Channel Balance Replacement

A quick learner from California says:
January 26, 2017
I need to replace the balances on my window and I cannot exactly make out the stamp code on the originals. It is either a "2720" or a "2730." How exact do I have to be? Would either one work for my window, as long as I ensure the L x W x D measurements are a match?

Thanks!
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Paul from SWISCO responded:
February 2, 2017
It's a good idea to be as exact as you can. I recommend removing your sash from the window and weighing it on a scale to get the exact weight. Any common bathroom scale would do.
A quick learner from California says:
February 2, 2017
Thanks Paul!
I was able to make out the model number on one of the balances by taking a photo and zooming in on the numbers. So I replaced both sides with the exact/correct channel balance.

I was assuming this would help the window to slide up/down more easily. While there is some improvement "up," the window still is very difficult to slide back "down," and even makes a squeaking noise now.

Do you have any suggestion for making the sliding operation more smooth? This an aluminum window (not vinyl) from the late 1980's. Should a try using a dry film lubricant spray and if so, what should I spray?

Thank you for your excellent help!
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Paul from SWISCO responded:
February 3, 2017
It sounds like you got the wrong spring strength for that balance. If the window won't close, then the springs are too strong. There isn't much you can do to fix the balances you have now if this is the case. I definitely recommend weighing your sash to make sure you get the right strength.
28" Series 371 Channel Balance
28" Series 371 Channel Balance
S371-28
$10.97
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