Austin97

I always use Motorcraft gear oil and friction modifier, not cheap, but not overpriced either and high quality. I wouldn't use oil stabilizer personally, but if you have good results go for it. I definitely wouldn't mix it with the trans fluid going in the transfer case, but again, if you've done it and it works for you it's your call.

steve491

If you're a broke college student why are you changing the diff oil? Check it and add some cheap 90 weight.
Since you already bought the Royal Purple just use it.

Austin97

He's probably changing it because $100 in maintenance will keep him from $1000 in repair bills... The same reason everyone should do the basic fluid changes.

1990-5.0-4x4

finally someone who agrees with me!! i have used royal purple in my diffs and transfer case on one of my other trucks, but i beat the **** out of it offroad and i was running 35's. it made it all run like silk though. i do like RP products, but they are super expensive. but when i have a little extra money, its worth it.
i did use motorcraft friction mod though, just to be on the safe side. lol
as far as the diff cover gaskets, do you guys suggest a single piece one or just rtv?

Austin97

The gaskets are garbage. Use Permatex Ultra Black silicone. It's expensive, but it's awesome stuff. I use it on oil pans too, it's great. Just do a 1/4" bead and go all the way around the bolt holes.

1990-5.0-4x4

cool. thanks man. i used the high heat red rtv on my last truck and it held up pretty good. i had to redo it once bacause it wasnt all the way cured before i drove it to work lol thankfully i only lost a couple drips on the drive and not the whole thing lol.

Austin97

I use the ultra black and drive the trucks right after I zip the bolts in man. Never a single leak, I've even done it on wait jobs and never once had a customer come back with a leak.

1990-5.0-4x4

is this something they would carry at autozone or a parts place like that? that sounds way more appealing to my ADD/ impatience lol

do you use anything to clean the inside of the diff out? like break cleaner or anything like that? last time i did it i sacrificed a microfiber towel to clean it out without leavin lint inside.

Austin97

Autozone lists it on their website so I imagine they'll have it in the store. If you go to Walmart you can get 12 rags for $2 in the automotive section, I got like $10 worth of those once and wash them when it's worth it and throw them away when they get too bad, sacrificing one of them is no big deal, they're like 15 cents. I just get the puddle out of the bottom of the housing too, don't worry about the little bit sticking to the ring and carrier. A little piece of lint won't do anything to those massive metal gears anyway, but I do pick it out if I see any.

One thing you need to make sure of is that the mating faces of the housing and cover are completely clean. I use an angle die grinder with a roloc 50 grit sanding disk on both sides and make them nice and shiney. If you don't have a grinder you'll have to scrape all the gasket material off, making sure not to gouge the housing.. and I'd probably use like brake clean and 50 or 80 grit sand paper to really get it clean. It'll take a lot longer than a grinder but it has to be super clean to get a good seal. Also tighten the bolts from the inside out, like torquing a head, so the cover gets pulled down evenly.

1990-5.0-4x4

yeah last time i did mine i sharpened a putty knife with a steel file to scrape off the covers and then brake cleaner and scraped and cleaned for about 10 mins on both the housing and cover.