Installing a Pinion Seal into a GM 10 Bolt Rear

Tools Needed:

• 3/8″ Ratchet with medium extension and 11mm socket
• 1/2″ breaker bar with 1 1/4″ socket
• Hammer
• Chisel
• Large screwdriver or small pry bar
• Various other pry tools that you may find useful
• Dremmel with cutoff wheel
• Wire Brush
• Oil drain pan

Parts Used:

• New Pinion Seal
• RTV Sealant
• Brake cleaner
• Speedy Dry

Note:

This set of instructions assumes that you have basic mechanical skills. This procedure assumes that you can do basic removal and reinstallation yourself.

Iroczone.com nor any of this article’s contributors can be held responsible for any problems that you have as a result of this article. This is presented for educational purposes only.

Procedure:

1. Jack up the rear of the car. Make sure that the jack stands are in a position that allows the rear end to droop (i.e. don’t put the jack stands under the axles), but also provides a safe, stable location for the car to rest in the air. I chose to put the stands under the front mount for the lower control arms, with a second set of stands under the fully drooped axle.
2. Disconnect your battery. There’s absolutely no benefit to doing this since you won’t be near any electronics, but all the good tech articles tell you to do this.
3. Once under the car, locate the rear of the driveshaft where it’s held to the rear yoke assembly.
4. Put the car into neutral with the emergency brake off, then get back under the car and rotate the driveshaft by hand until two of the bolts holding the u-joint into the yoke are facing down just like in Figure 1. Get back up, and put the car back into gear to prevent the driveshaft from turning, then get back under the car and use your ratchet with the 11mm socket to remove the two nuts. Get back up and put the car into neutral, then get back under the car, rotate the driveshaft until the other 2 bolts are down, then get back up to put the car back into gear, then get back down and remove those two bolts. Then get back up, then back down, then back up, then back down. Repeat 10 more times for a slimmer, more toned midsection and after 30 days, I guarantee that you’ll drop at least one dress size.
5. Now use your large screwdriver, small pry bar, or some other suitable tool to pop the driveshaft apart from the yoke. I do this by sticking a large screwdriver behind the u-joint and prying to separate the u-joint from the yoke. Just use caution to make sure that the bearing caps on the u-joint don’t come apart or you’ll wind up replacing that too. Once it’s done, drop the rear of the driveshaft down and swing it out of the way, but don’t remove it from the transmission or you’ll lose all of your transmission fluid.
6. Now you need to mark the large nut and the pinion shaft so that you can re-install the nut to the exact same place later. If you don’t do this, the preload on your pinion won’t be the same, which is something you want to avoid. A word of caution here: A sharpie or a paint mark might not survive after you remove the nut. If that happens, you’re not going to know when it’s reinstalled properly, so I would suggest something more permanent. I used a dremmel with a cutoff wheel to mark the threads and the nut. If you take it easy with the cutoff wheel, you’ll more or less just put a flat shiny spot into the threads and won’t do anything that could potentially damage the threads or the nut. You’re not trying to cut the thing off here, but just put a visible mark in it. Figure 3 shows my resultant mark, though it doesn’t show it terribly well.
7. Now you need to remove the nut holding the pinion on. Get back up and crank on your emergency brake or chock your rear wheels to prevent them from turning. Get back under the car (congratulations, you’re already halfway to a slimmer you!) and use your 1/2″ breaker bar with the 1 1/4″ socket to loosen the retaining nut. Once you remove that nut, the yoke should slide right off the pinion. If it doesn’t, you may need to persuade it with a rubber hammer. If that doesn’t work, persuade it with something harder (like a regular hammer) at your own risk. Mine slid right off without the use of any persuasion.
8. Your next step is to remove the pinion seal. To start off, take a look at your new one so that you’ll be familiar with the shape of the item, specifically the outer flange. Once you’ve burned that image into your retina, look at the pinion seal on your car and recognize the outer flange of that seal. What you need to do, after thoroughly cleaning the area so that crap doesn’t get into your differential, is to start tapping your chisel underneath that outer flange. I used a chisel of around 7/8″ width, but anything will work. You need to slowly work your way around as much of it as you can get. With careful chisel angles, you can work your way around approximately 70% of it, with the upper most area being pretty much inaccessable. Be careful not to mark up the differential housing, especially inside the area where the seal sits. Slowly keep working around it until you tap that lip up as much as you can. At that point you want to try angling the chisel slightly back toward you and striking it in a way to help slide the seal out of the differential. After you work that lip up, try a more blunt tool (such as a cold-rolled chisel or a dull screwdriver) so that you don’t just poke the chisel through the metal. The goal here isn’t to destroy the seal, but to slowly work it out of it’s resting place. Once you get past a certain point, you’ll really start to see it coming out, at which point it’s virtually ready to fall out. You’ll also get plenty of fluid pouring out, so be ready with a catch can and some speedy dry.
9. Once you’ve got the old seal out, thoroughly clean the area. Apply a very thin application of RTV to the outer ring of the new seal flange. Installing the new seal needs to be done with care so that you don’t distort it. The best solution is to find a large enough socket or other circular item to encompass the whole outer ring so that you can tap it evenly into place. If you don’t have such a device, you need to carefully use your hammer to tap all around the seal while using your hands opposite the part you’re hitting. If you just smack one spot with the hammer, the opposite side will pop out. For example, apply pressure to the 3:00 position and tap the 9:00 position with a hammer. This will take a while, but eventually you’ll get it to start to sink into place, then you just keep tapping all around until that outer lip is securely against the differential housing and a little bit of RTV squeezes out all around.
10. Once the seal is properly installed, everything else goes on more or less the way it came off. Put the yoke on and tighten the nut back to its original position and no further. Once that’s on, put the driveshaft back and install the caps that hold the u-joint into the yoke. Get up and down 20 times to put the car in and out of gear while you tighten the 4 bolts.
11. Use the 1/2″ ratchet to remove the upper plug in the differential, then fill it with your differential fluid of choice. If you have a limited slip rear end, make sure to also add the appropriate limited slip fluid. I’ve found that the GM Positrac fluid is about the best.
12. You’re done. Safely get the car off the jack stands, reconnect the battery (you didn’t really disconnect it, did you?) and go use the car. This information is provided as a guide.

It is not my responsibility if you damage your car or yourself by following these directions. If you do not feel that you are capable of performing this modification, leave it to a professional. If for nothing else, reading this will help you to appreciate why the installation is going to cost so much!