PTEN_0821 - 34

TOOL BRIEFING
Servicing hydraulic braking systems
Addressing squeaky brakes, pressure loss, and other braking
issues requires the right tools and equipment.
By Roy Ripple, Contributing Editor
B
rakes are kind of
like
offensive linemen - they
don't get noticed until
they do something wrong. All it
usually takes is a strange noise
or an unfamiliar feel in the brake
pedal to bring a responsible
driver straight to your shop for
a diagnosis.
VERIFY THE CONCERN, THEN
CHECK THE CAR OVER
When diagnosing a brake concern, the
critical first steps are the road test and the
visual inspection, as with all diagnoses.
The visual inspection is the most valuable
diagnostic tool in your toolbox. Looking
over the entire car, not just the system
you're diagnosing, allows you to get a feel
for the vehicle. You're never just repairing
a system, you're repairing a vehicle.
You should always record the thickness
of the brake linings first. OTC makes a
real nice brake pad thickness gauge that
allows you to get an accurate reading of
the inboard and outboard pads without
removing the caliper, and in some cases,
the wheel. Press the tip of the pen-size
tool against the brake rotor and pull the
gauge finger against the brake pad backing
(Figure 1). The results are easy to read and
displayed in plain view.
PINPOINT THE CAUSE OF
SQUEAKY BRAKES
When diagnosing a brake squeak, pay close
attention to the surface of the rotors. Look
for a sign that the pads might be hitting
the ridges on the outer edges of the rotor.
As a brake pad wears, sometimes the friction
material will mushroom out from
the sides of the pad and contact the ridge.
A shiny ridge is a sign that this could be
happening. Examine the contact surface
of the rotors. Any grooves that you see on
the rotor that have transferred to the brake
pads will cause a squeal. If the brake linings
pass, you can resurface the rotor and
clean up the brake pads with some 100
grit sandpaper; this should stop this type
of brake noise.
I highly recommend using an on-car
brake lathe when resurfacing rotors.
Spinning the rotor on its axle or hub bearing
makes for a much tighter cut. We use
the Pro-Cut PFM 9.2 DRO. It's simple to
hook-up, easy to move around the shop,
and always produces a nice cut. On-car
brake lathes save the time of having to
remove frozen or labor-intensive rotors.
They also allow the technician to stay in
his bay rather than carry rotors across the
shop to the brake lathe.
APPLY THE CORRECT PRODUCTS
TO PREVENT BRAKE NOISE
High-quality silicone-based caliper slide
grease should be applied to every place on
a brake caliper where metal touches metal.
This means caliper slide pins, anti-rattle
clips, and the edges of the brake pad backings.
Wheel bearing grease is too thick, and
white grease is too thin. Using the correct
lubricant will prevent a high percentage of
brake noise complaints. Permatex Silicone
Ceramic Extreme brake parts lubricant
applies evenly without running or wadding
up. This makes it possible to apply the
grease only where you need it to be without
it migrating onto the friction material.
Most quality brake pads come with a
noise suppressing material adhered to the
back of the pads. This is to prevent movement
between the brake pads and the cali34
PTEN AUGUST 2021 www.VehicleServicePros.com
p Figure 1 - Technician using OTC's brake pad
thickness gauge.
per, dampen vibration, and absorb noise
during braking. This small amount of friction
can create a loud brake noise. Products
are available that can be applied to the
back of the pads if they don't come with
the pre-applied sticky stuff. Aftermarket
noise dampening products are available
as an aerosol spray or as a paste in a bottle
or a tube. CRC Disc Brake Quiet aerosol
spray works well because it sprays on
evenly and dries quickly. It's crucial that
the spray dries completely before installing
the pads. Whichever product you choose
to use, it's important not to install a brake
pad with a bare metal back.
Alternatively, if you're diagnosing a
low or drifting brake pedal, first check for
an external leak. Not all brake fluid leaks
present themselves as puddles in the driveway.
Sometimes wetness around a caliper
piston or brake fluid behind the master
cylinder is enough to cause an issue at
the pedal. Don't forget to pull back wheel
cylinder boots and check for fluid that has
bypassed the cup seals.
After determining there are no leaks,
watch the calipers operate while an assis
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PTEN_0821

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