Troubleshooting Common Issues with the 1999 Cat 773 AHC Skid Steer

[MikePhua]

The Caterpillar 773 AHC (Automatic Hydraulic Control) skid steer loader is a reliable and versatile piece of machinery, designed to handle a variety of construction and landscaping tasks. However, like all equipment, it is prone to issues that may arise over time, particularly as it ages. One of the common problems faced by owners of older 773 AHC models is hydraulic system failure, which can prevent the loader from working as expected. In this guide, we will explore the typical issues that cause a 1999 Cat 773 AHC to stop working, focusing on the hydraulic system, troubleshooting techniques, and the steps to take for repairs.
Understanding the Hydraulic System in the Cat 773 AHC
The hydraulic system is the heart of any skid steer loader. It is responsible for powering key components, including the lift arms, bucket tilt, and drive system. In the case of the Cat 773 AHC, the system is designed to provide precise control of hydraulic movements, which is crucial for lifting, dumping, and maneuvering loads. A malfunction in this system can lead to a complete loss of function in these areas.
The hydraulic system in the Cat 773 AHC includes several key components:

• Hydraulic Pump: Converts engine power into hydraulic energy, driving the system.
  
• Control Valve: Regulates the flow of hydraulic fluid to various parts of the machine.
  
• Hydraulic Cylinders: Provide the force necessary to lift and tilt the loader arms and bucket.
  
• Hydraulic Hoses and Fittings: Transport hydraulic fluid to various components of the loader.
  

Common issues that can arise with the hydraulic system are often related to fluid levels, contamination, pump failure, or leaks.
Symptoms of Hydraulic System Failure
When the hydraulic system of a 1999 Cat 773 AHC begins to fail, several symptoms may appear. These include:

• Unresponsive or Slow Movements: If the loader’s arms or bucket are slow to respond, it may be a sign that the hydraulic pump is not providing enough pressure or that the fluid is low.
  
• No Movement: Complete lack of movement in the loader’s arms, bucket, or drive system is a clear indication that there is a hydraulic failure.
  
• Strange Noises: Unusual whining, grinding, or squealing sounds may indicate a hydraulic pump failure, air in the lines, or a problem with the control valve.
  
• Fluid Leaks: Hydraulic fluid leaks around hoses, cylinders, or the pump are a common sign of damage or wear.
  
• Erratic Control: If the controls for lifting or tilting the bucket behave unpredictably or intermittently, the problem may be related to the control valve or fluid pressure issues.
  

Common Causes of Hydraulic System Failure
Several issues can lead to a hydraulic system failure in the 1999 Cat 773 AHC. Understanding these common causes can help you troubleshoot the problem more efficiently.
1. Low Hydraulic Fluid Levels
One of the most straightforward causes of hydraulic issues is low fluid levels. Hydraulic fluid serves as both a lubricant and a pressure transmitter within the system. If the fluid level drops too low, it can lead to inefficient operation or complete failure of the hydraulic components.
Symptoms of Low Fluid:

• Slow or unresponsive movements.
  
• Whining or grinding noises coming from the pump.
  
• Increased engine temperature.
  

Solution:

• Check the hydraulic fluid level using the dipstick or sight glass.
  
• Top off the fluid with the manufacturer-recommended hydraulic oil if necessary.
  
• Inspect for any leaks in the system that could be causing fluid loss.
  

2. Contaminated Hydraulic Fluid
Hydraulic fluid can become contaminated with dirt, debris, or moisture over time, especially if the fluid is not changed regularly or if the system is exposed to harsh working conditions. Contaminated fluid can cause significant damage to the pump, valves, and cylinders by causing abrasion or clogging filters.
Symptoms of Contamination:

• Slow or erratic movements of the loader.
  
• Decreased lifting capacity.
  
• Unusual noises from the hydraulic system.
  

Solution:

• Change the hydraulic fluid according to the manufacturer’s service intervals.
  
• Replace the hydraulic filters to prevent further contamination.
  
• If the fluid has been heavily contaminated, you may need to flush the system and replace hoses or fittings that have become clogged.
  

3. Hydraulic Pump Failure
The hydraulic pump is responsible for converting engine power into hydraulic pressure. If the pump fails, the hydraulic system will no longer operate effectively. Common causes of pump failure include worn-out seals, internal wear, or cavitation (air entering the pump).
Symptoms of Pump Failure:

• The loader’s movements are very slow or completely unresponsive.
  
• A loud whining noise from the pump.
  
• Increased pressure in the hydraulic lines.
  

Solution:

• Inspect the hydraulic pump for any visible damage or signs of wear.
  
• Replace the pump if it is found to be faulty. It’s often more economical to replace the entire pump rather than attempting to repair it.
  
• Check for cavitation and ensure that the fluid is clean and at the proper level.
  

4. Leaking Hydraulic Lines or Cylinders
Hydraulic fluid leaks are a common issue with older equipment. These leaks can occur at the connections between hoses, fittings, or cylinders, and they reduce the efficiency of the hydraulic system.
Symptoms of Leaks:

• Noticeable drops of hydraulic fluid around hoses, cylinders, or the pump.
  
• Sluggish movements in the loader.
  
• Low fluid levels despite refilling.
  

Solution:

• Inspect all hoses, fittings, and cylinders for signs of leaks or damage.
  
• Replace any damaged hoses or seals.
  
• Tighten any loose fittings, but be careful not to overtighten and cause further damage.
  

5. Faulty Control Valve
The control valve regulates the flow of hydraulic fluid to the various cylinders that move the loader’s arms, bucket, or drive system. If the control valve malfunctions, it can result in poor or erratic control of the loader’s movements.
Symptoms of Control Valve Failure:

• Jerky or delayed response to operator controls.
  
• Inconsistent movement in the loader’s arms or bucket.
  
• Fluid leaking from the valve.
  

Solution:

• Check the control valve for any visible damage, blockages, or leaks.
  
• Clean or replace the control valve if necessary.
  
• Ensure that all electrical or mechanical connections to the valve are intact and functioning correctly.
  

6. Air in the Hydraulic System
Air entering the hydraulic lines can cause a loss of pressure and lead to erratic or unresponsive hydraulic movements. This typically happens due to a loose fitting or a damaged seal.
Symptoms of Air in the System:

• Spongy or jerky movements.
  
• Loss of lifting or dumping ability.
  
• Air bubbles in the hydraulic fluid.
  

Solution:

• Bleed the hydraulic system to remove any air trapped in the lines.
  
• Tighten all fittings and inspect for leaks that may allow air to enter the system.
  

Preventative Maintenance for the Cat 773 AHC
Regular maintenance is key to keeping your Cat 773 AHC operating smoothly and preventing hydraulic system failures. Here are a few tips:

• Check Fluid Levels: Always ensure the hydraulic fluid is at the correct level and top it off as necessary.
  
• Replace Filters Regularly: Change the hydraulic fluid and filters at the intervals specified by the manufacturer.
  
• Inspect for Leaks: Regularly check hoses, fittings, and cylinders for any signs of leaks and repair them promptly.
  
• Clean and Protect the System: Keep the hydraulic components clean and free from contaminants to ensure smooth operation.
  
• Monitor Performance: Pay attention to any unusual sounds or behavior from the loader, as they may be early signs of an issue.
  

Conclusion
The Cat 773 AHC is a robust machine, but like all heavy equipment, it is prone to issues over time. A malfunctioning hydraulic system can prevent the loader from operating correctly, causing delays and additional costs. By identifying common problems like low fluid, contamination, or pump failure, and taking the proper steps to repair them, you can restore your Cat 773 AHC to peak performance. Regular maintenance and attention to detail will help ensure the longevity of your machine and reduce the risk of major breakdowns in the future.