Got a 2006 ez loader trailer with surge brakes. The master cylinder was empty so I added fluid and attempted to bleed them. Took it out fishing and towed it about 90 miles round trip. Had no issues loading the boat. When I got back home and attempted to back it in the shop, I could not back it up due to the brakes not unlocking while in reverse. Put a key to override the brakes so I could put it in the shop. Do the brakes need to be bled more or is there something else I could do. Never had this issue until I tried to repair the brakes (I’m the second owner). Thanks.