On Wed, 27 Jul 2005 13:41:05 -0400, Sheldon Brown
wrote:

Quoth Jobst Brandt:
I don't see why that [bending the spring] was the only available
method. How did you initially poisition the brake caliper was with
pads adjacent to the rim? Why could the centerbolt not be
rotated? I don't believe it was riveted or welded in place.

The block on the centerbolt that had the groove for the middle of the
spring also had a concave groove on the other end.

The front one had a large radius to match the curvature of the front of
the fork crown.

The rear one had a smaller radius, transversely oriented groove that fit
snugly against the seatstay bridge.

These parts could not be rotated because of the curved interface to the
frame/fork.

Bending the spring was the _only_ way to adjust the centering.

And even when the springs and pivots were lubricated appropriately,
they often didn't stay centered very well. These were not high-tech
units with a lot of attention to good engineering. They were made to
be simple to install (even if that required some inelegant field
adjustment) and simple to service. That the installation and
servicing sometimes involved the use of two pairs of pliers or a
hammer to bend the spring was considered acceptable procedure. I've
seen various attempts to overcome the lack of reliable centering,
often including the use of a Nylock nut left somewhat loose at the
back end of the mounting so that the caliper could float a bit. That
latter technique was fairly common in the late '60s. It was
considered preferable to have it rub *lightly* but able to deflect
instead of having the brake rub hard on one side when it didn't return
properly for some reason...which was more often than a lot of people
could ignore.


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