Bobcat S250 Hydrostatic Pump Shaft Seal Repair Guide

[MikePhua]

Issue Overview
A common maintenance challenge on the Bobcat S250 skid steer loader involves oil leaks from the main seal on the hydrostatic pump drive shaft. This seal prevents hydraulic fluid from escaping the pump housing, maintaining system pressure and preventing contamination. Over time or due to wear, this seal can degrade, requiring replacement.
Repair Feasibility
Although the official Bobcat repair manual suggests removing the entire pump/engine assembly for seal replacement, many operators have successfully completed the repair with the assembly still installed. This approach is often favored in confined or home workshop spaces where heavy lifting equipment is limited.
Repair Procedure Highlights

• Gain access to the hydrostatic pump by removing the skid steer’s necessary panels and possibly pulley components.
  
• Carefully remove the seal retaining plates and surrounding components. Expect hydraulic fluid to leak; some operators drain hydraulic oil beforehand to minimize mess.
  
• Underneath the plates, locate the worn seal and carefully remove it without damaging the shaft.
  
• Install the new seal with its accompanying O-rings and retaining plates, ensuring orientation and fitment match OEM specifications.
  
• Use tools such as spring compressors or alternative methods (zip ties, door spring tools) to compress return springs during reassembly.
  
• Maintain cleanliness throughout the process to prevent contamination within the hydraulic system.
  
• Reassemble all components in reverse order and refill any lost hydraulic fluid, then test for leaks and performance before full operation.
  

Terminology

• Hydrostatic Pump: A pump that converts mechanical energy into hydraulic energy to power the loader’s drive systems.
  
• Drive Shaft Seal: A sealing element preventing fluid leakage from the pump shaft interface.
  
• Seal Retaining Plate: A component securing the seal in its housing.
  
• Return Spring: Spring mechanism that maintains tension on seals or other components for proper fit.
  
• Hydraulic Fluid Drain: Removing fluid to prevent spillage during disassembly.
  

Practical Advice

• Many operators report that the in-place seal replacement requires patience but avoids the complexity and risks of pump removal.
  
• Utilizing a vacuum system or draining the hydraulic reservoir reduces fluid loss during the repair.
  
• Proper spring compression tools or creative improvised methods can facilitate easier reassembly.
  
• Changing seals on both sides is advisable when accessible to avoid recurrent leaks.
  

Industry Insight
A technician shared experience replacing the steering pintle shaft seal similarly, cautioning about the bearing underneath that can be pushed out by hydraulic pressure if not managed. This emphasizes the importance of methodical disassembly and reassembly to avoid further damage.
Summary
Replacing the Bobcat S250 hydrostatic pump shaft seal is a challenging yet feasible maintenance task that can often be completed without removing the pump or engine assembly. Careful preparation, tool usage, and adherence to proper seal handling prevent hydraulic leaks and maintain machine reliability. This repair preserves the skid steer’s operational life while minimizing downtime and disruption in limited workspace settings.