Diagnosing Total Hydraulic Failure on a Case 1845B Skid Steer

[MikePhua]

The Case 1845B and Its Hydraulic Architecture
The Case 1845B skid steer loader was introduced in the early 1980s as part of Case’s push into compact equipment. With a reputation for mechanical simplicity and robust performance, the 1845B became one of the most widely used skid steers in North America. It featured a chain-driven transmission, a gear-type charge pump, and dual hydraulic pumps mounted directly to the engine flywheel housing. These pumps powered both the drive motors and the loader arms, making hydraulic integrity central to machine function.
The hydraulic system on the 1845B is fully dependent on engine rotation. The flywheel coupler transfers torque to the pump shafts, which in turn pressurize the system. Any failure in this mechanical link can result in total hydraulic loss, even if the engine runs smoothly.
Symptoms of Sudden Hydraulic Loss
A complete loss of hydraulics—both drive and loader functions—can occur abruptly. In one documented case, the operator attempted a tight turn in soft soil and immediately lost drive power. Within seconds, the loader arms also stopped responding. The engine continued to run without abnormal noise, and fluid levels appeared normal. Attempts to tow the machine were met with resistance, suggesting hydraulic lock rather than mechanical seizure.
This pattern points to a failure in the pump drive system rather than a fluid leak or valve malfunction.
Flywheel Coupler and Pump Shaft Inspection
The most common failure point in this scenario is the flywheel coupler—a rubber or composite disc that connects the engine flywheel to the hydraulic pump input shafts. Over time, the coupler can shear or strip its splines, especially under high torque conditions like aggressive turning or sudden load shifts.
To diagnose:

• Remove the front hydraulic pump and inspect the shaft for rotation
  
• Manually rotate the engine crankshaft and observe whether the pump shaft turns
  
• If the shaft remains stationary, the coupler or internal shaft is likely broken
  

In one field case, the operator rotated the crankshaft 90 degrees and noted that the pump shaft did not move. This confirmed a mechanical disconnect between the engine and pump.
Failures typically occur at the crankcase side of the shaft, where torque is highest. The splines may strip, or the shaft may shear entirely. If the coupler appears intact, the internal shaft should be removed and inspected for fractures or wear.
Charge Pump Function and Misleading Indicators
The charge pump, which primes the hydraulic system and maintains pressure for the drive circuit, may still appear functional even when the main pump is compromised. Turning the charge pump by hand and observing oil movement can give a false sense of system integrity. However, without torque transfer from the engine, the charge pump cannot sustain pressure under load.
To verify:

• Pour oil into the charge pump inlet and rotate manually
  
• Confirm oil movement, but do not assume full system function
  
• Check for pressure at test ports with engine running
  

If the charge pump appears to work but no hydraulic functions respond, the issue is almost certainly upstream—at the coupler or main pump shaft.
Tow Resistance and Hydraulic Lock
When attempting to tow a 1845B with failed hydraulics, resistance may occur due to locked drive motors. These motors are hydrostatic and require fluid bypass to allow free movement. Loosening the hydraulic lines at the pumps can relieve pressure and allow towing, but care must be taken to avoid contamination or fluid loss.
Best practices:

• Loosen lines slowly and allow pressure to bleed
  
• Cap or plug lines to prevent dirt ingress
  
• Tow at low speed and avoid sharp turns
  

In some cases, removing the drive chains or disconnecting the motor shafts may be necessary for long-distance towing.
Preventative Measures and Long-Term Reliability
To prevent future failures:

• Inspect flywheel coupler annually for wear or cracking
  
• Replace coupler every 2000–3000 hours or sooner in high-load environments
  
• Use OEM or high-quality aftermarket couplers with correct spline fit
  
• Monitor hydraulic fluid condition and change filters regularly
  
• Avoid aggressive maneuvers in soft terrain that stress the drivetrain
  

Operators in sandy or muddy conditions should be especially cautious. Soft ground increases resistance and torque demand, which can overload the coupler and pump shafts.
Conclusion
A sudden loss of hydraulics in a Case 1845B is often traced to a mechanical failure at the flywheel coupler or pump shaft. By methodically inspecting the torque transfer components and verifying shaft rotation, technicians can isolate the issue and restore function. These machines were built for durability, but even the toughest iron needs a solid link between engine and hydraulics. When that link breaks, the solution lies not in fluid levels or filters—but in the heart of the drive system itself.