Case 1845C M91 Tandem Pump: Troubleshooting and Insights

[MikePhua]

The Case 1845C skid steer loader is a versatile and reliable machine, frequently employed in construction, landscaping, and various industrial operations. A core component of the Case 1845C is its hydraulic system, which powers many of its essential functions, such as the lifting arms, bucket operation, and drive motors. At the heart of this system is the M91 tandem hydraulic pump. Understanding its function, common issues, and solutions is essential for maintenance and troubleshooting.
Understanding the M91 Tandem Pump
The M91 tandem pump on the Case 1845C is designed to handle high-pressure fluid and provide the necessary flow to the machine’s hydraulic systems. It’s a gear pump that combines two pumps within a single unit. The "tandem" designation refers to the arrangement of these pumps, which share a common housing but operate independently. One pump handles the auxiliary hydraulics, while the other is responsible for driving the machine’s wheels and lift arms.
The tandem pump plays a vital role in ensuring that the loader’s hydraulic systems function smoothly and with minimal downtime. However, as with any mechanical system, it is susceptible to wear and tear, leading to potential issues that require troubleshooting and repairs.
Common Issues with the M91 Tandem Pump

1. Loss of Hydraulic Power: One of the most common problems faced by Case 1845C operators is a loss of hydraulic power. This can manifest as slow or unresponsive movement in the loader arms or a lack of force when using the auxiliary hydraulics. The cause of this issue is often related to the tandem pump’s failure to provide adequate fluid flow, which may be the result of wear, contamination, or damage within the pump.
   
2. Leaks: Hydraulic leaks are another frequent issue in older machinery, and the M91 tandem pump is no exception. Leaks may occur at the pump seals or within the hydraulic lines, leading to a loss of hydraulic fluid and a drop in system performance. Not only does this pose a risk of system failure, but it can also be a safety hazard if the fluid leaks onto the ground or other components.
   
3. Overheating: Overheating can occur when the hydraulic fluid is not circulating properly or when the pump is under too much strain. This is often caused by a blockage or a clogged hydraulic filter, which reduces the pump’s ability to circulate fluid efficiently. Overheating can lead to serious damage to the pump, the hydraulic system, and other components if not addressed promptly.
   
4. Cavitation: Cavitation occurs when the pump is unable to draw in enough fluid, causing air to enter the system. This results in the formation of bubbles that can damage internal pump components, causing a loss of performance and potentially requiring expensive repairs. Cavitation is typically the result of low fluid levels or a damaged pump inlet, so keeping the system well-maintained is essential.
   

Diagnosing Problems with the M91 Tandem Pump
Proper diagnosis is crucial to effectively resolving any issues with the M91 tandem pump. Here are some common steps and tools used to diagnose problems:

1. Fluid Level Check: The first step in troubleshooting is always to check the hydraulic fluid level. If the fluid is low, it could cause a lack of pressure and lead to the aforementioned issues. Make sure the correct type of hydraulic fluid is used, as improper fluid can lead to pump damage.
   
2. Pressure Testing: Use a hydraulic pressure gauge to test the system’s pressure at various points, such as at the pump outlet or near the lift cylinders. A drop in pressure can indicate a problem with the pump or another component in the hydraulic circuit, such as a valve or hose.
   
3. Inspection for Leaks: Thoroughly inspect the M91 tandem pump and the surrounding hydraulic lines for signs of leaks. Leaking fluid can cause performance issues and indicate a damaged seal or hose. It’s also important to check for any oil contamination in the system, as this could signal a failure in the pump or filters.
   
4. Check for Overheating: Overheating issues can often be traced back to clogged filters or restricted fluid flow. If the pump is running hot, it is essential to clean or replace the hydraulic filters, ensure that the cooler is functioning correctly, and check for any obstructions in the system.
   
5. Listen for Unusual Noises: The M91 tandem pump, like all hydraulic pumps, operates smoothly when in good condition. If you hear any unusual noises, such as whining or grinding, this could indicate internal damage, air in the system, or cavitation.
   

Solutions for M91 Tandem Pump Problems

1. Replacing the Pump: If the pump is damaged beyond repair, replacing it may be the only viable option. The M91 tandem pump is a critical part of the hydraulic system, and using a damaged or malfunctioning pump will only worsen performance issues. Make sure to order the correct replacement parts from authorized dealers to ensure compatibility.
   
2. Seal and Hose Replacement: If leaks are identified, the first step is to replace any worn seals and hydraulic hoses. Using high-quality seals and hoses designed for the M91 tandem pump will prevent future issues and improve overall system reliability.
   
3. Regular Maintenance: Regular maintenance is essential for ensuring the longevity of the M91 tandem pump. This includes checking the fluid levels, changing the hydraulic fluid at recommended intervals, and cleaning or replacing the hydraulic filters. Keeping the system free from contamination will also help avoid pump failure and system inefficiency.
   
4. Fluid Management: Ensure that the correct hydraulic fluid is used and that it is in good condition. Contaminated fluid can damage the tandem pump and other hydraulic components, so it’s important to use clean, fresh fluid at the recommended viscosity and filtration levels.
   
5. Addressing Cavitation: To avoid cavitation, always maintain the correct fluid levels and ensure that the system is properly primed. If cavitation persists, it may be necessary to replace the pump inlet or check for restrictions in the fluid lines.
   

Conclusion
The Case 1845C M91 tandem pump is a critical component in ensuring the smooth operation of the machine’s hydraulic system. Proper maintenance, regular checks, and a solid understanding of potential problems can help prevent downtime and costly repairs. Whether you're dealing with hydraulic power loss, leaks, overheating, or cavitation, understanding the underlying issues and addressing them with appropriate solutions will keep your machine running efficiently.
By following proper maintenance schedules and addressing issues early, operators can extend the lifespan of their machines, ensuring that the Case 1845C remains a reliable workhorse on the job site.