Help to identify a replacement spring balance?

A handy person from Baytown, Texas says:
I have a house built in the '60's with inexpensive aluminum single hung, non-pivoting windows. Most will not stay open due to broken spring balances. Can you guys identify a replacement balance for the one in the example photo? It's 3/8" diameter, 28-1/2" tube length.
A customer submitted image of their spiral balances.
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Paul from SWISCO responded:
Thanks for posting! I recognize this bracket. Unfortunately, it is no longer available. With that in mind, we have two ways of going about this.

The first method requires a bit of handy work but may be preferable. You would need a Series 900 spiral balance and our 62-001 rivet. You would drill out the rivet on your existing bracket and then re-rivet it on to the new balance.

The other method may be a bit simpler. You would just need a Series 400 spiral balance and a new 17-031 bracket, which would then be screwed on to the bottom of the window sash. Would you have enough room to do that, though?

Either way, since the length of your balance tube ends on the 1/2", your balance may have to be custom made. Can you first confirm that your balance is, indeed, that length? Then, let me know which route you'd like to take.
A handy person from Baytown, Texas says:
Yes, tonight I reconfirmed the tube length is 28-1/2".

I honestly don't see how to screw item 17-031 onto the bottom of the sash. The bottom is not flat. It has a front edge and back edge and the bottom I suppose is the "in-between" those two edges and is pretty far up inside.

I'd like to try the first method you suggest. Before I order some parts to try on one window, do you have a sketch showing how my existing bracket catches the window edge? I have a working window I have tried to look at but the bracket is very hard to see as it's up along side the window edge. So not 100% sure what i'm trying to catch.

BTW - glad you found a solution, I have quite a few windows I'd like to fix if I can get the technique down on this first one.
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Paul from SWISCO responded:
We actually don't have a guide on these specific brackets, but you might want to look at our guide on how to install non-tilt spiral balances. The principle should be the same.
A handy person from Baytown says:
Thanks for the fantastic help so far (March 3rd post). I've now repaired my first of 22 windows and am looking to improve my method.

I have non-tilt windows with 7/16" diameter balances of varying lengths (16.25", 20", 24.5", 28.5"). I first repaired a 28.5" balance using a S900-29 (29") replacement balance. Initially I tried this. I removed the old balance end fitting (photo 4547) and put it on the new balance after pulling both the pins out of the end of the new balance. Tried to install but couldn't figure out how to make the old fitting "hook" somehow into the window channel hardware.

The window channel hardware is shown in photos. 4575 is looking up into the channel at an internal piece that looks like a short (1/2"??) long cylinder with a slot cut out of the side. This is up inside the channel and would appear to be intended to hook to somehow but I don't know how. 4

577 shows a notch in the side of the channel that I ended up using since I couldn't figure out how to make the old fitting hook into the existing slotted cylinder and stay put. I ended up removing the old fitting from the new balance and installing a small S hook made of coat hanger, photo 4581. I loaded the balance and then hooked the S hook into the notch previously shown in photo 4577. It works but obviously not the intended design.

My questions:

Any idea how that old fitting was supposed to be latched into the slotted cylinder?

Would the spiral balance 307 series be a better solution? Looks like their bottom fittings might work for my notch.

When original balance is odd size, I'm thinking ordering the standard length slightly longer will work fine as it did for my 28.5" connection. Is that the right way to go?

Thanks again for an excellent website and your excellent support! I have a lot of work to do and really appreciate it.
User submitted photos of a window balance.
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Paul from SWISCO responded:
Good thinking on the Series 307 balance. I think that was probably the best way to go, now that I think about it. My only concern is that the bottom extension of shoe might extended past the bottom of the sash and prevent the window from closing. On the 1/2" extended balances, I would go up to next size up.
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