Left Track Reversing in Forward Motion: Troubleshooting the John Deere 750C Series I LGP

[MikePhua]

The John Deere 750C Series I LGP (Low Ground Pressure) dozer is a powerful piece of heavy machinery used in various applications, including land clearing, grading, and construction. However, like all machinery, it can encounter operational issues, one of which is when the left track begins to reverse while the machine is in forward motion. This problem can be frustrating for operators, as it affects the machine's overall performance and can lead to inefficiencies in operations.
In this article, we’ll explore the potential causes behind this issue, discuss troubleshooting steps, and provide solutions to help restore the John Deere 750C LGP to full functionality.
Understanding the Problem: Left Track Reversing While in Forward
When the left track of the John Deere 750C LGP starts to move in reverse while the machine is in forward gear, it can be caused by several issues related to the drivetrain or the control system. This problem not only causes difficulty in maneuvering the dozer but can also lead to increased wear and tear on the tracks, final drive, and other components.
To effectively address this issue, it’s important to understand the key systems involved, including the hydraulic system, the transmission, and the final drive. Each of these systems plays a critical role in ensuring that the tracks move as expected.
Possible Causes of Left Track Reversing in Forward Motion

1. Hydraulic System Issues
   The John Deere 750C LGP relies on a complex hydraulic system to control the movement of its tracks. If there is an issue with the hydraulic flow to the left track, it can cause erratic behavior, including the track moving in reverse.
   • Hydraulic Control Valve Malfunction: The control valve directs hydraulic fluid to the appropriate track drive motor. If this valve is malfunctioning or worn out, it can send the wrong amount of fluid to the left track, causing it to reverse.
     
   • Hydraulic Pump Problems: If the hydraulic pump isn’t providing the correct pressure or flow, the track's drive motor may not receive the proper amount of hydraulic fluid, resulting in erratic or reversed movement.
     
   • Hydraulic Lines or Connections: Leaking or damaged hydraulic lines can also cause an uneven flow of hydraulic fluid, potentially leading to reverse motion in the track.
     
2. Final Drive Malfunction
   The final drive is the component responsible for converting the power from the engine and transmission into rotational movement for the tracks. A malfunction in the final drive system could cause the left track to reverse unexpectedly.
   • Internal Gear Damage: If there is internal damage to the gears or bearings in the final drive, the left track might not engage properly and could begin to reverse.
     
   • Final Drive Motor Issues: The motor that drives the tracks may have a malfunction, causing the hydraulic fluid to bypass or flow incorrectly, resulting in reverse motion.
     
3. Transmission Problems
   The transmission plays a vital role in controlling the direction and speed of the dozer. Issues in the transmission system, such as incorrect gear engagement or slipping clutches, could result in unintended movement, including reverse motion on one of the tracks.
   • Gearshift Malfunction: If the gearshift system isn't fully engaging or disengaging the gears properly, the system might send the wrong signals, causing the left track to reverse while the rest of the machine moves forward.
     
   • Clutch Problems: In some models, a failing clutch could cause one side of the drive system to engage incorrectly, leading to a situation where one track moves in the opposite direction.
     
4. Control System Issues
   The control system, which includes the joystick or steering levers, is responsible for transmitting the operator’s commands to the hydraulic and drivetrain systems. A fault in the electronic or mechanical parts of the control system could cause an unintended response, such as one track moving in reverse.
   • Control Valve Wear: Over time, the valves that control the track speed and direction can wear, resulting in inaccurate or uncommanded movements.
     
   • Wiring or Sensor Issues: A malfunctioning sensor or wiring issue can lead to incorrect feedback from the control system, causing one track to move in reverse.
     

Troubleshooting Steps

1. Inspect Hydraulic System
   Start by checking the hydraulic system for any signs of leaks, wear, or blockages. Look for damage to the hydraulic lines and fittings, and check the hydraulic fluid levels. If any of these components are faulty, replacing or repairing them may resolve the issue.
   • Test the hydraulic pressure to ensure the pump is working within the correct parameters.
     
   • Examine the hydraulic control valve and check for any signs of malfunction, such as excessive wear or sticking.
     
2. Examine the Final Drive
   Inspect the final drive components, including the gears and bearings, for signs of wear or damage. If the internal gears have become worn or damaged, the final drive may need to be rebuilt or replaced. Additionally, check the final drive motor for proper operation, ensuring it is receiving the correct flow of hydraulic fluid.
   
3. Check the Transmission and Clutches
   The next step is to inspect the transmission for proper gear engagement and clutch operation. Look for any signs of slipping or misalignment in the transmission components. If the transmission is not engaging correctly, the issue could be related to the gear shift linkage or internal components like the clutch packs.
   
4. Test the Control System
   Finally, check the control system for proper function. Inspect the wiring, sensors, and control valves to ensure they are transmitting the correct signals. Look for any corrosion, loose connections, or faulty components that could be causing the system to malfunction.
   

Solutions and Recommendations

• If the issue is related to the hydraulic system, replacing the hydraulic pump, control valve, or damaged hoses may resolve the issue. Make sure to use high-quality replacement parts and ensure the hydraulic fluid is in good condition.
  
• For final drive problems, consider rebuilding or replacing the final drive motor and checking the internal gears for wear. Be sure to replace any damaged seals or bearings that may be causing leaks or performance issues.
  
• Transmission problems may require a more in-depth inspection, and in some cases, a full transmission rebuild may be necessary. Ensure all clutches and gear components are properly functioning.
  
• If the control system is the culprit, replacing worn-out control valves or repairing faulty wiring should restore normal operation.
  

Conclusion
The issue of the left track reversing in forward motion on a John Deere 750C Series I LGP dozer can stem from several possible causes, including hydraulic system malfunctions, final drive issues, transmission problems, or control system faults. By following a systematic troubleshooting approach, you can identify and fix the root cause of the problem, ensuring that the dozer operates efficiently and safely. Regular maintenance and timely repairs will also help prevent similar issues from arising in the future.