I realize this is way distant from my usual material but it did happen on the way back from snagging the Traynor amp I described.
The following applies only to a Ford 8.8 open rear end, although I am keeping my eyes open for a Traction Lok unit. I'd lile to have limited slip this winter. If you don't know what rear you have check the driver's side door for a build code label or check the tag on the rear end itself. They look different from the seven inch rear anyway.
It was hot, sweaty, and I was sort of flogging the truck, and when I arrived in Louisville the Ranger burped out about a cupful of gear oil from the rear end pinion seal and dirtied up my sister's driveway. A trip to an auto parts emporium got me gear oil and a tool to remove the fill plug, and I put in 12 ounces of gear oil.
I should also mention that I'd changed the oil and filter and used Castrol 5W30 and when good and hot the oil pressure gauge would flicker when taking off from a stop. Some STP cured that but I'm going back to Valvoline for good.
On the trip home, at my next stop I put in 8 ounces of gear oil, then four ounces, and then the level maintained itself. However, it did make a mess in my driveway as well when I got home.
The critical point here is that the torque on the pinion nut crushes a sleeve which sets the preload for the differential gearset, and that is why care must be taken with disassembly and reassembly unless your idea of a fine day is removing and setting up a rear end.
These notes apply only to a 2wd 2002 Ford Ranger with the 8.8 rear end, 4.10 rear gears and an open rear end.
You've got to know what rear you're working on, and there are plenty of resources after you have gotten the code off the builder's data plate in the door jamb and/or the tag affixed to the rear end.
The first job is to mark with a punch and a hammer the driveshaft flange and the pinion flange and unbolt the driveshaft and get it out of the way. I used a hammer and a punch. The driveshaft is held in with bolts that take a twelve point 12mm box wrench. Then push the driveshaft out of your way.
The next task is to clean everything off with Brakleen or other suitable degreasers. Then, index mark the shaft, the nut, and the flange with something like paper white, lacquer, or anything. This is critical, because if you don't have these references you're screwed. Really. .
My impact wrench didn't do the job so I used a 1-1/16 socket, a breaker bar and a cheater pipe to remove the pinion nut which was the handle from my engine hoist. When the nut loosens, then take a ratchet and turn the nut off while counting the turns. In my case it was 16-1/2 turns.
Then, using a gear puller pull the flange and check the sealing surface for wear and grooves. Clean with scotchbrite if it is needed.
With a small hammer and a chisel or a screwdriver remove the old seal. Clean the area with solvent and remove the sealer if the seal was installed with it. Dress any scratches or dings with a small half round file.
One can then carefully install your new seal, first packing it with grease and wiping a little rtv on the outside.
Start it with a small hammer and then finish with a block of wood, making sure you don't damage the sealing surface or distort the seal itself. Make sure it's bottomed out on its mating surface.
Buy the best seal you can, either National, from the Ford dealer or CR if they sell in your area. Don't go cheap.
Reassemble in reverse order, counting the turns of the pinion nut until it bottoms out. Then, you can reef the nut down with your breaker bar and cheater pipe. All your index marks should now line up perfectly. Then you can reinstall your driveshaft.
If you've done this correctly you will have preserved your preload inside the differential.
You can now remove the cover to drain what's left in the differential and reinstall the cover, torquing the bolts to about 20 foot pounds in a star pattern.
The NAPA folks sell a gasket for this task which is more trustworthy than a mere bead of RTV. Reinstall the cover, gasket and a thin coat of sealer, bolt it up, and then let it sit for a good 24 hours cure time.
Refill the differential with about 2.7 quarts of a good grade of 80W-90W hypoid gear oil. A limited slip rear requires anti friction additive to the gear oil.
Take a road test to make sure you didn't damage the seal on installation and have to do it all over again