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Bent cantilever post
A mate asked me to replace the rather unsatisfactory cantilever brakes on his Tricross (they're not great, I know as I have one too and they're the only thing I don't like about it) with Tektro mini Vs. Removing the cantis today I found that the left rear post has been bent slightly inwards, probably in a crash (he commutes through central London and has been hit twice in the last 18 months). This makes it impossible to get the pad aligned parallel to the rim and so renders the brake all but useless. The options are bend it back myself or take it to a shop, but I have a feeling most shops would refuse to do anything involving bending metal for liability reasons. Has anyone done anything like this? Any information on likelihood of success and the best technique to use would be very welcome, thank you!
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21 comments
Many thanks for all the advice on here, much appreciated and it put me on the right track: looking at the bike again this morning I realised that the posts are removable but some previous owner (not my mate) had, perhaps in trying to patch up some crash damage, soldered the post into place. I've managed to melt the solder and extract the bent post now so off to the LBS when it opens to get a replacement and hopefully have it all fixed. Thanks again for the help!
If the seat stay bridge has a brake hole drilled then remove the canti and fit a caliper for the back.
Good shout, it does, looking into it.
I think key information here is missing: what material is the frame?
If it's steel: just genttly bend it back yourself, little by little.
If it's aluminium: go see a framebuiler and hope they can fix it at reasonable cost.
It's aluminium - as mentioned below, it's a £130 secondhand bike so he doesn't want to spend a fortune...
In tht case I would try to carefully bend it back myself, check for visible damage (cracks etc.), and if there aren't any, mount the brakes but also use a brake booster as a reinforcement.
Good idea on the brake booster.
Thanks never heard of them - never had a V-brake bike myself - will look into that.
The frame is alu - but the actual post... I'd have thought that was steel?
Yes, cantilever posts are always steel. But I can not imagine that it's the post itself that's bent, I've never ever seen that happen. Very probably it's the mount where the post is screwed in that's bent, and that mount is part of the frame.
Got it out now and turns out both were bent, the post only a millimetre or so but enough to send the pads askew, especially when combined with a small twist in the mount. A bit of judicious twisting (brake not frame!) and bodging and it's good.
Good to hear!
Another bike saved from the scrap heap! 👊
If it were me, and assuming it's only bent a little, and because it's a rear, I'd gently bend it back, winding in a bolt as I went to try to keep the threads OK. If you had a longer bolt which reached beyond the bend point, that might also provide some reinforcement in service.
I suspect the frame clearances might be too great but a deep drop dual pivot brake might also be an option?
I guess they're not removable posts? Before writing off, I'd consider taking it to a local frame builder and see what they say. If they're not keen on bending it, maybe cut the old post down, and then either drill & tap a new one in, or even braze one on. I've got Sven Cycles local to me, and he did something similar for a colleague with a seatstay light mount.
Personally I wouldn't be keen on bending it myself if it's aluminium.
Cheers, they're welded in. I'm sure an expert could do a good job but it's his beater commuter for which he paid £130 so bit of a law of diminishing returns on outlay...
I was going to suggest Winston Vaz who's not a million miles from you in Hither Green but then saw how much the bike cost. Still Winston's usually worth a visit for those seeking to repair rather than discard https://www.varonha.co.uk
They can't be welded in if it's an alloy frame, I assume you mean that the boss which the post screws into is welded to the frame? You should be able to unscrew the post and replace it?
Example https://www.ebay.co.uk/itm/382445765436?mkcid=16&mkevt=1&mkrid=711-12763...
Watch out there are different threads
Thanks I'll have a look at that tomorrow, would be great if they are screw ins.
I would guess the posts are steel and screw into alloy mounts welded to the seat stays. If the post is bent then a new post should fix it. If the mount is bent, or the stay twisted, I'd be tempted to try and nudge is back into shape especially if the caliper approach is not an option and the frame is disposable.
Another option is cheap v-brakes and twist one of the arms to compensate for the post.