The Torque Converter Clutch (TCC) is applied by fluid pressure,
which is controlled by a 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
Important: 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:
- Place your foot on the brake.
- Put the gear selector in DRIVE.
Notice: You may damage the transmission if you depress the accelerator for more
than 6 seconds.
- Depress the accelerator to approximately 1,200 RPM for no more
than six seconds.
A torque converter noise will increase under this load.
Torque Converter Clutch Shudder
The key to diagnosing Torque Converter Clutch (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. |
| • | Plug wires - Look in each end. If there is red dust (ozone)
or a black substance (carbon) present, then the wires are bad. Also look for
a white discoloration of the wire. This indicates arcing during hard acceleration. |
| • | 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 - The valve may let in too much or too little
unburnable exhaust gas and could cause the engine to run rich or lean. |
| • | MAP/MAF 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 - 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 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. |
| • | 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. |
