Window lift spring

Thanks for posting. It sounds like you need a new channel balance. I'm confident we can help, but that stamp is not an identifier; it just tells us the strength of the balance. We need to see pictures of the fittings on both ends of the metal channel, preferably with the balance removed from the window. Also, double-check the length of the metal channel. Do not include the end attachments in this measurement--based on the stamp, the metal channel is probably 29" long, but it's good to check to be sure. With all that information in hand we will do our best to narrow everything down for you from there. 

Thanks for your photos. Based on what I see here, you have either our S351-29 or S390-29, depending on the depth of the bottom shoe. That's the only difference between them. I recommend measuring your shoe and referring to our dimensions to confirm the best match.

Comparison of the S351 and S390 balance shoes.