Differential help

[ramlife68]

Just changed oil in diferentials... first question on front diff is I filled it till oil running back out and then capped it ( only a little over a quart in)...too much oil or ok? Or should I let the extra oil run out of fill plug?
Also this is what I saw when I opened fuller cap...black n feels like sandpaper

 

[Burla]

The first time you change the diffs you really should remove the cover because when they are broken in they can often create wear metals that should be cleaned off. Maybe do a short run or bite the bullet and do it right. Level is fine.