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Brakes
Do Your
Brakes Squeal?
Does your car
squeal when you apply the brakes? This could be the
sound of your "chirper", a signaling device built
into the system to warn you of worn brake pads. A
squealing or grinding noise also is characteristic
of the new, semi-metallic friction material used on
brake pads and linings. This material replaces the
hazardous asbestos previously used.
Brake
performance on vehicles of recent years is
significantly improved, as is the service life of
braking system parts. Unfortunately consumer
attitude toward preventive maintenance has not kept
pace with technology. A national consumer survey
showed vehicle neglect is on the rise even though
nearly half of motorists ranked brake failure as
their number one fear among driving
emergencies.
Surprisingly,
less than 20% identified brakes as a system to be
checked regularly.
The U.S.
Government Accounting Office reports that states
without vehicle safety inspection programs had
accident rates 17% higher than those with
inspection programs.
Whether or
not your vehicle's brakes are inspected
periodically, as they should be, be aware of the
signs of brake trouble and take corrective measures
at once.
Listen for
unusual noises when brakes are applied. To improve
hearing, try applying brakes at slow speeds with
windows down.
Note: Brake
work performed on time saves money as well as
lives. Some owners, to squeeze extra miles out of
their worn brake pads, have been known to disable
the "chirper" (mentioned earlier.) This is a
classic case of false economy. In addition to
affecting driving safety, metal-to-metal wear of
rotors or drums adds hundreds of dollars to a brake
system overhaul.
If brake
fluid needs topping off frequently, find and
correct the leak.
If brakes
pull to one side, if they shudder or if the pedal
pulsates, have a qualified technician check out the
trouble.
If the pedal
"fades", feels spongy or falls to the floor under
steady foot pressure, take the vehicle in for
service.
Invest in the
best quality brake work you can obtain. It's an
excellent form of insurance.
Anti-Lock
Brakes
If you don't
already own a car or truck equipped with an
anti-lock braking system (ABS), chances are you
will before long. Since 1995 more than half the
vehilces on the road have been equipped with
anti-lock brakes.
As a
potential lifesaver, ABS helps keep your car under
control should you jam on the brakes on a slick
road or under emergency conditions. The safety
benefits will be reduced, however, without proper
preventive maintenance and care. Neglecting ABS can
also lead to expensive repairs down the
road.
Too many
drivers, whether their cars have conventional
brakes or ABS, make the mistake of thinking that
replacing brake shoes and pads is all there is to
proper maintenance. What they need to be more aware
of is the system needs regular and proper
maintenance to prevent expensive damage down the
road.
What ABS
Does
In vehicles
with ordinary brakes, simply standing on the pedal
under poor traction conditions is likely to cause
one or more wheels to lock up, probably resulting
in a skid. To avoid skids, expert drivers rapidly
"pump" the brake pedal (releasing and re-applying
it) when they sense wheel lockup.
ABS provides
a similar pumping action. It automatically
re-applies brake pressure under stopping conditions
that make wheel lockup likely. But, ABS adds an
advantage. Unlike someone letting go of the brake
pedal and stepping back on it, ABS can do it much
faster, sensing impending skids and directing its
'modulated braking' to whichever wheel, or wheels,
would have locked otherwise.
How ABS
Works
Most of the
brake parts in a car equipped with ABS are similar
to those on cars without it.
Although
there are many similarities, cars with ABS have
several additional parts. ABS brake systems have
speed sensors that measure wheel speed and relay
this information to an onboard electronic control
unit. This unit calculates vehicle speed and during
a lockup, signals a hydraulic actuator which in
turn applies and releases the brakes as many as 10
times per second.
Speed signals
from the wheels are sent to a central ABS computer.
The computer compares wheel deceleration rates to
the programmed vehicle while the car is braking. If
any of the wheels are slowing more rapidly than the
others, the computer can tell it's about to lock
up. If the computer determines that a wheel is
approaching lockup, it then sends a signal to the
hydraulic valve block for that wheel.
The hydraulic
unit valve block contains a quantity of brake fluid
under very high pressure. It also has valves that
can bleed off brake line pressure to any wheel(s)
that may be about to lock up, while the other
brakes keep working. Once the danger of wheel lock
up has passed, pressurized brake fluid is again
allowed to reach that brake, which resumes slowing
the car. The process takes place very quickly and
may be repeated several times each
second.
Maintenance/Service
Implications
Most routine
brake maintenance on ABS equipped cars and trucks
shouldn't cost much more than servicing ordinary
brakes.
Too many
drivers, whether their cars have conventional
brakes or ABS, make the mistake of thinking that
replacing such 'friction material' as brake pads
and shoes is all there is to brake maintenance.
They need to be aware that it isn't and that all
brakes with or without ABS need regular maintenance
to prevent expensive damage. Skimping on
maintenance with ABS can lead to even more
extensive and expensive problems than with ordinary
brakes.
The hydraulic
side of ANY car's braking system needs preventive
maintenance. For example, regularly flushing out a
car's or truck's brake fluid and replacing it with
fresh fluid goes a long way toward preventing brake
problems as the vehicle ages.
Since most
brake fluid naturally absorbs moisture from the
atmosphere, the only way to fight this problem is
to regularly flush and replace the fluid every 2
years or 24,000 miles."
Symptoms
of Brake Failure
Noises
Your brake
system may be crying for help if you're hearing
strange noises when you depress the brake. Two of
the most common are squeaks and
grinding.
Squeaks
Friction from
the brake lining causes heat. Under extreme
conditions this can damage the pads and/or lining,
brake drums and rotors.
Grinding
A metallic
grinding sound indicates your brake pads are worn
through. Metal-to-metal contact will damage drums
or rotors.
Low or Fading
Brake Pedal
Do your
brakes require pumping to stop the car? Does the
pedal sink to the floor board when you're stopped
at a light? There may be a leak in the brake
system, air in the brake lines, or the need for a
brake adjustment.
Pulling to
one side or brake drag
Worn or
uneven brake linings or a damaged brake line can
cause your vehicle to pull to one side. Brakes that
are out of adjustment or have contaminated fluid
can cause brakes to drag.
Inspecting
Your Brakes
1. Master
Cylinder
The master
cylinder, heart of the brake system, contains a
reservoir for brake fluid. It is located on the
firewall and should be checked periodically to
ensure the proper fluid level.
2. Brake
Lines
Attached to
the master cylinder, steel brake tubing runs to all
four wheels. Brake lines should be inspected for
rust, which can lead to leaks. If the lines are
damaged they should be replaced.
3. Brake
Hoses
Rubber brake
hoses run from the brake lines to the brake
calipers and wheel cylinders. Constant exposure to
road grime, dirt, salt and other elements can cause
the rubber to become brittle and crack, leading to
brake failure.
4. Linings
and Pads
The pads and
brake shoe linings should be checked periodically
for uneven or excess wear, glazing, or saturation
from brake fluid or grease.
5. Calipers
and Wheel Cylinders
Brakes are
activated by brake fluid pressure from the master
cylinder pushing a piston located in the caliper or
wheel cylinder against the pad or shoe. A leak can
cause erratic braking or brake failure.
6. Bearings
and Seals
Wheel
bearings should be inspected and lubricated
periodically. Worn wheel bearings, which can cause
faulty steering as well as erratic braking, should
be replaced.
7. Parking
Brake
The parking
brake should be adjusted periodically.
Changing
Your Brake Fluid
Brake Fluid
Change
Brake fluid
is the lifeblood of your braking system. Periodic
flushing about every 25,000 miles removes
contaminants that can change clean fluid into brown
mud.
Many
mechanics advocate using silicone brake fluid. The
advantage of silicone is that it does not attract
water into the braking system, greatly extending
the life of brake seals and lines. On the down
side, silicone is triple the cost of regular brake
fluid. Additionally, silicone is to water what oil
is to vinegar. Unabsorbed moisture can collect in
low spots and rust out the hydraulics. Also, some
silicones may not be compatible with regular
glycol-based fluids, requiring a complete overhaul
of the brake system to change over.
Brake
System Checklist
Brakes
require more than occasional relining to maintain
peak performance. Inspect annually for corroded
brake lines and cut, abraded or heavily
weather-checked brake hoses.
Disc brakes
can benefit from periodic removal of the brake pads
and "exercising" of the brake calipers.
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