Was the box across the top of the door,if so and you had to unbolt the cover
then you have what is known as a reverse spring box very old and not worth
the hassle to repair or put back together.Check with your nearest stockist
for a replacement Gardors web site will help you there in finding
one,although you may find them difficult to obtain as they are no longer
manufactured.

If the spring was in a box down the side then they are even older and
equally dangerous