I'm new to the portal and popup campers. I just bought a 1979 Rockwood popup tent trailer, Model HW 1006, I think, with old style chain/spring lifter mechanism. Suffered a back lifter mechanism failure overcranking it down. I pulled cabinetry removed back lifter mechanism, had a blacksmith cut it open and repair the broken chain link, weld back together and replaced in good order. When I try to raise back end, I get tension in the chain from crank to lifter gear immediately and it pops chain off crank. I cannot find where the resistance or binding to lifting is, lifter poles are recently lubricated, slide easily and seem to want to go up. Anyone else have similar issues and how did it get resolved?