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There is some slight movement of my canti brake arms on the brake bosses when the lever is pulled. It's pretty minimal but I'd be interested if if this is intended and whether it might cause any issues? I've added a short Video to illustrate the issue.

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Virtually all cantilevers have some amount of movement there, because if they didn't they would bind. Your video shows an unusually large amount though. That can cause chatter and squeal.

What to do about it if anything depends on what brake this is, and if there's anything going on with the bosses.

If it's a brake with an integral pivot (no dynamic surface between the frame and the brake), this problem can be within the brake itself. That can seem like it shouldn't happen because the whole point of integral pivots is better QC/tolerance in this area, but it has happened.

If it's not an integral pivot (brake bushing and the frame boss create a dynamic surface), make sure the bolt is tightened properly such that it bottoms against the end of the boss.

If the bosses are replaceable, make sure they're tightened in fully.

It is possible, though uncommon, for a frame (probably a weird and/or old one) to have a boss that's too long. If so it's possible to fix it by shortening it with a file. What length they're "supposed to be" is something of a deep dive topic.

If you wanted to not modify the frame, you could shim the back of the brake with something to take up the slop.

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  • It's a set of Shimano XTR BR-M900 which has an inner bushing as seen here. The bolt tightens against this inner sleeve/bushing not against the boss itself. The issue is the same at front and rear. New frame. close-up
    – user430
    Commented Mar 24 at 17:11
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    If I'm not mistaken your comment implies that it's the brake design itself causing this and it's independent of the canti bosses? Either way, I'd be comfortable riding them to see how well they work. (plot twist: I had these calipers back when XTR was the new kid on the block, they're not great, but I can totally understand the retro appeal)
    – Lamar Latrell
    Commented Mar 24 at 19:14
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    I've looks at the video. It does not look anything out of the ordinary. Since it's a Shimano model, I would not worry, there is a margin of error and I am confident that it's within the margin of error. When you brake, does it do a good job? Are there any issues? If not then it's good. Do you know of anyone who has the same style of brakes on their bikes? It's good to compare.
    – MindDBike
    Commented Mar 26 at 10:11

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