Transmission removal and replacement (R&R) is a critical task that requires precision, expertise, and attention to detail. For auto technicians and mechanics, understanding the intricacies of adaptive strategies, fluid procedures, and road testing is essential to ensure successful repairs and satisfied customers. This guide will walk you through the “do’s and don’ts” of transmission R&R, covering key aspects such as adaptive strategies, cooler flushing, fluid fill procedures, test drives, and troubleshooting.
ADAPTIVE STRATEGIES FOR TRANSMISSION LEARNING
One of the most overlooked complexities in transmission replacement is ensuring the vehicle properly “learns” the new unit. Many vehicles, especially those from GM and Toyota, employ adaptive strategies to adjust themselves to the new transmission. Failure to reset and relearn these systems properly can lead to harsh shifting or even premature transmission damage.
DO’S:
- Perform Proper Resets: Always reset the Powertrain Control Module (PCM) through the correct procedure. For example:
- Ford: Disconnect the battery for five minutes, turn the key on, and touch the battery cables together (Known as KAM reset). Some Ford models, like the AF21-B, disconnect the battery for 20 minutes.
- GM with Allison LCT 1000 Transmission: Use a scan tool to initiate the FastLearn process and follow its driving instructions to recalibrate the system.
- Toyota and Lexus “U” Series Transaxles: Execute a PCM memory reset using a scan tool.
- Test Drive Properly Post-Reset: Make sure you follow specific relearn drive cycles as recommended by the manufacturer to ensure smooth operation.
DON’TS:
- Skip the Reset: Skipping the reset can result in inefficient learning, leading to rough shifts and potentially damaged internal components.
- Ignore Manufacturer Instructions: Each vehicle model may have different procedures. Ignoring these specific instructions can void warranties or lead to unnecessary repairs.
FLUSHING THE TRANSMISSION AND COOLER
Transmission and cooler flushing have become standard practices during overhauls and repairs. However, while beneficial in many scenarios, improper or unnecessary flushing can cause more harm than good.
DO’S:
- Flush System Correctly: Use dedicated flushing equipment for accurate and thorough flushing.
- Encourage Routine Fluid Exchanges: Advise customers to follow regular fluid exchange schedules (annually is recommended).
- Replace Failed Coolers: If a cooler fails or is clogged, replace it immediately to avoid contaminating the new transmission.
DON’TS:
- Flushing High-Mileage Vehicles: Avoid flushing vehicles with high mileage if they have never been serviced. New fluid can cause damaged clutches in older transmissions to fail prematurely.
- Reuse Faulty Coolers: A cooler is either good or bad. Reusing a failing cooler can contaminate the transmission and lead to repeat failures.
- Ignore Cooler Failures: A clogged or damaged cooler can result in transmission overheating and eventual failure.
KEY PROS AND CONS OF FLUSHING
PROS:
- Minimal mess for technicians.
- There is no need to replace the pan gasket.
- It can save time during repairs.
CONS:
- Does not allow inspection of debris in the transmission pan.
- May push debris or contaminants into the cooler.
- It can damage worn clutches in older transmissions.
- Proper Fluid Fill Procedures
- Ensuring the correct transmission fluid level is critical to the performance and longevity of the transmission. Low or incorrectly filled fluid can lead to catastrophic failures.
DO’S:
- Check the Dipstick Regularly: Refer to manufacturer guidelines for correct fluid levels during idle operation.
- Ensure Every Compartment is Properly Filled: Check the sump and other regions where the fluid is used to ensure adequate lubrication.
DON’TS:
- Ignore Warning Signs of Low Fluid: If the transmission runs low, it causes cavitation (air in the fluid), overheating, and eventual failure.
- Overfill the System: Overfilling can lead to aeration, causing erratic performance and damage.
RULES FOR EFFECTIVE TEST DRIVES
Post-repair test drives are crucial to diagnosing and verifying the success of transmission repairs. Following proper testing procedures saves time and ensures high-quality results.
DO’S:
- Recreate the Customer’s Concern: Whenever possible, have the customer demonstrate the issue so you can properly assess it.
- Perform Preliminary Tests: Complete pressure and cooler flow tests to rule out more straightforward issues before removing the transmission.
- Test in All Driving Conditions: Drive in every range, adjust throttle positions, and try scenarios like bypassing the cooler or manipulating the EPC with a scan tool.
DON’TS:
- Remove the Transmission Prematurely: Never remove the unit until you are confident about the root cause of the issue and whether it is within the transmission itself.
- Ignore Computer Systems: For computer-controlled transmissions, check the system for Diagnostic Trouble Codes (DTCs) and monitor signal wires to determine if the issue lies outside the transmission.
TIPS FOR AN ON-LIFT TEST:
- Push or pry on servo covers while monitoring for movement.
- Tighten the bands completely for temporary testing.
- Run the system with no oil for 5–10 seconds (only for diagnosing specific neutral movement issues).
- Troubleshooting Challenges
- Dealing with recurring failures or unique issues like clutch or band burns requires understanding the cause. Burnt clutches or bands are typically caused by:
- Insufficient pressure to support the load, which could result from leaks or low line pressure.
- Shifting into a bind-up, where components engage when they shouldn’t (e.g., due to cross leaks).
AVOID RECURRING PROBLEMS:
Reassess repair techniques and ensure you’re following manufacturer-approved procedures.
Replace any faulty parts that could reproduce failures, such as incorrect valve body gaskets for a specific application.
ELECTRICAL CHECKS AND ADD-ON WORK
Electronic issues often contribute to transmission failures, especially in modern vehicles with PCM-controlled units.
DO’S:
- Check the Grounding System: Ensure proper grounding between the engine, transmission, and frame to avoid short circuits.
- Diagnose Electrical Signals: A weak or improperly connected battery can severely affect electronically shifted transmissions.
DON’TS:
- Neglect Brake Light Circuits: For example, in a Ford F450, low brake light resistance can prevent proper torque converter lock-up by not triggering the PCM.
Removing and replacing a transmission involves much more than simply swapping out parts. From understanding adaptive strategies to flushing systems and conducting thorough test drives, every detail matters. Following these do’s and don’ts ensures your work is efficient, reliable, and performed to the highest standard.
Looking to elevate your skills and minimize costly mistakes? Stay informed, follow manufacturer guidelines, and strive to refine your techniques with each repair. Your attention to detail is what keeps vehicles running smoothly and customers driving away satisfied.
