LX90

I'm having my 4.10s installed this weekend and was wondering about gear oil. The factory weight recommended is 80w-90. I wanted to use Royal Purple, but they don't make 80w-90, but they do make a 75w-90. Now I've heard that youcannot us the 75w-90 with the 8.8 LSD, but I also heard that youcan use it. So I'm alittle confused. One guy says you cannot use it because it messes with the LSD diffs, I called another performance turning shop and the guy said they use 75w-90 all the time. Any help clearing this up would be great. Also I'm aware of the Ford additive needed for the limited slip. Thanks as always for the help!

GodAmGT00

I've used 85-140 w/ great success.. Don't forget Friction Modifier.. Although w/ a good synthetic, you may not need the modifier...

Also note, although it shouldn't have made a difference, that I had an Eaton Center section....


JT

LX90

Yeah I forgot to mention it's the stock Diff, haven't changed it.

sitnlopro99gt

I run redline 75w-90

sprostang

Yeah, if you use royal purple, you don`t need the modifier.

LX90

So is the RP 75w-90 gear oil ok then? I notice that when you buy a complete ring gear set, sometimes they come with RP 75w-90.

sitnlopro99gt

There is friction modifier already in both of those I didn't add any this time as I didn't think I needed to with it already in there and I havent had probs.