Synthetic vs Dino lube in rear diff

[Fasterthangas]

Decipha;

Why do you advise against running synthetic rear diff lube even when prescribed by the Ford engineers?

[decipha]

Because conventional can never hurt anything.

Synthetic if thats all the diff has ever had is fine to continue to use.

However if going from conventional to synthetic or putting synthetic in a diff not specifically designed for it then it will cause excessive wear on the clutches and much more prone to humming and even causing leaks which can further damage the diff. Tossing conventional in a diff designed for synthetic is perfectly fine too. Hence its best to do conventional.

[Fasterthangas]

Because conventional can never hurt anything.

Synthetic if thats all the diff has ever had is fine to continue to use.

However if going from conventional to synthetic or putting synthetic in a diff not specifically designed for it then it will cause excessive wear on the clutches and much more prone to humming and even causing leaks which can further damage the diff. Tossing conventional in a diff designed for synthetic is perfectly fine too. Hence its best to do conventional.

Interesting. I just installed new Ford gears and 31 spline Trac Lok. I did the 500 mile break in using conventional. Being in Phoenix; I would think that synthetic would handle the extreme heat better. The only time synthetic causes leaks is when it cleans away sludge left behind from dino oil. This sludge plugs up would be leaks in gasket gaps and such. This is often due to lack of maintenance. Quality synthetic has much better detergents.

[Fasterthangas]

I just remembered that I'm running the Cobra carbon clutches in the rear. I wonder if the carbon clutches require different fluid?