You’ll prep with a 12mm, 10mm hex, and 24mm socket, about 7 qts of 75W‑90 gear lube, and replacement crush washers; work on level ground with chocks and jack stands. Remove skid plates, locate fill and drain plugs, loosen fill first, drain for 10–15 minutes, replace washers, refill until gear oil drips, torque plugs, and inspect for leaks after a short drive. Follow intervals and fluid specs for best results if you want step‑by‑step guidance.
Prep: Tools, Fluids (Quantities), and Safety Checks
Start by laying out the tools and fluids you’ll need and confirming safety measures before you jack up the truck. You’ll gather essential equipment: a 12mm socket for skid plates, a 10mm hex key for differential plugs, and a 24mm socket for rear differential and transfer case drain/fill plugs. Stock roughly 7 quarts of 75W-90 gear lubricant — about 1.5 qts each for the front differential and transfer case, and ~3.2 qts for the rear. Bring replacement gaskets (for example, part 90430-18008 for the transfer case) to prevent leaks on reassembly.
Implement safety precautions: work on level ground, chock wheels, and use rated jack stands after lifting. Warm the drivetrain with a short drive to thin old fluid for cleaner draining. Before removing any drain plug, confirm the fill plug loosens easily to avoid being stranded with a drained housing. Organize parts and fluids so the service proceeds efficiently and confidently.
Locate Plugs and Skid Plates (Photos & Access Tips)
Before you drain anything, remove the front skid plates with a 12mm socket—support each plate as you back out the last bolts so it doesn’t drop—and inspect the plate and mounts for damage. Use photos to document orientation and fastener locations for reinstall. This is skid plate maintenance in practice: check for bends, cracks, and loose or missing hardware before proceeding.
Locate the front differential drain and fill plugs; they require a 10mm hex key. Photograph plug faces and surrounding seals so you can verify leak sources during differential inspection. For the rear differential and transfer case, identify their larger plugs—24mm sockets fit these plugs. Note plug accessibility and any obstructions; loosen the rear fill plug first as a procedural safety step (do not drain yet). Measure clearances and plan jack or stand placement to maintain safe access. Work methodically, capture reference photos, and confirm all skid plate mounts are serviceable before moving to fluid removal.
Drain & Fill: Rear Differential and Transfer Case (Step-by-Step)
Once you’ve confirmed the fill plug will come out, loosen it first on both the rear differential and transfer case so you won’t be trapped with a drained unit you can’t refill. Position a drain pan, remove the drain plug, and use proven drain techniques: let oil stream freely for 10–15 minutes until flow slows. Replace the drain-plug washer with a new one before reinstalling to guarantee a seal.
With drain complete, fill each housing with ~1.5 quarts of 75W-90 gear lubricant — the recommended fluid type — until lubricant begins to drip from the fill hole, confirming correct level. Reinstall and hand-tighten fill and drain plugs; torque per manufacturer specs if you prefer, but avoid overtightening.
Clean surrounding areas, then take a short drive and recheck for leaks. Record mileage and plan the next service at 20k–30k miles under normal conditions. This methodical routine frees you from guesswork and keeps driveline components reliable.
Service the Front Differential (Skid-Plate Removal, Drain, Refill, Reassembly)
With the rear differential and transfer case drained and filled, move on to the front differential by first removing the skid plates with a 12mm socket, supporting the plates as you loosen the last bolts so they don’t drop. Loosen the fill bolt with a 10mm hex key before removing the drain bolt; that prevents airlocks and lets the fluid flow. Position an oil drain pan under the differential and let roughly 1.3–1.4 quarts of old oil drain for 10–15 minutes until the stream slows. Replace the drain plug washer, torque the drain plug, then refill through the fill hole until oil drips out, observing fluid colors for contamination clues. Install and tighten the fill plug. Reattach skid plates, securing all hardware. Start and take a short drive, then inspect for leaks. If you hear unusual differential noises after driving, stop and recheck fluid level and seals. This methodical service restores control and keeps your 4Runner liberated on the trail.
Inspect, Troubleshoot, and Recommended Fluids & Intervals
Inspect the differential and transfer case fluids every 20,000–30,000 miles under normal use (10,000–15,000 miles for frequent off‑road or heavy towing) and check for leaks, fluid color, and metallic contamination each service. You’ll perform a basic fluid analysis each interval: note color, odor, and particles; dark oil with fine metallic sheen is acceptable, but chunks or grinding metal signals internal wear. Verify drain and fill plug crush washers and replace them—don’t reuse. Use Toyota-recommended 75W-85 GL-5 for front/rear differentials (75W-90 GL-5 is a common substitute). For the transfer case, use Genuine Transfer gear oil SAE 75W or an equivalent like Redline MT-LV 70W/75W GL-4.
- Check for external leaks at seals and housings during inspection.
- Sample fluid for magnetic particle or visual fluid analysis.
- Record mileage and next interval in your maintenance log.
- Replace crush washers and torque plugs to spec.
- If contamination appears, service immediately and diagnose internals.
Frequently Asked Questions
How Often Should You Change the Differential Fluid in a 4runner?
You should change differential fluid every 20,000–30,000 miles for normal use, 10,000–15,000 if off‑roading or towing; highway use can stretch to 60,000. Use differential maintenance tips and check transfer case function.
How Much to Replace a Transfer Case on a 4runner?
Like a worn map guiding you, transfer case costs typically run $1,500–$3,000; you’ll choose replacement options from OEM ($800–$1,500) or aftermarket, and you’ll want early diagnosis to minimize labor and risks.
How Often Should I Change Diff and Transfer Case Fluid?
You should change differential and transfer case fluid every 20,000–30,000 miles under normal use, 10,000–15,000 when towing/off‑roading; Toyota’s first differential service at 150,000 miles; specify correct fluid types and service intervals.
What Is a Differential and Transfer Case Service?
Like tuning a clockwork engine, a differential and transfer case service replaces old gear oil, inspects seals, and verifies differential function while performing transfer case maintenance to preserve drivetrain freedom, reliability, and four-wheel engagement.
Conclusion
You’ve given the drivetrain a polite, mechanical spa: drained old grit, topped off with proper lubricants, and reassembled with clean fasteners and correct torque. Follow the service intervals, check seals and breathers, and treat weird noises or leaks as early invitations to inspect. With routine attention and the right fluids, your 4Runner’s diffs and transfer case will keep behaving—and quietly handing you dependable traction for many miles.
