Town & Country LWB AWD V6-3.8L VIN L (2000)
Drive/Propeller Shaft: Testing and Inspection
Rear Drive Line Noise Diagnosis
OVERVIEW
Different sources can be the cause of noise that the rear drive line module assembly is suspected of making. Refer to the following causes for noise
diagnosis.
REAR CARRIER ASSEMBLY NOISE
The most important part of rear carrier service is correctly identifying the cause of failures and noise complaints. The cause of most rear carrier
failures is relatively easy to identify. The cause of rear carrier noise is more difficult to identify.
If vehicle noise becomes intolerable, an effort should be made to isolate the noise. Many noises that are reported as coming from the rear carrier may
actually originate at other sources. For example:
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Tires
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Road surfaces
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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)
Rear carrier noises are normally divided into two categories: gear noise or bearing noise. A thorough and careful inspection should be completed to
determine the actual source of the noise before replacing the rear carrier.
The rear carrier assembly rubber mounting bushings help to dampen-out rear carrier noise when correctly installed. Inspect to confirm that no metal
contact exists between the rear carrier 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 technicians. 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
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Swerving the vehicle from left to right to detect wheel bearing noise.
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All rear carrier 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 rear carrier 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 rear carrier.
Tire noise changes with different road surfaces, but rear carrier 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 continues, 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 during 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 objectionable gear noise occurs, note the driving conditions 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 vehicle. Being aware of this will enable a technician to
separate bearing noise from gear noise.
Drive pinion bearing noise that results from defective 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