Diagnosing Jumpy Forward Motion in the Gehl 4835 Skid Steer

[MikePhua]

The Gehl 4835 and Its Mechanical Design
The Gehl 4835 SXT skid steer loader was introduced in the late 1990s as part of Gehl’s compact equipment lineup, designed for contractors, landscapers, and agricultural users. With a rated operating capacity of approximately 1,650 lbs and powered by a 60-horsepower diesel engine, the 4835 featured a hydrostatic drive system and dual joystick controls for steering and loader operation. Its popularity stemmed from its rugged frame, responsive hydraulics, and ease of maintenance.
Gehl, founded in 1859 in Wisconsin, built its reputation on agricultural machinery before expanding into construction equipment. The 4835 was part of a broader push into the skid steer market, competing with Bobcat, Case, and New Holland. Thousands of units were sold across North America, and many remain in service today due to their mechanical simplicity and parts availability.
Symptoms of Jumpy Forward Motion
Operators have reported a rhythmic surging or “high-low” sensation when traveling forward in the 4835. This jumpiness often disappears when carrying a load or when the steering handle is held in a precise position. The issue is typically isolated to forward travel and does not affect reverse or loader functions.
Common symptoms include:

• Uneven acceleration in forward motion
  
• Machine lurching or pulsing under light load
  
• Smooth operation when bucket is loaded
  
• Sensitivity to joystick position
  

These symptoms suggest a control imbalance or hydraulic inconsistency in the drive circuit, particularly affecting one side of the propulsion system.
Hydrostatic Drive System and Steering Control
The Gehl 4835 uses a dual hydrostatic drive system, where each side of the machine is powered by a separate hydraulic motor. Steering is achieved by varying the flow to each motor via joystick input. The joysticks are mechanically linked to control valves that modulate hydraulic pressure and direction.
Key components include:

• Drive pumps: Variable displacement pumps supplying flow to wheel motors
  
• Wheel motors: Hydraulic motors driving each side independently
  
• Control valves: Regulate flow based on joystick input
  
• Linkage rods: Connect joystick movement to valve actuation
  

If one side’s control valve or linkage is misaligned, it can cause uneven flow, resulting in surging or jumpy motion.
Potential Causes and Field Diagnosis
Several mechanical and hydraulic issues can contribute to the jumpy behavior:

1. Joystick Linkage Misalignment
   
   1. Over time, the mechanical linkage between the joystick and control valve can wear or shift. If the linkage is slightly off-center, the valve may not open smoothly, causing inconsistent flow. This explains why holding the joystick in a precise position temporarily resolves the issue.
      
   2. Hydraulic Flow Imbalance
      
   3. If one drive pump or motor is delivering slightly more or less flow than the other, the machine may surge as the system compensates. This can be caused by:
      • Internal wear in the pump or motor
        
      • Air in the hydraulic lines
        
      • Contaminated fluid or clogged filters
        
   4. Load Compensation Behavior
      
   5. The machine may behave more smoothly under load because the hydraulic system stabilizes with increased resistance. This suggests that the issue is more pronounced during low-pressure operation, pointing to a control sensitivity problem rather than a mechanical fault.
      
   6. Valve Spool Wear or Binding
      
2. The control valve spools may be worn or sticky, especially if the machine has high hours or has been exposed to dirt and moisture. A sticky spool can cause erratic flow changes, leading to surging.
   

Recommended Inspection and Solutions
To address the issue:

• Inspect joystick linkage for wear, looseness, or misalignment
  
• Clean and lubricate all pivot points and bushings
  
• Check hydraulic fluid level and condition; replace if discolored or contaminated
  
• Replace hydraulic filters and bleed the system to remove air
  
• Test drive pumps and motors for flow consistency using a flow meter
  
• Inspect control valve spools for smooth movement and signs of scoring
  

If the issue persists, consider swapping joystick linkages side-to-side to isolate whether the problem follows the control or remains with the drive motor.
Anecdote from the Upper Midwest
A snow removal contractor in Minnesota experienced similar symptoms with his Gehl 4835 during light travel between job sites. The machine surged forward unpredictably unless the bucket was loaded with salt. After inspecting the joystick linkage, he found that one rod had worn a notch into its pivot bracket, causing uneven valve actuation. A quick weld and file job restored the bracket, and the machine returned to smooth operation. He now checks linkage alignment monthly during winter prep.
Preventive Maintenance and Long-Term Reliability
To maintain consistent drive performance:

• Lubricate joystick linkages every 100 hours
  
• Replace hydraulic fluid every 500 hours or annually
  
• Inspect valve spools and drive motors during seasonal service
  
• Monitor machine behavior under varying loads to detect early signs of imbalance
  

The Gehl 4835’s mechanical controls are durable but require periodic adjustment to maintain precision. Unlike newer machines with electronic drive-by-wire systems, the 4835 relies on physical linkages that can drift over time.
Conclusion
Jumpy forward motion in the Gehl 4835 is often caused by minor misalignments or wear in the joystick linkage and control valve system. While the symptoms may seem erratic, they typically stem from predictable mechanical causes. With careful inspection and routine maintenance, operators can restore smooth travel and extend the life of this dependable skid steer. The 4835 remains a workhorse in the field, and its quirks are part of what makes it a favorite among seasoned operators.