Window keeps sliding

Thank you for contacting us. It sounds like you need a new pivot bar. However, we can't make a suggestion without the original. The balance appears to match the Series 140 so all we can do is suggest the pivot bars that are usually used with this assembly. That would be the 26-398, 26-405, and 26-454 but they're only the tip of the iceberg. We have no idea if it will work in the window. If they have another window in the house that still has a pivot bar then we will need to see it. We can only offer an educated guess if not.