Craftsman GDO won't stay closed
Hi. I have an older style GDO; no sensors, etc. It just goes up & down. It is Sears model 139.53600, 1/2 HP. I used to have a 1/3 HP Sears 139.53210 on this door. The door was unbalanced, and it eventually ground off the teeth on the main plastic gear. I have repaired the problem with the door balance, and I replaced the old operator with this 1/2 model I had laying around. OK, so here's the current problem. When I close the door, it appears to operate normally, until the door is fully closed. Then, about 2 seconds later, the door opens again. I tried adjusting the up/down force, no luck. I also played w/ the adjustments on the travel, and it doesn't seem to help. Any ideas, experts? Thanks.