Drive train Fluid Changes

[robbcwz]

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]

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]

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?

 

[schaggatron]

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?

 

[Lightning Struck]

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?

Open diff, no friction modifier.

 

[schaggatron]

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.

 

[KNTRDR]

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]

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.

 

[schaggatron]

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?

 

[SueroRD]

Do you remember which is the size of the torx in the front differential? Thanks in advance

 

[LuxST]

Anyone have a video or picture for the fluid change on the front differential? Back side is easy. Thanks.

 

[Rodeorowdy]

Anyone have a video or picture for the fluid change on the front differential? Back side is easy. Thanks.

Almost a year and a half later and no reply. Bumping this to hopefully get an answer.

 

[KNTRDR]

Almost a year and a half later and no reply. Bumping this to hopefully get an answer.

The procedures for both diffs were posted on these forums a while back…not photo/video but the factory instructions with diagrams. It was as simple as removing the front plastic splash shield from underneath (lots of screws/clips), and then two plugs on the diff - one for filling, one for draining. If memory serves the drain was an allen head. They (the instructions) should still be somewhere on the forum.

 

[Rodeorowdy]

Yes, I have seen those instructions you mentioned. But it is a drawing and not the same as a photo video.
May I ask, how did you lift your vehicle up to access the front differential?

I’ve studied the front differential and determined it would be best to lift up the right wheel to drain and then let it down as low as possible, so I could still get underneath to fill with 0.6 of a quart, equal to 19 ounces.
Any remaining residual lubricant, plus the 19 ounces I add, should make the level correct.
Thank you for any comments