BRAKING & COLLISION AVOIDANCE
May 2018 | VehicleServicePros.com 35
Air disc brakes (ADB) continue to grow in
popularity, and there are a number of reasons
for this. Improved safety, shorter stopping
distances, consistent stopping power and
more effi cient maintenance practices all help
to lower both the cost per mile as well as vehicle
downtime. As an example, the estimated
time for a wheel-end drum brake shoe change
and general maintenance hovers around the
one-hour mark, while an air disc brake pad
change out takes approximately 15 minutes.
Brake performance is also a big advantage of
the ADB system. Th is brake system can withstand
the higher temperatures that oft en occur
in a severe duty or transit application much
more effi ciently than a drum brake system. A
vehicle will be less susceptible to fade because
of this attribute. Rather than the drum moving
away from the friction material as temperatures
increase, the rotor will expand and move
into the brake friction material to continue effi -
cient braking.
Proper maintenance is key
Fleets likely to see maintenance savings with
air disc brakes are the fl eets in the medium
to heavy duty application range, ranging
from regional line-haul vehicles to refuse
and transit bus applications. Even though
air disc brakes are easily maintained, they
still require a thorough inspection from time
to time.
First, make sure technicians are well trained
in the service of the caliper. Brake manufacturers
provide great training classes and have
maintenance manuals for their products.
A common issue that occurs in the fi eld is
the breaking of the shear adapter, which is
used to extend and retract the tappets. When
attempting to make a brake adjustment, be
sure to fi rst ensure the vehicle is properly lift -
ed and the wheels are chocked. Also, make
sure the parking brake has been released,
allowing technicians to make tappet adjustments.
If the shear adapter is torqued aft er the
tappets have fully retracted, this will cause
the shear adapter to fail. Th is component is
manufactured to do this to prevent damage
to the caliper. If the shear adapter continues
to fail, this indicates that the internal adjuster
is not functioning properly and that caliper
will need to be replaced.
For over-the-highway vehicles, the condition
of brake pads should be inspected approximately
every four months. More extreme
duty cycles should be inspected more oft en
initially so that the estimated time between
pad changes can be established.
Some caliper manufacturers use wear indicators,
which are marked on the side of the
caliper, to estimate when the pads are ready
to be changed. Another indicator that it may
be time to change brake pads is if the tappet
boots are clearly visible.
Importance of
preventative maintenance
Just like drum brakes, preventive maintenance
is critical with air disc brakes. A service interval
should be established for checking the
running clearance between the brake pads and
the rotor. Ensuring that a fl eet is not wearing
their pads to a less-than-minimal thickness is
critical to maintenance costs. If pads are worn
too thin and there is metal-to-metal contact
between the rotor and the pad backing plate,
this may cause extreme temperatures, noise,
vibration and very likely destruction of the
internals of the caliper assembly. Th is can be
very expensive to repair.
If the friction material of the pads is worn
down to 2mm or less, they should be replaced.
If the pads measure more than 2mm, but
there are pad surface irregularities such as
signifi cant taper end-to-end or top-to-bottom,
material missing, excessive cracking, etc.,
they must also be replaced. Also consider if
the pad may wear beyond the 2mm before
the next scheduled inspection. Brake pads
should always be replaced on both ends of
an axle at the same time.
Conclusion
Overall, ADBs can help shorten vehicle downtime
because they are easier to maintain
compared to drum brakes. It is still important,
however, to establish preventative maintenance
schedules on this area of the vehicle to
ensure optimal life of the braking system.
Maintenance
considerations for
air disc brakes
With the increased adoption of air disc brakes, it is
still crucial to implement a thorough PM program.
By David Inman
TECHNICAL SALES, TMD FRICTION
TMD Friction (tmdfriction.com) focuses on the development
and manufacturing of friction materials needed for
safe braking. In 2011, the company was acquired by Japanbased
Nisshinbo Holdings Inc. Inman works directly with
fleets and product distributors to test brake performance
and support with any technical issues. He has been with
the company since 2011, moving to his current engineering/
sales position in mid-2016.
» Even though air disc brakes are easily
maintained, they still require a thorough
inspection from time to time.
Image courtesy of TMD Friction
/VehicleServicePros.com
/tmdfriction.com
