Toyota Pinion (and t-case) Seal Replacement / ..

If you see gear oil leaking out around the pinion flange on your differential, it is likely that the seal inside is the cause of the leak. You should first check that the breather for the axle housing is not plugged, as this can lead to increased pressure inside the axle when it heats up and that can cause oil leaks as well. A related issue is if the nut on the pinion flange has worked loose and you can feel a little play at the flange. This may cause a slight leak and you'll also feel a slight vibration in that driveshaft at speed when you just back off the gas pedal. In this condition, you have unloaded the shaft and any play in the flange can lead to a vibration that will not be there under load.

 
  If you have a relatively low pinion angle (i.e. the pinion flange is below the level or the gear oil fill hole in the axle, you might want to drain some gear oil or be prepared to catch whatever comes out of the pinion shaft hole. Elevating the opposite end of the truck may help contain the oil. Then, un-stake the pinion flange nut. Use a 30mm, 6-sided regular socket to remove the pinion nut (avoid the 12-point sockets - too easy to strip the nut and impact sockets are often too thick to fit down around the nut - and if you have a VW, this is the same size as the front axle nut), count the number of turns needed to remove it and reinstall with the same number to retain the pinion bearing pre-load. With the pinion nut, washer and flange removed, the pinion seal is revealed. You may be able to remove the seal with a flat-bladed screwdriver, but be very careful not to damage the pinion shaft in doing so. I chose to use a seal puller like this to remove mine. I picked it up for about $7 from Harbor Freight. You slip the end of the puller along the pinion shaft, catching the lip of the seal, then use a hammer to tap on the T and pull the seal out.  
 

 
  I used a new seal from Toyota, p/n 90311-38047. Be sure to apply some grease along the inside of the seal lip and make sure the pinion flange sealing surface is not grooved. If it is the new seal may leak, a new flange is available from the dealer. I found a 50mm socket that worked well to push the new seal into place. A rubber mallet may work as well, tapping gently around the periphery of the seal to seat it evenly. To help prevent leaks, you can apply some RTV silicone sealant (gear oil rated compound, Toyota FIPG orange or Permatex Ultra-gray should be good) to the splines of the pinion shaft prior to sliding the pinion flange on. Reinstall the flange, washer and nut. If the old nut is in decent shape, it can probably be reused, if not a new nut is available from the dealer. Tighten the nut the same number of turns as it took to remove it and tighten no more than about 90 ft.lbs. or until the stake mark aligns with the groove in the pinion shaft. Check the flange for play and for being overly tight. If it feels OK, re-stake the lip of the nut with a punch and hammer to keep it from loosening up, then re-install the driveshaft bolts, tighen to factory spec. (~54 ft.lb.) and you are done. If you drained the gear oil, be sure to replace it before driving, approx. 2.5 qts. of GL-5 should do it.  
 

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