If I remember from the videos I've watched on installing a full length rack, I think you have to slide the cross bars out the end of the rails. So you have to pop the plastic caps for the main rail mounts, unbolt the mounts completely on one end, and loosen on the other, and slide the cross bars out the open end. Then reverse the process to re-assemble with just the rails. But I may misremember the video I saw.