John Deere 672G Circle Drive Problems and Field Repair Insights

[MikePhua]

The 672G and Its Role in Precision Grading
The John Deere 672G motor grader was introduced as part of Deere’s G-Series lineup, designed for road maintenance, site preparation, and fine grading. With an operating weight of over 42,000 lbs and powered by a 225 hp Tier 4 Final engine, the 672G features a six-wheel drive system, advanced load-sensing hydraulics, and electronic blade control. Deere, founded in 1837, has sold thousands of G-Series graders globally, with the 672G becoming a preferred choice for municipalities and contractors seeking reliability and precision.
At the heart of its grading performance is the circle drive system—a mechanism that rotates the moldboard to adjust blade angle during operation. When this system fails or behaves erratically, grading efficiency drops and component wear accelerates.
Terminology Note

• Circle Drive: A gear-driven system that rotates the moldboard (blade) around its center pivot.
  
• Moldboard: The curved blade used to cut, spread, and shape material.
  
• Slip Clutch: A protective device that limits torque to prevent gear damage.
  
• Circle Gear: A large ring gear that interfaces with the drive pinion to rotate the moldboard.
  

Common Symptoms of Circle Drive Failure
Operators may encounter several issues with the circle drive system:

• Moldboard rotation stalls or hesitates under load
  
• Audible grinding or clicking during blade movement
  
• Circle fails to hold position during grading
  
• Excessive backlash or play in the blade angle
  
• Fault codes related to hydraulic or electrical control
  

In one case, a 2015 672G began slipping during moldboard rotation, especially when cutting compacted gravel. The operator noticed that the blade would rotate partially, then stop abruptly, accompanied by a loud pop. Inspection revealed wear in the slip clutch and contamination in the circle gear housing.
Inspection and Diagnostic Strategy
To diagnose circle drive issues:

• Check hydraulic pressure to the circle motor
  
• Inspect the slip clutch for wear or improper adjustment
  
• Examine the circle gear teeth for pitting or deformation
  
• Test the electronic control system for fault codes
  
• Verify moldboard alignment and pivot resistance
  

Recommended tools:

• Hydraulic test kit with pressure gauges
  
• Torque wrench for clutch adjustment
  
• Inspection camera for gear housing
  
• Diagnostic laptop with Deere Service Advisor software
  

A technician in Alberta used a borescope to inspect the circle gear teeth and discovered metal shavings from a chipped pinion. Replacing the gear and flushing the housing resolved the issue.
Slip Clutch Behavior and Adjustment
The slip clutch protects the circle gear from overload. If set too loose, it slips prematurely; if too tight, it risks gear damage. Proper adjustment involves:

• Measuring torque resistance during rotation
  
• Setting clutch preload to factory spec (typically 300–400 ft-lbs)
  
• Inspecting clutch plates for glazing or wear
  
• Replacing springs and friction discs if out of tolerance
  

A contractor in Georgia found that adjusting the clutch preload restored smooth moldboard rotation and eliminated the popping noise during grading.
Hydraulic and Electrical Integration
The circle drive motor is hydraulically powered and electronically controlled. Faults may arise from:

• Low hydraulic flow due to clogged filters or worn pump
  
• Electrical signal loss from damaged harnesses
  
• Sensor misalignment affecting blade position feedback
  
• Software mismatch after firmware updates
  

Solutions include:

• Replacing hydraulic filters and checking pump output
  
• Inspecting wiring near articulation joints
  
• Calibrating blade position sensors
  
• Updating control module software
  

A fleet in British Columbia upgraded their 672G firmware and saw improved blade responsiveness and fewer fault codes during slope grading.
Preventive Maintenance and Component Longevity
To extend circle drive life:

• Grease the circle gear daily using high-pressure fittings
  
• Inspect clutch and gear housing every 500 hours
  
• Flush hydraulic fluid annually
  
• Monitor blade rotation torque during operation
  
• Avoid rotating the moldboard under heavy load or while stationary
  

A municipality in Maine added torque checks to their seasonal maintenance and reduced circle gear failures by 60% over three years.
Operator Stories and Field Wisdom
A grader operator in New Zealand noticed his blade drifting during finish passes. After checking the circle drive, he discovered that the slip clutch had worn unevenly. Replacing the clutch and realigning the moldboard restored full control and improved grading accuracy.
Meanwhile, a technician in Texas rebuilt the circle gear housing after water intrusion caused rust and gear pitting. He installed a new seal kit and added a drain port to prevent future accumulation. The machine returned to service with quieter operation and smoother blade rotation.
Conclusion
Circle drive issues in the John Deere 672G can stem from mechanical wear, hydraulic inconsistencies, or electronic faults. With structured diagnostics, proper clutch adjustment, and preventive maintenance, most problems can be resolved without major teardown. In a machine built for precision, the circle drive is the pivot point of performance. Keeping it healthy means keeping the grade sharp, the blade responsive, and the operator in control.