may2022 - 27

sensor devices are available as an option on the
Bendix ADB22X Air Disc Brake for tractors and
trailers. Sensors are installed on the pads. When
friction thickness reaches approximately 3.5mm,
the system triggers a signal. A diagnostic code or
message is then created and made available to the
telematics system.
The WABCO MAXXUS 2.0 has also incorporated
pad wear sensors. OEs can incorporate the sensor
data into their telematics system. Meritor's EX+
LS Air Disc Brake offers an electronic pad wear
warning indicator as optional equipment.
Disc brake maintenance
As manufacturers have made design enhancements
to improve disc brake life, technicians should not
take that as a cue to relax preventive maintenance.
" One of the myths out there is that air disc
brakes don't need to be inspected as much, "
Bendix's McComsey said. " But it's still a brake, and
it needs to be inspected just as often as a drum
brake. Refer to our service data sheet that provides
recommended inspection intervals, which vary
slightly by application. "
Generally speaking, wheels-on inspections
should happen at least every four months for
OTR applications and every three months for
buses, vocational trucks, and delivery vehicles.
Technicians can check pad thickness by monitoring
the mechanical wear indicators. Additionally,
rotors can be checked for cracks. McComsey said
tools like mirrors and borescopes can improve the
visual inspection process.
If any issues are observed during a wheelson
inspection, a more thorough wheels-off
inspection should be scheduled promptly. And
even when no issues are detected, a more thorough
wheels-off inspection should happen at
least once a year. Technicians should inspect
the pads and entire rotor surface for cracks, as
well as running clearances, adjuster operation,
and caliper travel. Tappet and boot assemblies
should also be inspected along with all related
caps and hoses.
It is important to regularly check the condition
of the caliper. " Every year, a technician should
check the condition of the various parts of the
caliper, such as plugs, protective cups, thrust plate
guide pins, adjustment spindle bellows, and slide
function, " Haldex's Ślimakowski said.
Drum brake developments
Manufacturers have also been making design
improvements to extend drum brake life.
" One of the most recent changes we've made has
been the move to improved coatings and assembly
processing to counter the impact of corrosion on
the overall brake system, " said Pat McNamara, VP
of sales and marketing at TSE Brakes, a provider of
brake chambers, slack adjusters, and brake-sensing
technologies.
" Frictions are now lasting 300,000 to 400,000
miles in some cases, " said Frank Gilboy, director
of foundation drum brake and actuators at
Bendix. " The period in between disassembling
the system to make repairs or replacements is
a lot longer. The risk is that things aren't being
looked at as often. So, in reality, longer-lasting
components actually reinforce the importance
of understanding the preventive maintenance
intervals recommended by the manufacturer. "
Technicians should regularly inspect the friction
for abnormal wear and cracks. Additionally,
it's important to measure the free play to ensure
that it remains within the allowable 3/8 " to 5/8 "
range. If the free play falls outside of this range,
look for any signs of damage. Brake stroke should
also be checked and compared to the specification
for that chamber. The S-cam and slack adjusters
should always maintain proper lubrication.
McNamara said there are key maintenance
aspects with respect to brake chambers as well.
ÜLook for worn, loose, or missing chamber mounting
nuts.
ÜEnsure proper chamber mounting and alignment.
ÜEnsure that breather caps aren't damaged or
missing.
Just like with disc brakes, technology is beginning
to provide some assistance to technicians
working on drum brakes. For instance, TSE Brakes
has introduced TSE-Sense. Currently available for
trailers, TSE-Sense continuously monitors brake
stroke and transmits the data to a data integration
box mounted on the sliding tandem frame. The
box communicates with the trailer's telematics
system to alert technicians to stroke issues.
Cut that slack adjuster
some slack
When it comes to drum brakes, automatic slack
adjusters continue to frustrate many technicians.
But those frustrations are often a matter
of misinterpretation.
According to Bendix's Gilboy, it is amazing
how many slack adjuster problems go away when
technicians take the time to grease the slack
adjuster, cam tube, and other areas so everything
can move freely. " This can really be a problem
on trailers because they can get ignored a little
more, leading to more slack-related problems
over time, " Gilboy explained.
If excessive brake stroke is ever suspected, ZF's
Rose said the first thing a technician should do is
conduct the CVSA applied stroke test to confirm
that there is a brake adjustment issue. From there,
it's important to follow manufacturer test procedures
to ensure that the slack is working properly.
One procedure that must be avoided is manually
adjusting an automatic slack adjuster. If
brake stroke is excessive, it is usually a sign that
either the slack adjuster is worn out and needs
to be replaced or that something else is going on.
Excessive wear of the cam head, bushings, or rollers
could cause brakes to fall out of adjustment,
but many times, the problem simply lies with a
lack of lubrication.
If it's concluded that the slack adjuster doesn't
need to be replaced, Rose said the next step is to
simply begin doing visual checks of the various
components throughout the system. One thing to
look for is worn components. For various reasons,
a technician will sometimes reuse certain hardware
and other components when doing a brake
job. That same thing could have happened when
» A thorough wheels-off inspection of the brake
system should occur at least once a year.
Photo: Bendix Commercial Vehicle Systems
a slack adjuster was replaced in the past, and the
same mounting hardware was reused.
Sometimes a slack adjuster simply needs to
be replaced. When that is the case, Meritor's Kay
said that it is best practice to replace slack adjusters
in axle sets or pairs to maintain balanced
braking performance.
When it comes to any braking system, safety
is always the number one consideration-and
balance, stopping distance, longevity, and ease
of maintenance all play into that.
May 2022 | FleetMaintenance.com
27
Remote control enables
solo brake testing
A remote-controlled trailer tester, such as the Alpha Mutt 5700
Series from IPA, can help technicians test pushrod travel and
verify proper slack adjuster operation on trailer drum brakes.
To test a slack adjuster, simply back off on the adjustment,
and then utilize the remote control to repeatedly
apply and release the brakes. With each cycle, the brakes
should come closer to the final adjustment. Repeat until
the brakes are properly adjusted. If the auto slack adjusters
fail to adjust the brakes, this will be revealed quickly.
While conducting these tests, a technician should also observe
side-to-side brake timing (balanced brakes). It should never
be assumed that full brake engagement happens at the exact
same time. Delayed braking from one side can lead to trailer
sway, loss of control, and premature wear of brake system
components. Delayed-release (stuck) brakes can also lead to
trailer fires since engaging the brakes for too long will result in
a buildup of heat. All of these problems can be revealed and
fixed quickly with the use of a remote-controlled trailer tester.
By using a trailer tester, a technician can work alone without
a helper because they can keep an eye on the brake timing
while engaging the brakes with the remote control. For further
efficiency gains, the use of a tablet at the trailer axle allows
the technician to both operate the air brakes and test the ABS
system all in one location. The Alpha Mutt tablet, for instance,
can access trailer ABS information, read and clear codes, and
operate the air brakes and electrical circuits of the trailer.
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may2022

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