rear diff fluid
Snowboard season cometh..
Joined: Jan 2006
Posts: 5,406
Likes: 1
From: Gulf Coast of Florida
75W140 fully synthetic (I use Royal Purple) and a little under 4 quarts
Opened on 1/14/2012 - found using the forum search feature:
https://www.ford-trucks.com/forums/1...end-fluid.html
Opened on 12/14/2011 - found using the forum search feature:
https://www.ford-trucks.com/forums/1...iff-fluid.html
Opened on 8/13/2011 - found using the forum search feature:
https://www.ford-trucks.com/forums/1...iff-fluid.html
My point is that 99% of the questions any one will ask have probably been answered already. The 3 links above were the most obviously related to your query.... out of 17 pages of results, with 15 lines per page - that's over 250 other threads that had the words "rear diff fluid" in them.
I'm not trying to bash you and only you, and don't want to turn you away from asking questions, but if you do a little research first, you wouldn't be waiting for the answer, you'd have found in less than 5 minutes and been on your way to getting another project completed.
Opened on 1/14/2012 - found using the forum search feature:
https://www.ford-trucks.com/forums/1...end-fluid.html
Opened on 12/14/2011 - found using the forum search feature:
https://www.ford-trucks.com/forums/1...iff-fluid.html
Opened on 8/13/2011 - found using the forum search feature:
https://www.ford-trucks.com/forums/1...iff-fluid.html
My point is that 99% of the questions any one will ask have probably been answered already. The 3 links above were the most obviously related to your query.... out of 17 pages of results, with 15 lines per page - that's over 250 other threads that had the words "rear diff fluid" in them.
I'm not trying to bash you and only you, and don't want to turn you away from asking questions, but if you do a little research first, you wouldn't be waiting for the answer, you'd have found in less than 5 minutes and been on your way to getting another project completed.
Snowboard season cometh..
Joined: Jan 2006
Posts: 5,406
Likes: 1
From: Gulf Coast of Florida
If running "dino" gear oil, you will need the FM; if running fully synthetic, then you shouldn't need the FM. If you run Full Syn and feel binding in turns, park on a downhill slope, open the fill plug on the rear diff, and add just 1oz. of the FM. Put the plug back in and go for a drive. You don't want too much FM in there, since that will neutralize the effectiveness of the posi - i.e. too much slipping. You want just enough not to bind in corners, but enough to let the posi work.
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Senior User
Joined: Jan 2010
Posts: 240
Likes: 0
From: blue springs Missouri
I do use the search a lot but I'm in my patrol car and am driving just figured I'd ask really quick instead of driving and searching at the same time. Plan on changing this week. So thanks for the quick responses.
Cargo Master
Joined: Feb 2010
Posts: 2,298
Likes: 94
From: Delta, CO
I'd have to disagree on the "need" for friction modifier when running synthetic. I run Royal Purple fully synthetic 75w140 for almost 100,000 miles with no FM added, and a fully functional posi.
If running "dino" gear oil, you will need the FM; if running fully synthetic, then you shouldn't need the FM. If you run Full Syn and feel binding in turns, park on a downhill slope, open the fill plug on the rear diff, and add just 1oz. of the FM. Put the plug back in and go for a drive. You don't want too much FM in there, since that will neutralize the effectiveness of the posi - i.e. too much slipping. You want just enough not to bind in corners, but enough to let the posi work.
If running "dino" gear oil, you will need the FM; if running fully synthetic, then you shouldn't need the FM. If you run Full Syn and feel binding in turns, park on a downhill slope, open the fill plug on the rear diff, and add just 1oz. of the FM. Put the plug back in and go for a drive. You don't want too much FM in there, since that will neutralize the effectiveness of the posi - i.e. too much slipping. You want just enough not to bind in corners, but enough to let the posi work.
When I changed mine I got the syn fluid with no FM so that I could add just enough to take the binding out, like you said too much FM just makes for a one wheel wonder. IIRC I had to use about 3 oz of the FM
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