mass increases
the chance for noises to occur. Vehicle manufacturers use more anti-rattle
clips and hardware to help control brake noise. Brake systems run at much
higher temperatures, requiring improved lubricants.
Pulsation issues increased when rotors went from integral
hub/rotor assemblies to over-the-stud mounted assemblies. Corrosion between the
assembled hub, rotor, and wheel gives rise to runout and pulsation issues.
As vehicles continually change, we may leave some problems
in the past, but we look for new tools, procedures, and information to solve
issues on modern cars and trucks. Servicing modern vehicles is more exacting
and detail-oriented. Leaving out important steps increases the chance for
customer complaints and comebacks. Thorough
inspection, diagnosis, and repair procedures are the best way to keep
customers satisfied and their vehicles performing up to their expectations.
Resolve your customer's major and minor
brake complaints with a subscription to ChiltonPRO, the smart technician's
guide to new technologies and old. Just click here
to see ChiltonPRO and learn what's coming next to your service bay.
A muscle car enthusiast and drag racer, Jim Marotta is a freelance automotive writer with more than 20 years experience in the automotive industry.
25 May 2011 12:14 PM
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