Troubleshooting Jerky or No Reverse Movement in Bobcat 753 Left Side

[MikePhua]

When operating a Bobcat 753, if you experience jerky or no reverse movement on the left side, but forward motion is fine, it's a sign that something is amiss with the machine's drive system. The Bobcat 753 is known for its reliability and versatility in various construction applications, but like all equipment, it can develop issues over time. This article will explore the common causes of jerky or no reverse movement, provide troubleshooting steps, and help you understand the mechanisms behind this issue.
Understanding the Bobcat 753 Drive System
The Bobcat 753 is equipped with a hydraulic drive system that powers the movement of the machine. The drive system is controlled by a combination of hydraulic pumps, motors, and valves. The system operates both the forward and reverse movements by controlling the flow of hydraulic fluid to the drive motors. When there's a problem with the hydraulic flow or the components in the drive system, you may experience issues such as jerky movements or a complete lack of reverse motion on one side.
Common Causes of Jerky or No Reverse Movement
There are several potential causes for jerky or no reverse movement in a Bobcat 753. These issues typically stem from problems with the hydraulic system, drive motor, or electrical controls. Here's a detailed breakdown of the most common culprits:
1. Low Hydraulic Fluid Level or Contamination
One of the most common reasons for jerky or no reverse movement is low hydraulic fluid levels or contaminated hydraulic fluid. The Bobcat 753 relies on hydraulic fluid to power its drive motors. If the fluid level is low or the fluid is dirty, it can affect the performance of the hydraulic system, causing the machine to malfunction.

• Signs of Low or Contaminated Hydraulic Fluid:
  • Jerky movement or failure to move in one direction.
    
  • Reduced lifting capacity.
    
  • Increased noise from the hydraulic system.
    

Solution: Check the hydraulic fluid level and inspect for contamination. If the fluid is low, top it off with the appropriate type of hydraulic oil. If the fluid appears dirty or has particles, perform a hydraulic fluid change and replace the filter.
2. Faulty Hydraulic Motor or Drive Motor
The hydraulic motor is responsible for driving the wheels or tracks in both forward and reverse directions. If the motor on the left side is malfunctioning, it could cause jerky movement or a complete failure to move in reverse. This could happen due to wear and tear, internal damage, or fluid flow issues.

• Signs of a Faulty Hydraulic Motor:
  • One side of the machine moves while the other side does not.
    
  • Jerky or uneven movement in reverse.
    
  • No movement at all in reverse.
    

Solution: Inspect the hydraulic motor for leaks, damage, or excessive wear. If the motor shows signs of damage, it may need to be repaired or replaced. Check the motor's hydraulic connections to ensure they are free from blockages.
3. Hydraulic Valve or Control Issues
The Bobcat 753 uses control valves to direct the flow of hydraulic fluid to the drive motors. If there is an issue with the valve, such as a blockage or internal failure, it can disrupt the fluid flow and cause jerky or no reverse movement. Additionally, the directional control valve, which changes the flow of fluid between forward and reverse movements, could be faulty.

• Signs of Valve or Control Issues:
  • Loss of control over direction.
    
  • Jerky movement, particularly in one direction.
    
  • Difficulty engaging reverse or forward motion.
    

Solution: Inspect the hydraulic control valve for signs of wear or blockage. If the valve is malfunctioning, it may need to be cleaned, repaired, or replaced. In some cases, air trapped in the hydraulic system could also cause control issues, so bleeding the system may help resolve the problem.
4. Hydraulic Pump Problems
The hydraulic pump generates the pressure needed to move the hydraulic fluid through the system. If the hydraulic pump is failing, it can cause inadequate fluid flow, leading to issues with movement, including jerky or no reverse action. This could be due to internal wear or damage to the pump components.

• Signs of a Failing Hydraulic Pump:
  • Reduced performance in all directions.
    
  • Jerky or uneven movement when moving forward or in reverse.
    
  • Increased hydraulic system noise.
    

Solution: If you suspect a hydraulic pump issue, you should have the pump tested for proper pressure and flow output. If the pump is faulty, it will need to be replaced or repaired.
5. Electrical or Sensor Malfunctions
The Bobcat 753 utilizes electrical sensors and wiring to control the hydraulic system and movement. If there is an issue with the electrical system, such as a malfunctioning sensor or faulty wiring, it can cause the machine to behave erratically or fail to reverse. A defective sensor can send incorrect signals to the hydraulic system, resulting in movement issues.

• Signs of Electrical or Sensor Issues:
  • No response or jerky movement when engaging reverse.
    
  • Electrical errors or warning lights on the control panel.
    
  • Inconsistent machine behavior when switching between forward and reverse.
    

Solution: Check the electrical system, including sensors and wiring, for any loose connections, damaged wires, or error codes. Use a diagnostic tool to identify any electrical faults, and replace any faulty components as needed.
Steps to Diagnose and Fix Jerky or No Reverse Movement
Diagnosing the issue of jerky or no reverse movement on a Bobcat 753 can be a step-by-step process, as multiple components could be at fault. Here's how to proceed:
Step 1: Check Hydraulic Fluid Level and Condition
Start by inspecting the hydraulic fluid level. If the level is low, top it off with the recommended fluid type. If the fluid appears dirty or contaminated, perform a complete fluid and filter change.
Step 2: Inspect the Hydraulic Motor
Next, inspect the left-side hydraulic motor for any signs of damage, leaks, or wear. Look for any obvious signs of fluid leakage or physical damage that could be affecting its operation. If the motor is faulty, it will likely need to be repaired or replaced.
Step 3: Test the Hydraulic Valves
Check the hydraulic control valve for proper function. Ensure that there are no blockages in the fluid pathways. If you suspect an issue with the valve, cleaning or replacing it may resolve the problem.
Step 4: Test the Hydraulic Pump
If the hydraulic motor and valves are functioning properly, the issue could be related to the hydraulic pump. Have the pump tested for pressure and flow output. If it is not producing enough pressure, the pump may need to be replaced.
Step 5: Inspect Electrical Components
If the hydraulic system checks out, the issue may be electrical. Inspect the wiring, sensors, and control system for any faults. Use a diagnostic tool to scan for error codes and test the functionality of the sensors and electrical components.
Preventive Maintenance Tips
To prevent issues like jerky or no reverse movement from occurring in the future, regular maintenance is key:

• Change hydraulic fluid regularly to keep the system clean and operating smoothly.
  
• Inspect the hydraulic system for leaks or damage before and after each use.
  
• Check for electrical issues periodically to ensure all sensors and wiring are functioning properly.
  
• Follow the manufacturer's guidelines for load limits and operating conditions to avoid overstressing the hydraulic system.
  

Conclusion
Jerky or no reverse movement on the left side of a Bobcat 753 can be caused by several factors, including low hydraulic fluid, faulty hydraulic motors, valve issues, pump problems, or electrical malfunctions. By systematically diagnosing the issue and addressing the root cause, you can restore the proper function of your Bobcat 753 and prevent further damage to the machine. Regular maintenance and timely troubleshooting will help extend the lifespan of the machine and keep it running smoothly.