Rear Diff Dripping

[dogren]

Truck is an '01 with 160,000 miles and now has a slow drip at the bottom of the rear diff. Nothing major, yet. Anything special to consider when going after the seal? Are most folks using the purple "magic" from GM, or other synthetic? Any and all thoughts would be appreciated.
Dave

[DmaxMaverick]

Is it leaking from the cover, or pinion seal? Or, could it just be the drain plug? If you've overfilled it at any time, and the vent tube was blocked, it could cause leakeage due to pressure build up in the assy.

If it's the cover, toss the gasket and use an RTV friendly with your lube. Some of the gear lubes are not friendly with standard RTV, and the RTV will turn to goo. The GM gray gasket maker (like used on the valve covers) is good, and shouldn't react with the synthetic lubes. Regular black or blue RTV will, with some lubes. Better yet, go with a MagHytech, or similar cover, which uses an O-ring gasket, and no sealant. Just lube the O-ring well. Added bonuses are increased capacity, temp probe bung, aluminum, and better heat transfer.

If it's the pinion seal, nothing special there. Be sure to mark the location of the driveshaft and pinion yoke, and measure the torque applied to the nut, and reinstall it exactly as it was before. Overtightening will throw off the pinion gear crush spacer. Check the pinion yoke well, and look for scoring on the sealing surface. If it's scored, you can use a "Speedy-Sleeve" to correct the sealing surface in many cases. Otherwise, you'll need a new yoke. You will need a new self-locking nut for the install. Do not reuse the old nut. The driveshaft should be reinstalled in the same orientation as it was before. Now would be a good time to replace the U-joints, as well, if you haven't done it recently.