I recently purchased a Mag-Hytec Dana 70 Rear Diff cover. I am planning on putting it on this weekend. I am a little confused on what gear oil to go back with, can you guys help me out? It is a limited slip rear end. So do I buy regular synthetic gear oil and add the friction modifier? Or do I need to put in Limited slip gear oil Plus the Friction Modifier? I wasn't sure if I purchase Limited slip gear oil, is the friction modifier still needed?

 

Depends on what lube you bought. I stick with the big manufacturers for my truck....I use the Texaco lube for my NV5600 and went with Royal Purple synthetics in the diffs...I think 140/80 but it's been a while and they are probably due!!

What truck? What year? How many miles? The clutch packs wear thin after around 50 K so you may not even need to apply any LS modifier...

I didn't add any after finding my rear wasn't grabbing while doing slow figure 8's in a smooth paved parking lot...I can still get a bit of grab when starting quick in the dirt so mine still locks up a little.

Search Friction Modifier and read up. I can't remember if it makes the fluid grabbier or slipperier!!

 

You can use either conventional 80-90 or synthetic of whatever weight you choose according to your driving type. Meaning, if you tow heavy all the time then you'll want a thicker viscosity like 75-110 or 75-140. If you dont tow heavy or very often then conventional 80-90 will be perfectly fine. If you live where the ambient temps regularly drop into the subzero levels then you'll want to run a thinner synthetic.

Either way, conventional is fine and synthetics are generally just better for the more extreme situations.

All conventional gear fluid will require a friction modifier which will reduce the LS clutch chatter. But most, if not all, synthetic gear fluid will already contain friction modifier in the recipe. Although that doesnt mean that whatever amount is included will be enough as I've seen some synthetics still allow clutch pack chatter and required more and more friction modifier.

What you do choose is probably going to depend on whats most available to you too so just see whats out there and decide.

Limited slip clutch packs are commonly abused because most people have no idea how they work and dont realize that one wheel burn outs and aggressive u-turns or running different size tires on the same axle will quickly ruin a set of clutches. But that said, they arent always ruined completely as they can be "re-stacked" to regain their ability to function.

Below is a link with information specific to that axle.

Dodge Ram Dana 70 Axle Specifications

 

I'd stick with Mopar brand or there recommendations, but "Six Slug" is a straight shooter & knows his stuff, like he said Royal Purple is good stuff.

 

I have used the Amsoil 75-90 and 75-110 and I like it.

 

I've used both the Amsoil 75w90 and Royal Purple. If you use a synthetic, you shouldn't need any limited slip additive. If you feel any binding or popping during tight turns, then you'd probably want to add a small amount.

As far as the gear oil weight, I like the lighter stuff.

 

Same as Midnite as far as gear oil weight, but I run Lucas, and add 8ounces of the friction modifier. If my memory serves me, 6 pints to fill that diff cover to the line on the magnetic dipstick. Never had binding or popping/chatter.

Tip: if your diff cover uses a 3/16 allen to tighten/remove the drain plug, be careful, as that plug can seize up, and snap that allen tip off, leaving the tip seized inside the socket of the drain plug. Since I've bought and installed mine back in 2008, I see Geno's garage sells Mag Hytec replacement plugs, that use 1/4" allen's, which are beefier. If it were me, and yours has the smaller style 3/16" plug, I would either anti-seize the threads, or call Mag Hytec or Geno's Garage and order the stouter style drain plug. Believe me when I say you're going to muff up that beautiful cover trying to unthread that drain plug with channel locks because of a broken allen tip imbedded into the socket.

I've since ordered up replacement plugs for all the diff covers and tranny pans for my 93 dodge and 02 powerstroke.

 

Thats a good heads up..... Thank you.