Transmission torque converter lockup issues can be a complex and frustrating problem for vehicle owners and mechanics alike. These issues can manifest in various ways, such as the converter not staying locked, cycling between locked and unlocked states, or slipping under heavy acceleration. Understanding the underlying causes and implementing the right diagnostic and repair strategies is crucial for resolving these problems effectively.
Diagnosing Torque Converter Lockup Issues
Measuring the Speed Ratio Across the Converter
One of the key steps in diagnosing torque converter lockup issues is to measure the speed ratio across the converter. This can be done using specialized diagnostic equipment, such as a transmission scan tool or a dynamometer. By measuring the input and output speeds of the converter, you can determine if the lock-up clutch is functioning correctly.
The ideal speed ratio across a locked torque converter should be close to 1:1, indicating that the input and output speeds are nearly identical. If the speed ratio deviates significantly from this, it may indicate a problem with the lock-up clutch, such as slippage or improper engagement.
Example Speed Ratio Measurements:
– Fully locked converter: Speed ratio of 0.95 to 1.05
– Partially locked converter: Speed ratio of 0.80 to 0.95
– Unlocked converter: Speed ratio of 0.60 to 0.80
Analyzing Misfire Counts and Transmission Tables
In some cases, torque converter lockup issues may be related to the transmission’s misfire tables. Incorrect or outdated misfire tables can lead to slip and improper lock-up behavior. To address this, you’ll need to correct the misfire tables in the transmission’s tune or programming.
Additionally, the partial lockup function engineered into some transmissions can also contribute to converter shudder, premature converter clutch failure, and diagnostic trouble codes (DTCs) such as code 1870. This partial lockup function can affect performance and lead to teeth-cracking shifts at low throttle. To prevent these issues, it’s recommended to configure the transmission tables to allow lock-up only in specific gears and under certain conditions.
Example Transmission Table Configurations:
– Allow lock-up in 4th and 5th gears only
– Enable lock-up only above a certain engine load or speed threshold
– Disable partial lockup functions to prevent shudder and premature clutch failure
Resolving Torque Converter Lockup Issues
Adjusting Converter Lock vs. Unlock Points
One common cause of torque converter lockup issues is the converter lock and unlock points being too close together. This can result in the converter cycling between locked and unlocked states, leading to performance problems and potential damage to the transmission components.
To address this, you’ll need to adjust the converter lock and unlock points in the transmission’s programming or calibration. This may involve modifying the transmission control module (TCM) or engine control module (ECM) parameters to ensure a wider separation between the lock and unlock thresholds.
Example Converter Lock/Unlock Point Adjustments:
– Increase the lock point by 100 RPM
– Decrease the unlock point by 100 RPM
– Ensure a minimum 200 RPM difference between lock and unlock points
Configuring Transmission Tables for Optimal Lockup
As mentioned earlier, properly configuring the transmission tables to allow lock-up only in specific gears and under certain conditions can help improve performance and reliability. This approach can also increase low-speed fuel efficiency by reducing the amount of time the converter is in a partially locked or unlocked state.
When configuring the transmission tables, consider the following factors:
– Engine load and speed thresholds for lock-up engagement
– Gear-specific lock-up settings (e.g., lock-up in 4th and 5th gears only)
– Disabling partial lockup functions to prevent shudder and premature clutch failure
By carefully tuning the transmission tables, you can ensure that the torque converter lock-up function operates as intended, providing optimal performance and fuel efficiency while minimizing the risk of related issues.
Conclusion
Addressing transmission torque converter lockup issues requires a comprehensive understanding of the transmission’s operating parameters, the torque converter’s behavior, and the use of appropriate diagnostic equipment and techniques. By measuring the speed ratio across the converter, analyzing misfire counts and transmission tables, and properly configuring the lock-up settings, you can effectively diagnose and resolve these complex problems, ensuring optimal transmission performance and reliability.
References:
- 700 R4 Lock Up Converter Problems
- Torque Converter Lockup Issue
- Torque Converter Lock Up Clutch Problem or Something New
- Torque Converter Lock Up
- Problems with Torque Converter Lockup
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