See title. Is it the spring lifting one side off the ground or is it something else like the cable on that side? Thanks for any advice!
Edit: From what I can tell the door and the floor are both slightly off level in opposite directions. I also just replaced the bottom seal in an attempt to fix this.
Looks like the concrete falls off on the right.
The gasket at the bottom of your overhead compresses to help create a seal along an uneven surface, but it can only do so much. Your gap may be too large to seal before the door bottoms out completely on the left. That said, there is adjustments that set where the door comes to a stop when closing, check your manual and see if the overhead can lower further.
If you check the level of both the door and the slab it will let you know which one is causing the gap. I would guess that a gasket would be the best fix. If it is the door DO NOT try to fix it yourself. Those springs can very easily kill you. I have known life long contractors that will do everything in a house but a garage door. Garage doors are not DIY.