Diagnosing and Resolving Bobcat 751 Lift Arm Shuddering Issues

[MikePhua]

The Bobcat 751 is a versatile, compact skid steer loader commonly used in various construction and landscaping tasks. However, like all machinery, it can experience issues over time. One of the common complaints reported by operators of the Bobcat 751 is lift arm shuddering. This phenomenon, often occurring when the lift arms are raised or lowered, can affect the machine's performance, leading to reduced efficiency and potential damage if not addressed properly.
In this article, we will explore the causes of lift arm shuddering, the impact it can have on your machine, and effective troubleshooting and solutions to address this problem.
What is Lift Arm Shuddering in the Bobcat 751?
Lift arm shuddering refers to a jerky or stuttering movement of the lift arms, usually noticeable when the operator is moving them slowly or making slight adjustments. It is often felt as a vibration or sudden jolt in the machine's hydraulics, causing the arms to hesitate or move erratically.
This issue is particularly problematic because it can interfere with precise movements, making tasks such as grading, loading, or lifting delicate materials more difficult. Additionally, consistent shuddering can lead to accelerated wear and tear on the machine's hydraulic system, affecting the overall lifespan of the Bobcat 751.
Common Causes of Lift Arm Shuddering

1. Hydraulic Fluid Contamination
   • Hydraulic fluid contamination is one of the most common causes of shuddering in any skid steer loader, including the Bobcat 751. Over time, dirt, debris, or even moisture can enter the hydraulic system, causing the fluid to become thick or contaminated.
     
   • Solution: The hydraulic fluid should be inspected regularly for contamination. If necessary, replace the fluid and install a new hydraulic filter to ensure smooth operation.
     
2. Low Hydraulic Fluid Levels
   • Low hydraulic fluid levels can lead to erratic behavior of the lift arms. Inadequate fluid can cause air to enter the system, which reduces the efficiency of the hydraulic pumps and valves, resulting in jerky movements.
     
   • Solution: Always ensure that the hydraulic fluid is at the proper level. Check the fluid level regularly, and top it up if necessary. Additionally, inspect for leaks around the hydraulic hoses and fittings, which could cause the fluid to drain out.
     
3. Worn or Faulty Hydraulic Pump
   • A hydraulic pump that is worn or malfunctioning can cause inconsistent pressure to be sent to the lift arms. This results in jerky movement as the system struggles to maintain smooth hydraulic flow.
     
   • Solution: If you suspect a worn hydraulic pump, a pressure test can help diagnose whether the pump is functioning within the manufacturer's specifications. If the pump is faulty, it may need to be replaced or repaired.
     
4. Improperly Adjusted Lift Arm Linkage
   • The linkage system that connects the lift arms to the machine’s hydraulic cylinder can become misaligned or improperly adjusted. This misalignment can create uneven force distribution, leading to lift arm shuddering.
     
   • Solution: Check the lift arm linkage for signs of wear or damage. Ensure that all pivot points and joints are lubricated and properly adjusted. If any parts are worn, replace them to restore smooth movement.
     
5. Faulty or Worn Hydraulic Cylinders
   • Hydraulic cylinders are responsible for converting hydraulic pressure into mechanical force to lift and lower the arms. If the seals in the cylinders are worn or damaged, or if the cylinders themselves are bent or scored, they can cause uneven pressure distribution, resulting in shuddering.
     
   • Solution: Inspect the hydraulic cylinders for any visible damage or leakage. If a seal is damaged, it may need to be replaced. In severe cases, the entire hydraulic cylinder may need to be rebuilt or replaced.
     
6. Contaminated or Old Hydraulic Filters
   • Old or clogged hydraulic filters can restrict the flow of hydraulic fluid, causing pressure fluctuations that lead to shuddering. This is particularly noticeable when the system is under load, such as during lift arm operations.
     
   • Solution: Replace the hydraulic filters regularly, as specified by the manufacturer. A clean filter ensures proper fluid flow, helping to prevent shuddering and other hydraulic system issues.
     
7. Electrical or Control Valve Issues
   • The control valve that regulates the flow of hydraulic fluid to the lift arms can sometimes malfunction or become dirty. If the valve is sticking or not operating smoothly, it can cause uneven hydraulic fluid distribution, leading to lift arm shuddering.
     
   • Solution: Inspect the control valves for signs of dirt, damage, or malfunction. Cleaning or replacing the valve can resolve issues related to inconsistent hydraulic flow.
     

Steps to Resolve Lift Arm Shuddering

1. Inspect and Replace Hydraulic Fluid
   The first step is to check the hydraulic fluid levels and condition. If the fluid is contaminated or low, it should be drained and replaced with fresh fluid. Don’t forget to also replace the filter to ensure that no contaminants remain in the system.
   
2. Check the Hydraulic System for Leaks
   Inspect the hoses, fittings, and connections for any signs of leaks. Leaking hydraulic fluid not only causes low fluid levels but also compromises the system’s pressure, resulting in lift arm shuddering.
   
3. Test the Hydraulic Pump
   If the fluid is fine and there are no leaks, it may be time to test the hydraulic pump. A pressure test will reveal whether the pump is providing the correct pressure to the system. If the pump is malfunctioning, it should be replaced.
   
4. Adjust the Lift Arm Linkage
   If the linkage is misaligned, it can lead to uneven pressure distribution. Adjusting the linkage or replacing worn parts can improve lift arm movement and reduce shuddering.
   
5. Inspect the Hydraulic Cylinders
   Look for any leaks, bends, or damage on the hydraulic cylinders. Replace any faulty parts, such as seals, or rebuild the cylinders if necessary.
   
6. Replace Hydraulic Filters
   If the filters are clogged or old, they can obstruct the hydraulic flow, causing issues with the lift arms. Replacing the filters regularly will ensure that the hydraulic system functions smoothly.
   

Conclusion
Lift arm shuddering in the Bobcat 751 is a common issue that can stem from several factors, including hydraulic fluid problems, worn components, and misalignment of the lift arm linkage. By addressing these potential causes promptly, you can restore the smooth operation of your machine and prevent further damage. Regular maintenance, including checking fluid levels, replacing filters, and inspecting hydraulic components, is key to keeping the Bobcat 751 running efficiently and extending its lifespan. With the right care, your skid steer loader can continue to perform reliably on the job site for years to come.