need some help, In a bind here

I believe it might also be possible you simply have a bad seal in one or both rear calipers. The reason residual valves are used in drum systems is that the master can return fast enough to cause a slight vacuum and draw air in past the cups on the drum pistons, eventually building up air. Most disk systems don't need them because the pistons dont really return much. If you read the explanation in some of the old shop manuals, the flex in the lip of the piston seal causes the caliper pistons to return a tiny amount. Maybe the seals have gotten a bit hard