Well, I am not so sure about that - when I originally took the shutter apart (it was already non functioning from neglect) the spring was still there, though somewhat degraded, it had kinks. But when I tested the shutter with that spring still in place, I observed that it did nothing but spin the gears in reverse, and the tension really IS too low to do anything - it literally applies no pressure on the gear train until the shutter is fired.
I am not 100% certain but I think that the tension on that spring is too weak to overcome the tension of the other springs in the shutter assembly or to have any effect on the slow speed. For example the other hair springs in the shutter assembly have enough power to throw the shutter speed cam off the camera and across the table if let go by accident, but the coil spring is so weak it can be stopped by blowing on it..!
I also found this post on flickr:
http://www.flickr.com/groups/rolleicord/discuss/72157622994267498/
rolleiflux says:
Hey, thanks for the reply.
I figured it out (sort of). There was a coil on the gearset that got bent out of shape that was preventing the gears from rotating freely, thereby inhibiting the last gear (quadrant wheel?) from engaging fully into its slot. I tried to straighten the coil, but in another case of blunderitis, I ripped the coil straight out. Because the quadrant wheel is spring-loaded, the gearset seemed to still function without the coil so I just put the rest of the shutter back together and tested it. Magically, most of the shutter speeds, especially the slow gears, tested out to be more accurate than before. I assume the coil plays a role in reliability and long-term accuracy, so I don't expect my newfound awesomeness to last too long.
Oh wells, lesson learned.
I'm curious - what damage might occur if the speed cam is not on when I cock the shutter? I'm guessing it has to do with the speed cam engaging something or another?