march2021 - 17

Hester explains that inspection frequency
depends on the component's exposure to a variety of forces.
" Ride components that play a role in the 'feel' of
the trailer and interact between the tires and the
ground are primarily the air spring, shock absorber, and pivot bushing, " he says. " Hendrickson has
continued its efforts to maximize performance
of these critical components through the development of products like ZMD Zero Maintenance
Damping technology. The ZMD system eliminates
the need for an external damping component
such as a shock absorber. Instead, the suspension
damping function has been incorporated into the
suspension air springs. This eliminates the need
to inspect and maintain the shock absorber while
also maintaining ... ride quality and performance. "
Furthermore, fasteners throughout the suspension system must be inspected and maintained in
strict adherence to recommended intervals and
guidelines from manufacturers to maximize the
lifecycle of the system as a whole.
Link's Molitor advises that fasteners, either
installed or serviced without the proper torque,
will come loose. A loose fastener can wreak havoc
to the structural integrity of the suspension and
pose reliability issues.
" Once you start having a fastener moving
around, for pivot connections and such, it is going
to go through the path of least resistance, " Molitor
says. " Say the pivot connection on a frame bracket is loose. As you accelerate, that axle is going
to go back as far as that fastener clearance will
allow it. Once it goes back there, it might actually
start moving the metal because there is so much
force there. The break cycle is cyclical, [and it is
then] slammed forward. It is going to increase that
motion that is allowed every shift cycle. If it was
a hole to start, it will turn into a slot. "
Molitor continues that holes will be deformed
into oblong shapes so extensive that drivers will
notice the movement. If such an instance is not
corrected early enough, instead of replacing a
fastener, frame brackets or control arms will need
to be replaced as the metal has been worn out.
Technicians should look for worn paint or rust
underneath the fasteners during inspection,
Molitor advises, which is indicative of a loose
fastener allowing movement. He further recommends steam cleaning the chassis, removing dirt
and grime to allow for a clear visual inspection of
all suspension components. After a steam clean,
rust or paint removal should be easy to identify,
alerting technicians that the connection is not tight.
Specific to air ride suspensions, another area
pertinent to the inspection procedure is the air
system and the quality of air reaching components
in that suspension.
" If you maintain your air system, it can help
extend the life of [air ride] suspension components like leveling valves, air bags, and any other
component that has to route that air and control
that air, " Hogg says. " If your air compressor is
passing oil and your air dryer is not properly
removing that all, and it is getting into your air
system ... that is what we find when we find failures. Most of the time when we pull an air valve
off prematurely, we look at the line going into
the leveling valve and we find contamination.

That contamination has to be detected before it
gets there. "
Hogg recommends drivers be adequately
trained so that when draining an air tank, they
can perform a diagnostic. If excessive oil is vacated along with moisture when draining the tank,
the vehicle should be serviced to determine the
cause, Hogg advises.
" It could be something as simple as your
air filter is getting too dirty and it is affecting
systems down the line, " he says. " I wonder how
many people connect those dots ... When you get
a contaminated air leveling valve and that valve is
not maintaining the right frame height, you could
be beating up a transmission. How bad would it be
to have to replace a transmission when you really
had a bad air filter? "

Tire maintenance and monitoring

It is no secret that tires are one of the most
commanding expenses of any fleet operation.
Having an understanding that suspension maintenance will play into tire performance, fleets should
diligently monitor and maintain the suspension.
As for maintaining the tires, first and foremost,
fleets should monitor tire pressure.
" Along with alignment, make sure you are
maintaining your tire pressure, " Meritor's Bernens
advises. " I have been in fleets where the driver just
kicks the tire and says, 'Yep, it's good!' I don't know
about you, but I can't tell the difference between
90 psi and 100 psi with my foot - but your tires can
tell the difference and they will wear differently. "
Tire inflation is a key aspect that affects both
tread wear and suspension performance. If a tire
is overinflated, it will cause accelerated wear in
the center of the tire face, Link's Molitor says.
" Your center tread is going to be shallower than
the outside, " he explains. " And if [a tire] is underinflated, then you will get cupping. "
" Proper alignment and tire inflation pressure
are typically at the top of the list of factors that
influence tire wear, " Hester says. " Solutions like
Hendrickson's TIREMAAX tire pressure control
system help with maintaining these critical performance factors. TIREMAAX PRO is an advanced
automatic tire pressure control system that is
capable of actively inflating, relieving, and equalizing tire pressures across all wheel positions. "
Link offers a convenient tool called the Cat's Eye
which facilitates a visual diagnostic applicable for
dual tires placed in tandem.
" The Cat's Eye connects the two and then it gives a
very good visual indication to the driver if the pressure is too low, " Molitor explains. " It helps to make
sure that the inner and outer tire are always at the
same pressure ... If you have an inside and outside
tire that are different pressures, they are different
diameters. And if they are different diameters, you
will create tons of wear on the one that is smaller in
diameter because it is going to be scrubbing. "
Tire maintenance not only impacts tire performance, but also affects suspension performance.
" Let's say that you have drastically different
tire pressures on one side of the vehicle than the
other, " Bernens suggests. " You are going to have a
pivot bushing then doing more work on one side
than the other, and so it is going to wear faster. If

your tire pressure is off enough, you can cause
additional work on your suspension, which is
going to lead to you replacing more components
sooner than you want. "
Diligent monitoring and recording of tire wear
can reveal hidden suspension issues.
" Whether it is diagonal wear across the face,
scalloping, feathering, or any other tire wear
symptoms, everything is cause and effect, "
SAF-Holland's Ryan advises. " Root causes of wear
can be an assortment of things like worn bushings,
broken shocks, loose bolt connections, overloaded
axles, or misaligned axles. Identifying the root
cause is the game changer that allows technicians
to concisely find and fix the underlying issue. I
would highly encourage fleets to give technicians access to TMC's Recommended Practice on
tire wear - RP 219. No matter the wear patterns
identified, it is covered with probable causes and
solutions to your issue. "
Tire shoulder wear is one key indicator of an
alignment issue.
" If you see the inside or the outside groove is
not as deep anymore, that is usually an alignment
issue, " Molitor says. " The alignment usually shows
up on one face or the other, either the outboard of
the tire is wearing or the inboard of the tire is wearing too much. And then, unfortunately, you get some
scalloping in the tires as well. And that is usually
an indication that your tires are hopping too much. "
Uneven cross-axle wear should not be
dismissed, but rather investigated.
" You could have tires on one side of the vehicle that are wearing rapidly compared to other
tires, " Hogg notes. " Everybody does not always
attribute that to the suspension, but if you have
a weak suspension component on one side of one
axle, then more weight gets shifted to that wheel
position. And if more weight gets shifted to that
wheel position, then the tire has to bear the brunt
of that and you will see more scrub on that tire. "
In the end, establishing a practice of recording
and comparing tread depth and wear patterns can
create an atmosphere that can serve to diagnose
cause rather than chasing effects.
" If you are really monitoring your tread depth
and you are paying attention to that and relating or
correlating those tread depths to one another, you
might just get a good sign, or a good indicator, that
you may have a suspension problem just by looking
at tire wear, [especially] how rapidly it wears on one
position versus others, " Hogg continues.
It is through this performative correlation
between the suspension and the tire that diligent
maintenance wins out. By adhering to best practices, inspections, regular PMs, and strict monitoring
and recording, fleets can not only maintain both
their suspensions and tires but also use one to
maximize the other.
" Suspension systems are critical to the stability of a vehicle and to maximizing many of the
components on that vehicle, " Hogg concludes. " I
think that the industry would be wise to spend a
little extra time evaluating the condition of their
suspension system during their preventive maintenance program. "
For related content, visit:
FleetMaintenance.com/equipment

March 2021 | FleetMaintenance.com

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march2021

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