Replace the knife shoe or the whole window balance?

A home owner from colorado says:
July 25, 2011
I have several of these windows where the channel balance knife shoe (part 15-014)has broken. On a couple of them both sides are broken and the top portion of the window falls down unless the window is latched closed. Do I need to replace the channel balances (19") on these windows or can I just replace the shoes?
User submitted photo of their channel balance knife shoe.
Profile picture of Casey
Casey from SWISCO responded:
July 26, 2011
Generally a broken balance fitting is a sign of needed replacement balances, however if the balances are less than 5 years it may be worth trying to replace the fittings. If you do decide to replace just the fittings, you will need to clamp down the balance cord in a vice so that it does not jump out of the block and tackle. Take care, it is under a lot of pressure. Be sure to wear safety glasses.
Balance knife lock Shoe
Balance knife lock Shoe
15-014
$1.09
19" Series 751 Channel Balance
19" Series 751 Channel Balance
S751-19
$10.45
How to install a ribbed tilt channel balance with knife lock shoe
How to install a ribbed tilt channel balance with knife lock shoe
VIDEO
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Classifying Channel Balance Fittings
Classifying Channel Balance Fittings
GUIDE
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