Another diff fluid thread

[rzr6-4]

Manual is calling out 75w-90 front and rear, but I often see guys running the 75w90 front but 75w-140 rear. Not sure if different years call for a different weight or some personal preference.

If I use the 75w-90 for both, how much would it take?

Also, it specifically says in a couple places that limited slip additive is not required. Is that because its an open diff or because they're designed not to need it? Going drifting I've always been able to get them to both spin, but with enough power you can get open diffs to spin both no problem. And if I'm in deep mud/snow I put it in 4wd and everything locks so I've never really figured out exactly what it is.

 

[62Blazer]

Either weight gear lube is fine. I would probably recommend what is stated in the manual, but if some people get a warm fuzzy for using 75w-140 it won't hurt anything.
Limited slip additive is a friction modifier that some clutch based limited slips (i.e. use friction to keep both tire spinning) require. The limited slip in the HD truck is a torsen based design, therefore no clutches or friction is going on and thus why no additive is needed.