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Here's what I learned after changing the front and rear differential fluid and the transfer case fluid today. Total cost was about $200. Half of that is the t-case fluid, which is Mopar proprietary.
I generally followed this video, which is excellent:
Always pull the fill plug first before you pull the drain plug. If you can’t get the fill plug out, then you want to know that before you drain all the fluid in your diff and make your truck immobile. My TRX’s plugs all readily came out. No problems.
Creating some space to work made the job very simple. I used Rhino Ramps Max. A pair of them is rated to 16,000 lbs, so four should be sufficient for a 6,000 lb truck. Putting the truck in 4L made it easier to creep up on them slowly. Like Sammy Hagar said, use one foot on the brake and one on the gas to creep up there slowly.
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Some of the bolts holding on the front skid plate seem to have a 5/8 head rather than 16mm. I brought both 6-point sockets under the truck, and the 5/8 fit better on the front skid.
The rear diff is easiest. I torqued the drain and fill plugs to 20 ft-lbs. I used Amsoil 75W-140 synthetic severe gear lube. I bought 3 quarts and had plenty left in the final bag. The drain plug is a 1/4" drive square (just put a 1/4" extension in there. 3" long will do). The fill plug is a 3/8" square (just put a 3/8" drive extension in there. 3" long will do).
The transfer case is the most difficult of the three, but it's still not a bad job at all. Getting around the exhaust pipe requires a longer extension that you will use for only that fill plug. When you pull the drain plug the fluid is going to gush, so be ready for it. It flows out much faster than the front and rear diff. Position your drain pan well in front of the drain hole. Finally, here's a trick I used to waste less of the new fluid:
1. Take one of the clean, unused pointed fill caps from the Amsoil fill bags and install it on the first transfer case fluid bottle.
2. There's just going to be some fluid loss with this one, but it'll be fine. Tip it into the fill hole as best you can. Drain it all the way.
3. Now go back to your workbench and crack open a new bottle of the transfer case fluid. Use a clean funnel to pour about half of it into the empty bottle you just emptied.
4. Put the pointed fill tip back on the half full bottle. Now go dump it into the t-case. At half full, it won't squirt out on you as you tip it over to angle it into the fill hole.
5. Repeat with half full bottles until you get the t-case filled.
I also torqued the t-case plugs to 20 ft-lbs. I bought 3 quarts of Mopar 68049954AC and had almost a full quart left over. If you were stingy with every drop, you might get away with 2 quarts. But I wouldn't want to chance it. Both drain and fill plugs are 3/8" square. The drain plug will be fine with your 3" extension. You will need a 6" extension for the fill plug, in order to get around the exhaust pipe.
The front diff is easy with the skid plates removed. It uses an 8mm allen key on both plugs. I did not have a way to torque this one to spec, so I used judgment. I also aligned the pink marks that seem to have been put there at the factory on the plugs and the diff body. I filled with Amsoil 75W-90 synthetic severe gear lube. I bought 2 quarts and had some left over in the second bag.
My rear diff fluid showed a little metal sheen in the drain pan. The magnetic plug also had a little bit of grime stuck to it that I cleaned. I was happy to get that fluid changed. The t-case and front diff honestly looked great. There probably wasn't much value in changing that fluid, but it's good for my peace of mind. At this point (1400 miles) all my oil and driveline fluids except the transmission fluid have been changed. I wanted to get the break-in particles out of there.
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I honestly can't tell if any of the diffs were underfilled. I know that excess never ran out of the fill plug hole when I pulled the fill plug before draining. But I didn't do the science experiment of measuring the volume drained from each. I know there's more in there now than when I started, because I re-installed with fill plugs with fluid still weeping.
This is a straightforward job and one I would recommend, given the reputation of our trucks for having under-filled diffs from the factory, and given the fact I like to give a little extra TLC to my $100k truck with 702hp motor...but that's just me.
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