Solving Pilot Control Slop on the John Deere 35D

[MikePhua]

The John Deere 35D mini excavator is a versatile and reliable piece of equipment used in a variety of construction and landscaping tasks. As with any piece of machinery, wear and tear can eventually cause issues that may affect its performance. One common problem reported by operators of the John Deere 35D is slop in the pilot controls, which can compromise the machine's precision and response time. This article will delve into the causes of pilot control slop, how to diagnose it, and offer practical solutions to resolve the issue.
Understanding Pilot Controls
Pilot controls are hydraulic systems used in modern excavators to control the movement of the boom, arm, bucket, and swing functions. These controls are typically more sensitive and easier to use than traditional mechanical controls, offering smoother operation and better precision. They operate using hydraulic pressure to move valves that control the machine’s movements.
Over time, the pilot control system can develop "slop" or unwanted movement within the controls. This can manifest as excessive play or delayed response in the joystick or levers, making it difficult for the operator to achieve fine control of the excavator.
Causes of Pilot Control Slop
Pilot control slop on the John Deere 35D can be caused by several factors, many of which are related to wear and improper maintenance. The following are some of the most common causes of this issue:
1. Worn Pilot Control Valve Seals

• What It Means: The pilot control system uses valves to direct hydraulic flow to various parts of the machine. If the seals in these valves wear out over time, hydraulic fluid can leak, causing reduced pressure and leading to slop in the controls.
  
• Symptoms: If you notice inconsistent response when moving the joysticks, or if the joystick feels "loose" or overly sensitive, it could be due to worn pilot valve seals.
  

2. Dirty or Contaminated Hydraulic Fluid

• What It Means: Hydraulic systems rely on clean fluid to operate smoothly. If the hydraulic fluid becomes contaminated with dirt, debris, or water, it can cause friction and restrict the proper flow of fluid through the system.
  
• Symptoms: The controls may become sluggish, and you may notice irregular or erratic movements of the boom or arm. Contaminated fluid can also cause overheating, which can worsen the issue.
  

3. Pilot Pressure Imbalance

• What It Means: The pilot pressure system is responsible for sending hydraulic fluid to the control valves. If there is an imbalance in pressure, typically caused by a faulty pressure regulator or pump, it can lead to inconsistent control responses.
  
• Symptoms: Operators may experience a delay or hesitation in control inputs, making it difficult to operate the machine precisely. Pilot pressure imbalances can also cause excessive wear on the control system components.
  

4. Wear in Control Linkages

• What It Means: The physical linkages connecting the operator’s controls to the pilot valve system can wear out over time, causing play or slop in the system.
  
• Symptoms: You may notice that the joysticks or levers feel loose or have too much range of motion without corresponding movement in the machine.
  

5. Faulty Pilot Control Valve

• What It Means: The pilot control valve is the central component in the hydraulic circuit that interprets the operator’s input and converts it into hydraulic pressure. If the valve is worn out or malfunctioning, it can lead to slop in the controls.
  
• Symptoms: If the valve itself is malfunctioning, operators may experience inconsistent operation or delays in the movement of the boom or bucket.
  

Diagnosing the Issue
Diagnosing pilot control slop can sometimes be challenging because the causes may not always be immediately visible. Here are the steps to properly diagnose the issue:
1. Check the Hydraulic Fluid

• Ensure the fluid is clean and at the proper level. If the fluid looks dirty, replace it with fresh, manufacturer-recommended fluid.
  
• Check for water contamination or debris in the fluid, which can indicate that the hydraulic system needs a more thorough cleaning.
  

2. Inspect the Pilot Control Valve

• Look for signs of wear or damage in the valve. Check for leaks or inconsistent hydraulic pressure when the controls are in use. Using a pressure gauge can help measure the pressure at various points in the hydraulic system.
  
• If you suspect a problem with the valve, consider replacing the seals or the entire valve assembly.
  

3. Test Pilot Pressure

• Using a pilot pressure gauge, check the system's pressure readings. Low or fluctuating pressure can point to problems with the regulator or pump. Ensure the pressure is within the specifications provided by John Deere.
  

4. Inspect Control Linkages

• Examine the linkages connecting the joysticks or levers to the pilot valve. Check for any loose, bent, or worn components that could introduce play in the controls.
  
• Tighten or replace any parts as necessary to restore proper function.
  

5. Check for External Leaks

• Inspect the entire hydraulic system for leaks, particularly around the pilot control valve and associated hydraulic lines. Any leaks can compromise the performance of the system and contribute to slop in the controls.
  

Solutions to Fix Pilot Control Slop
Once you've identified the cause of the pilot control slop, here are some solutions to fix the issue:
1. Replace Worn Pilot Valve Seals

• If the seals in the pilot valve are worn or damaged, replacing them is essential. Be sure to use OEM parts to ensure compatibility and performance. This will restore the hydraulic pressure and eliminate the slop.
  

2. Flush and Replace Hydraulic Fluid

• If the fluid is contaminated or dirty, drain and replace it with clean, high-quality hydraulic fluid. Flushing the system will help remove contaminants that may be causing friction or blockage.
  

3. Adjust Pilot Pressure

• If pilot pressure is too low, check the regulator and pump. Replacing a faulty pump or adjusting the pressure regulator can help restore the system to normal function and remove any hesitation or slop in the controls.
  

4. Repair or Replace Control Linkages

• If there is excessive play in the linkages, tightening or replacing them will eliminate the slop. Regular maintenance of these parts can help prevent wear and ensure precise control.
  

5. Replace the Pilot Control Valve

• If the valve itself is malfunctioning, replacing it is often the best solution. Consult your John Deere dealer for the correct part numbers and installation instructions.
  

Preventive Maintenance to Avoid Slop Issues
To prevent pilot control slop from reoccurring, it’s important to follow a regular maintenance schedule for the hydraulic system. Here are some tips for keeping the pilot control system in optimal condition:

• Regularly inspect the hydraulic fluid: Keep the fluid clean and at the proper level. Replace the fluid as recommended in the operator’s manual.
  
• Check for leaks: Periodically inspect the hydraulic system for leaks, especially around the pilot control valve and linkages.
  
• Test the hydraulic pressure: Regularly monitor pilot pressure to ensure it remains within the recommended range.
  
• Lubricate control linkages: Keep the linkages well-lubricated and replace worn components to maintain smooth operation.
  

Conclusion
Pilot control slop on the John Deere 35D mini excavator can be a frustrating issue for operators, but it is generally preventable and repairable with the right diagnostic approach. By regularly maintaining the hydraulic system, checking for contamination, and addressing any worn components early, you can keep your excavator performing at its best. Whether it’s replacing seals, adjusting pressure, or cleaning the system, taking the time to fix pilot control slop will ensure smoother, more precise operations, leading to increased productivity and less downtime on the job.