I have a 20ft tandem axle boat trailer with drum surge brakes on one axle with a Atwood actuator. The brakes have been dragging and one has locked up on two occasions. I have replaced inner/outer wheel bearings and grease seals so I have eliminated that as being the issue. When I press down on the actuator it goes down about 1/2" before I feel any pressure and I have to pull it back to the "released" position at the 1/2" mark. Where should I start looking as to what is causing the issue?. When I had the hubs off doing the bearings I backed the brake adjusters as far loose as they would go