I have an 04 2500 4x4 and need to service both differentials. I wanted to use something a little cheaper and better than Mopar Synthetic 75W-90 that my Chilton manual specifies. The only thing I'm worried about is the manual says for my model and year to not add LS additive and I think the Red Line synthetic oil says its in there.

 

More info front axle is 9.25 rear is 10.50 and is an anti spin differential.

 

you can use Mobile one 75-90 but I think for towing you are supposed to use 75-140

if you have the LSD then just add the friction modifier which I think it 3oz per qrt of oil

 

I talked with a technician at Red Line today. He said the 75W90 Gear Oil does have some friction modifier in it but it is made for my type of differential. If using in a LSD you need to ad their additive. Here is a study of gear oils http://www.synthetic-oil-tech.com/Ge...te%20Paper.pdf

 

I believe that the 2500's have a gear driven LSD like the DTT, and require no special LSD additive. You should be fine with the Red Line even though it has LS additive in it, it shouldn't cause any problems.

think of it this way, you have it, but don't need it. You get in trouble when that equation is the other way around.

nateroach

 

Do they still make the 75-90NS? It's pretty much the same stuff, just without the friction modifiers. That's what I ran in the transmission of my 01 Subaru, because the friction modifiers made the syncros not work as well.

 

i dont think they do horatio, or the 75-145ns i went to buy some as i have a open diff with 4.56 gears and my guy said to get the high temp stuff cause we live in a hot state and i use it to tow and run f150's into the dirt ...and i ended up using a synthetic that had additive in it and he said i could with no adverse affects

 

Good explanation. That's basically what the technician said but he added that if you have a differential that required friction modifiers even though there is a little in there you still need to ad their Limited Slip Friction Modifier to it as well.

I saw it in a local auto parts but they may have discontinued it because it's not on their website. The 75W140 NS GL-5 Gear Oil is still listed though.

 

Yep. LSD in the 2500's don't use clutch packs which is why the friction modifier isn't needed, but if the oil does have the stuff in it, it won't hurt anything at all. it'd be the same as adding that oil to an open diff. Makes no difference. Now, adding an entire bottle of the modifier(7oz.) might cause some engagement issue's, but as far as just the oil itself....I wouldn't think twice of adding it to a 2500. heck, the Mobil 1 LT has the stuff in it and lots of 2500/3500 guys run it with no troubles.