Troubleshooting Inconsistent Hydraulic Pressure on the 1994 Lull 644 Highlander II

[MikePhua]

The 1994 Lull 644 Highlander II is a versatile telehandler widely used in construction and material handling tasks. Known for its powerful hydraulics and impressive lifting capabilities, this machine can handle a variety of demanding jobs. However, when it suffers from inconsistent hydraulic pressure, operators can experience significant performance issues. In this article, we will explore the potential causes of hydraulic pressure inconsistencies, how to troubleshoot them, and how to maintain the hydraulic system for optimal performance.
Understanding the Lull 644 Highlander II's Hydraulic System
Hydraulic systems are crucial for the functionality of telehandlers like the Lull 644 Highlander II. The hydraulic pressure is responsible for lifting and extending the boom, operating the attachment, and controlling other key functions. When the hydraulic system is operating correctly, it provides smooth and consistent performance.
However, if the pressure becomes inconsistent—either fluctuating or dropping too low—it can lead to poor lifting capabilities, slow response times, and even total hydraulic failure. Understanding why this happens and knowing how to fix it is essential for minimizing downtime and ensuring the longevity of the equipment.
Common Causes of Inconsistent Hydraulic Pressure
Inconsistent hydraulic pressure can result from several factors, ranging from minor issues like low fluid levels to more complex problems like pump malfunctions. Below are some common causes for this issue and what operators should look out for.
1. Low Hydraulic Fluid Levels
One of the most common reasons for inconsistent hydraulic pressure is low hydraulic fluid levels. If the fluid is too low, the pump cannot generate the necessary pressure to operate the system efficiently. Low fluid can also lead to air entering the system, which causes erratic pressure and even potential damage to hydraulic components.
Symptoms:

• Inconsistent boom or attachment movements
  
• Slow response times
  
• Unusual noises from the hydraulic pump
  

Solution:

• Check Fluid Levels: Ensure that the hydraulic fluid is at the recommended levels. Always use the correct type of hydraulic fluid as specified by the manufacturer.
  
• Inspect for Leaks: If the fluid level is low, check for leaks around hoses, seals, and the pump. Leaks can cause a steady drop in fluid levels, leading to inconsistent pressure.
  

2. Dirty or Clogged Hydraulic Filters
Hydraulic filters play a crucial role in keeping the fluid clean by removing dirt, debris, and other contaminants. Over time, these filters can become clogged, reducing fluid flow and leading to inconsistent hydraulic pressure.
Symptoms:

• Slow or jerky boom movement
  
• Difficulty operating attachments
  
• Increased operating temperatures
  

Solution:

• Replace Hydraulic Filters: If the filters appear dirty or clogged, replace them immediately to restore proper fluid flow.
  
• Clean the System: In cases where the hydraulic fluid has been contaminated, it may be necessary to flush the system and replace the fluid to ensure optimal operation.
  

3. Worn or Damaged Hydraulic Pump
The hydraulic pump is the heart of the hydraulic system. If it’s worn, damaged, or malfunctioning, it can lead to inconsistent hydraulic pressure. This can happen over time with extended use, especially if the pump is not properly maintained.
Symptoms:

• Sudden drops in pressure
  
• Lack of power when lifting heavy loads
  
• Abnormal sounds from the pump (e.g., whining or grinding)
  

Solution:

• Inspect the Pump: If you notice inconsistent pressure, check the hydraulic pump for signs of wear, leakage, or damage.
  
• Replace the Pump: If the pump is damaged or worn, it may need to be replaced to restore proper hydraulic pressure.
  

4. Air in the Hydraulic System
Air trapped in the hydraulic lines can cause erratic hydraulic pressure, leading to a spongy or inconsistent response. This is often due to a leak in the system or improper filling of hydraulic fluid.
Symptoms:

• Spongy or slow boom movements
  
• Sudden pressure fluctuations
  
• Air bubbles or foamy fluid in the reservoir
  

Solution:

• Bleed the System: Purge any air from the hydraulic lines by following the manufacturer’s instructions. Typically, this involves running the machine with the controls in various positions to allow the air to escape.
  
• Check for Leaks: Inspect the hydraulic lines, seals, and connections to ensure that there are no leaks allowing air to enter the system.
  

5. Faulty Pressure Relief Valve
The pressure relief valve is designed to protect the hydraulic system from overpressure by releasing excess fluid. If this valve becomes faulty or clogged, it may cause pressure inconsistencies or prevent the system from operating at its optimal level.
Symptoms:

• Inconsistent pressure when operating the boom or attachments
  
• Noisy operation
  
• Pressure surges during normal use
  

Solution:

• Test the Pressure Relief Valve: Check the pressure relief valve to ensure it is functioning properly. If the valve is stuck or malfunctioning, it may need to be cleaned, adjusted, or replaced.
  

6. Malfunctioning Control Valves
The control valves direct the hydraulic fluid to different parts of the machine, such as the boom, attachments, and steering. If these valves are clogged, damaged, or malfunctioning, it can lead to inconsistent hydraulic pressure and poor performance.
Symptoms:

• Inconsistent control over boom movements
  
• Hydraulic system slow to respond or fails to respond
  
• Unresponsive or jerky operation
  

Solution:

• Inspect the Control Valves: Check the control valves for blockages, wear, or malfunction. Clean or replace the valves as necessary to restore proper operation.
  

Steps to Troubleshoot Hydraulic Pressure Issues

1. Check Fluid Levels: Always start by checking the hydraulic fluid levels and topping off if necessary. Low fluid levels can often be the simplest cause of inconsistent pressure.
   
2. Inspect for Leaks: Look for leaks around the hydraulic lines, hoses, and connections. Leaks can reduce fluid levels and lead to pressure fluctuations.
   
3. Examine Filters: Ensure that the hydraulic filters are clean and free from contaminants. Replace the filters if necessary.
   
4. Test the Hydraulic Pump: If pressure issues persist, test the hydraulic pump to ensure it’s functioning properly. If the pump is failing, it may need to be replaced.
   
5. Bleed the System: If you suspect air in the system, bleed the hydraulic lines to remove any trapped air.
   
6. Check the Pressure Relief Valve: Ensure the pressure relief valve is operating correctly. Adjust or replace the valve as needed.
   

Preventive Maintenance Tips
To avoid hydraulic pressure issues in the future, regular maintenance is key. Here are a few tips to keep the hydraulic system in top condition:

• Regularly check fluid levels and replace hydraulic fluid when it appears contaminated or old.
  
• Inspect hydraulic filters and replace them on a regular schedule, depending on the manufacturer’s recommendation.
  
• Perform regular system checks to ensure there are no leaks or air in the system.
  
• Service the hydraulic pump periodically to catch any signs of wear early on.
  

Conclusion
Inconsistent hydraulic pressure in the 1994 Lull 644 Highlander II can be caused by several factors, including low fluid levels, clogged filters, a failing hydraulic pump, or air in the system. By understanding the potential causes and following the recommended troubleshooting steps, you can resolve hydraulic pressure issues and maintain the machine’s performance.
Regular maintenance and early detection of issues are crucial to ensuring that the hydraulic system functions smoothly and efficiently. By staying proactive with maintenance, you can extend the life of your Lull 644 Highlander II and ensure that it continues to perform reliably on the job site.