I would like to change the oil in the rear axle and also in the front axle.
What are my choices as to oil, regular and synthetic, and how much friction modifier additive should I use? Do I need to flush the housing if I change to synthetic?
F250 SD 7.3l 4 x 4 XLT supercab
the back axle will have synthetic from factory, so you will want to stay that way. I went with lucas when I changed mine because that was all I could find locally. Royal purple is a favorite, and has the friction modifier in it already. You will want to first find out if you have an open or limited slip diff before adding any modifier. It is also a good time to look into replacing the back cover with the 08+ alum finned cover. You can use guzzle's site for instructions and tips. Welcome to guzzle's Ford PSD Maintenance Web Page
I did my front without any problem a month or so ago..Ford now reccomends 75W-140 synthetic for front and rear.... tried to do the rear yesterday and could not get the cover to come off! going to wait a few months until it warms up and i can spend some more time, probably going to take out the spare tire too for more room. but overall a simple process. i used the factory motorcraft.