Differential fluids

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Dec 17, 2010 | 09:44 AM

firemankato

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From: SW Iowa

Differential fluids

My truck has reached the 100,000 mile mark so I figure its about time to change the major fluids. What are your opinions on the oil in the front and rear ends? I have stock 3.73 gears with the factory LS (wish I could afford a locker). Thanks!

2002 Superduty CC 4x4 5.4L 6 speed manual

Dec 17, 2010 | 09:57 AM

bpounds

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From: Whittier, CA

75W140 synthetic in the rear, plus friction modifier for the limited slip. I recommend Mobil 1 and get the one that has the FM in it already.

The front is spec'd at 75W90, but lots of guys just use the same stuff as the rear.

Dec 17, 2010 | 12:12 PM

mikesmayhem

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From: Stacy, MN

I used AMSOIL in my rear diff. and it worked great no FM needed.

Dec 17, 2010 | 03:01 PM

firemankato

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From: SW Iowa

Thanks for the help. Are they better than Motorcraft?

Dec 17, 2010 | 03:27 PM

bpounds

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From: Whittier, CA

Quote:

Originally Posted by firemankato

Thanks for the help. Are they better than Motorcraft?

Not necessarily better, but Mobil 1 is easier to find, at least as good, and probably cheaper. Also, if you go with Motorcraft, you will have to buy the friction modifier separate and add it.

Dec 17, 2010 | 09:38 PM

rymac320

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ford now recommends 75W-140 synthetic in the front as well

Dec 17, 2010 | 09:55 PM

bpounds

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From: Whittier, CA

Quote:

Originally Posted by rymac320

ford now recommends 75W-140 synthetic in the front as well

Got a citation for that? Like a TSB or something?

The 2011 owners manuals still says 80W90 for the front axle.

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Dec 18, 2010 | 01:36 AM

rymac320

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nothing in writing, no. two different ford dealerships told me ford now recommends 75W-140 for front and rear so thats what i put in (motorcraft). i did them last month. for some reason i think there are postings somewhere on this forum about the 75W-140 too...

my owners manual for 2004 says 75W-90 for the front and 75W-140 for the rear.

maybe both dealerships were wrong or maybe it has changed again for 2011..?

just my .2