Well this opens up a whole new can of worms. One more thing to worry about.

Do you happen to know the failure rate (failures/100 vehicles)?

Does it usually fail within the first 10k miles? 20K? 50k? 100k?

Is Ford denying waranty claims based on improper maintenance?

So do you think I would be safe if I changed both front and rear diff fluid every other oil change? Or would every oil change be better?

 

Factory diff fluid and transfer case fluid is good for 100k.

 

why is this in the GD?

 

Because the OP decided he wanted to post it in here. You have a problem with that?

 

I don't work at a dealership but a indebendent shop and most that I have seen failed around 50k-75k. Once you do the first one for break in you won't have to do it for 80k-100k. I had one that we replaced the diff in and it came back in 3k and it looked like the fluid had been in it for 100k we warenteied the fluid since it came in with in warrenty and the advisor didn't let him know that it needed to be done befor 80k.

 

The factory diff fluid is good for 100k. However, when you regear with aftermarket gears, THEN you need to follow a breakin procedure which involves a fluid change at 500 miles.

 

Factory diff fill is good for 100K. It is a synthetic fluid. There is no need to change it sooner unless you are changing something like your cover. I switched to a Mag-Hytec cover so I changed my fluid but that was around 50K. Do not judge the fluid by appearance. If you have a LS you will have very foul smelling gray looking fluid. That is normal. Smell that tube of friction modifier next time you add one. It is bad smelling stuff.

 

Your way old school. That isn't even close to true anymore. A good example is I just popped the diff cover off of my F-350 at 95,000 miles. Never has been off. The oil was great and there was no wear. Tooth pattern was great. The problems you see with differentials has NOTHING to do with the factory oil. There is no such thing as break in oil anymore. My focus has 110,000 miles and right from the start new I have changed the oil every 5k because that is easy to remember. And I am changing it too often. The oil can easily go 7,500 miles with my driving habits. The car still runs like it was new.