Symptoms
Unknown service history, whining diffs, a 4WD system that's never been exercised.
The fix, step by step
- Always break the fill plug loose first.
- Rear diff and transfer case use 24 mm plugs; the front diff needs a 10 mm hex after removing the 12 mm-bolted skid plates.
- Drain each, fit new washers, and refill until it drips from the fill hole.
- Toyota-Club's owner's-manual data calls for GL-5 75W-90 in the front diff and transfer case but GL-5 80W-90 in the rear (some owners run 75W-90 throughout); 4Runners.com quotes roughly 1.5 qt front, 1.5 qt transfer case and 3.2 qt rear.
- Cycle 4Hi and 4Lo afterwards.
Tools & part numbers
- 24 mm socket
- 10 mm hex
- 12 mm socket
- fluid pump
- GL-5 75W-90 and 80W-90
- washers 90430-18008 (t-case), 12157-10010 and 90430-24003 (diffs)
Where to buy the parts
Gear oil & drain-plug gaskets — 2005 4Runner catalogRockAuto ↗
Hunting a used or discontinued part? Search eBay Motors for Toyota 4Runner 4th Gen parts →
Rated for a competent home mechanic with a decent tool kit. Confirm torque figures, fluids and procedures against the factory service manual for your VIN, support the truck on stands rather than a jack, and work at your own risk (disclaimer). Some parts links are affiliate links, which pay us a small commission at no cost to you.