I have an up & over metal garage door that stays up when I open it most of the time. The problem is that every now and again it drops down again, by anything from about 6 inches to 2 or 3 feet. This often happens some time I have opened it and carried on, happily believing it has decided to stay open. It's already taken a lump out of the top of my head and it's only a matter of time before it drops on to the roof of the car as I back it out. This would not be a good thing.
Its the type that has a large metal spring just above the door, the full width of the opening. At each side of the door opening is a vertical track in which a nylon wheel attached to the garage door runs. There is also a taut wire running from a reel on the end of the big spring to help pull this wheel up.
The big spring was dry and rusty so I gave it a good soaking in WD40 and that seemed to improve things for a while, but the problem soon came back. I've sprayed everything I can see with WD40 but it's still not right. Any suggestions would be welcome.
Thanks
Steve