Differential Fluid (non torsen)

[WildHorse]

So after I put the diff back together, what are you guys replacing the factory fluid with ? Or are you using the factory 75w90 + friction modifier ? I was thinking 75w140 with already added friction modifier. I really don't care if I lose .1 mpg haha. Thanks.

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[WildHorse]

Noone? Mkay.. Anyways decided to go with Royal Purple 75w140 full synthetic.

 

[Dominant1]

Ford motorcraft 75/85 specifically designed for Ford seals..and don’t forget the friction modifier...

 

[WildHorse]

Ford motorcraft 75/85 specifically designed for Ford seals..and don’t forget the friction modifier...

Thanks. And if you use upgraded seals ?

 

[Dominant1]

Should still be fine..

 

[WildHorse]

Should still be fine.

But your using Amsoil Severe Gear 75/90 Diff oil, so what's the difference to say Royal Purple, other than a higher hot rating with built in friction modifier ?

 

[Dominant1]

Im switching my rear differential soon to 3:15’s and its getting Motorcraft 75/85 gear oil and friction modifier. The amsoil is good oil but i had axle seal leaks since I started using it, even after replacing the seals. So I’m going back to motorcraft synthetic.

 

[WildHorse]

The amsoil is good oil but i had axle seal leaks since I started using it, even after replacing the seals. So I’m going back to motorcraft synthetic.

Yeah my seals leaked too, with the factory fill. That's why I upgraded to Yukon seals, Timken bearings, etc. Also went from 3.31 to 3.73.

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