Replacing a pinion seal may seem a little intimidating at first, but it’s a job that you can do yourself in the driveway in a few hours. There a few things you should know however in order to avoid creating more costly repairs down the road and also to the job right the first time. If you already know about things like crush sleeves and pinion preload then you can skip, The Basics, below. If not then read on. We have included a very basic primer to help you see the big picture a little better.
What You Will Need
For this project we have ordered a new yoke, Crown part # 83503388, and new seal, Crown part # 5072473AA. We don’t know yet if we are going to need the yoke but we suspect we will (more on that later) and we can send it back if not. We also will be using an air impact, a seal puller, some RTV silicone, and some of 80W-90 GL-5 gear oil.
First we are going to mark the nut, yoke, and differential with a paint marker and count the threads sticking out beyond the nut. In this case we have two full threads and we can just see the edge of the third. In theory and if we don’t need the new yoke, we should be able to put everything back in the exact same position. This will help to ensure that the pinion bearings are preloaded the same amount as before disassembly (see The Basics, above).
Now that we have a reference mark, we can take our air impact gun and remove the pinion nut. Make sure your air impact gun is set to spin the correct way! This is one time that you don’t want to find out after the fact that your impact gun is tightening the nut. With the nut and washer removed, you can pull remove the pinion yoke with a gear puller or by lightly tapping it with a ball peen hammer.
With the pinion yoke removed, we can inspect the yoke. Remember that new yoke we purchased? In our experience pinion seals usually fail for a reason. If you look at the figure to the left, you can see the reason. In this case there are two grooves worn in the yoke on the surface that the seal rides on. We know it defies logic that a rubber seal can wear grooves in a cast yoke, but when you think about the dirt and grit we wiped off to get this picture, it makes a little more sense. In this case the grooves are deep enough to be easily noticeable to the touch. If we put this yoke back into our axle with a new pinion seal, it will only be a matter of time before the seal fails again. At this point we could install a repair sleeve but we prefer a new yoke.
In the picture to the right we have transferred our paint mark to the new yoke. If you are using a new yoke, as we are here, keep in mind that slight variance in the dimensions of the new yoke versus the old can make the paint marking invalid. The mark will still be useful but we are not going to be able to rely on it completely because we have introduced a non-original component into the game.
With the yoke out of the way it is time to pull the old seal. We didn’t include any pictures of that but the seal puller wasn’t sufficient by itself. It kept tearing through the thin metal of the seal. We had to get a chisel behind the lip of the seal and bend the outside ring of the seal inward. Doing so took enough of the fight out of the seal that it finally came out with the seal puller. Take care not to damage the surface that the seal presses into.
Installation of the new seal is as simple as gently and carefully tapping it into place with a hammer. We like to pre-lube the rubber seal surface with gear oil and put a light coat of RTV silicone around the metal mating surface of the seal where it presses into the housing. We prefer to put the silicone on the seal instead of the housing because that way, as the seal is pressed in, the excess silicone will be forced out of, instead of into, the differential case. Use care tapping the seal into place to ensure that it goes in evenly. If it becomes cocked off too far to one side or you hit it too hard, you can damage the seal.
Now that the new seal is in place we are ready for the final install. This is one area where hand tools make a lot of sense but if you’re careful, you can snug it up with the air impact. We used the lowest setting and used the hole in the impact socket to count the turns as we got close. We know from setting up axles that it takes a LOT of pressure to crush a crush sleeve. The problem is, once it starts to go, the preload ramps up quick! In this case we hit the point where we felt we were going to be adding preload and stopped just shy of our mark (see image to right). If we were using all original components, we would be back out our mark now.
Don’t forget to top of your differential with the correct gear oil. In this case we know from the owner’s manual that 80W-90 API GL-5 is the right stuff. Also, do not to forget to use Loctite on the u-joint strap bolts when reinstalling the driveshaft. By the way, it doesn’t hurt to Loctite your pinion nut as well. The pinion nut on the Jeep TJ Dana 30 is self-locking, but it is one nut you want to make sure doesn’t move. Another option is to punch the threads in a couple of places on either side of the nut with a center punch. You will still be able to remove it with an air impact but punching the threads will help keep the nut from backing out under operation.