Diff and Transfer case fluids

[tech10002]

I'm gonna have my truck on a lift this weekend to change the shocks, so I want to go ahead and change the fluid in both diffs and the transfer case.

The book shows a bunch of different weights for the different axles. Can anyone tell me what I need for an 06 F-250 4x4 with 3.73 gears or at least tell me how to figure out what axle types I have? How much will it actually take in each axle and the xfer case? I know the book shows capacities, but often it actually takes less than the spec in my experience with other vehicles. Do I need any kind of special additives in the rear end since it's limited slip?

I just want to make sure I don't screw anything up since this is the first change I've done.

[67ModStang]

Your front should be the dana 60 and uses 75w-90 @5.9 pints. Rear should be the ford 10.5" using 75w-140 @ 7 pints plus the ford xl-3 friction modifier. Tranfer case just uses ATF @ 4 pints.

[bismic]

My manual states 5.8 pints of 80W-90 gear oil for the F250/F350 Dana 60 front differential. Use a synthetic.

FYI - The differential fluids are considered "Good for Life" fluids by Ford (unless submerged or other problems detected).

For the Transfer Case, the manual states that the fill is only 2 quarts (4 pints as 67ModStang stated), but mine took 3 quarts to get to the top fill bolt - maybe I overfilled it??? (didn't think it was possible due to the simple design). Any good synthetic oil with the Mercon V rating would be good.

Rear Axle:
F250/F350 10.5 Axle - 6.9 pints of 75W-140 Synthetic (For the OP - This is what you have)
F350 Dana 80 Axle - 8.5 pints of 75W-90 Synthetic
F450/F550 Dana S110/S130 Axle - 14.0 pints of 75W-140 Synthetic

The manual also states to use 8 oz of the friction modifier in the limited slip differentials, but I have read where many folks add a little less than that - they feel it performs better w/ no apparent reliability issues. Maybe others will comment.

Also - some oils for the differential come w/ the friction modifier already added.

[tech10002]

Mine has never been in water, so do I not need to change the diff fluids? I read a thread here somewhere that said you were supposed to change it at 60k. If I don't have to spend the money, I'd rather not.

Does the transfer case use Mercon SP or just standard fluid?

[67ModStang]

The owners manual does state that there is not a service interval on the Ford rear axles which explains why it calls for 75w-140 unlike the Dana80 using 75W-90. IMO I would change it out anyway. Mercon SP is not necessary for the xfer case. I do recall it taking more than 2 qts to get to the fill plug on mine like Bismic stated. Just get an extra qt of everything to make sure you have enough.

[03-blue-Powerstroke]

Does the transfer case use Mercon SP or just standard fluid?

When I changed the fluid in my transfer case I used regular Mercon ATF. Its hard to just pour the fluid in there though so you will need a funnel or a fluid extractor tool.

[w_huisman]

Is the friction modifier required in the rear end if a good synthetic 75w-140 is used, such as Mobile 1 75w-140 syn?

[03-blue-Powerstroke]

Yep its required unless the fluid already has it in it.

[06lariat4x4]

when changing the t case fluid i was told to jack up the front of the truck so more fluid drains. when u fill it do you lower the truck or leave it like how u drained it??

[MoyockPowerstroke]

I had the rear lower than the front (good idea)....Used Mobil1 ATF Syn 2.2qt, same stuff I used in my PowerSteering flush. Mobil1 75w-140 LS Syn in the rear diff and Mobil1 75w-90 LS Syn in the front.