Spiral Balance question

A quick learner from USA says:
I just installed a pair of 29" 306 spiral balances and after a few cycles of the window one of the balances came apart. I'm wondering if this was caused by a length issue. I ordered the same length as was in the window but it doesn't have a "stop" on the spiral as the SWISCO balance appears to have.

The height of the sliding portion of the window is 30 1/4" and the body of the balance, as installed, extends 28" above that. Under full extension the balance would be 58 1/4" long.

Did I get the correct length balance for this window?

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Tom from SWISCO responded:
Hey, good to see you again. I'm not sure what the issue is, that is very strange. I'm also not sure what you mean by "stop." Do you mean the 15-066 shoe? If so, I don't think the Series 306 is what you need.

I think it would be best if we start from the beginning, to avoid any confusion. Let's not worry about the size of the window and instead concentrate on the old balance. What is the length of the original tube? What is its diameter? Can you also tell me the weight of the sash? Finally, please clarify what you mean by "stop." It may help if you show us a couple of pictures of the old balance.
A quick learner says:
The length of the tube is 29" and the diameter is 3/8". I don't know the weight of the sash. The spiral part of the SWISCO balance has what appears to be a rivet through the end that is inserted into the body. This is what I referred to as the "Stop". I assume it keeps the balance from coming apart. Which is what happened to mine.
User submitted photos of a window balance.
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Paul from SWISCO responded:
I'm not sure what the problem could be. I'm still not sure what you mean by "stop." Do you mean the spiral came completely out of the tube, or did the 15-066 shoe come off the rivet?
A quick learner from Albuquerque says:
Yes, the spiral came completely out of the tube.
I think me mentioning the stop is not helping.

Let's just go with, I installed a balance sized per SWISCO's instructions and when I lowered the window the spiral came out of the tube.
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Paul from SWISCO responded:
Thank you. Honestly, I'm not sure what went wrong. If your original balance tube was 29" long, then I see no reason why you should have had issues. Let's start by getting the weight of the sash that this balance is meant to support, as well as the height and width for the visible glass. Maybe with that information we can determine what the issue is.
A quick learner says:
I don't think weight is the problem. The length of the balance is the issue. If you look at the first picture you see that the overall length of the original is almost 31.75". The overall length of the SWISCO balance is less than 30". The original balance has more range before it comes apart. Based on this I decided to reinstall the SWISCO balances but I moved the point where the tube attaches to the window frame down. The window works fine.

I have more windows to fix and I need to decide if I should buy 30" balances or stay with the 29" balances and move the attachment point down. I'm leaning toward 30" balance because it would make it easier to insert into the window. The sliding portion of the window is 30.25" tall and it's a pain trying to insert a 29" balance into the window and guide it into the rubber piece at the top.
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Paul from SWISCO responded:
Ah, I see. I agree with your full assessment. If moving the balance down an inch worked, then reason dictates using the S306-30 would provide the same effect.
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