Questions about differential fluid

[dajoes90]

Hi guys,

I'm planning on change the rear differential fluid and i'd like to know which brand is the most reliable to use and how can I make sure I need to use the additive in a simple way. I've been reading lots of posts here on the forum so if you know one that explains all, please put the link. Also on the owner's manual requires to use transmission fluid 75W-90 Synthetic but here I read that is better to use 75W-140, what should I use?\

Thanks!

 

[Mbrooks420]

75-140 was an updated thing, and is the correct oil to use. Check the rear axle code on the drivers door. Post the code here, and we'll tell you if you have a limited slip. ( I know D4 is 3.73 limited slip)

 

[dajoes90]

Here's the picture:

 

[Mbrooks420]

You have a 3.55 open, no need for friction modifier.

 

[dajoes90]

Thanks!! So just to clarify, with 2 qtrs. of 75W-140 will be good to go? And if it's synthetic the better will be, right?

 

[drdoom]

I do not believe you need additive for that axle. Use the 75/90 in front axle (4x4 or AWD models). Use the 75/140 in rear.

 

[MrPulldown]

Then there is the whole "overfill" option. I recently changed out my rear diff fluid. After doing so and posting about it, someone asked if I overfilled the diff as the manual suggested. I did not. You also need a 3/4" square drive to remove the drain plug. Remember to remove fill plug before draining. Here is a link to my post.

I now own a 3/4" square drive adapter. A tale of rear diff fluid change.

 

[dajoes90]

Done with no issue, pretty easy to do it and now car runs smooth that it used to do.

Thank you all for your tips!

 

[TechGuru]

 

[lincolnshibuya]

Both are good, price is where I lean to and you need a friction modifier for the Lucas if you have limited slip (extra $$). What I noticed is that no parts store beats the price in walmart..

 

[dajoes90]

I've used the Valvoline 75W-140 full synthetic, bought it online at Advance Auto Parts because I had a big discount. Bought also the seal gasket market for nothing, because I realized too late that the differential cover was impossible to take it out. Is it possible that after changing the oil, the car mileage is better? Feel like is using less gas that it's used to do.

 

[TechGuru]

Both are good, price is where I lean to and you need a friction modifier for the Lucas if you have limited slip (extra $$)

 

[Mbrooks420]

I’ve ran the Lucas in my Explorer and Both Mountaineers. No adverse noises or feel from the rear diffs. My other Mounty has well over 200k and the limited slip still functions.