How to replace a rear pinon seal. Why replace: Obviously if you see your differential oil spilling out it needs replaced. Also, if part of your dust cover(plastic piece) is broken, I recommend replacing both the seal and cover for safety reasons. After alot of off-roading and camping mud can get behind these and cause the seal to dry rot, so check your seals for a good clean look and keep your differentials lubricated. My seal was cracked from mud grinding behind the dust cover, so it was easy to diagnose. Fluid was all down my driver line and spinning everywhere. This how-to was performed on my 03 FX4 Supercab with 5.4L with 9.75 rear end. Materials: 12mm wrench (12 point) 13mm socket (6 point) 1-1/8 deep well socket Reversible Puller Flat head screw driver Ratchet strap (to hold up drive line) Impact wrench New pinion seal (mine is the 9.75") most are 8.8's Gear Lubricant - SAE 75W-140 (to replace lost fluid) SOME CALL FOR other fluids so check your axle code! I actually used royal purple SAE 75W-140. We used the picture at the end of the how to for a friends nissan. Brake Cleaner/Fine sand paper for cleaning Torque wrench Blocks to keep the vehicle from rolling. 3" PVC pip coupler or 3.5" for 9.75 (Used to push in new seal without hammering edges)* I used the top off an acetylene tank for this. I wont post a pic of all materials used, just make sure you have the proper seal. I bought both to give you an idea of the difference in the two. Removing Parts and prepping to install new seal First: (Materials used: Blocks) Park the truck in the flattest spot you can find. Now crank the truck if it has electronic 4WD and turn it off. This will help lock the front tires when you release the drive line later on. Now block up all 4 tires just to be safe. Second: (Materials used: 12mm wrench(12point) and 13mm socket) Before you proceed it is useful to mark lines on the mount and drive shaft linage to line them up proper. Your crush sleeve would probably mount it directly back to where your yoke is suppose to be, but take precautions and makes sure you keep it in 4-wd(if applicable). Use a 12mm wrench/socket (MUST BE 12 POINT, NOT 6) to loosen the 4- bolts holding the drive line to the differential. *Where the rear U-joint is, removing the U-joint itself is not necessary* Once you have those loosened the 4 bolts you can use a 6 point socket to unscrew them the rest of the way off to be a little quicker. Third: Materials Used (Ratchet strap) Once all 4 bolts holding the driver line are removed make sure the truck is still secured by the blocks and safe for you to be under it. Now use the ratchet strap to hold up the drive line and get it out of your way, not letting it scrape the ground. Fourth: Materials used(1-1/8" deep well socket and Impact gun With the drive line off the back, you should see this: Now its time to remove the mounting plate for the drive line which is held on by a 1-1/8" nut. I used a 140ft-lb impact gun for this part.