erly lubricated and protects the bearings from
premature failure.
Th e tapered bearings consist of a cup, cage, rollers
and an inner race. Th e bearings are meant to
provide operational reliability under heavy loads
and misaligned conditions. Additionally, tapered
bearings are meant to handle a combination of
radial and thrust loads.
Th e hubcap keeps the oil or grease in the wheel
28 Fleet Maintenance | November/December 2017
hub, maintaining suffi cient lubrication to the
bearings. Hubcaps also may include additional
features such as a site window, a center fi ll plug
and a side fi ll plug (some of which may contain a
magnet to check for any metal wear).
Additional components of a wheel end include
the spindle nut and wheel nuts.
Th ere are a variety of spindle nut styles, including
but not limited to a standard nut system, a
stamped nut system, a castle nut system and a
double nut system. Th e use of these spindle end
components varies by truck or trailer manufacturer,
so always follow manufacturer recommendations
for spindle nut torque procedures.
Th e wheel nut is designed to provide clamp
force while maintaining optimized torque/tension,
reducing operating costs with extended life and
improved fuel economy. Selecting the proper
wheel nut can help reduce the potential
of catastrophic failure, as loosened
wheel nuts can result in wheel-off conditions
as well as reduce the operating life
of the wheel end’s seals and bearings.
Common causes of
wheel off conditions
Th ere are two common causes of wheeloff
s: loss of clamping force on the wheels
and bearing failure.
Typically, loss of clamping force is a
result of improper installation, such as
improper torque or products not meeting
the minimum torque requirements
set by the OE manufacturer. If there
is not enough torque or a technician
overtorques, the studs can become
overstretched and can fail over the life
of the wheel end.
It is important to
inspect wheel ends
to ensure safety and
maximize over-theroad
performance. VehicleServicePros.com/11078899
Proper care and maintenance of
the bearings also is critical to avoiding
wheel off conditions. Cleaning the
bearing in a solvent bath is important to
remove foreign materials. Making sure
the bearings are clean will help extend
wheel end life aft er re-installation.
Recommendations for
proper inspection
It is important to inspect a vehicle’s
wheel ends periodically for safety and to
maximize over-the-road performance.
Recommendations can vary by manufacturer,
some as little as 50,000 miles
or every six months, to every 100,000
miles or every 12 months.
To prepare the vehicle for inspection,
fi rst put the vehicle in park and block
the wheels to prevent the vehicle from
rolling. Th en, raise the axle until the
tires are off the fl oor and make sure
that the vehicle is properly supported
with safety stands.
It is very important to note service
technicians should never work under
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