Bobcat S550 Rolling When Not Moving: Common Causes and Solutions

[MikePhua]

Bobcat skid steer loaders are well-known for their performance, versatility, and ability to work in various challenging environments. Among the popular models, the Bobcat S550 stands out for its powerful engine, enhanced lifting capabilities, and exceptional maneuverability. However, like any piece of machinery, the S550 is not immune to mechanical issues, and one common problem owners might encounter is the loader rolling when it is not supposed to be moving. This problem can be perplexing and concerning, as it might affect both safety and machine operation.
In this article, we will explore the potential causes of the Bobcat S550 rolling when it is not in motion, what steps you can take to resolve the issue, and how to prevent it in the future.
Understanding the Bobcat S550's Drive System
Before diving into potential issues, it is important to understand how the Bobcat S550's drive system works. The S550 is equipped with a hydraulic drive system that powers the wheels or tracks. The system uses two high-flow hydraulic pumps to drive the motors, which in turn rotate the wheels or tracks to provide movement. This system also includes a brake mechanism to prevent the machine from rolling when the operator is not engaging the controls.
The hydraulic system is designed to hold the loader in place when it is stationary. If there are issues with the system, the machine may exhibit strange behaviors such as rolling even when the machine is not in motion.
Potential Causes of Rolling When Stationary

1. Brake System Malfunction
   The most likely cause of the Bobcat S550 rolling when not moving is a malfunction in the brake system. The hydraulic brake system is designed to keep the machine stationary when the controls are not engaged. If there is an issue with the brake solenoid, fluid pressure, or internal components, the brakes may not hold properly, allowing the machine to roll.
   Common Brake System Issues:
   • Hydraulic pressure loss: A drop in hydraulic pressure can cause the brakes to disengage.
     
   • Faulty solenoid: The solenoid that controls the brake release may be malfunctioning or worn out.
     
   • Worn brake pads: Over time, brake pads can wear down, leading to insufficient stopping power.
     
2. Hydraulic System Issues
   The S550 uses a hydraulic drive system to power its wheels, and if there are issues with the hydraulic system, it can cause the machine to roll unexpectedly. Hydraulic fluid is responsible for maintaining pressure in the system, and any leakage or fluid loss can lead to a lack of power for braking.
   Common Hydraulic System Problems:
   • Low hydraulic fluid levels: A lack of fluid can reduce brake efficiency and cause unwanted movement.
     
   • Hydraulic pump failure: If the hydraulic pump is not operating correctly, it might not provide enough pressure to hold the machine in place.
     
   • Hydraulic fluid contamination: Contaminated fluid can clog or damage critical components, leading to improper functioning of the brakes.
     
3. Drive Motor or Transmission Issues
   The drive motors in the S550 are responsible for powering the machine’s wheels, and any issue with these motors or the transmission can lead to unexpected movement. While it’s less common, a malfunction in the drive motors or transmission could cause the machine to roll, even when the control handles are not being engaged.
   Potential Drive Motor/Transmission Issues:
   • Internal leak in the motor: An internal leak can reduce the braking effect, causing the machine to roll.
     
   • Faulty transmission valve: If the valve that controls transmission pressure is malfunctioning, it may not lock the wheels properly.
     
4. Faulty Parking Brake
   A secondary brake system, typically known as a parking brake, is often included in skid steer loaders like the Bobcat S550. If the parking brake is not engaging correctly, the loader could roll even when it is supposed to remain stationary. This can happen if the parking brake mechanism is worn out or not properly adjusted.
   Potential Causes:
   • Incorrect parking brake adjustment: If the parking brake is not adjusted properly, it might fail to engage fully.
     
   • Worn components: Over time, the components of the parking brake, such as cables or springs, can wear down, causing it to malfunction.
     

Troubleshooting and Fixes

1. Check Hydraulic Fluid Levels
   The first step in troubleshooting the issue is to check the hydraulic fluid levels. Low fluid levels can cause inadequate hydraulic pressure, which may prevent the brakes from engaging properly. Ensure that the fluid is at the proper level, and if it is low, refill it with the recommended fluid.
   
2. Inspect the Brake System
   Inspect the hydraulic brake system to ensure that the solenoid is functioning properly and there are no leaks in the brake lines. If the solenoid is faulty, it should be replaced. Additionally, check the brake pads for wear and replace them if necessary.
   
3. Examine the Parking Brake
   Inspect the parking brake system to ensure that it is properly adjusted and engages fully when the lever is pulled. If the system is not engaging properly, it may need adjustment or component replacement.
   
4. Test the Drive Motors and Transmission
   If the brake system and hydraulic fluid levels check out, then it might be time to inspect the drive motors and transmission. A professional technician should be able to perform diagnostic tests to check for internal leaks, faulty valves, or other issues that could be causing the machine to roll.
   
5. Consult a Bobcat Technician
   If all else fails, it’s a good idea to bring the machine to an authorized Bobcat service center. Trained technicians will have the necessary tools and expertise to diagnose the problem accurately and make the required repairs.
   

Preventative Maintenance Tips
To prevent issues like this from occurring in the future, it’s essential to perform regular maintenance on your Bobcat S550. Here are some key tips:

• Regularly check hydraulic fluid levels: Low fluid levels can affect both the drive and brake systems. Always maintain the proper fluid level and replace it as necessary.
  
• Inspect the brake system: Regularly check the brake pads for wear and ensure the solenoid is functioning properly.
  
• Keep the parking brake in good condition: Perform periodic inspections and adjustments to the parking brake system to ensure it’s engaging properly.
  
• Schedule routine service: Have your Bobcat S550 inspected by a professional technician at regular intervals. This can help catch small issues before they turn into larger, more costly problems.
  

Conclusion
The Bobcat S550 rolling when not moving can be a serious concern, but with proper diagnosis and maintenance, the issue can be resolved. Common causes include hydraulic system issues, brake system malfunctions, drive motor problems, and faulty parking brakes. By checking the hydraulic fluid, inspecting the brake and parking brake systems, and addressing any issues with the drive motor or transmission, you can ensure your Bobcat S550 continues to operate smoothly and safely. Regular maintenance is the key to keeping your loader in top condition and avoiding unexpected problems down the road.