DaChew

This is an old thread. I came across it via google and I thought I would clarify and amplify some of the information to make it a little more complete.

First off, contrary to the above, you do not need a crush sleeve - You will not be removing the pinion. Nor will you be opening the differential.

To change the front differential pinion seal on the 99 Silverado you would do the following:

Remove the negative lead off of the battery. The truck will be in neutral most of the time and that means the key will have to be in the on position and that means that many of the electrical systems will be active and that will drain your battery. Jack the vehicle up at all four corners. This will make it easy to spin the driveshaft while you're under there. If your truck is a Z-71, remove the skid pad beneath the front axle. Drain the differential by removing the drain plug. If you don't, the oil will drain on you when you remove the diff seal. Get a white or silver paint marker and mark the position of the driveshaft as it connects to the flange. You want to put everything back exactly the way it was when you reassemble - even the U-Joint cap straps. Remove the four U-Joint strap bolts - this is where being able to spin the driveshaft by hand comes in handy. You can spray penetrating oil on the caps if they're rusted to the flange to help get them loose. You don't have to remove the shaft at the transfer case, simply wire it up out of the way of the diff flange. Now mark the position of the flange nut, count the threads showing and check the resistance of the flange turning with a beam torque wrench - you can also use a click torque wrench by setting it so it clicks just as the flange begins to turn. Now you have to decide how you're going to hold the flange while you loosen the flange nut. There are tools at the local auto parts store to do this, you can use a strap wrench, a large pipe wrench will work, you can take one of the U-Joint straps and use it as a template to drill a couple of holes in a length of steel and bolt it to the flange - up to you. You are going to need a breaker bar to get that nut loose though. Remove the nut. Use a two jaw gear puller, 3" or 4" inch will work, to pull the flange from the pinion. I have a rigid paint scraper that does a dandy job of working itself under the lip of the seal and levering it out. I can even use it to pull a seal without damaging it by working slowly. You can also certainly use a screwdriver or small chisel and remove it by prying it out it if you like. Just be careful of what you are jamming in there, there are bearings right on the other side of the seal. Once you have the seal out, be prepared for gear oil to drip out - it will, even though you've drained the diff.. Clean the area with some paper towel. Grease the back side of the new seal lips, smear some gear oil around the seal where it contacts the flange. There will be old RTV sealant on the pinion splines and inside the flange, clean that up. Inspect the area where the flange contacts the seal and clean it lightly with some sandpaper if there's a ridge. Apply some new RTV, just a small bead to seal the splines, on the inside of the flange. You should be able to press the new seal mostly into place with just your hand. Then you can use a really big socket or seal driver to press it the rest of the way in - I prefer a 1" wooden dowl and light taps with a rubber mallet to seat the seal. Line up the flange on the pinion splines according to your marks and press it on until you can get the washer and nut on. Hold the flange from turning and tighten the nut to draw the flange onto the shaft. Tighten the nut until it seats. Check the number of threads showing, use your torque wrench to get it back to the same resistance when turning (The new seal will add a small amount of resistance so, keep that in mind). When it feels right, your set, reconnect the driveshaft according to your marks, refill the differential, put the skid plate back on.