air in the calipers and front lines. Once you get clean fluid with no air from the front bleeders, I would move to the rears (passenger, then driver). It's possible the rears won't be affected at all because they're plumbed from a single hardline that runs all the way back to the master cylinder, but it depends on how much fluid you lost during the front install and if enough air got into the system. It's really not a bad idea to clean out the rears of any old fluid and possible air bubbles and should only take a few pumps on each corner.
