Spicer Tire Pressure Control - Manual (Page 7)

Wheel bearing adjustment is just as important
to good air seal life as it is to good oil seal
life. Improper adjustment allows excessive
play and runout in the seal and results in
reduced seal performance. Always follow the
recommended practices of the axle supplier
and The Maintenance Council of the
American Trucking Associations to assure
satisfactory performance.
It is very important that seals which are
performing properly not be disturbed
unnecessarily during routine maintenance for
brakes or other wheel end repairs. The wheel
end equipment utilizes an outboard mounted
brake drum design so that brake repairs can
be made without disturbing the hub. Removal
of the wheels with the hub and brake drum as
a unit is not recommended, and may necessi-
tate replacement of all seals, both air and oil.
Even if these seals are to be replaced, proper
installation will be extremely difficult with the
wheels and drums attached to the hub, with a
higher likelihood of damage to the seal. The
specification of hub piloted wheel designs
allows the removal of dual wheels with only
ten fasteners, avoiding the additional labor
requirements of older stud piloted designs.
Removal and replacement of drive axle hubs
will also demand addition of lube through the
hub lube fill hole to assure sufficient wheel
end lubrication to the inner bearing. This
lubrication must be added after the axle
shafts, but before the wheels are installed.
Vehicle Air System – A final area demanding
additional maintenance attention is the vehi-
cle air system, including the compressor and
the dryer. The adjustment of tire pressures
requires the use of far more air than normal,
where air is used primarily for braking.
Increases in both compressor duty cycle
(percent on time) and continuous on time
make the load on the air system far more
severe and demanding of special attention.
As the actual air system impact is strongly
dependent on the application, i.e. how fre-
quently the tire pressure system is being
used to adjust pressures, it is not possible to
predict with certainty how often a particular
fleet or owner will need to service the com-
pressor and air dryer, but it is essential for
users to determine a maintenance cycle that
works for their application. While getting
acquainted with the use of Tire Pressure
Control in your operation you should pay
particular attention to the air dryer to
determine a proper service interval for you.
Initially, a daily look at the discharge from the
dryer will tell you if the system is working
properly. Oil or any discharge other than water is cause for investigation and correc-
tion. Maintenance personnel should also be
checking air dryer cartridges and the air
supply tank for signs of contamination
monthly until the first replacement is
necessary, and then checking cartridges at an
interval half way to the period of the first
change until you are comfortable with the rate
at which they are losing effectiveness.
Operators should also be instructed to drain
the vehicle supply tank from which the
system draws its supply completely every
night. Any water observed coming from the
tank while draining deserves to be looked
into, as a properly working air dryer will not
allow water into the air tank during a working
day. Manual drain valves should be installed
which do not require the operator to stand by
the truck while the tank is depleted to zero
psi, as even air from a properly working air
system contains sufficient moisture to
condense in the tank during overnight drops
in ambient temperature.
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