Do you have spring-return brake levers?
Can you remove the brake cable and then test the action of the brakes without a cable in play at all? Or ideally, install just a loose piece of cable and actuate the brakes manually from the separate cable. If you see the same behavior without any cable in play, it confirms the issue in the brake. Any binding in your brake cable or brake lever would cause that symptom.
Just spit-ballin' here, but the problem is in the brake, then my hunch it is probably not the rollers & wedge. My hunch is that the problem is binding in the pivot point of the calipers. It is super-simple mechanically, and if that pivot is not smooth, then the spring will not be able to deliver enough force to pull the triangle back down. If you remove the triangle, do you feel smooth spring & return action compared to the front brake?
Since you have 2 brakes, have you tried swapping the front & rear to see if the problem moves with the caliper or stays with the installation location?
Can you remove the brake cable and then test the action of the brakes without a cable in play at all? Or ideally, install just a loose piece of cable and actuate the brakes manually from the separate cable. If you see the same behavior without any cable in play, it confirms the issue in the brake. Any binding in your brake cable or brake lever would cause that symptom.
Just spit-ballin' here, but the problem is in the brake, then my hunch it is probably not the rollers & wedge. My hunch is that the problem is binding in the pivot point of the calipers. It is super-simple mechanically, and if that pivot is not smooth, then the spring will not be able to deliver enough force to pull the triangle back down. If you remove the triangle, do you feel smooth spring & return action compared to the front brake?
Since you have 2 brakes, have you tried swapping the front & rear to see if the problem moves with the caliper or stays with the installation location?