This will be a series of posts so that I can include all the pictures for the guide. Thank you Amanda for the help with the pictures. *DISCLAIMER* I intend for this to be educational only and don't claim for it to be a replacement for a factory qualified mechanic performing routine maintenance. I am not responsible for the completeness or material herein.

The first step is to get your supplies ready. You will need gloves, differential fluid, friction modifier for you LSD guys, RTV silicone, plastic scraper, shop rags, and 13mm socket and ratchet. I am using nitrile gloves because I find they are stronger and more resistant to oils and solvents. I chose Mobil 1 75W/140 for the diff fluid.


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Now that you have your supplies ready, it is time to tackle the diff cover. The diff on my truck along with you 1500 guys is the DC 9.25" rear end manufactured by AAM. Notice the 12 bolts and the stop sign shape.

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I worked under the truck and didn't us any ramps or vehicle stands. The driveway was sloped so that the oil would drain towards the back. I like to begin by loosening up the top bolts first. After the top 2 are loose, I start on the bottom and work up the sides so that the fluid flows out of the bottom. I just loosen them all up in the manner outlined above and let the fluid flow out until it stops dripping. Once the bolts are loose, you can break the bottom loose and it really flows out. Let it go until it quits dripping. My fluid was pretty clear. The picture looks like the ground is slopped, but I promise it is level. The fluid is going off to the left because of the wind. It was pretty windy today.

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After it has stopped dripping fluid, take the diff cover off of the rear axle housing. You'll notice the old RTV stuck to both the cover and the housing.

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Now is a good time to take a look at the gears in the housing. Look for pieces of metal, chipped or broken teeth, etc. Here is a picture of the grey, metal gunk off of the magnet at the bottom of the housing. I also wiped out the inside to be sure I got all the old oil out. I didn't find any big metal particles, just the fine metal sludge on the magnet. Guess I'm kind glad I have the open differential. Nah, still wish I had the LSD. Sorry for the blurry pic. I was trying not to get the oil on my wife's brand new digital camera. It is the new Nikon P1, nice camera.

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If everything checks out okay, it is time to clean up the housing and the diff cover. Take the plastic scraper and scrape off all the old RTV. If you don't get it all off you can take some brake cleaner on a rag and it will rub right off. That is what I did and it works great. It also cleans the surface and gets an oil free surface for the RTV to adhere to. I missed a small spot on the housing before I took the picture, but I went back and got rid of it before I bolted things back up. The bottom pic shows a metal scraper. On second thought, I got my plastic scraper, but didn't pick up the metal scraper yet. Use a plastic scraper as mentioned above.

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Now that everything is cleaned up, it is now time to put the RTV silicone on the diff cover. Place a 1/8" continuous bead around the bolt holes and around the entire cover sealing surface. Follow directions for set-up time. I let mine sit 5 minutes before I bolted it up.

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After it has set up, it is time to bolt it up. What I did was placed it and started one bolt up top and one bolt on the bottom. I then tightened all of the bolts by hand until finger tight. I then proceeded with the socket and ratchet. I first tightened them up about half of the way and used a star type sequence to achieve a symmetrical and even thightness. Then I went back and tightened them down in the same star type sequence to maintain a evenly distributed tightness. I didn't measure them with a torque wrench, but it is pretty tight. Not Superman tight, but pretty snug. You'll notice an even squish of the RTV all around the flange. If it was tightend equally and you put an equal amount of RTV on the sealing surface, it should be pretty symmetrical squish all around the diff cover. It isn't hard to achieve this, you'll see when you do it.

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Now I let the RTV cure for 2 hours before I added the differential oil. After 2 hours, I added the Mobil 1 75W/140. It was a little over 2 quarts. Check the fluid level height for your model year and you're good to go. Then go do a few figure-8's and drive down the road a bit. After you get home and you're on a level surface, recheck the fluid level, add as necessary.

*NOTE* For you LSD guys, make sure you ADD THE FRICTION MODIFIER FIRST, before adding the diff oil so that you know you have the friction modifier in the differential.

There, you are done. Now you can sit back and smile knowing that you did this simple maintenance task and have no reason not to do it AND save money at the same time. Total cost for me was $52 and about 3 hours of my time from start to finish.

 

Hey Doc,
Just read your write up of the diff service----Outstanding!!!! I would be inclined to suggest becoming a service writer, but I know you have much Higher ambitions than that, and have no doubt that you will achieve them. I would like to mention here though, that speaking to the guys that have the larger 10.5" and 11.5" Diffs in the 2500 and 3500 LSD's--they don't require the friction modifiers, just the straight gear oil.

Thanks, for a really great article and great pics to accompany too!!!