balancers for 2003-3ra Milgard single sash windows

Thanks for posting! The Series may very well be our Series 385, but you should check the depth of the shoe to confirm that it's the same 1-3/32". 

As for the stamp option, 2940 indicates a sash weight of 23 through 28 pounds, as indicated on the S385-30 store page. Are you saying you weighed your sash and got 40 pounds? If so, that means you want the 2870 instead, which carries 39 through 42 pounds. 

Thanks for clarifying, I understand now. No, the last digit in the stamp is not a direct indication of sash weight, so odds are it is not 40 pounds. This last digit is just a sequential indicator of weight ranges, from weakest to strongest. We have a chart on the S385-30 store page that tells you exactly how much weight each option supports. If you haven't reviewed that chart then I recommend that you do so.

Your original stamp of 29-4 is a match for our 2940, which you'll see is only designed to carry 23 through 28 pounds. If the sash was 40 pounds then the window would probably slam close the second after you open it.

Thanks for checking. So if your sash is 22.5 pounds then you might want to consider the 2930 option, which carries 16 through 23 pounds. The choice is ultimately yours, though; if 29-4 has been working fine all these years then you may want to just stick with that. If you always found the windows to be a bit too hard to close, though, then going with the weaker 2230 would be the better option.

The guide you show here could have a few different replacement options. The first thing to check is our 18-188, which is the same width as your original at 5/8", but I'm not sure about the other dimensions (which you can see on its store page). There are a lot and they're all sorta equally important so you definitely want to look them over.

The second option is our 18-009. This may be the better choice, but you'll note that it has a top edge that sticks out a little further. If the dimensions match, and I think they will, then you can still use this but you have to trim that top edge down with sandpaper or a utility razor. 

Yes, that is my concern. Your sash weight technically falls in the 2930 range so you should be okay, but since the 29-4 has worked perfectly well so far I sort of don't want to mess with success. There is a risk that the 2930 will be too weak, yes, but on the same hand there is a risk that the 2940 will be too strong.

Of course there is an equal chance that both options will work just fine and there's nothing to be concerned about. I just want to make you aware of the different possibilities you may encounter.

Gotcha, that makes a lot of sense. As far as lubrication I would recommend some silicone spray in the track and white grease for the spring itself.