I'm going to change my rear differential oil today. Is it as simple as taking cover off, draining, installing cover and refilling? Is there a trick to not making a huge mess when draining? Also, what is the torque specs for tightening the bolts back on the cover?

 

It's a fairly simple job, especially if you know a couple of tricks.

The cover is a lot like a trans pan, in that there is no drain plug. You drain the diff by removing the cover. Like a trans pan, you don't want to just pop it off. Oil will gush out all at once.

My diff dose not use a gasket, it uses silicone sealant only. I have heard that all of the 2500 diffs are the same way, but I can't be sure.

Remove all the bolts except two down towards the bottm. Loose them up about 1/4" or so. Gently pry the cover away so the oil drains out. Use a big pan - not for the volume but to catch all the drips. I also use a large flat Depends pad to catch any spills.

Reassembly can be a little difficult. You have to apply the goo to one surface, then hold the pan in the right place while you try to get a couple of bolts started. There is - of course - an easier way.

Get two bolts the same size as the cover bolts. Cut the heads off, and cut a screw driver slot in the end where the head was. Thread those in a couple of turns, one on each side. Then you simply slide the cover on to those studs while you set the other bolts.

If you reassemble with The Right Stuff, you can refill pretty quickly. It comes in a can like Cheese Whiz, and sets up really fast. The label says you can use right away. But I'v found if you let it set up for an hour or two it seals better.

Don't use too much. If it spooges into the the inside of the diff, it will contaminate the oil. Not bad for the gears, but bad for the bearings.

I don't know what the torque specs are, but it's not very much. Like a valve cover, you don't want to overtighten and distort the cover. I use lock tite on the bolts.

While you have the cover off, you might consider adding a drain plug; either to the pan or to the bottom of the diff.

 

I changed mine out at like 21k miles. It looked pretty bad, and I had not forded any creeks. Its like you said, just put a pan underneath the cover and when you loosen those bottom bolts just pull it from the axle just a little and it will just drain straight down into the pan.
You reuse the gasket.
I put on one of the PML aluminum covers with a drain plug on the bottom and a top file plug, when I changed mine last time. Makes it easier next change.
I think you should look in the owners manual for the weight of the differential oil, it calls for something specific. I can't remember exactly which weight.
I used the Mobile-1 synthetic it may have been the 75w-140 ? There is a 75w-90 , I would look in the manual it tells you exactly.
Its a good easy job, wipe it down to get all the metal shaving out, put the cover back on with the gasket in place. Then fill it back up to the fill hole with oil.
That gear oil has a smell to it, its thick.
Have a good one !

 

All 3rd gens come with a reusable gasket. It calls for 75w-90, but some run 75w-110 or even 75w-140 if they tow heavy a lot of the time.

I have a Mag Hytec on the rear that makes changing the oil a breeze. It adds to the capacity, almost 8 quarts! It has a dipstick and drain plug.

 

^^^Mine came with a reusable gasket.

 

I heard the first change looks bad just because of some factory assembly grease that mix's in the oil. it looks bad but isn't.

 

My 03 has a reusable one.

 

My 04.5 has reuseable gaskets, and I filled the diffs last time with Amsoil 75w40 Severe Gear Lube. It's easy.. Just unbolt the cover, drain, put cover back on and refill through the drain plug.

 

Do NOT fill completely. 1/4 below the fill plug to allow for expansion. Otherwise, your going to lose the pinion seal.