to TMC RP 640 for instructions on how to properly
identify these systems.
It is important for technicians be able to identify
the wheel-end system, to ensure proper maintenance
Th ere are some key items to look for when identifying
the wheel-end system, Maye says. First, look
for the chassis decal or wheel-end identifi cation on
the hub cap, to confi rm wheel-end type and lubrication
specs. If this information is unavailable,
the technician can disassemble the wheel-end to
inspect the unit. Maye says many manually adjusted
and some pre-adjusted wheel-ends will use a
variety of diff erent types of spindle nuts, and those
nuts should include steps for proper installation.
Th e key indicator of a pre-adjusted wheel-end
is the presence of a bearing spacer.
“If the wheel-end includes a bearing spacer,
disregard the spindle nut installation instructions
specifi c to manual bearing adjustment and
follow the instructions from the manufacturer of
the pre-adjusted wheel-end assembly,” Maye adds.
Th e wheel-end system type dictates the components
replaced in the system during service. Rick
Domin, Lead Technical Trainer for wheel hub and
bearing supplier Timken, advises manually-adjusted
wheel-ends require the replacement of
cups and cones. For pre-adjusted wheel-ends, in
addition to the cups and cones, the technician will
need to replace the bearing spacer.
“If the technician removes the wheel-end and,
aft er removing the retaining nut, notices the entire
hub assembly must be removed and there is an
inner and outer seal, they are most likely dealing
with a unitized bearing and must replace them as
a whole assembly,” Domin adds.
It is also important to evaluate the benefi ts of
repairing versus replacing the wheel-end unit. As
is the case with aged or high-mileage vehicles, the
hub casting, bearings or bolts may be severely
worn or damaged.
“Many times a technician is not properly trained
to determine if these components are suitable for
26 Fleet Maintenance | June 2018
re-use,” Maye advises. “When the cost of components
to rebuild the wheel-end, the labor involved,
the additional time out of service for the vehicle and
the liability for the repair is considered, wheel-end
replacement is oft en the best option. Th e new wheelend
can be quickly installed and oft en times comes
with an extended warranty. Th e new assembly will
put the wheel-end back to as new condition.”
Importance of proper lubrication
“Th e three critical components for wheel-end
performance are bearings, lubricant and the seal,”
explains Stemco’s Purvis. “TMC’s recommended
lubricant practices show that lubricant condition
is a leading indicator of wheel-end health.”
Lubricant leakage is symptomatic of a larger
issue – oft en due to seal failure because of improper
wheel bearing adjustment. Th is goes back to the
importance of measuring proper endplay.
When it comes to lubricants, there are two types
of lubrication processes for traditional wheel-end
systems – oil bath wheel-ends and semi-fl uid
Always review information from the manufacturer
on the process for lubricating pre-adjusted
» Here a technician installs a pre-set spacer
to a pre-adjusted wheel end system. Preadjusted
wheel-end systems provide a
preset amount of preload during component
assembly by the manufacturer.
Photo courtesy of Timken
conditions is less timeconsuming
efficient in the long run
to preventing damage.
and unitized hub assemblies.
While it is the fl eet’s decision on what type of
lubricant to use, TMC and manufacturers have
suggestions on how to select the right lubricant
for the intended application.
Preload or endplay?
Importance of proper bearing adjustment measurements
A lot of people in the industry
don’t understand that
preload and endplay are
mutually exclusive. You have
one or the other, not both.
Setting bearings to either
preload or to endplay will
have a significant impact on
performance in wheel bearing
arrangements in terms of
bearing life, friction and proper
functioning of the bearing.
Preload can be defined as a
compression force applied
to the bearings to secure
them inside the wheel hub,
remove all axial clearance
and hold the assembly under
load to keep the tapered
rollers in the best position.
Wheel-end play is the free
movement of the bearings
and wheel assembly along the
length of the spindle, often
referred to as a “loose setting.”