I went ahead and looked at the AM site (my wife doesn't like it.....
, BUT I do....
). Anyway, typically differential bearings will last approx. 100k miles before needing replacement (with normal driving). However, you
WILL need the installation kit for $36- mainly because it gives you a new crush sleeve (which isn't reusable), and pinion nut and ring gear bolts (which may not be reusable according to Ford). Other things like the shims, marking compound and loctite just make the install easier.