I am reading my haynes manual and am a little confused. If I am changing out both diffs. can I use Mobil 1 75w-140 in both?

i believe u can use it in both, if ur gona use synthetic it doesn't matter if its limited or open diffys because synthetic oil doesn't need an additive for the limited slip like normal gear oil does. i'm gona be doing this, this summer so if anyone else can back me up plz do.

i believe u can use it in both, if ur gona use synthetic it doesn't matter if its limited or open diffys because synthetic oil doesn't need an additive for the limited slip like normal gear oil does. i'm gona be doing this, this summer so if anyone else can back me up plz do.

Ummm.... You can use synthetic for the front but the 75-140 is overkill for the front. You will just have worse mpg.

It may require an addative. The factory ford fill 75-140 is synthetic and they add friction modifier for the LS aplications. Even other manufacterers that are designed for LS rears say that it still may require friction modifier. You can always try it without first and see if you get lockup on sharp turns. Then add as needed.

so what weight for the front? and is there a synth for that?

Overkill? Please explain

Synthetic 75-90 for the front and synthetic 75-140 for the rear. If you dont tow you can go with synthetic 75-90 for the rear as well. I did a lot of research on this as I have changed both front and rear to Redline synthetic 75-90.

Did you use any additive in the rear or just synth only?

I tow and use Amsoil 75 w 90 in the rear. I do not use a friction modifier.

Great, I think I'll switch to mobil 1 75w 90 for both diffs. I wonder if I'll see any MPG improvment?

Did you use any additive in the rear or just synth only?

I used part of a bottle of LS addative as I didnt want to have to crawl under there again. It works great.

You may notice a slight mpg increase. I havnt check to see if mine has changed yet. Too soon. Al could tell you though. He has had his in for some time now.

what does the book call for in the rear end, 75w 90 or 75w 175? i thought it was 75w 90 for both...??????

it depends on the year. 98 and later use synthetic 75-140 for the rear and 80-90 for the front. Im not sure about the 97. You will be fine with synthetic 75-90 all around unless you do heavy towing.