pics of my 2940 and 2950

Thanks for contacting us, Ken. I'm afraid neither balance you're showing here is the S385-30. They are both very, very different in more than just stamp. This is actually kind of a unique situation. Allow me to explain.

Before we go any further, I think it's important to clarify that the stamps are not identification codes or product numbers of any kind. All a stamp does is indicate the calibration of the spring and suggests the length of the metal channel. This makes sense given your post; the 2950 stamp indicates a stronger spring than 2940. It was probably too strong for your sashes.

The primary method of cataloging balances is via the combination of nylon fittings, which is what determines a balance's Series. In your case, you're showing us two very, very different Series. The 2950 balance is a special Series with a distinct pulley system and an extended cord. We'll call this "Balance 1." The 2940 balance is a more standard product that is commonly acquired. We'll call this "Balance 2." 

On paper, they're completely incompatible. Balance 2 technically shouldn't be used to replace the original Balance 1 since it lacks that extended cord I mentioned. In most cases, when you use a Balance 2 to replace the special Balance 1, the cord yanks out of the pulley when you close the window because it isn't long enough. That this didn't happen to you means that you are very lucky.

So you have two options. You can continue using Balance 2 to repair the rest of your windows and hope for the best. Since it worked to repair one window, you can logically assume it will work for the rest. However it's no guarantee, and I can't predict any complications you may run into in the future. Although your windows closed without the cord yanking out of the pulley, there could still be undue strain put on the pulley that we don't know about. This could shorten their lifespan considerably. On the other hand, they could be 100% fine and you'll get many years of service out of them.

Your other option is to opt to return to Balance 1, but it will have to be a special order since it's not a standard part. If you go this route then we'll need you to tell us the exact weight of the sash so that we can calculate the proper calibration of the spring. I don't want to just bump you down to 2940 because the rating system is a little different than the one used for Balance 2. It's best not to take our chances.

Ultimately, it's up to you. Please let me know how you wish to proceed.

Hey, Ken! I'm happy to be of help. I just want to make sure your windows have the best hardware for the job.

As long as Balance 2 has had no issues, then I think we can be safe going with them. Looking at your nylon fittings, I recommend the S395-30 channel balance (with the 2940 option, of course). This comes with a 19-005 top and 15-001 bottom, so as long as those match up then you should be good to go.

Please let me know if you have any questions!

Great Ken! Let us know how you make out, and thanks for considering our business, we really do appreciate it.