Torque Converter Diagnosis
The torque converter clutch (TCC) is applied by fluid pressure,
which is controlled by a pulse width modulated (PWM) solenoid
valve. This solenoid valve is located inside of the automatic
transmission assembly. The solenoid valve is controlled through a
combination of computer controlled switches and sensors.
Torque Converter Stator
The torque converter stator roller clutch can have two different
malfunctions.
| • |
The stator assembly freewheels
in both directions. |
| • |
The stator assembly remains
locked up at all times. |
Poor Acceleration at Low Speed
If the stator is freewheeling at all times, the car tends to
have poor acceleration from a standstill. At speeds above 50-55
km/h (30-35 mph), the car may act normally. For poor acceleration,
you should first determine that the exhaust system is not blocked,
and the transmission is in First gear when starting out.
If the engine freely accelerates to high RPM in NEUTRAL, you can
assume that the engine and the exhaust system are normal. Check for
poor performance in DRIVE and REVERSE to help determine if the
stator is freewheeling at all times.
Poor Acceleration at High Speed
If the stator is locked up at all times, performance is normal
when accelerating from a standstill. Engine RPM and car speed are
limited or restricted at high speeds. Visual examination of the
converter may reveal a blue color from overheating.
If the converter has been removed, you can check the stator
roller clutch by inserting a finger into the splined inner race of
the roller clutch and trying to turn the race in both directions.
You should be able to freely turn the inner race clockwise, but you
should have difficulty in moving the inner race counterclockwise or
you may be unable to move the race at all.
Noise
Note: Do not confuse this
noise with pump whine noise, which is usually noticeable in PARK,
NEUTRAL and all other gear ranges. Pump whine will vary with line
pressure.
You may notice a torque converter whine when the vehicle is
stopped and the transmission is in DRIVE or REVERSE. This noise
will increase as you increase the engine RPM. The noise will stop
when the vehicle is moving or when you apply the torque converter
clutch, because both halves of the converter are turning at the
same speed.
Perform a stall test to make sure the noise is actually coming
from the converter:
| 1. |
Place your foot on the
brake. |
| 2. |
Put the gear selector in
DRIVE. |
| 3. |
Depress the accelerator to
approximately 1,200 RPM for no more than 6 seconds. |
|
Caution: You may damage the transmission if you depress the
accelerator for more than 6 seconds. |
A torque converter noise will increase under this load.
Torque Converter Clutch Shudder
The key to diagnosing TCC shudder is to note when it happens and
under what conditions.
TCC shudder which is caused by the transmission should only
occur during the apply or the release of the converter clutch.
Shudder should never occur after the TCC plate is fully
applied.
If the shudder occurs while the TCC is applying, the problem can
be within the transmission or the torque converter. Something is
causing one of the following conditions to occur:
| • |
Something is not allowing the
clutch to become fully engaged. |
| • |
Something is not allowing the
clutch to release. |
| • |
The clutch is releasing and
applying at the same time. |
One of the following conditions may be causing the problem to
occur:
| • |
Leaking turbine shaft
seals |
| • |
A restricted release
orifice |
| • |
A distorted clutch or housing
surface due to long converter bolts |
| • |
Defective friction material on
the TCC plate |
If Shudder Occurs After TCC has Applied
If shudder occurs after the TCC has applied, most of the time
there is nothing wrong with the transmission.
As mentioned above, the TCC is not likely to slip after the TCC
has been applied. Engine problems may go unnoticed under light
throttle and load, but they become noticeable after the TCC apply
when going up a hill or accelerating. This is due to the mechanical
coupling between the engine and the transmission.
Once TCC is applied, there is no torque converter, fluid
coupling, assistance. Engine or driveline vibrations could be
unnoticeable before TCC engagement.
Inspect the following components in order to avoid misdiagnosis
of TCC shudder. An inspection will also avoid the unnecessary
disassembly of a transmission or the unnecessary replacement of a
torque converter.
| • |
Spark plugs - Inspect for
cracks, high resistance or a broken insulator. |
| • |
Coil - Look for a black
discoloration on the bottom of the coil. This indicates arcing
while the engine is misfiring. |
| • |
Fuel injector - The filter may
be plugged. |
| • |
Vacuum leak - The engine will
not get a correct amount of fuel. The mixture may run rich or lean
depending on where the leak occurs. |
| • |
EGR valve (Petrol) - The valve
may let in too much or too little unburnable exhaust gas and could
cause the engine to run rich or lean. |
| • |
MAP sensor - Like a vacuum
leak, the engine will not get the correct amount of fuel for proper
engine operation. |
| • |
Carbon on the intake valves -
Carbon restricts the proper flow of air/fuel mixture into the
cylinders. |
| • |
Flat cam - Valves do not open
enough to let the proper fuel/air mixture into the
cylinders. |
| • |
Oxygen sensor - This sensor
may command the engine too rich or too lean for too long.
|
| • |
Fuel pressure - This may be
too low. |
| • |
Engine mounts - Vibration of
the mounts can be multiplied by TCC engagement. |
| • |
Axle joints - Check for
vibration. |
| • |
TP Sensor (Petrol) - The TCC
apply and release depends on the TP Sensor in many engines. If the
TP Sensor is out of specification, TCC may remain applied during
initial engine loading. |
| • |
Cylinder balance - Bad piston
rings or poorly sealing valves can cause low power in a
cylinder. |
| • |
Fuel contamination - This
causes poor engine performance. |
Torque Converter Evaluation and Diagnosis
Replace the torque converter if any of the following conditions
exist:
| • |
External leaks appear in the
hub weld area. |
| • |
The converter hub is scored or
damaged. |
| • |
The converter pilot is broken,
damaged, or fits poorly into the crankshaft. |
| • |
You discover steel particles
after flushing the cooler and the cooler lines. |
| • |
The pump is damaged, or you
discover steel particles in the converter. |
| • |
The vehicle has TCC shudder
and/or no TCC apply. Replace the torque converter only after all
hydraulic and electrical diagnoses have been made. The converter
clutch material may be glazed. |
| • |
The converter has an imbalance
which cannot be corrected. |
| • |
The converter is contaminated
with engine coolant which contains antifreeze. |
| • |
An internal failure occurs in
the stator roller clutch. |
| • |
You notice excessive end
play. |
| • |
Overheating produces heavy
debris in the clutch. |
| • |
You discover steel particles
or clutch lining material in the fluid filter or on the magnet,
when no internal parts in the unit are worn or damaged. This
condition indicates that lining material came from the
converter. |
Do not replace the torque converter if you discover any of the
following symptoms:
| • |
The oil has an odor or the oil
is discolored, even though metal or clutch facing particles are not
present. |
| • |
The threads in one or more of
the converter bolt holds are damaged. Correct the condition with a
new thread inset. |
| • |
Transmission failure did not
display evidence of damaged or worn internal parts, steel particles
or clutch plate lining material in the unit and inside the fluid
filter. |
| ⇒ |
If the vehicle has been exposed to high mileage
only. An exception may exist where the lining of the torque
converter clutch dampener plate has seen excess wear by vehicles
operated in heavy and/or constant traffic, such as taxi, delivery,
or police use. |
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