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Mafac Competition + modern brake / shift levers (road bike)
#1
Some of you have already read me whining about my old road bike that I now use for light trails and stuff. I have the following problem:
- old Mafac Competition brakes
- soldered on studs for the brakes (so: no new brakes possible)
- new levers seem to have a different mechanical advantage than the old ones (new: pulls 14mm of cable, old: about (20 +/-2) mm of cable, hard to measure when not installed)
The old brakes just do not seem to work with the new levers (and if I measured correctly, they cannot). Any ideas? I just received a pair of adapters (to use V-brakes with road bar levers), but so far it is a mess, you can sort of get a glimpse of it behind the seat post.
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#2
You might experiment with how high/low you put the crossover cable hanger. Raising or lowering this will change the effective cable pull ratio. I'd have to think harder than I care to at the moment to figure out which way you want to go though...
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#3
These may help:

http://sheldonbrown.com/canti-trad.html
http://sheldonbrown.com/cantilever-geometry.html#mechanical
http://sheldonbrown.com/harris/mafac.html
http://sheldonbrown.com/brandt/brakes.html
Nigel
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#4
Yup, read those already. The cable is as low as it gets (no adjustment of the yoke cable length possible), and replacing the brake is out of the question as there is no part no. 541E/452E as on the EV at http://sheldonbrown.com/harris/mafac.html instead the bosses are brazed to the frame, saving, dunno, 57g each brake (or somesuch).
However I feel a bit embarrassed, as I was just able to fix (at least) the front brake (still have the weird V-brake adapter thingy in the rear) yesterdaynight. And yes, it was suggested on one of the pages Nigel linked.
Remedy:
  • disassemble brake and clean especially the pivots
  • grease pivots / bosses, reassemble
  • use better housing than the standard Shimano stuff (which is... soft, squishy, flexes), I now have the (still inexpensive) most basic Jagwire housing as this is what my LBS stocks together with the Shimano stuff.
  • enjoy better braking performance
I also use Koolstop Salmon coloured brake pads and have (as mentioned) the yoke cable as low as possible and tried to adjust the brake shoes to be as square to the rim as humanely possible. Now, while not being able to lock the front wheel, I at least can achieve almost maximum deceleration. Thanks for thinking about it!
The cable flex was (in hindsight) quite obvious, not only in the rear, but also in the front. I had not thought it would make such a tremendous difference with such a short cable! This is likely the most important factor in this setup!
Actually rereading
http://sheldonbrown.com/cantilever-geometry.html Wrote:If you have too much mechanical advantage, the brake lever will bump up against the handlebar before the brake shoe has moved far enough to engage the rim.
yup, this is what I have. So I need to lower the MA.
Quote:Three separate factors determine the mechanical advantage of any particular cantilever braking system. The total mechanical advantage of the system is the product of all three multiplied together:
Thus: lower the MA of the brake by lowering the MA of the yoke cable. I guess I'll have to draw a diagram to see what that means with the Mafac brakes where the pivot is in a different place than in Sheldon's sketch.

Edit:
Reading it again, I find
http://sheldonbrown.com/cantilever-geometry.html Wrote:With wide- and medium-profile cantilevers, the mechanical advantage of the cantilever unit increases as it travels inward
So: with wide profile cantis (as are the Mafacs), have the canti arms as far out as possible.
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