•
WHEELS
AND
TIRES
22-11 VEHICLE VIBRATION
Vehicle vibration can
be
caused by:
• Tire/wheel unbalance
or
excessive runout
• Defective tires with extreme tread wear
• Nylon overlay flat spots (performance tires only)
• Incorrect wheel bearing adjustment
(if
applicable)
• Loose
or
worn suspension/steering components
• Certain tire tread patterns
• Incorrect drive shaft angles
or
excessive drive
shaft/yoke runout
• Defective
or
worn U-joints
• Excessive brake rotor
or
drum runout
• Loose engine
or
transmission supports/mounts
• And
by
engine operated accessories Refer
to the
appropriate Groups
in
this man
ual for additional information.
VIBRATION
TYPES
There are two types
of
vehicle vibration:
• Mechanical
• Audible. Mechanical vehicle vibration
can be
felt through
the seats, floor pan and/or steering wheel. Audible vehicle vibration
is
heard above normal
background noise.
The
sound
can be a
droning
or
drumming noise. Vibrations
are
sensitive
to
change
in
engine
torque, vehicle speed
or
engine speed.
ENGINE TORQUE SENSITIVE VIBRATION
This vibration can
be
increased
or
decreased by:
• Accelerating
• Decelerating
• Coasting
• Maintaining
a
constant vehicle speed
VEHICLE SPEED SENSITIVE VIBRATION
This vibration condition always occurs
at
the same
vehicle speed regardless
of
the engine torque
or en
gine speed.
ENGINE SPEED
{RPM}
SENSITIVE VIBRATION
This vibration occurs
at
varying engine speeds.
It
can
be
isolated
by
increasing
or
decreasing
the en
gine speed with the transmission
in
NEUTRAL posi
tion.
VIBRATION
DIAGNOSIS
A vibration diagnosis should always begin with
a
10 mile (16 km) trip (to warm the vehicle and tires).
Then
a
road test
to
identify the vibration. Corrective action should
not be
attempted until
the
vibration
type has been identified
via a
road test. During the road test, drive the vehicle
on a
smooth
surface.
If
vibration exists, note
and
record
the
fol
lowing information: • Identify
the
vehicle speed range when
the
vibra
tion occurs
• Identify the type
of
vibration
• Identify the vibration sensitivity
• Determine
if
the vibration
is
affected
by
changes
in vehicle speed, engine speed and engine torque. When the vibration has been identified, refer to the
Vibration Diagnosis chart
for
causes. Consider cor
recting only those causes coded
in
the chart that
are
related
to
the vibration condition.
Refer
to
the following cause codes and descriptions
for explanations when referring
to
the chart.
TRR—Tire
and
Wheel Radial Runout: Vehicle
speed sensitive, mechanical vibration.
The
runout
will not cause vibration below
20
mph (32 km/h).
WH—Wheel Hop: Vehicle speed sensitive,
me
chanical vibration.
The
wheel
hop
generates rapid
up-down movement
in
the steering wheel. The vibra
tion
is
most noticeable
in the 20 - 40
mph
(32 - 64
km/h) range. The wheel hop will not cause vibration
below
20
mph (32 km/h). Wheel hop
is
caused
by a
tire/wheel that
has a
radial runout
of
more than 0.045 of-an-inch (1.14 mm).
If
wheel runout
is
accept
able
and
combined runout cannot
be
reduced
by re
positioning the tire
on
wheel, replace tire.
TB—Tire/Wheel Balance: Vehicle speed sensitive,
mechanical vibration. Static tire/wheel unbalance
will not cause vibration below 30 mph (46 km/h). Dy
namic tire/wheel unbalance will
not
cause vibration
below
40
mph (64 km/h). TLR—Tire/Wheel Lateral runout: Vehicle speed
sensitive, mechanical vibration. The runout will
not
cause vibration below
50 - 55 mph (80 - 88
km/h).
Excessive lateral runout will also cause front-end shimmy. TW—Tire Wear: Vehicle speed sensitive, audible
vibration. Abnormal tire wear causes small vibration in
the 30 - 55
mph
(88
km/h) range. This will pro
duce
a
whine noise
at
high speed.
The
whine will
change
to a
growl noise when the speed
is
reduced. W—Tire Waddle: Vehicle speed sensitive, mechan
ical vibration. Irregular tire uniformity
can
cause
side-to-side motion during speeds
up to 15
mph
(24
km/h).
If
the motion
is
excessive, identify
the
defec
tive tire and replace
it.
U A J—Universal Joint (Drive Shaft) Angles:
Torque/vehicle speed sensitive, mechanical/audible
vibration. Incorrect drive shaft angles cause mechan ical vibration below
20
mph (32 km/h) and
in
the
70
mph (112 km/h) range. The incorrect angles can also
produce
an
audible vibration
in
the 20
-
50 mph (32
-
80 km/h) range. Caster adjustment could
be
required
to correct the angles. UJ—Universal Joints: Engine torque/vehicle
speed sensitive, mechanical/audible vibration.
If
the
