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Drive train Fluid Changes

robbcwz

New Member
Messages
6
Reactions
8
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2
Location
Prairieville, LA, USA
#1
2021 ST with 30,000 miles. Lot of highway use; minimal towing use.

Would strongly recommend changing the transfer case and front differential fluids at, or before, 30,000 miles. Trans fluid and rear differential fluids looked in good shape (changed anyways) but the transfer case fluid was starting to turn from pink to brown and the front differential fluid was just plain ugly! I think the small capacity of these last two is why the oil deteriorates so much.

The front differential is (relatively) tiny and holds 0.6 quarts (75W140) so it definitely has a hard, hot life. I plan on changing it again in 15,000 miles for sure.

The transfer case is only 1.1 quarts (MERCON LV) and also sees a pretty hard life.

All are easy access for the changes but the transfer case drains all over the cross member and the front diff torx plugs (why use Torx here when the others are 3/8" square drives?) seems to have been installed by Thor and were a PITA to remove - long extension bar needed on both plugs.
 

Cdubya

1000 Post Club
Messages
1,443
Reactions
699
Points
262
Location
NE Ohio
Vehicle
2020 Explorer ST
#2
Wanted to thank you for the info here. I lost some differential oil with the frint speed sensor removal but didnt have the oil at the time to top it off. Because of your info, I drained and filled the front differential and transfer case. Have 52k miles so far.
 

randyknight

Member
Law Enforcement
Messages
159
Reactions
71
Points
27
Location
Chelsea, AL
Vehicle
2022 Explorer ST
#3
2021 ST with 30,000 miles. Lot of highway use; minimal towing use.

Would strongly recommend changing the transfer case and front differential fluids at, or before, 30,000 miles. Trans fluid and rear differential fluids looked in good shape (changed anyways) but the transfer case fluid was starting to turn from pink to brown and the front differential fluid was just plain ugly! I think the small capacity of these last two is why the oil deteriorates so much.

The front differential is (relatively) tiny and holds 0.6 quarts (75W140) so it definitely has a hard, hot life. I plan on changing it again in 15,000 miles for sure.

The transfer case is only 1.1 quarts (MERCON LV) and also sees a pretty hard life.

All are easy access for the changes but the transfer case drains all over the cross member and the front diff torx plugs (why use Torx here when the others are 3/8" square drives?) seems to have been installed by Thor and were a PITA to remove - long extension bar needed on both plugs.
Did you use any friction modifier, or anything for the front and rear Diff and transfer case?
 

Messages
168
Reactions
64
Points
27
Location
Iowa
#4
The manual calls for 75w-85 for the rear diff. Would I need a friction modifier if I went out and got a quart of Motocraft 75w-85?

If so, what kind?
 

Messages
168
Reactions
64
Points
27
Location
Iowa
#6
Open diff, no friction modifier.
Thank you. One more question. The manual says to put it in neutral… is that necessary? Wa shuts curious as to why it should be in neutral and not in park on a flat surface with the parking brake on.
 

Messages
317
Reactions
164
Points
37
Location
Burlington, ON, Canada
#7
Thank you. One more question. The manual says to put it in neutral… is that necessary? Wa shuts curious as to why it should be in neutral and not in park on a flat surface with the parking brake on.
I was a lube tech for 8 years and must have serviced about a thousand differentials…I’ve never known one that needed to be in a specific gear/neutral/etc…I’d love to hear the explanation for that too
 

TMac

1000 Post Club
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Location
Knoxville, TN
#8
It makes absolutely no difference to the diff from being in either park or neutral. Most likely the service manual writer copied this from another source.
 

Messages
168
Reactions
64
Points
27
Location
Iowa
#9
Thank you.

It’s crazy how little room there is between the subframe and the fill plug on the rear diff. Like what crazy tool do they use to remove/put back the full plug? A super low profile 3/8” ratchet?
 



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