October 2017 | VehicleServicePros.com 33
Consider the following recommendations
when inspecting the drivelines, according to
Meritor’s Iott:
Use Proper Lighting During Inspection. Use
a bright light to see the full picture and fi nd
more potential problems earlier and prevent
more severe failures.
Check for Movement in the U-joint Prior to
Greasing. Movement allotments are determined
by the manufacturer. For example, in Meritor’s
Xtended Lube MXL and Permalube RPL Series
U-joints movement should not exceed .006 inch
in any direction.
Check Center Bearings. Th ese may require
replacement if there is excessive movement
between the rubber bushing and the mounting
bracket, or any movement in the bearing
assembly itself. For example, Iott says to follow
these guidelines during inspection:
• Slip Yoke. Movement at the slip spines should
not exceed .017 inch
• End Yoke. Any movement on the end yoke
splines will require replacing with a new
yoke, nut and U-joint mounting straps.
“Re-tightening this connection rarely works
and the problem typically recurs,” Iott says.
• U-joint mounting hardware. Any loose
mounting hardware or straps should be
replaced with new parts.
U-joint Greasing. Always check the driveline
system prior to any greasing of a component.
“Go old school... more is better in this situation,”
Iott says. “Continue pumping grease into the
U-joint until you see clean grease purging from
all four journal caps. A major U-joint failure
mode is associated with a technician’s failure
to purge all four trunnion caps.”
Slip Yoke Greasing. Purge grease and water
from the slip yoke seal until clean grease
appears from the seal. Moisture ingestion is a
big problem, Iott says, in the slip joint assembly.
Driveshaft Phasing. Proper end yoke or slip
yoke phasing is required on a driveshaft to
eliminate driveline vibration. An “In Phase”
driveshaft has the ears of the yoke in alignment.
An “Out of Phase” driveshaft has the ear of the
yoke out of alignment by 90 degrees or more.
“Because either situation may be correct, technicians
must contact the OEM to determine
correct phasing requirements for a specifi c year
and model truck,” Iott recommends.
Spec’ing Correct Components. It’s important to
specify the right components for your vehicle,
especially if you are choosing a system designed
for engine downspeeding, Dana’s Bosler says.
“An engine running at lower rpms places
signifi cantly higher torque stresses in the
driveline system and improper spec’ing
can lead to premature and extended
maintenance needs,” Bosler says. Downspeeding
is a new truck drivetrain confi guration
that increases fuel effi ciency, but it has
an eff ect on the driveline torque, Meritor’s
Iott explains.
“Th is spec confi guration increases the driveline
torque and the increased torque can have
an impact on driveline as a potential overload
situation if the driver puts the truck into wrong
place at the right time,” he says.
Common
Mistakes
or Oversights
Th e lack of attention to detail in the
inspection process is a leading cause of failures,
Meritor’s Iott says.
Common oversights occur in:
Loose Fasteners: Technicians will overlook
loose fasteners at the center bearing mounting
and loose end yoke nuts at the major components,
such as axles, transmissions and center bearings.
Checking for vertical or rotational movement at
these locations can prevent failures later in the
driveline’s life, Iott says.
Slip Yoke Shaft : “Checking for slip yoke spline
wear is simple and easy, moving the shaft up
and down to gauge the amount of movement,”
Iott says. “Th is check is commonly overlooked
by technicians.”
Greaseable U-joint Purging: As previously
mentioned, technicians commonly overlook
purging all four journal caps during the planned
maintenance greasing period. Grease must purge
all four positions for proper U-joint life. Th is is
the most common preventable maintenance
U-joint failure.
Furthermore, the use of standard chassis
grease can break down and become ineff ective,
negatively impacting performance, Dana’s Bosler
explains. Instead of this, Bosler recommends
using a synthetic grease specifi cally formulated
for universal joints. For example, Dana off ers the
SPL Series product line.
Bigger Picture. PACCAR Parts’ Product Director
Pepe Ramos says a common oversight is “not looking
beyond the damaged components to potential
down-line or up-line issues.”
PACCAR Parts (www.paccarparts.com), a division
of PACCAR, Inc., is a global distributor of
aft ermarket parts for heavy and medium duty
trucks, trailers, buses and engines.
Warning Signs for Technicians
While vibration oft en occurs in trucks, and there
can be many contributing factors to the source of
it, explains Dana’s Bosler.
“When it comes to the driveline, balance issues,
along with excessive looseness in universal joints
or slip splines, are key indicators that parts are
worn,” Bosler says.
Page 34
The Role Of The Driveline
The driveline connects
the transmission to the
rear axle input, explains
PACCAR Parts’ Product
Director Pepe Ramos.
PACCAR Parts (www.
paccarparts.com), a
division of PACCAR, Inc.,
is a global distributor
of aftermarket parts
for heavy and medium
duty trucks, trailers,
buses and engines.
“The driveline transmits
the energy output from
the transmission to the
rear axle input,” Ramos
says. “It also acts as
a torsional damper
between the transmission
and rear axle. This
protects both transmission
from rear axle stall
and protects the rear
axle from harmful transmission
accelerations.”
According to Meritor’s,
Product Technical
Specialist Eric Iott,
the driveline’s main
components comprise
the end yoke (or flanges),
U-joint (sealed or
greaseable), fastener
hardware (straps), weld
yoke, tube, bearing
stub shaft, center
bearing, washer and
nuts, slip yoke assembly
(slip yoke, spline plug
and sealing system)
and main shafts.
Meritor, Inc. (www.meritor.
com) is a global supplier
of axle, brake and
suspension solutions
to OE manufacturers
and the aftermarket.
The main shafts include:
Coupling shaft
assembly. The section
between the transmission
that contains
the center bearing.
Depending on the vehicle’s
wheelbase, there
could be more than
one coupling shaft.
Slip shaft assembly.
This shaft attaches to
the coupling shaft(s)
and to the rear axle
input. Due to suspension
movement, this
shaft contains a slip
yoke assembly, which
enables the suspension
to move freely
without binding or
damaging the driveshaft
assembly during suspension
articulation.
Inter-axle shaft
assembly. This shaft,
which has the potential
for the most wear in the
driveline system, is only
used when a tandem or
tridem axle assembly is
designed into a chassis.
It is a relatively short
shaft − less than 35
inches − that attaches
the forward axle carrier
to the rear carrier. The
shaft’s operating angles
are steeper and larger
due to the closeness
and design of the axle
packaging system. It is
also attached to two
independently moving
axles, which means it
is constantly changing
angles and length.
U-Joint Styles:
• Half-round or fullround
designs; some
offer extended
lube intervals up
to 100,000 miles
• Sealed U-joints;
lubricant intervals
are not required,
reducing maintenance
and lowering overall
maintenance costs.
» The
design of Dana’s
SPL 350 driveshaft
allows it to handle the
higher torque stresses that
result from engine downspeeding.
Photo Courtesy of Dana Incorporated