Drain and refill both diffs with API GL-5 75W-90 synthetic gear oil every 30,000 miles, or every 15,000 if you wheel or tow. R51 rear diff takes about 3 US pints (1.5 quarts); R51 front takes 1.95 quarts. If you have the optional limited-slip rear, add the Nissan friction modifier or the LSD will chatter on tight turns.
Three generations, same basic procedure, three different fluid amounts. WD21 (1985–1995) ran Dana 44a-style axles on early trims and a Nissan H233 rear on others. R50 (1996–2004) uses Nissan's R200A rear and the front IFS R180 or similar. R51 (2005–2012) carries the R200B rear and a front IFS housing. Capacity differs slightly between generations, but the API GL-5 75W-90 synthetic spec is universal.
Two plugs on each housing: a fill plug (higher) and a drain plug (lower). Always crack the fill plug loose first. If the fill plug is seized or the head is stripped, you discover that BEFORE you've drained the housing dry — otherwise you have an empty diff and no way to refill it. Some R51 fill plugs use a 10mm hex/Allen drive; some use a 3/8" square drive that a ratchet handle fits directly into. Confirm yours before reaching for tools.
The R51 rear diff with the optional limited-slip clutch pack needs Nissan's friction modifier added to the fluid (Nissan part KLD20-00001 or equivalent). Without it, the clutches grab in turns and you get a noticeable chatter on slow tight corners. Most R51s came with an open rear — only the off-road trims and some 2008+ packages got the LSD. Check the door sticker or look for the "Limited Slip" badge on the tailgate.
Fill until fluid runs out the fill hole. That's it. Do not measure. The fill hole IS the level gauge. If you measure and pour, you'll either overfill (vent leak) or underfill (whine). Run fluid pump until it dribbles back at you, install the plug, done.
| Part | Vendor | Est. price |
|---|---|---|
| Mobil 1 75W-90 Synthetic Gear Oil (1 quart) | Mobil 1 | ~$14 |
| Liqui Moly 75W-90 GL-5 Synthetic Gear Oil | Liqui Moly / Z1 Off-Road | ~$18 |
| Drain/fill plug crush gasket | Nissan | ~$1 |
| Limited slip additive (rear only if R51 LSD) | Nissan | ~$12 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.