I have recently inherited my father's 05 f150 xlt 5.4L 3v. The stock rear diff ratio is 3.55 and I would like to replace the diff with 4:10 gears. Will they fit in the stock axle housing? And do I have to replace the axle shafts?
Also, if i change the rear diff do i have to do anything to the front diff gears?
thanks

 

Front and rear gears have to match.

 

If you do the math and figure out exactly what size tire diameter on the front would equal the overall drive ratio on the rear you could run a different size front and rear tire and not have to change gearing.

 

No, gears need to match front and rear.

I assume you want to change the gears because you want bigger tires on the truck. To follow your idea, here is an example combo of what you would need (if you can find the combo). Rear tire 35" diameter, Front tire 30.3" - not 30.2 and not 30.4.

Put matching gears front and rear and put whatever tires you want on it.