Steering Control Shaft Leaks on the Bobcat 863

[MikePhua]

Introduction
The Bobcat 863 skid steer loader is a rugged, durable machine that has earned a reputation among contractors and rental yards for its simplicity and workability. It’s powered by hydraulics, with drive motors, steering linkages, a chaincase, and control shafts all working together to move and steer the machine. Among its more frequent maintenance issues is leakage at steering control shafts and carrier seals—this can lead not only to hydraulic fluid loss but also to loss of traction, messy chaincase overflow, and eventually component damage.

Technical Concepts

• Carrier Seal: Seal located in or around the steering/motor carrier shaft (inside the chaincase) that prevents hydraulic oil from leaking out into the chaincase or out through shafts.
  
• Chaincase: The enclosed housing in the skid steer that contains the drive motors, gears, shafts, and is partly filled with oil to lubricate and cool moving parts.
  
• Drive Motor: Hydraulically driven motor whose output connects to wheels via shafts and carriers; it handles converting hydraulic flow and pressure into mechanical rotation.
  
• Hydraulic Internal Leak: When oil escapes from inside hydraulic components via seals, plugs, or breaches—this may not be visible externally unless oil builds up in the chaincase or leaks through vents.
  
• Hex Plug on Carrier Shaft: A threaded plug (often factory installed) at the end of a hollow carrier shaft; if fitted improperly or protruding, it can be a failure point for leaks.
  

Common Symptoms
Users with Bobcat 863 machines often report:

• Hydraulic oil level in the tank slowly dropping while chaincase oil level rises.
  
• Machine staying “dry” externally until chaincase overflows; leaks then appear from axles, vent holes, or covers.
  
• Steer or drive feeling “draggy” or sluggish—fluid leakage inside the chaincase reduces available pressure or causes fluid mixing.
  
• Oil pooling under the machine or in the belly pan (under the chaincase or steering shafts).
  

Root Causes
From field investigations, experienced mechanics have identified a few key failure modes:

1. Worn Carrier Seals
   These seals, which interface between the drive motor/axle carrier and the chaincase, degrade with time and wear. Once compromised, hydraulic oil escapes into the chaincase.
   
2. Defective Factory Hex Plugs
   Early or defective manufacturing of carrier shafts included hex plugs that were either mis-machined or protruded beyond the proper surface level. If the plug is loose or not seated properly, it allows internal pressure to push oil out along the shaft.
   
3. Axle / Shaft Wear
   Grooved or worn shafts cut into seal lips, reducing seal effectiveness.
   
4. Chaincase Overfill or Plug Blockage
   Sometimes users notice that vents or drain plugs in the chaincase are blocked, causing accumulation of leaked oil and masking origin of leak.
   
5. Leak Paths via Vent or Cover Plates
   Once chaincase is full, oil finds a path via vent holes, axle boots, or around covers; these visible leaks are symptoms, not root causes.
   

Diagnosis Steps
To accurately locate and confirm a leak at steering control or carrier shafts, the following steps are effective:

• Clean the area thoroughly: degrease, remove dirt and oil from chaincase, covers, axle boots. A clean area makes it easier to see fresh leaks.
  
• Run the machine under load (e.g. drive, turn, operate attachments) to build internal hydraulic pressure. Observe for any fresh seepage around shafts, hex plug areas, or seals.
  
• Inspect the hex plug at carrier shaft: check whether it is flush or protruding; check for looseness.
  
• Remove side covers or access plates to visually inspect seals on drive motors and carrier shafts.
  
• Check chaincase oil level and hydraulic oil level to see whether oil is migrating from hydraulic system into chaincase.
  
• If possible, remove the drive motor / carrier assembly to press out the carrier shaft and inspect seal lips and shaft surface for wear or damage.
  

Repair and Solutions
Once diagnosis confirms a leak at steering control shafts or carrier seals, these have proved effective fixes:

• Replace worn seals. Seal kits covering the carrier seals are available. Make sure correct size and material are used.
  
• Replace or reseat the hex plug properly when it is the source. If a factory defect causes a loose or protruding plug, either replace the plug or the shaft (or carrier assembly). Some users have opted for new carrier shafts when the plug is irreparably bad.
  
• Address shaft wear: if grooves or scoring exist on the shaft, those must be smoothed or replaced to prevent recurring seal damage.
  
• Clean or unblock chaincase drains and vent holes to ensure leaked oil does not accumulate and hide new leaks.
  
• Use proper torque on bolts for carrier assembly/drive motor mounts. Loose components can vibrate and accelerate seal wear.
  

Case Story
One operator with a 1997 Bobcat 863 was finding hydraulic tank oil disappearing slowly while chaincase kept filling. No obvious external leaks until the chaincase overflowed, causing oil to pour out around axles and under the machine. After carefully removing the drive motor, they found the hex plug on the carrier shaft protruding slightly and a rough groove on the shaft. Replacing the shaft plus new carrier seals solved the leak permanently. The operator reported that after that repair, oil loss stopped completely for over 18 months of heavy use.

Preventive Practices
To avoid recurring leaks in steering control shafts or carrier carrier seals, routine maintenance helps:

• Inspect carrier seals during scheduled preventive maintenance (e.g. every 500-1000 hours).
  
• Keep all covers, side plates, and vent/drain plugs clean so you can spot fresh leaks early.
  
• Check hex plugs at carrier shafts for looseness or protrusion whenever performing drive motor or chaincase work.
  
• Maintain hydraulic oil cleanliness; contamination accelerates seal and shaft wear.
  
• Avoid letting chaincase overfill—monitor levels.
  

Conclusion
Leaks at the steering control shafts or carrier seals in a Bobcat 863 are a known weak point—often traced to worn seals or faulty hex plugs. Though leaks may seem only messy, their effect on chaincase oil contamination, drive motor lubrication, and component lifespan makes them serious. Accurate cleaning, inspection, and targeted repair (seal or shaft replacement) typically resolve the issue. With vigilant maintenance, these problems can be identified early, keeping the machine reliable and reducing both fluid loss and repair downtime.