If you are getting ZERO fluid to the rear, check or replace the rubber line going from the frame rail to the rear axle. The rubber deteriorates over time and can block up stopping your fluid. Then check the hard line front to back and over the axle to make sure it's not pinched, kinked etc.
If the lines are good, and you are getting fluid but no pressure try getting one of these:
http://www.harborfreight.com/brake-bleeder-and-vacuum-pump-kit-69328.htmlYou can bleed your brakes by sucking the fluid through. That way if you have an impossible bubble somewhere so you cant generate a pedal, this should suck it out and get solid clean fluid through.
Remember to thoroughly bench bleed the new MC when you put it in. This is key since the pedal can't get the MC through full stroke so you will always have a bubble trapped there.