My 1939 GMC COE drivers window continuous to drop down a few inches even though I have replaced the spring. Is there any adjusting to increase tension on the regulator spring without trying to rebend the hook...
Compare each side by counting the number of turns in the spiral. See if they match. If they don't, the preload might not be properly set. It could be that it is just worn out. Replacements are about $25. https://www.ebay.com/itm/233339969315
This is a 1939 car regulator, but you get the idea: You can rotate the spring outer loop the way that increases tension, 360º, and re-hook it.
I had the same problem on my '32 pickup and found my window crank was worn out, I replaced it and it window never dropped again. The site below list a kit for a GMC truck. HRP Regulator kit
spring has been replaced along with other components, you mentioned preload is there another way besides rotating spring 360 deg?
spring is new and no slack in components, not possible to rotate 360 deg, too tight. Don't know if spring end can be rebent, kanda doubt it....
Behind the tin cover is actually a kind of friction clutch and spring set up. They actually wear out; the external coli spring is actually just a helper spring just to raise the window.
Looking at the photo of what Hotrodprimer posted you see the spring inside is actually holding tension to the tin cover. There's your problem, it's probably broken. Winding the external spring isn't going fix your problem.
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