Bleeding Air from Hydraulic Lines on the John Deere 772A Grader

[MikePhua]

Hydraulic systems are integral to the smooth operation of many heavy machines, including graders like the John Deere 772A. These systems are responsible for powering a wide range of functions, from raising and lowering the blade to adjusting the machine's steering. However, one common issue that can disrupt the operation of hydraulic systems is the presence of air in the hydraulic lines. Air can cause erratic or sluggish hydraulic responses, and in some cases, may even lead to complete system failure. Properly bleeding air from the hydraulic lines is an essential maintenance task that ensures the system functions optimally. This article delves into how to bleed air from the hydraulic system of the John Deere 772A grader, the importance of maintaining the hydraulic system, and practical tips for troubleshooting.
Understanding the Hydraulic System of the John Deere 772A
The John Deere 772A, a popular grader model in the construction and road maintenance industries, uses a sophisticated hydraulic system to control various components. These include the blade, the circle drive, and the articulation mechanism, which allows the grader to pivot for better maneuverability. The hydraulic system is powered by a high-pressure pump that circulates hydraulic fluid through a network of hoses and valves.
One of the most common issues with hydraulic systems is air entering the lines, which can result from various sources such as improper fluid levels, faulty seals, or a hydraulic fluid leak. When air is trapped in the lines, it can cause the hydraulic fluid to lose its pressurized properties, leading to poor performance. In extreme cases, air can prevent the hydraulic system from operating altogether, making it necessary to perform an air-bleeding procedure.
Symptoms of Air in Hydraulic Lines
Before getting into the procedure for bleeding the air, it’s important to recognize the symptoms of air in the hydraulic system. These include:

1. Erratic or Slow Hydraulic Movements: If the machine’s hydraulic functions, such as raising the blade or steering, respond sluggishly or in an unpredictable manner, this could indicate that air has entered the system.
   
2. Unusual Sounds: You might hear a gurgling or whining sound coming from the hydraulic system, which can be a sign of air bubbles circulating in the hydraulic fluid.
   
3. Reduced Performance: A noticeable reduction in the power or speed of hydraulic movements could indicate that the air is disrupting the pressure within the system.
   
4. Fluid Leaks: Sometimes, air in the hydraulic lines can lead to internal leaks or external leakage, as the seals may not maintain proper pressure.
   

If you observe any of these symptoms, it’s essential to address the problem promptly by bleeding the hydraulic system.
The Importance of Bleeding Air from Hydraulic Lines
Bleeding the hydraulic lines ensures that any trapped air is removed, allowing the hydraulic fluid to maintain its proper pressure. This process helps restore the efficiency of the system, reducing the risk of equipment failure and extending the lifespan of the hydraulic components.
Neglecting this maintenance can lead to several issues:

1. Overheating: Air in the lines can cause the hydraulic fluid to heat up, which may lead to the degradation of the fluid and accelerated wear on the system.
   
2. Damage to Hydraulic Components: Consistent exposure to air can lead to cavitation, a condition where air bubbles form and collapse in the hydraulic fluid. This can cause significant damage to pumps, valves, and seals.
   
3. Decreased Efficiency: Air in the lines reduces the overall efficiency of the hydraulic system, causing slower responses and erratic behavior during operation.
   

How to Bleed Air from the Hydraulic Lines of the John Deere 772A
To ensure the hydraulic system is free of air and functions correctly, follow these steps for bleeding the lines:

1. Prepare the Equipment and Tools:
   • Ensure the machine is on a flat, stable surface.
     
   • Gather necessary tools, including wrenches, a drain pan for excess fluid, and a clean cloth to prevent contamination.
     
   • Wear gloves and eye protection to safeguard against hydraulic fluid splashes.
     
2. Check Hydraulic Fluid Levels:
   • Before starting the bleeding procedure, verify that the hydraulic fluid is at the correct level. Low fluid levels can contribute to air entering the system. Refer to the John Deere 772A owner’s manual for the exact fluid capacity and recommended type.
     
   • If needed, add the appropriate hydraulic fluid to bring the level up to specification.
     
3. Locate the Bleeding Valve or Ports:
   • The John Deere 772A typically has a bleed valve on each main hydraulic cylinder or at a convenient point in the system. These valves allow air to escape when the system is under pressure.
     
   • Consult the machine’s service manual to locate the exact positions of these bleed valves.
     
4. Start the Machine and Engage the Hydraulic System:
   • Start the engine of the John Deere 772A and engage the hydraulic functions, such as the blade and steering, to pressurize the hydraulic system.
     
   • Leave the machine running at idle to avoid overloading the pump during the process.
     
5. Open the Bleeding Valve:
   • Begin with the highest point in the hydraulic system, usually the main control valve or the most elevated cylinder, and open the bleed valve slowly.
     
   • Allow the air to escape while monitoring the fluid for any signs of air bubbles. The fluid should begin to flow steadily without foam or gurgling sounds.
     
   • Once the air has been purged from the system and only clean hydraulic fluid is coming out, close the valve tightly.
     
6. Repeat the Process for All Cylinders and Components:
   • Move through the hydraulic system, repeating the process for each component, such as the blade lift cylinders and steering mechanisms.
     
   • Be sure to check all valves and cylinders, as air could be trapped in any of these sections.
     
7. Test the System:
   • After bleeding all components, test the hydraulic system by operating the blade, steering, and other controls. The movements should be smooth and responsive without any jerky or slow actions.
     
   • If the problem persists, recheck the system for any hidden air pockets or leaks in the lines.
     
8. Check for Leaks:
   • After bleeding the air from the system, inspect the hydraulic lines and components for any fluid leaks. Leaks can be indicative of damaged seals or fittings that need to be replaced.
     

Common Troubleshooting Tips
If bleeding the system does not resolve the issue, consider the following troubleshooting steps:

1. Check for Fluid Contamination: Contaminants in the hydraulic fluid, such as dirt or water, can affect the system's performance. Drain and replace the fluid if necessary.
   
2. Inspect for Leaks: Look for leaks around the pump, hoses, and cylinders, as these can allow air to enter the system.
   
3. Verify Hydraulic Pump Operation: Ensure that the hydraulic pump is functioning correctly and is not damaged. A malfunctioning pump can cause erratic pressure and poor performance.
   

Preventing Air in Hydraulic Lines
To prevent air from entering the hydraulic system in the future, consider the following:

1. Regular Fluid Checks: Keep an eye on the hydraulic fluid level and condition. Regularly inspect for signs of contamination or degradation.
   
2. Proper Seals: Ensure that all seals and O-rings are in good condition to prevent air from leaking into the system.
   
3. Avoid Overfilling: Do not overfill the hydraulic system, as this can cause excessive pressure and lead to air pockets.
   

Conclusion
Bleeding air from the hydraulic lines of the John Deere 772A grader is an essential maintenance procedure that ensures the hydraulic system operates efficiently and reliably. By following the outlined steps and performing regular checks on fluid levels and system components, operators can avoid costly repairs and maintain the grader’s performance over the long term. Whether you’re dealing with erratic hydraulic movements or preparing for routine maintenance, knowing how to properly bleed the system is a key skill for any grader operator.