cantilever design oddity?
 

Why does the end of this spring extend about a mile too long?
Is there a reason, or do I just have the cheapest cantis ever made?

http://i.imgur.com/gqVcuzY.jpg

http://i.imgur.com/YDJxreJ.jpg

It's a handle that allows quick tesioning or releasing of the spring.

Very handy.

No, the cheapest cantis made were the Chang Star clones of your DiaCompes. I don't know why the spring is long but those brakes works quite well, even with the original levers. I have two sets on mid 80's mtn bikes.

Neat.
So, I could feasibly use this handle and lift the spring right over that nut?

(P.S. I just acquired the bike...thus the layer of grime.)

Exactly. This makes it much easier to connect/disconnect the straddle cable, which is needed when you're removing the wheel.

Releasing the tension on the spring also makes it easier to adjust the alignment of the brake shoes, which that bike desperately needs.

Yes, no doubt.
I've yet to do anything to the bike...except marvel at how many frame/fork/dropout bosses it has!