Adding disc Brakes

[FLMTBer]

Are there ways to add disc brakes to wheels that aren't set up for them? The wheels I have came off a Schwinn Excursion from a few years ago. I was able to use the front brake with a little adjusting because I used the fork from the schwinn. But I have no back brake as of now. There are no posts for the brakes, it's disc only. I have not done any serious riding yet but it doesn't look good.