Daewoo NUBIRA, User Manual

Page: 677 / 685

FIVE–SPEED MANUAL TRANSAXLE 5B – 5
DAEWOO V–121 BL4
DIAGNOSIS
ISOLATE NOISE
Identify the cause of any noise before attempting to repair
the clutch, the transaxle, or their related linkages.
Symptoms of trouble with the clutch or the manual trans-
axle include:
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A great effort required to shift gears.
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The sound of gears clashing and grinding.
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Gear blockout.
Any of these conditions requires a careful analysis. Make
the following checks before disassembling the clutch or
the transaxle for repairs.
Road Travel Noise
Many noises that appear to come from the transaxle may
actually originate with other sources such as the:
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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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Exhaust system.
These noises may vary according to the:
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Size of the vehicle.
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Type of the vehicle.
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Amount of insulation used in the body of the ve-
hicle.
Transaxle Noise
Transaxle gears, like any mechanical device, are not ab-
solutely quiet and will make some noise during normal op-
eration.
To verify suspected transaxle noises:
1. Select a smooth, level asphalt road to reduce tire
and resonant body noise.
2. Drive the vehicle far enough to warm up all the lu-
bricants thoroughly.
3. Record the speed and the gear range of the trans-
axle when the noise occurs.
4. Check for noises with the vehicle stopped, but with
the engine running.
5. Determine if the noise occurs while the vehicle op-
erates in:
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Drive – under a light acceleration or a heavy
pull.
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Float – maintaining a constant speed with a light
throttle on a level road.
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Coast – with the transaxle in gear and the
throttle partly or fully closed.
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All of the above.
Bearing Noise
Differential Side Bearing Noise
Differential side bearing noise and wheel bearing noise
can be confused easily. Since side bearings are pre-
loaded, a differential side bearing noise should not dimin-
ish much when the differential/transaxle is run with the
wheels off the ground.
Wheel Bearing Noise
Wheel bearings produce a rough growl or grating sound
that will continue when the vehicle is coasting and the
transaxle is in NEUTRAL. Since wheel bearings are not
pre–loaded, a wheel bearing noise should diminish con-
siderably when the wheels are off the ground.
Other Noise
Brinelling
A brinelled bearing causes a ”knock” or ”click” approxi-
mately every second revolution of the wheel because the
bearing rollers do not travel at the same speed as the
wheel. In operation, the effect is characterized by a low–
pitched noise.
A brinelled bearing is caused by excessive thrust which
pushes the balls up on the pathway and creates a triangu-
lar– shaped spot in the bearing race. A brinelled bearing
can also be caused from pressing one race into position
by applying pressure on the other race.
A false indication of a brinelled bearing occurs as a result
of vibration near the area where the bearing is mounted.
Brinelling is identified by slight indentations, resulting in a
washboard effect in the bearing race.
Lapping
Lapped bearing noise occurs when fine particles of abra-
sive materials such as scale, sand, or emery circulate
through the oil in the vehicle, causing the surfaces of the
roller and the race to wear away. Bearings that wear loose
but remain smooth, without spalling or pitting, are the re-
sult of dirty oil.
Locking
Large particles of foreign material wedged between the
roller and the race usually causes one of the races to turn,
creating noise from a locked bearing. Pre–loading regular
taper roller bearings to a value higher than that specified
also can result in locked bearings
Pitting
Pitting on the rolling surface comes from normal wear and
the introduction of foreign materials.
Spalling
Spalled bearings have flaked or pitted rollers or races
caused by an overload or an incorrect assembly that re-
sults in a misalignment, a cocking of bearings, or adjust-
ments that are too tight.
After completing these checks, refer to the ”Diagnosis
Chart” in this section.