Originally Posted by
stronglight
If you have Dia-Compe 981 cantilevers it is easy.
I have them on my 86 Voyageur. This model (possibly others too) featured a brilliantly conceived hidden adjustment slot for moving the arms up or down a few mm. to make them equally suitable for either size wheel.
I think these cantis were available from the early 80s. See the photos here showing details of a disassembled brake to better understand what I mean:
http://www.flickr.com/photos/strongl...7606108523956/
I'll back up Stronglight's suggestion on the Dia compe 981s. But also, most vertically adjustable cantis will be able to adjust to the difference in rim wall height from 27" to 700C, which is just a difference of 4mm (700c rims are 8mm smaller in diameter, so 4mm smaller radius).
I had a 1988 Voyager and I also switched from 27" to 700C. I used Shimano BR-MC70 cantis (1st gen XT) which to the best of my recollection did not have a vertical height adjustment and they still worked great. It depends in each case where the manufacturer placed the canti posts vertically relative to the rim. You'd think this would be a standard height but it varies quite a bit. If they're placed higher than usual and the canti is also at the bottom of its vertical working limit, the transition to 700C wheels may not be possible. If the cantis are lower than usual, then the transition will be easy-peasy. If they're at typical height, most cantis with a vertical adjustment will work.