april2023 - 27

added. " If it's out of spec, there is even more to do.
You might have to pull the slack adjuster off, pull
the cams and bushings out and put new bushings
back in. You might find that the clevis pin
is seized into the slack adjuster. Now you have to
spend time working that out. You don't have to
do any of this on a disc brake because everything
is internal. "
To service a disc brake, the friction removal
process simply involves a spring clip, pin, and
pad-retaining bar. Then you just pull out the
worn pads. Next, push the caliper all the way
inward, inspect the guide pin boots to make
sure they aren't torn, ensure that the caliper
can slide freely, and inspect the boots on the
tappets (pistons) in the caliper. If everything
checks out OK, clean the carrier, measure rotor
thickness to ensure it is within spec, and drop
the new pads in.
" A technician can typically do all of that within
15 minutes per wheel end, " Pfost said, adding
that a thorough drum brake inspection can push
upwards of an hour.
" There will always be a technician who says
they can change out brake shoes in 10 minutes, "
Pfost continued. " They probably can, but they
haven't done any measuring. If a drum brake job
isn't done properly, you can run into problems
like adjustment issues and hang-ups later in the
brake's life. "
There are also more moving parts with a
drum brake. Plus, those parts are exposed to the
elements, which increases the opportunities for
contamination and damage.
" With a disc brake, you just have a caliper, rotor,
and hub, " Pfost said.
One potential issue with a disc brake is if the
rotor becomes damaged. Pfost said replacing a
rotor is more time-consuming than replacing
a drum. The caliper carrier assembly must be
removed, followed by the hub and rotor. The standard
repair time is around 100 minutes.
" Premature failures will always have an
adverse impact to any ROI, " Pfost said. " But over
the long-term, a rotor's life expectancy is longer
than that of a drum, helping reduce the total cost
of ownership. Fleets could use our Bendix ADB
Value Calculator (valuebybendix.com) to see the
directional difference. "
Tips to maximize lifecycle ROI
The best thing a fleet can do to maximize lifecycle
ROI on their brakes is to stay on top of wear.
This is especially the case with disc brakes where
the ROI proposition hinges a lot on preserving
the rotor.
According to Pfost, rotors are designed to
last at least several hundred thousand miles in
on-highway applications with properly scheduled
maintenance.
" Inspection for premature pad and rotor wear
and early detection of conditions such as cracking
or discoloring are vital to ensuring the life of
the rotor, " Pfost said. " Drums get changed with
every friction/shoe replacement. "
He added genuine Bendix pads and rotors can
provide " at least two or three pad lives per rotor. "
When inspecting the rotor, a technician should
» Guide pin and tappet (piston) boots are a
simple and inexpensive, yet crucial component
to protecting a disc brake. Boots help keep
dirt, moisture, and other contaminants from
reaching other vital components. Shown here
are torn tappet boots that should be replaced.
Bendix
look for rust or corrosion which may indicate that
the brake isn't functioning properly. " Damage
such as a rough surface or gouge on the rotor
braking surface may indicate that the pad is fully
worn and the metal back plate is contacting the
rotor, " Cummins-Meritor's Kay said.
With respect to pad wear, brake manufacturers
are giving technicians some assistance. For
instance, Cummins-Meritor's EX+ air disc brakes
feature a visual wear indicator that allows for
easy wheels-on pad wear inspection.
Bendix offers pad-wear sensing technology for
their disc brakes. End-of-life alerts are issued at
3.5mm, helping technicians schedule service
before the friction wears out and the backing
plates destroy the rotor. " Now we're improving
this technology through continuous-wear sensing
that identifies the percentage of friction left,
communicating in real-time through the vehicle's
telematics system, " Holley said.
When maintaining disc brakes, technicians
should also keep an eye on the caliper. The caliper
should move freely, about 1mm, when braking
occurs.
" A technician can check this by grasping the
caliper and moving it axially with the parking
brake off, " Kay explained. " No movement may
indicate that the caliper may have an issue and
should be inspected further. Excessive movement
in the axial direction may indicate that
the internal adjuster is not keeping up with pad
wear and should be inspected further. Excessive
up and down movement may indicate slide pin
or bushing wear. "
Another thing fleets can do is consider the environment
a given vehicle is operating in.
" Working in wet, corrosive, or dirty environments
will wear brakes faster, " Kay said. " A fleet
maintenance department must keep good records
and adjust to any changes as they happen. "
Adjusting to changes is really what maximizing
brake lifecycle ROI is all about. Staying ahead of
friction wear helps preserve other vital components.
So, one of the questions a fleet must ask
itself is, how much time and money will it cost
to stay ahead?
» Very minor damage at a brake pad's
edge may be acceptable, but major
damage to the pad's surface (as shown
here) requires the pad to be replaced.
Bendix
» " Hot spotting " or " leopard spotting "
on the drum is an indicator of friction
that's improperly rated for the vehicle.
Replace with a properly rated friction.
Bendix
» Cracks extending from one edge
of the rotor to the other are not
acceptable. Rotor must be replaced.
Bendix
April 2023 | FleetMaintenance.com
27
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april2023

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