So I changed the brushes on my Dewalt 611 after it stopped in the middle of a job. The brushes were very, very worn down. While putting the back side brush in (towards the z-column) I accidentally snagged the spring with the pigtail of the brush and knocked it off the little hook. So it spun around a couple of times. I cannot figure out how to re-tighten it (without it while the router does in fact turn on, it clearly has bad contact as it is somewhat rough sounding). I tried removing the spring and hand winding it (easy) but I can’t get the spring back on the little prong that holds it once it is wound as the inner circle gets too small. There must be a way to deal with this since Dewalt has replacement springs so that would imply there is some way to tighten the spring?
The spring doesn’t apply a lot of pressure on the brush so maybe you are trying to wind it up too much. Here is a video of it being replaced. How to change the brushes on a DeWalt 611 router - YouTube
Turns out the easiest way is to remove the metal plate the spring attaches to (screw to the right) then you can easily wind it to make it match the other. Worked fine afterwards.