I am looking at the cover and there is no obvious drain plug. Does one have to remove all or most of the bolts for a change? It still has the original fluid in it. The manual says under "normal" conditions it should not need changing - but I dont like that.... Vacation and towing to the Sierra's is coming and I want everything done and checked that can be....

 

Lezmark just loosen all the bolts then take a flat head screwdriver and pry on the bottom of the cover. This will let all the fluid to drain. Depending on how you drive and how many miles that you have on your truck you should be ok but if you are going to be taking a long trip you can change your diff fliud out, it wont hurt anything. Also once you have removed the cover check inside the diff, just make a visual inspection of the ring and pinion also make sure that your gasket is still good after removing. If not just change it they are really cheap. Hope this helps, have a safe trip

 

Thanks!!!!!

 

Make sure you pick up some gasket maker before you rip everything apart. Also pick up a scraper to scrape the old gasket off of the housing and cover. A hammer and a screwdriver will help pry the cover off.

 

Yikes, you probably should have changed your diff fluid 3 or 4 times by now.

Remove all the bolts except for the top 2 (just loosen them), carefully pry the bottom of the Diff cover up so that the fluid can empty into the pan. After that, remove the top bolts, scrape off all the old gasket material (from diff housing and diff cover), get a can or two of brake cleaner and some lintless rags and clean everyting up really good (including the diff cover and everyhing inside the pumpkin including the ring and pinion etc.) spray it all down reall good with brake clean and dont be scared to use a couple of cans. Next, clean off the magnet in the diff housing (bottom). Get some good RTV and apply a thin bead to the diff cover. Wait ~20 minutes for the RTV to skin and then insall onto the hosuing. Wait for the RTV to finish curing and add your diff fluid (synthetic in the rear is a really good idea). Dont forget a bottle or so of Friction Modifier if you have a limited slip.

Second gens with Dana differentials dont have gaskets.

 

This would be a good time to switch to synthetic oil. There's a lot of info here about syn's. Got Amsoil gear lube in mine.