Axle Seal Replacement on the Bobcat 843 and the Challenges of Single-Piece Axle Design

[MikePhua]

The Bobcat 843 and Its Place in Skid Steer History
The Bobcat 843 skid steer loader was introduced in the 1980s as part of Bobcat’s push into higher-capacity compact equipment. With a rated operating capacity of approximately 1,700 lbs and a robust hydraulic system, the 843 was designed for construction, landscaping, and agricultural use. Bobcat, founded in 1947 and headquartered in North Dakota, pioneered the skid steer concept and remains one of the most recognized names in compact equipment globally.
The 843 featured a chain-driven axle system and a mechanical layout that allowed for high torque transfer in a compact footprint. However, its original single-piece axle design introduced challenges when servicing components like seals and bearings, especially on the rear axle.
Terminology Annotation

• Axle Seal: A rubber or composite ring that prevents hydraulic fluid or gear oil from leaking at the axle shaft interface
  
• End Play: The axial movement of the wheel or axle shaft, used to assess bearing wear
  
• Chaincase: The enclosed compartment housing the drive chains and sprockets
  
• Porta-Power: A hydraulic ram tool used to apply force in confined spaces
  

Identifying Seal Failure and Assessing End Play
A leaking axle seal on the Bobcat 843 often presents as oil seepage around the wheel hub, accompanied by increased end play. If the wheel moves in and out slightly when lifted, the bearings may still be serviceable. However, excessive movement suggests bearing wear and the need for a more comprehensive rebuild.
To assess end play:

• Jack up the machine and secure it on stands
  
• Remove the wheel and manually shift the hub in and out
  
• Measure movement with a dial indicator or feeler gauge
  
• Compare against service manual tolerances (typically under 0.010 inches)
  

If end play exceeds acceptable limits, replacing both the seal and bearing is recommended.
Disassembly Strategy for Rear Axle Seal Replacement
Rear axle seal replacement on the 843 is notably more complex than the front due to limited access and the proximity of hydraulic components. The original single-piece axle requires internal force to be removed, often necessitating a porta-power and shims.
Step-by-step approach:

• Steam clean the machine to remove debris and oil residue
  
• Raise the loader arms and secure the cab in the upright position
  
• Remove the wheel and steering linkage on the affected side
  
• Loosen or remove the hydraulic pump mounts for clearance
  
• Open the chaincase and remove the sprocket retainer bolt (often Loctited and torqued heavily)
  
• Insert a bottle jack between the axle flange and frame to press the axle outward
  
• Extract the outer bearing and seal, inspecting the seal surface for scoring or pitting
  

If the axle shaft is damaged, replacement is necessary. Bobcat offers a two-piece axle retrofit that simplifies future service by allowing external seal installation.
Special Tools and Installation Techniques
Installing the new seal requires precision. For the single-piece axle, a specialized tool centers the seal and sets its depth within the axle tube. Without this tool, misalignment can lead to premature failure.
Recommended tools:

• Seal driver matched to axle diameter
  
• Depth gauge or collar to ensure proper seating
  
• Torque wrench for sprocket retainer bolt (typically 150–200 ft-lbs)
  
• Loctite 271 or equivalent for bolt threads
  

For the two-piece axle, the seal installs from the outside, eliminating the need for internal press tools. This design also reduces labor time and improves long-term serviceability.
Cost Considerations and Dealer Alternatives
Labor costs for rear axle seal replacement can exceed $1,200 at a dealership, not including parts. DIY repair can reduce expenses significantly but requires mechanical skill and proper tooling.
Estimated costs:

• Seal and bearing kit: $80–$150
  
• Replacement axle (if needed): $300–$500
  
• Specialized seal driver: $50–$100
  
• Shop time: 6–10 hours depending on experience
  

Some operators opt to upgrade to the two-piece axle during seal replacement to simplify future maintenance. Others choose to outsource the job entirely, especially if the axle shaft shows wear or the chaincase is contaminated.
Field Anecdotes and Practical Advice
One technician shared that during a rear axle seal replacement, the hub released violently after heating the keyway and striking it with a sledgehammer. The hub shot nearly 20 feet across the shop, underscoring the importance of controlled force and proper restraint.
Another operator noted that breaking the drive chain and using a porta-power was the only reliable method to remove the rear axle on his unit. He recommended steam cleaning the machine beforehand to avoid contamination during disassembly.
Tips for success:

• Photograph each step during teardown for reference
  
• Label bolts and components to avoid confusion
  
• Replace seals and bearings in pairs to ensure balance
  
• Inspect chaincase oil for metal shavings or water intrusion
  

Conclusion
Replacing a leaking axle seal on the Bobcat 843—especially on the rear axle—is a labor-intensive but manageable task with the right tools and preparation. Understanding the differences between single-piece and two-piece axle designs, assessing end play accurately, and using proper installation techniques are key to a successful repair. For owners committed to maintaining their machines, this procedure not only restores performance but extends the life of a classic workhorse in the compact equipment world.