Brake Problems Brake Fluid ABS Brake Pad Materials
The most common cause of brake complaints and poor performance is
noises and vibration or pulsation. Brake pad friction formulation has a
great impact on preventing these problems. By varying certain
ingredients, engineers can modify a formula to better suit various
vehicle applications. The key to understanding which type of formula
performs best for a particular application is simplified by looking at
original equipment (OE) recommendations. Today, there are three
universally accepted “flavors” of friction formulations; semi-metallic,
non-asbestos organic (NAO) and ceramic.
Semi-Metallic Friction Formulations
A semi-metallic brake pad consists of a lining that uses steel wool as a
reinforcing fiber. Most semi-metallic friction materials contain at
least 60% steel by weight. The steel fibers act as the framework to lock
the friction ingredients together. Semi-metallic pads provide better
high temperature performance and wear characteristics than conventional
non-asbestos linings. Semi-metallic lining gained in popularity during
the early 1980s with the introduction of the front-wheel drive passenger
car. Typical braking characteristics on a FWD vehicle calls for
approximately 80% of the braking to occur in front, meaning it is
critical to install a pad that was stable at higher operating
temperatures and pressures. Non-asbestos organic and ceramic pads were
not designed for most of those vehicle applications and should not be
substituted for vehicles originally equipped with semi-metallic pads.
Non-Asbestos Organic Friction Formulations
Non-asbestos organic (NAO) brake pads consist of organic fibers that are
used to reinforce the friction materials and provide strength to the
brake pad. NAO friction material contains less than 20% steel by weight.
NAO brake pads were designed to replace harmful asbestos linings and
were popular on pre-FWD vehicles. Typically, this consisted of larger
vehicles that shared more even braking between the front and rear
brakes.
Ceramic Friction Formulations
Ceramic brake pads have gained in popularity over the past several
years, but few realize that ceramic has been in use since the mid 1980s.
Ceramic pads contain no steel fibers. Instead, this formulation uses
ceramic and copper fibers to manage heat dissipation. When installed on
originally equipped ceramic vehicles, ceramic pads have three primary
advantages. First, ceramic fibers are stable under a wide range of
temperatures, providing more consistent performance. Secondly, ceramic
fibers minimize harmonic pad vibration, a leading cause of squeal, to
reduce brake noise. Lastly, ceramic formulations are said to be less
abrasive, which minimizes brake rotor wear, a primary cause of wheel
dust. The best way to insure the benefits of using a ceramic pad is to
follow original equipment (O.E.) recommendations.
What happens if a mis-matched brake lining is installed? Lining that is
more aggressive than the O.E. material may cause the brakes to feel
over-sensitive or “grabby.” A mis-match in friction material could also
alter front-to-rear brake balance, increasing the risk of brake lock up
on slick surfaces, especially if the more aggressive lining ends up on
the back brakes. If the replacement linings are less aggressive than the
original material, the vehicle may require increased pedal effort and
take longer to stop, reducing a driver’s confidence in handling the
vehicle.
Replacing Brake Rotors with Quality units
A rotor may not look complex on the surface, but if the
manufacturer did not take the time to match the fin pattern or
metallurgy, it could be worse than if you had machined the old rotor.
Premium rotors typically use the same casting configuration as Original
Equipment (same number of cooling ribs between the faces and same
pattern). Vehicle manufacturers use different cooling rib configurations
to optimize cooling for specific vehicle applications and to reduce
harmonics that contribute to brake noise. If rotors with a different rib
design or configuration are installed, it may create cooling and/or
noise problems.
Most economy rotors use a standard cooling fin configuration because it
simplifies the casting process and consolidates part numbers. But the
trade-off may be reduced cooling performance. If an OE rotor has 37 ribs
and an economy rotor has only 32, cooling may be reduced 8%-10%. This
can make the rotors run hotter, which shortens pad life and causes
rotors to warp quickly. Lab tests have also shown that some economy
rotors are much noisier than OE or premium replacement rotors (85
decibels versus 50 decibels).
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