It is likely you have manual adjust brakes. And I believe the auto adjust brakes on a trailer adjust themselves going forward, not backing up.
My brakes began to seem weak last year. I adjusted the brakes and it was like night and day. Before adjusting when I manually actuated the IBC all the way it would slow me but not abruptly so. After adjusting the brakes, it will slide all four tires. Had to turn my controller setting down.
Lots of brake adjustment info on the net. Easy and simple to do with a cheap brake tool from auto parts store.
