Trouble installing window balance

A home owner from USA says:
I just installed two S385-18 option 1720 sash balances, but the window will not go in. It appears the balance channel is too tall. Now what.

2. I installed two S385-30 option 2950 balances and that window wobbles.

What a day, and more windows to do. I'm the same customer missing the 2 take out clips.

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Tom from SWISCO responded:
Hey, Dale. I'm not sure what the problem is. First, make sure you watch our video on the proper replacement of non-tilt window channel balances.
Next, can you confirm that you purchased the appropriate balances? How long was the balance for the first window, where you're using the S385-18? What do you mean when you say the window wobbles. Is it possible the sash was not replaced properly in the window?
A quick learner from Kent,Wa says:
The S385-18 were installed right. The balance is taller than the original, so I cut the window slots to fit. Now the window rockets up and down.

The other sash, I just don't know what is wrong. Both balances snapped right in, and the window slides up and down easily, but it wobbles like it is too small for the frame. Could one balance not be hooked? The window is heavy, so your advice on whether or not to reinstall would be helpfull.

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Paul from SWISCO responded:
Thanks, Dale. It sounds like you ordered the wrong balances for your windows.

The S385-18 is too tall. Even if you cut the window slots, it likely won't operate correctly. What was the size of the original balance? What is the weight of the window sash, as well? If you got a different sized balance, it's possible the spring strength is off, too.

As for the second balance, it's harder to say. Are you 100% positive that you have the Series 385 balance? Did it match the old balance exactly, including the bottom shoe? If the bottom shoe was a different size, it would account for why the window is wobbling.
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