Kubota M4900 Axle Bearing Replacement - Tear Down

Main ideas / lessons

• The speaker is troubleshooting a Kubota M4900 steering knuckle/axle bearing failure after noticing gear oil leaking from the bottom of the steering knuckle.
• Although the usual repair would be replacing the bearing and seal, this teardown suggests more internal damage (e.g., metal shavings/balls and scoring).
• The goal is to fully disassemble (“tear down”) enough to assess how extensive the damage is so they can generate an accurate parts list and order the correct components.
• The video emphasizes key decision points, especially whether to:
  • Reuse a worn/possibly damaged hub/part, or
  • Replace additional components to ensure the bearing will seat correctly and avoid repeat failure.

Method / workflow shown

Initial setup

• Recognize the problem: gear oil came out of the bottom of the steering knuckle.
• Plan: tear down the assembly to determine whether the repair is limited (bearing + seal) or extends inward to other components.

Stabilize and prepare

• Lower the tractor/adjust height so the damaged side is lower than the other side to help manage leaks.
• Place a catch under the leak.
• Remove the tire (mentioned as likely necessary) to access parts.

Disassembly steps

• Remove a retaining component using appropriate tools (a brass rod is used first to avoid damaging the steel).
• Use controlled prying/lifting to separate components:
  • A screwdriver or pry bar lifts slightly to start movement.
  • Steady pressure + slight wiggle continues until parts come free.
• Identify components:
  • Ball bearings and associated parts are found contaminated with metal debris.
  • Inside surfaces show heavy scoring from metal contact.
  • A part/bearing/race separates from the shaft:
    • The retaining ring is removed using pliers.

Inspection and damage assessment

• Confirm internal damage:
  • Metal shavings/pieces are present.
  • Surfaces are scored and “messed up” inside the housing.
  • A part likely identified as a bearing race shows pronounced scoring.
• Additional checks:
  • Some bearings appear “in pretty good shape,” but at least one housing-side component is not in good condition.
  • The shaft looks comparatively less damaged than the gears/bearing areas.

Evaluate reusability

• Some components show wear, but the key concern is whether critical surfaces will allow proper function:
  • The speaker is unsure whether the bearing/hub interface will seat correctly if reused.
• They test ideas informally (e.g., “try an old bearing to see if it works”), but express doubt about reuse.

Cleaning / preparation for repair

• Strong emphasis on thorough cleaning, since the bearing will sit in the damaged area and must seat properly.

Apply penetrating fluid (for disassembly help)

• Use PB Blaster (a chlorine version) as a penetrating spray with a functioning nozzle/jet.

Decide parts to replace

• Likely replacement scope discussed:
  • Replace the bearing and seal inside the housing.
• Ongoing uncertainty:
  • Whether to replace the hub/outer part, since scoring/wear may affect bearing seating.

Wrap-up

• After teardown, the speaker will order parts, complete the repair, and post a follow-up video.

Specific details mentioned (equipment / products / tools / parts)

Gloves

• Harbor Freight gloves (mentions “5 mil” and possibly 7 mil).

Tools and techniques

• Brass rod to avoid damaging steel
• Pry bar / screwdriver for gentle lifting
• Pliers for retaining ring removal
• Tr-bar mentioned during removal/handling

Penetrating fluid

• PB Blaster (chlorine version)

Parts referenced

• Steering knuckle
• Bearings
• Seal
• Bearing race
• Retaining ring
• Possibly a shim
• Hub (a potential replacement decision)
• Gear/gear assembly (scored internally)

Speakers / sources featured

• Speaker / creator: “Milat Farms” (the channel host; intro includes “hi guys welcome to Milat Farms…”)
• No other named people are featured.
• Product sources referenced: PB Blaster; Harbor Freight gloves.