I had a set or Ribbit (typical Cyclocross brakes, Mafac copies) on my
Atlantis that did a very similar thing.

I am not familiar with Paul's brakes so this may not apply (some
brakes have an internal bushing and don't have a bushing riding
directly on the cantilever post on the frame).  Also Jim may be
entirely correct in his explanation; without researching on the
internet my mind took me down a different path.

After fiddling around with the usual things, I noticed the Ribbits had
a lot of clearance between the cantilever post on the fork and the
inside diameter of the bushing in the brakes (a loose fit on the
posts).  This allowed the toe to change; as the brakes were applied
the the force on the pads took up the clearance between the posts and
the brakes tending to rotate the brakes to a "toe-out" position.

I changed to Shimano XT High Profile cantilevers (which have very
little slop) and the problem stopped completely.  Sometimes more toe
than seems reasonable can help shuddering brakes; some things flex
more than we would like to believe.

I tend to run the straddle cables quite high, the Shimanos on the
Atlantis I have the straddle cable about 1/2" above the lower headset
cup.  The Mafacs on the Quickbeam the straddle cable is a few inches
above the lower headset cup.  Makes for a very firm feel at the brake
lever.

Angus

On Feb 18, 9:09 pm, rw1911 <rw1...@gmail.com> wrote:
> I'm assuming (hoping) this is a simple setup issue...
>
> I've recently installed Paul brakes (neo-retro front, touring rear) on
> my relatively new to me 700c All-Rounder.  The rears are wonderful, if
> not too powerful...  I can skid at will.  However, I'm experiencing
> extreme shudder and fork flex on the front.
>
> The headset is tight and the pads are toe'd to contact forward. Under
> low to medium speed braking, I can see/feel  the fork flex (a lot!)
> and shudder.  The straddle cable is set at about the top third of the
> lower headset cup.  I've cleaned the rim and while it has gotten
> slightly better with use, is this a matter of adjustment or is the neo-
> retro too powerful?
>
> One thing I noticed during installation is that the Paul brakes sit a
> good bit higher on the studs than the Shimano's they replaced.  Could
> this be contributing to the flex in the mounting studs and/or fork?
>
> Any experience/advice is appreciated.

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