Spiral rod popped out

Question

I bought a replacement 28" series 900 spiral balance for my window. I measured the broken one and it is 28". When I put the new one in, the spring portion pops out of the casing when I shut the window all the way down. What does that mean? Wrong size? Do I need to put the mounting screw in little lower to lower the spindle a little? I know the rod is not the wrong size because I triple checked the size.
Any suggestions?
Thank you.

Tom · Accepted Answer

It definitely sounds like an issue with the length. The tube of the old balance may be the same, but I wonder about the inside spiral. I would carefully measure the inside spiral from your old balance and compare it to the new to see if they're the same. You may have a type of special balance that needs a longer spiral.