Front diff lube
Postmaster
Joined: Sep 2002
Posts: 3,077
Likes: 1
From: None of your business
I wouldn't think that it would hurt anything except for MPG a little bit if any. But the only reason why I'd do it is if I had enough left over from a rear end fluid change. Even then I'd go out and buy the 75W90.
Personally, I run Mobil 1 75w90 in boths diffs with no problems.
Mike
Personally, I run Mobil 1 75w90 in boths diffs with no problems.
Mike
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FTE Legend
Joined: Aug 2004
Posts: 37,887
Likes: 20
From: North Central Rural Sask.
Right now I have regular 80/90 in both doffs, but I was going to change the back to some 75/140 and the amount I would have to buy, I just figured maybe I would slap it in both diffs!
Senior User
Joined: Jul 2004
Posts: 479
Likes: 1
From: Syracuse
Originally Posted by preppypyro
Will probably do that, its cheaper anyways 
Tell me about it, I replaced my rear diff. cover yesterday.
10.25" diff cover = 23.00 USD
Bottle of friction modifier = 4.00 USD
3 qts. 75W140 synthetic = 47.00 USD
BTW, you won't gain any mpg using 75/90.
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Fleet Owner
Joined: Jan 2004
Posts: 26,007
Likes: 575
From: Brentwood,CA
why would you use a 90w in the rear? thats a very dumb idea. the clearances between the crush bearings are pretty big. i would not use a 90w. ford issued a TSB about this.
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Senior User
Joined: Jul 2004
Posts: 479
Likes: 1
From: Syracuse
Originally Posted by ford390gashog
you guys are also paying too much for lube. you can get mobil 1 for 7.99 , royal purple for 8.99 and conoco synthetic for 10.99.
The only reason I paid big for the oil is because I was at the dealer to pick up the cover and friction modifier. It was just worth it to me to do a 1 stop shop. I don't know if the parts stores carry friction modifier, and they certainly don't have the axle brgs for my truck. The brgs weren't bad, but I wanted to put new seals in, so I just did it all man. Next time I will definately get oil somewhere else though! Ouch!
. Rob
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Joined: Mar 2004
Posts: 169
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From: hallville
Hay 7700rob I'm off topic here but I was wondering if all 4x47700 have a 10.25 diff .I thought I had a 9.75 or something in mine . It;s a 2002 sc 4x4 7700. I just thought maybe when I'm on this site i should know what difff is in it. It's a posi 3.73 ratio and looks enormous. Specially the axle tubes. How do ya tell?