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1 Introduction / 1.7 Noise, Vibration and Abnormal Noise | PDF pages 25-26
1.7 Noise, Vibration and Abnormal Noise
1.7 Noise, Vibration and Abnormal Noise
1.7 Noise, Vibration and Abnormal
Noise
1.7.1 Description and Operation
1.7.1.1 Diagnostic Information and Procedures
Wind/Air Noise
– Keep performing the road test to check if the wind noise
is completely eliminated or check for other locations of
Note
leakage.
When the technician checks the faulty position, the
– After confirming all locations of leakage through road
test, return to the repair workshop to carry out permanent
assistant should drive the vehicle, otherwise, it may
repair using professional, reasonable positioning methods
cause personal injury.
and sealing materials.
To accurately determine the location of wind noise, it is
Vibration
necessary to test drive in the vehicle. Generally speaking,
Most of the high speed vibrations are caused by the loss of
wind noise comes from major and minor leakages, and if the
wheel dynamic balance. If vibrations maintain after dynamic
leakage is not eliminated during repair process, the only way
balance, possible causes include:
is to reduce rather than eliminate the wind noise.
– The tire is out of round
During test drive, the maintenance personnel should carry the
– The rim is out of round
following tools to help diagnose the exact location of wind
– There is hardness deviation in tires
noise:
• Echometer
All causes of vibrations cannot be detected by measuring the
free runout of tires and wheels. The three causes as
• Masking tape
mentioned above are called load radial runout. The faulty
• Caulking strip
vehicle must be repaired by replacing the original tire and
• Marker pen
wheel assemblies with known tire and wheel assemblies in
• Screwdriver
good condition.
Carry out road test in accordance with the following
Low speed vibrations that occur at a speed below 64 km/h are
procedures:
usually caused by runout. High speed vibrations that occur at
• Select a route in which straight streets run in east, south,
a speed above 64 km/h are usually caused by unbalance or
west, and north directions.
runout.
• Select a street with less traffic or reduced noise to avoid
Correction of Uneven Tires
affecting the test.
Generally two ways can be used to correct tires that has been
• Conduct road tests under a speed at which the customer
thinks the noise is the most obvious or the noise is heard. It
properly balanced but still vibrate. One way is to use an
is strictly forbidden to exceed the legal speed limit.
automatic machine tool to mount the tires on the machine tool
• Wind noise heard in the following situations is deemed as
and remove a small amount of rubber from the high points on
exterior wind noise.
the tread on the left and right sides of the tire by means of
– Wind noise can be heard when driving immediately after
grinding. Corrections of tires in this way are usually
lowering the window.
permanent. Standardized operations will not have a
– The wind noise disappears immediately when pasting
noticeable impact on the appearance of the tire and the
the tape to individual trim sealing strips and gaps.
service life of the tire tread. It is not advisable to repair tires
• Interior wind noise is attributable to air escaping from the
using edged machine tools during corrections of tires, as this
vehicle. Adopt the following methods to eliminate the noise:
will shorten the service life of the tires and cannot tackle the
– Paste tape to the pressure relief valve on the body door
root of the problem.
lock post once the location of leakage is detected. Air
Another way is to remove the tire and rotate the tire 180° on
pressure can immediately establish in the vehicle,
intensifying the wind noise.
the rim. This method can be used only when the cause of
vibration is determined, i.e., the tire and wheel assembly
– Confirm the location of leakage using a echometer.
through diagnosis and confirmation. Vibrations can occur in
– Paste masking tape to temporarily repair the leakage.
intact wheel assembly when using this method.
Abnormal Sound
Before removing the tire from the wheel, mark the position of
the valve core on the tire to restore the tire to its original
The door squeaks in use
position.
Check whether the door hinge lacks lubrication.
Abnormal Sound
– Operate the door back and forth and listen carefully
Repair of Abnormal Sounds Abnormal sounds mainly arise
whether the door squeaks
from relative movement between vehicle parts which actually
– Lubricate the door hinge with rust remover and apply
should not exist. Three ways can be adopted to repair
grease.
abnormal sounds:
1.7.1.2 Repair Guidance
– Securely fasten the parts to eliminate relative movement
Wind/Air Noise
during driving.
– Separate the parts so that the parts do not contact each
Exterior wind noise
other while working.
Seal the clearance (if any) on the vehicle with special sealing
– Isolate the parts so that they do not make abnormal
strip.
sounds during movement. Uniform, low-friction surfaces can
eliminate viscous sliding between parts.
Vibration
On-board balancing of wheels and tires
On-board balancing can correct vibrations caused by
unbalanced brake disc.
1. When performing dynamic balancing on the vehicle, it is
forbidden to remove the balance weight installed during
wheel dynamic balancing under the vehicle.
2. If the balance weight to be added for dynamic balancing
weighs above 25 g (1 lb), two balance weights can be
installed on the inner rim and the outer rim respectively.
Under-car balancing of wheels and tires
Carry out wheel dynamic balancing using an electronic under-
car balancing machine. The dynamic balancing machine is
easy to use and can be use for both static balancing and
dynamic balancing. Unlike on-board balancing, the under-car
balancing machine cannot be used for correction of
unbalanced brake discs. The under-car balancing can
overcome this weakness by fixing the wheels to the balancing
machine and passing a cone through the back of the center
hole rather than through the wheel nut hole.
Directional assembly of wheels and tires
Wheels and tires are assembled in the factory by matching
the radially thick position of the tire (also known as the high
point) to the position on wheel with minimum radius (also
known as the low point).
The high point of the tire is initially marked with red paint or a
label is attached to the outer wall of the tire when leaving the
factory.
The low point of the wheel is at the position the valve core.