Chrysler Dodge Caravan 2002, Руководство пользователя, Страница: 105 / 2399

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Wheel bearings
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Engine
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Transmission
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Exhaust
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Propeller shaft (vibration)
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Vehicle body (drumming)
Driveline module noises are normally divided into
two categories: gear noise or bearing noise. A thor-
ough and careful inspection should be completed to
determine the actual source of the noise before
replacing the driveline module.
The rubber mounting bushings help to dampen-out
driveline module noise when properly installed.
Inspect to confirm that no metal contact exists
between the driveline module case and the body. The
complete isolation of noise to one area requires
expertise and experience. Identifying certain types of
vehicle noise baffles even the most capable techni-
cians. Often such practices as:
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Increase tire inflation pressure to eliminate tire
noise.
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Listen for noise at varying speeds with different
driveline load conditions
•
Swerving the vehicle from left to right to detect
wheel bearing noise.
All driveline module assemblies produce noise to a
certain extent. Slight carrier noise that is noticeable
only at certain speeds or isolated situations should be
considered normal. Carrier noise tends to peak at a
variety of vehicle speeds. Noise is NOT ALWAYS an
indication of a problem within the carrier.
TIRE NOISE
Tire noise is often mistaken for driveline module
noise. Tires that are unbalanced, worn unevenly or
are worn in a saw-tooth manner are usually noisy.
They often produce a noise that appears to originate
in the driveline module.
Tire noise changes with different road surfaces, but
driveline module noise does not. Inflate all four tires
with approximately 20 psi (138 kPa) more than the
recommended inflation pressure (for test purposes
only). This will alter noise caused by tires, but will
not affect noise caused by the differential. Rear axle
noise usually ceases when coasting at speeds less
than 30 mph (48 km/h); however, tire noise contin-
ues, but at a lower frequency, as the speed is
reduced.
After test has been completed lower tire pressure
back to recommended pressure.
GEAR NOISE (DRIVE PINION AND RING GEAR)
Abnormal gear noise is rare and is usually caused
by scoring on the ring gear and drive pinion. Scoring
is the result of insufficient or incorrect lubricant in
the carrier housing.
Abnormal gear noise can be easily recognized. It
produces a cycling tone that will be very pronounced
within a given speed range. The noise can occur dur-
ing one or more of the following drive conditions:
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Drive
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Road load
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Float
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Coast
Abnormal gear noise usually tends to peak within
a narrow vehicle speed range or ranges. It is usually
more pronounced between 30 to 40 mph (48 to 64
km/h) and 50 to 60 mph (80 to 96 km/h). When objec-
tionable gear noise occurs, note the driving condi-
tions and the speed range.
BEARING NOISE (DRIVE PINION AND
DIFFERENTIAL)
Defective bearings produce a rough growl that is
constant in pitch and varies with the speed of vehi-
cle. Being aware of this will enable a technician to
separate bearing noise from gear noise.
Drive pinion bearing noise that results from defec-
tive or damaged bearings can usually be identified by
its constant, rough sound. Drive pinion front bearing
is usually more pronounced during a coast condition.
Drive pinion rear bearing noise is more pronounced
during a drive condition. The drive pinion bearings
are rotating at a higher rate of speed than either the
differential side bearings or the axle shaft bearing.
Differential side bearing noise will usually produce
a constant, rough sound. The sound is much lower in
frequency than the noise caused by drive pinion bear-
ings.
Bearing noise can best be detected by road testing
the vehicle on a smooth road (black top). However, it
is easy to mistake tire noise for bearing noise. If a
doubt exists, the tire treads should be examined for
irregularities that often causes a noise that resem-
bles bearing noise.
ENGINE AND TRANSMISSION NOISE
Sometimes noise that appears to be in the driv-
eline module assembly is actually caused by the
engine or the transmission. To identify the true
source of the noise, note the approximate vehicle
speed and/or RPM when the noise is most noticeable.
Stop the vehicle next to a flat brick or cement wall
(this will help reflect the sound). Place the transaxle
in NEUTRAL. Accelerate the engine slowly up
through the engine speed that matches the vehicle
speed noted when the noise occurred. If the same
noise is produced, it usually indicates that the noise
is being caused by the engine or transaxle.
3 - 26 REAR DRIVELINE MODULE
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REAR DRIVELINE MODULE (Continued)