Some useful info on vibration diagnosis by Billy Ray posted on JU:
10-16-2006, 09:23 AM
Be sure to print this out because I probably won't do this again.
Vehicle vibration can be caused by:
² Tire/wheel unbalance or excessive runout
² Defective tires with extreme tread wear
² Nylon overlay flat spots (performance tires only)
² Incorrect wheel bearing adjustment (if applicable)
² Loose or worn suspension/steering components
² Certain tire tread patterns
² Incorrect drive shaft angles or excessive drive
² Defective or worn U-joints
² Excessive brake rotor or drum runout
² Loose engine or transmission supports/mounts
² And by engine operated accessories
Refer to the appropriate Groups in this manual
for additional information.
There are two types of vehicle vibration:
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
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:
² Maintaining a constant vehicle speed
VEHICLE SPEED SENSITIVE VIBRATION
This vibration condition always occurs at the same
vehicle speed regardless of engine torque or engine
ENGINE SPEED (RPM) SENSITIVE VIBRATION
This vibration occurs at varying engine speeds. It
can be isolated by increasing or decreasing the engine
speed with the transmission in NEUTRAL position.
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 following
² Identify the vehicle speed range when the vibration
² Identify the type of vibration
² Identify the vibration sensitivity
² 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. (see below)Consider correcting
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, mechanical
vibration. The wheel hop generates rapid
up-down movement in the steering wheel. The vibration
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 acceptable
and combined runout cannot be reduced by repositioning
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). Dynamic
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
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 produce
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, mechanical
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 defective
tire and replace it.
UAJ—Universal Joint (Drive Shaft) Angles:
Torque/vehicle speed sensitive, mechanical/audible vibration.
Incorrect drive shaft angles cause mechanical
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 U-joint is worn it will cause vibration with almost
any vehicle speed/engine torque condition.
DSY—Drive Shaft and Yokes: Vehicle speed sensitive,
mechanical/audible vibration. The condition
will not cause vibration below 35 mph (56 km/h). Excessive
runout, unbalance or dents and bends in the
shaft will cause the vibration. Identify the actual
cause and repair/replace as necessary.
WB—Wheel Bearings: Vehicle speed sensitive,
mechanical/audible vibration. Loose wheel bearings
cause shimmy-like vibration at 35 mph (56 km/h)
and above. Worn bearings will also produce a growl
noise at low vehicle speed and a whine noise at high
vehicle speed. The wheel bearings must be adjusted
or replaced, as applicable.
AN—Axle Noise: Engine torque/vehicle speed sensitive,
mechanical/audible vibration. The axle will not
cause mechanical vibration unless the axle shaft is
bent. Worn or damaged axle pinion shaft or differential
gears and bearings will cause noise. Replace the
defective component(s) as necessary.
SSC—Suspension and Steering Components:
Vehicle speed sensitive, mechanical vibration. Worn
suspension/steering components can cause mechanical
vibration at speeds above 20 mph (32 km/h).
Identify and repair or replace the defective component(
EA—Engine Driven Accessories: Engine speed
sensitive, mechanical/audible vibration. Vibration can
be caused by loose or broken A/C compressor, PS
pump, water pump, generator or brackets, etc. Usually
more noticeable when the transmission is shifted
into the NEUTRAL position and the engine speed
(rpm) increased. Inspect the engine driven accessories
in the engine compartment. Repair/replace as
ADB—Accessory Drive Belts: Engine speed sensitive,
audible vibration. Worn drive belts can cause a
vibration that produces either a droning, fluttering or
rumbling noise. Inspect the drive belt(s) and tighten/
replace as necessary.
DEM—Damaged Engine or Transmission Support
Mounts: Engine speed sensitive, mechanical/
audible vibration. If a support mount is worn, noise
or vibration will occur. Inspect the support mounts
and repair/replace as necessary.
ES—Exhaust System: Engine speed sensitive,
mechanical/audible vibration. If loose exhaust components
contact the vehicle body they will cause noise
and vibration. Inspect the exhaust system for loose,
broken and mis-aligned components and repair/replace