CAT 120G Transmission Problems: Diagnosis and Solutions

[MikePhua]

Introduction: Understanding the Transmission Issue
The CAT 120G motor grader is a reliable piece of equipment used in road construction, grading, and other heavy-duty tasks. However, one common issue that operators may encounter is transmission problems. These problems can manifest in several ways, such as difficulty shifting gears, slipping gears, or a complete failure of the transmission. In this article, we will discuss the potential causes of transmission problems in the CAT 120G and provide solutions to help resolve the issue and keep your machine running smoothly.
Common Symptoms of Transmission Problems
Before delving into the causes, it's important to identify the symptoms that indicate transmission issues in the CAT 120G. Common signs of a failing transmission include:

• Slipping Gears: The grader may unexpectedly shift out of gear or fail to stay in gear.
  
• Hard Shifting: Difficulty shifting between gears, often accompanied by grinding or resistance.
  
• Loss of Power: The machine may lose power, especially when moving uphill or under load.
  
• Unusual Noises: Grinding or whining noises from the transmission when engaging or shifting gears.
  
• Erratic Speed Changes: The grader may exhibit uneven acceleration or deceleration, particularly when transitioning between gears.
  

Possible Causes of Transmission Problems

1. Low or Contaminated Transmission Fluid
   

Transmission fluid is essential for proper gear lubrication and hydraulic operation in the CAT 120G. Low or contaminated fluid can cause the transmission to perform poorly, leading to slipping gears, hard shifting, and overheating.
Solution: Check the transmission fluid levels and condition regularly. If the fluid is low, top it up with the correct type of fluid. If the fluid is dirty or contaminated, perform a fluid change and replace the filters to maintain smooth operation.

1. Worn or Damaged Clutch Packs
   

Clutch packs are responsible for engaging and disengaging the gears in the transmission. Over time, the clutch packs can wear out, leading to slipping or difficulty shifting gears.
Solution: Inspect the clutch packs for signs of wear or damage. If the clutch packs are worn, they may need to be replaced to restore proper function and prevent further transmission issues.

1. Faulty Transmission Solenoid
   

The transmission solenoid controls the flow of hydraulic fluid to various parts of the transmission system. A malfunctioning solenoid can cause improper shifting or failure to shift at all, leading to erratic behavior from the transmission.
Solution: Test the transmission solenoid for proper operation. If the solenoid is malfunctioning, it should be replaced to restore normal transmission function.

1. Damaged Transmission Pump
   

The transmission pump is responsible for circulating hydraulic fluid throughout the transmission system. A failing pump can cause low hydraulic pressure, leading to slipping gears and poor shifting performance.
Solution: If you suspect the transmission pump is faulty, perform a pressure test to check its output. If the pump is not generating the required pressure, it may need to be replaced or repaired.

1. Internal Transmission Damage
   

In some cases, the transmission may experience internal damage, such as broken gears, damaged shafts, or worn bearings. This can lead to a complete failure of the transmission if not addressed promptly.
Solution: If internal transmission damage is suspected, a complete disassembly of the transmission is required for inspection and repair. In many cases, this may involve replacing damaged components or rebuilding the transmission.
Steps for Diagnosing and Fixing Transmission Issues

1. Check Fluid Levels and Condition
   

Start by checking the transmission fluid levels. If the fluid is low, top it up with the correct type of fluid. If the fluid appears dirty or contaminated, perform an oil change and replace the transmission filter to ensure proper fluid flow.

1. Inspect the Clutch Packs
   

Examine the clutch packs for signs of wear, such as slipping or overheating. If the clutch packs are damaged, they will need to be replaced to prevent further transmission issues.

1. Test the Transmission Solenoid
   

If shifting problems persist, test the transmission solenoid to ensure it is functioning correctly. If the solenoid is faulty, replace it with a new one to restore proper shifting.

1. Check the Transmission Pump
   

Perform a pressure test on the transmission pump to ensure it is generating the necessary hydraulic pressure. If the pump is not functioning correctly, it will need to be repaired or replaced.

1. Inspect for Internal Damage
   

If all external components appear to be in good condition, and the problem persists, internal transmission damage may be the issue. In this case, disassemble the transmission and inspect all internal parts for damage. Replace any broken or worn components.
Preventive Maintenance Tips
To prevent future transmission problems in the CAT 120G, regular maintenance is essential:

• Regular Fluid Checks: Check the transmission fluid levels and condition frequently. Replace fluid and filters as per the manufacturer’s maintenance schedule to ensure smooth operation.
  
• Inspect the Clutch and Solenoid: Periodically check the clutch packs and transmission solenoid for wear and functionality.
  
• Monitor Transmission Performance: Keep an eye out for any symptoms of transmission issues, such as slipping or hard shifting, and address them promptly before they worsen.
  
• Hydraulic System Maintenance: Ensure the hydraulic system is properly maintained, as hydraulic issues can directly affect transmission performance.
  

Conclusion: Keeping the CAT 120G Transmission in Top Condition
Transmission problems in the CAT 120G can be caused by various issues, from low fluid levels to internal damage. By regularly checking the fluid, inspecting key components like the clutch packs and solenoid, and addressing any signs of wear or malfunction, operators can prevent costly repairs and extend the lifespan of the transmission. Regular maintenance and early detection of problems are key to keeping the CAT 120G motor grader operating efficiently and reliably for years to come.