To properly diagnosis the lock-up (TCC) system, perform all electrical testing
first and then the hydraulic testing.
The torque converter clutch (TCC) is applied by fluid pressure which is controlled
by a solenoid located inside the valve body. The solenoid is energized by completing
an electrical circuit through a combination of switches and sensors.
Functional Check Procedure
- Install a tachometer or scan tool.
- Operate the vehicle until proper operating temperature is reached.
- Drive the vehicle at 80-88 km/h (50-55 mph)
with light throttle road load.
- Maintaining throttle position, lightly touch the brake pedal and check
for release of the TCC and a slight increase in engine speed (RPM).
- Release the brake slowly accelerate and check for a reapply of the lock
up clutch and a slight decrease in engine speed (RPM).
Torque Converter Evaluation
Torque Converter Stator
The torque converter stator roller clutch can have 1 of 2 different type malfunctions
:
| • | Stator assembly freewheels in both directions. |
| • | Stator assembly remains locked up at all times. |
Condition A - Poor Acceleration Low Speed
The vehicle tends to have poor acceleration from a stand still. At speeds above
50-55 km/h (30-35 mph), the vehicle may act normal. If poor
acceleration is noted, it should first be determined that the exhaust system is not
blocked, and the transaxle is in 1st gear when starting out.
If the engine freely accelerates to a high RPM in neutral (N), it can
be assumed that the engine and exhaust system are normal. Checking for poor performance
in drive and reverse will help determine if the stator is freewheeling at all times.
Condition B - Poor Acceleration High Speed
The engine RPM and vehicle speed is limited or restricted at high speeds. The
performance when accelerating from a standstill is normal. The engine may overheat.
Visual examination of the converter may reveal a blue color from overheating.
If the converter has been removed, the stator roller clutch can be inspected
by inserting 2 fingers into the splined inner race of the roller clutch and trying
to turn freely clockwise, but not turn or be very difficult to turn counter clockwise.
Noise
Torque converter whine is usually noticed when the vehicle is stopped and the
transaxle is in drive or reverse. The noise will increase when engine RPM is increased.
The noise will stop when the vehicle is moving or when the torque converter clutch
is applied 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 a 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.
- Press the accelerator to approximately 1,200 RPM for no
more than 6 seconds.
A torque converter noise will increase under this load.
Important: This noise should not be confused with pump whine noise which is usually noticeable
in park (P), neutral (N), and all other gear ranges. Pump whine will vary with
pressure ranges.
The torque converter should be replaced under any of the following conditions:
| • | External leaks in the hub weld area |
| • | The Converter hub is scored or damaged. |
| • | The converter pilot is broken, damaged, or fits poorly into the crankshaft. |
| • | Steel particles are found after flushing the cooler and cooler lines. |
| • | The Pump is damaged or steel particles are found in the converter. |
| • | The vehicle has TCC shudder and/or no TCC apply. Replace only after all
hydraulic and electrical diagnoses have been made. Lock up clutch material may be
glazed. |
| • | The converter has an imbalance which cannot be corrected. |
| • | The converter is contaminated with engine coolant containing antifreeze. |
| • | Internal failure of stator roller clutch |
| • | Heavy clutch debris due to overheating, blue converter |
| • | Steel particles or clutch lining material found in fluid filter or on
magnet when no internal parts in unit are worn or damaged indicates that lining material
came from converter. |
The torque converter should not be replaced if:
| • | The oil has an odor, is discolored, and there is no evidence of metal
or clutch facing particles. |
| • | The threads in one or more of the converter bolt holes are damaged. Correct
with thread insert. |
| • | Transaxle failure did not display evidence of damage or worn internal
parts, steel particles, or clutch plate lining material in unit and inside the fluid
filter. |
| • | The vehicle has been exposed to high mileage, only. The exception may
be where the lock up clutch damper plate lining has seen excess wear by vehicles operated
in heavy and/or constant traffic, such as taxi, delivery, or police use. |
