On 25-02-18 00:07, Emanuel Berg wrote:
Here are a couple of pics to facilitate the
discussion:

http://user.it.uu.se/~embe8573/bike/brake/

I've heard that

1) the long spring pin should be in the
middle boss hole

2) the pads/shoes/blocks should be slightly
pointing inward on the rim on the front
end

3) the arms should be vertical

4) between the cable anchor bolt/cable
clamp and the noodle/guide should be
39mm of cable

Is there a trick/algorithm to achieve all this?
I have put together several but 1, 2, 3 don't
come automatically for me


Concerning point 2, "toe-in", I just use the Kool-Stop brake shoes. The
back end is slightly raised, so the toe-in comes automatically. Another
possibility would be to put a piece of very thin cardboard under the
back end of the brake shoe when tightening the bolt.

What hasn't worked for me is a special tool like this one:
https://www.veloplus.ch/AlleProdukte...hevonTacx.aspx
In theory that tool holds the brake shoes just where they should be,
including with proper toe-in. However, I always ended up with the brake
shoes at the lower/inner edge of the rim (towards the hub). This isn't
good, because as the brake shoes wear and get thinner the brake will
engage farther down in the rim. If it starts at the edge, later it will
be partly off the rim towards the center**. So this could be a point 5
in your list.

**And many years ago a friend crashed when the brake shoes went
completely off the rim into the spokes.


For your point 3, the only adjustment for the arms being more or less
vertical is, at least for the Shimano BR-M750 that I have, whether the 3
mm washer is on the rim side and the 6 mm one on the outer side, or vice
versa. You might want to check this with an inflated tire in place, to
make sure that there is clearance further up on the brake. Otherwise,
closer to vertical gives more mechanical advantage.

I haven't worried at all about your point 4, and just adjust the cable
so that there is minimal clearance between pads and rim. Whether more or
less than 39 mm would depend on rim width, so not a constant for all
bikes (and for my BR-M750 the service instructions anyhow say to have 45
mm or more).

With the older cantilever brakes things were more complicated. See
http://www.sheldonbrown.com/cantilever-geometry.html

Ned