Many moons ago (I was a child DIYer) I was fixing just such a garage
door, with my accident prone father, which had exactly the same problem.
I found out first hand just how much power is in the spring when we
slipped while re-attaching the wire to the wheel. The wire became
wrapped around two of my fingers and very nearly pulled them off.
Luckily the wire came free just before it pulled my fingers into the box
containing the spring and I got away with some very painful bruising.

Anyway, we tried adding a couple of extra twists to the spring but it
just broke so we replaced it. I don't remember where we got it from
though. Give it a good coat of grease once you have it in place.

Finally, always work with the door propped fully open. Sounds like a
stupid bit of advice but having the door closed is why I nearly could
only count to 8.

Graham (10 years without a visit to the A&E department and going strong)

Steve wrote:
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