UNRELATED NOISE
Some driveline trouble symptoms are also
common to the engine, transmission, wheel bearings, tires, and
other parts of the vehicle. Ensure cause of trouble actually is in the
drive axle before adjusting, repairing, or replacing any of its parts.
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NON DRIVETRAIN NOISE
A few conditions can sound just like drive
axle noise and have to be considered in pre-diagnosis. The 4
most common noises are exhaust; tires, CV/universal joints and
wheel trim rings. In certain conditions, the pitch of the exhaust
gases may emit gear whine. At other times, it may be mistaken for
a wheel-bearing rumble. Tires, especially radial and snow, can
have a high-pitched tread whine or roar, similar to gear noise.
Also, some non-standard tires with an unusual tread construction
may emit a roar or whine. Defective CV/universal joints may cause
clicking noises or excessive driveline play that can be improperly
diagnosed as drive axle problems. Trim and moldings also can
cause a whistling or whining noise. Ensure none of these
components are causing the noise before disassembling the
drive axle. |
GEAR NOISE
An improper gear pattern, gear
damage, or improper bearing preload can cause a
“howling” or “whining” noise from the
ring and pinion gear. It can occur at various speeds and driving
conditions, or it can be continuous. Before disassembling axle to
diagnose and correct gear make sure that tires, exhaust, and
vehicle trim have been checked as possible causes |
CHUCKLE
This is a particular rattling noise
that sounds like a stick against the spokes of a spinning bicycle
wheel. It occurs while decelerating from 40 MPH and usually can
be heard until vehicle comes to a complete stop. The frequency
varies with the speed of the vehicle.
A chuckle that occurs on the
driving phase is usually caused excessive clearance due to
differential gear wear, or by a damaged tooth on the coast side of
the pinion or ring gear. Even a very small tooth nick or a ridge on
the edge of a gear tooth is enough the cause the noise. This
condition can be corrected simply by cleaning the gear tooth nick
or ridge with a small grinding wheel. If either gear is damaged or
scored badly, the gear set must be replaced. If metal has broken
loose, the carrier and housing must be cleaned to remove
particles that could cause damage. |
KNOCK
This is very similar to a chuckle,
though it may be louder, and occur on acceleration or
deceleration. A gear tooth that is damaged on the drive side of the
ring and pinion gears can cause knock. Ring gear bolts that are
hitting the carrier casting can cause knock. Knock can also be due
to excessive endplay in the axle shafts. |
CLUNK
Clunk is a metallic noise heard
when an automatic transmission is engaged in Reverse or Drive,
or when throttle is applied or released. It is caused by backlash
somewhere in the driveline, but not necessarily in the axle. To
determine whether the axle causes driveline clunk, check the total
axle backlash as follows:
1. Raise vehicle on a frame or
twin post hoist so that drive wheels are free. Clamp a bar between
axle companion flange and a part of the frame or body so that
flange cannot move.
2. On conventional drive axles,
lock the left wheel to keep it from turning. On all models, turn the
right wheel slowly until it is felt to be in Drive condition. Hold a chalk
marker on side of tire about 12" from center of wheel. Turn
wheel in the opposite direction until it is again felt to be in Drive
condition.
3. Measure the length of the
chalk mark, which is the total axle backlash. If backlash is one inch
or less, drive
axle is not the source of clunk noise. |
BEARING WHINE
Bearing whine is a high-pitched
sound similar to a whistle. Malfunctioning pinion bearings usually
causes it. Pinion bearings operate at drive shaft speed. Roller
wheel bearings may whine in a similar manner if they run
completely dry of lubricant. Bearing noise will occur at all driving
speeds. This distinguishes it from gear whine, which usually
comes and goes as speed changes. |
BEARING RUMBLE
Bearing rumble sounds like
marbles being tumbled. A malfunctioning wheel bearing usually
causes it. The lower pitch is because the wheel bearing turns at
only about 1/3 of drive shaft spe |
CHATTER ON TURNS
This is a condition where the entire
front or rear of vehicle vibrates when vehicle is moving. The
vibration is plainly felt as well as heard. Extra differential thrust
washers installed during axle repair can cause a condition of
partial lock-up that creates this chatter. |
AXLE SHAFT NOISE
Axle shaft noise is similar to gear
noise and pinion bearing whine. Axle shaft bearing noise will
normally distinguish itself from gear noise by occurring in all
driving modes (Drive, cruise, coast and float), and will persist with
transmission in Neutral while vehicle is moving at problem speed.
If vehicle displays this noise condition, remove suspect parts,
replace wheel seals and install a new set of bearings. Re-
evaluate vehicle for noise before removing any internal
components. Vibration is a high frequency trembling, shaking or
grinding condition (felt or heard) that may be constant or variable
in
level and can occur during the total operating speed range of the
vehicle. The types of vibrations that can be felt in the vehicle can d
into 3 main groups:
- Vibrations of various unbalanced rotating parts of the vehicle.
- Resonance vibrations of the body and frame structures caused by rotating
of unbalanced parts.
- Tip-in moans of resonance vibrations from stressed engine or exhaust
system mounts or driveline flexing modes.
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