i have a 2006 F150. I had the front and rear differential seals replaced by my mechanic since they were leaking. Upon replacement of the front seal, the mechanic found a hairline crack going from the seal housing and running up the differential. Is there any way to repair the crack? Otherwise it takes me to my second question. How difficult is it to replace the differential. I have some experience working on cars, but im not a everyday mechanic. Is it pretty safe to do myself, or better to shell out $300 to get it replaced? From my understanding of the gear ration, an H9 axle code on the door would indicate i have a 3.55 ratio. I have found one on ebay:
http://www.ebay.com/itm/06-07-08-For...xWHvpj&vxp=mtr

 

You will have to unbolt the drive shaft, cv axles, remove the front cross member, and then the axle will drop out. I'd want the truck on a lift to do all this.

 

Setting up the gears in the center section of an axle is not for the beginner.
You would probably be best taking to a shop to set up the gears. Getting it wrong would cause noise and premature failure of the gear set.

 

Sorry, I see that you are looking to replace the whole assembly. The need to set up the gears doesn't come into play.