I think that is the answer, you can note from my Cant's the pivot bolt is much farther away from the pad. Your gonna have to go {Retro} this timePeriod cantilevers will do if you can find them, they are designed for closer clearances
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My Orbit with Tektro/ Shimano mash-up brakes
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and a 1970's frame with some 80's DiaCompe
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Need a pair to match that front end though! $$You need the sort of cantis that have the old style brake bad, not ones that bolt on
Shimano STX, Alivio, XT, LX, DX etc, rears can catch the heel though if not the 'low profile' type
These look rather sexy
Dia-Compe CR-X Cantilever Rear Brake | eBay
Classic style Cantilever brake. Material: Forged aluminum Arms. Wide Body Design. We will respond to your complaint within 24 hours, usually much sooner. How do I make a complaint?. We can arrange to collect an item from you.www.ebay.co.uk