Troubleshooting Arm Drift Issues in Bobcat 773 G with Hand Controls

[MikePhua]

The Bobcat 773 G is a widely recognized skid steer loader known for its power, compact size, and versatility. With a robust engine and a variety of attachments, it is commonly used for lifting, loading, digging, and even snow removal. However, like any piece of machinery, the Bobcat 773 G can experience operational issues. One such issue that operators sometimes encounter is when the arms, controlled by hand controls, drift downward despite being in a neutral or raised position. This article will explore the possible causes of this problem, provide troubleshooting steps, and offer solutions to fix the drifting arms.
Understanding the Bobcat 773 G and Its Hand Control System
The Bobcat 773 G is part of Bobcat’s G-series of skid steer loaders, featuring a hydraulic system designed to manage the machine’s lift arms, bucket, and other attachments. This system is controlled by a set of hand controls that allow the operator to precisely manipulate the lift arms, tilt the bucket, and engage auxiliary functions.
The hand control system uses hydraulic actuators, valves, and cylinders to perform these functions. Hydraulic fluid is pumped from the reservoir to the cylinders, which extend or retract depending on the operator’s commands. When the control system malfunctions, especially with issues like arms drifting downward, it can significantly affect the machine’s performance and safety.
What Causes the Arms to Drift Downward?
When the arms of the Bobcat 773 G begin to drift downward after being raised or while in a stationary position, it often indicates a problem with the hydraulic system. The root cause can be traced to one of several issues that affect the fluid pressure or the flow of hydraulic fluid. Below are the common causes of this problem:

1. Hydraulic Cylinder Seal Failure
   

The most common cause of drifting arms is the failure of seals within the hydraulic cylinders that control the lift arms. The seals are responsible for maintaining pressure in the cylinders to keep the arms in place. If the seals wear out or become damaged, hydraulic fluid can leak past them, causing the arms to slowly lower on their own.

1. Worn or Damaged Hydraulic Valve
   

The hydraulic valve that controls the flow of fluid to the lift arms could also be at fault. If the valve sticks or doesn’t properly shut off the flow of fluid when the operator releases the control lever, fluid will continue to flow, leading to unintended movement. A valve with worn-out seals can also cause leakage, resulting in drifting.

1. Hydraulic Fluid Contamination
   

Contaminated hydraulic fluid can cause problems in the hydraulic system, leading to erratic behavior like arm drift. Dirt, metal shavings, or moisture can interfere with the smooth operation of the hydraulic valves and cylinders, reducing the system's ability to maintain pressure and causing the arms to drift downward.

1. Damaged or Leaking Hydraulic Hoses
   

If the hydraulic hoses that carry fluid to the lift cylinders are damaged, worn, or leaking, they can cause a loss of hydraulic pressure. This loss of pressure will result in the arms not being able to stay in the desired position and will cause them to drift downward.

1. Internal Hydraulic Pump Issues
   

The hydraulic pump in the Bobcat 773 G is responsible for generating the pressure needed to operate the lift arms. If the pump is worn out or not operating at optimal pressure, it can lead to inconsistent fluid flow, which might result in drifting arms. While less common than other causes, a failing hydraulic pump could contribute to this issue.

1. Improper Hydraulic Fluid Levels
   

Low hydraulic fluid levels are another common cause of drifting arms. If the fluid is not at the proper level, the pump cannot generate enough pressure to keep the lift arms in place. Similarly, overfilled fluid levels can cause air to be trapped in the system, which may also lead to erratic movements.
How to Diagnose the Drifting Arm Issue
Diagnosing the drifting arm issue involves systematically checking each component of the hydraulic system. Here are the steps you can take to pinpoint the source of the problem:

1. Check Hydraulic Fluid Levels
   

Begin by checking the hydraulic fluid level in the Bobcat 773 G. Low fluid levels can lead to a loss of pressure in the hydraulic system, causing the arms to drift. Ensure that the fluid is clean and at the recommended level. If the fluid appears contaminated, it’s essential to change it.

1. Inspect Hydraulic Cylinders for Leaks
   

Visually inspect the hydraulic cylinders for any signs of leaks. Look for wet spots on the cylinder rods or around the seals. If you find leaks, the seals may need to be replaced. A pressure test can also be conducted on the cylinders to confirm if they are holding pressure correctly.

1. Examine the Hydraulic Control Valve
   

The control valve is responsible for directing hydraulic fluid to the lift cylinders. Check the valve for any signs of wear or damage. If the valve is not shutting off the fluid supply properly, it may need to be replaced. Ensure that the valve is operating smoothly when the hand controls are engaged.

1. Test for Hydraulic Hose Leaks
   

Inspect all hydraulic hoses for signs of wear, cracking, or leaks. If a hose is found to be leaking, it should be replaced immediately. Leaks can cause a significant loss of pressure, leading to drifting arms.

1. Inspect the Hydraulic Pump
   

While this issue is less likely to be caused by the hydraulic pump, it’s worth checking the pump’s performance. If the pump is not producing the correct pressure, it can contribute to problems with hydraulic function. The pump’s output can be tested with a pressure gauge to ensure it’s within specifications.

1. Look for Signs of Contamination
   

Check the hydraulic fluid for any signs of contamination, such as discoloration or the presence of particles. Contaminated fluid can clog valves, damage seals, and impair the operation of the hydraulic system. If contamination is detected, the fluid should be flushed, and the filter replaced.
Solutions to Fix the Drifting Arms
Once the root cause has been identified, the following solutions can be applied to fix the drifting arms:

1. Replace Worn Hydraulic Seals: If the seals in the hydraulic cylinders are found to be worn or damaged, they must be replaced to restore proper function. Replacing the seals will prevent hydraulic fluid from leaking and maintain pressure in the cylinders, stopping the drift.
   
2. Repair or Replace the Hydraulic Control Valve: If the control valve is faulty or not sealing properly, it should be repaired or replaced. This will ensure that hydraulic fluid is correctly directed to the cylinders and held in place when the controls are released.
   
3. Replace Hydraulic Hoses: Damaged or leaking hydraulic hoses should be replaced. Ensure that the new hoses meet the specifications provided by Bobcat for the 773 G.
   
4. Flush the Hydraulic System and Replace Fluid: If contamination is found in the hydraulic system, the fluid should be flushed and replaced with fresh fluid. It’s also essential to replace the hydraulic filter to remove any debris or particles that might have entered the system.
   
5. Repair or Replace the Hydraulic Pump: If the pump is found to be underperforming, it may need to be repaired or replaced. A well-functioning pump is crucial for maintaining the correct pressure in the hydraulic system.
   

Preventative Maintenance to Avoid Drifting Arms
To avoid future issues with drifting arms, it’s essential to follow a regular maintenance schedule for the Bobcat 773 G’s hydraulic system. Here are some tips for maintaining the hydraulic system:

• Regularly check and top off hydraulic fluid levels.
  
• Inspect hydraulic cylinders, hoses, and valves for leaks and wear.
  
• Change the hydraulic fluid and filter at the intervals specified in the operator’s manual.
  
• Use high-quality hydraulic fluid that meets Bobcat’s specifications to prevent contamination.
  
• Perform regular pressure tests on the hydraulic system to ensure it’s functioning correctly.
  

Conclusion
The drifting arms issue in the Bobcat 773 G is typically caused by problems within the hydraulic system, such as worn seals, hydraulic valve issues, fluid contamination, or hose leaks. Diagnosing and resolving the problem involves checking the hydraulic fluid, inspecting the cylinders and hoses, and testing the pump and control valve. With the right maintenance practices and timely repairs, operators can prevent this issue and ensure their Bobcat 773 G continues to perform reliably on the job. Regular care and attention to the hydraulic system will keep the machine in optimal condition for years to come.