And you are right, there is no residual valve in the master cylinder of newer cars. You need to put the proportioning/metering valve back in the system. but still if your master cylinder is working you should have rear breaks if the line goes straight from the MC to the rear breaks. Adjustable prop valve and add residual valve should work. like Dave says sounds like you have a caliper sticking and no vac. at the booster also.

http://www.ecihotrodbrakes.com/brake_facts.html