What weight of gear oil should I use for my 88 Dakota 3.9 V6 2WD 7.25 rear end?

 

From the factory service manual, page 0-18 :

The actual weights depend on the temperatures you'll see. From the right side, same page:

Hope that helps some!

RwP

 

I want to do 80W-140, would I need to use a limited slip additive? Would I need to use regular 80W-140 or synthetic 80W-140? Thanks RalphP!

 

I don't believe the 7.25 ever came with a limited slip so you do not need the friction modifier. Conventional vs synthetic...everybody has an opinion on that but for gear oil my inclination is that it doesn't really matter, except perhaps when differentials are put to extreme use, then maybe it's wise to consider fluids carefully. But you're not going to be putting the 7.25 to any kind of extreme use.

 

I'd use synthetic, but as tbugden says, it really doesn't matter.

It'll probably be 75W140 today; I don't think you can even FIND 80W140 gear oil anymore.

As to the "extreme use", if you NEED synthetic in your truck's rear end, you also NEED something bigger than a 7.25. (That;'s proveable, BTW, not just an opinion.)

RwP

 

That's right! I mean't to type 85W-140. I will most likely with Valvoline 85W-140. I greatly appreciate the info! Might change the rear diff fluid this Saturday!