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I have an older model Trek mountain bike. I took it to the shop for an annual tuneup and they called me to say that the rear brake broke off the frame and that it can't be fixed. The entire brake is off the frame - is there really no fix for this situation?

Rear Brake Side 1

Missing Brake

Rear Brake Side 2

  • Since the flange is still there I'd think you could MacGyver something using a hardware store bolt. – Daniel R Hicks Jul 16 at 2:25
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    @MaplePanda it's on the frame. just below centre of the picture there is a tab of metal poking towards the spokes with a hole in it. Instead of a hole there should be a brake boss sticking up/backwards/towards the lens for the brake to slide onto. No boss, no brake. – Swifty Jul 16 at 6:51
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    Do you ride in places with salt on the roads? Before starting any kind of repair, I'd give the frame a look-over for rust and corrosion, with special attention to the remaining three brake bosses. If one's gone the other might be bad too. – Criggie Jul 16 at 11:15
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    Everything can be fixed if you throw enough money at the problem. I think they meant it's not economically feasible. – Mast Jul 16 at 13:18
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    @MaplePanda it's a 'cantilever brake' where the two brake arms are pulled together by a straddle wire. V-brakes use the same mounting but operate a bit differently. – Swifty Jul 17 at 16:19
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The brake pivot broke off the frame in a very unusual way. A framebuilder may be able to contrive a pretty cheap way of fixing it by putting a new pivot stud in. This would still require removing the paint in the area, but it wouldn't necessarily be that bad.

Minimum prices for framebuilders to even get into repair j jobs are typically in the $100-200 range in the US depending on where you are. It's the kind of thing where a simple and fast fix may be possible but the equipment and skill to achieve it are costly.

Removing and replacing the canti braze-on entirely would be technically easy but far more time consuming. The offset needs to closely mirror the other side, so either both would need to be replaced or the left side replacement would need to be carefully selected and/or modified.

The bike shortage situation is such that some things that weren't worth it in the past might be now.

You could also fix it by just putting a long reach BMX sidepull caliper on the back, like an Odyssey 1999. These are mediocre brakes but this would be a cheap way to get it functional again. You would need to be careful to get one with long enough reach. To be honest this is a pretty obvious path and it doesn't speak well of the shop to not suggest it, unless they did the measurements and found it was longer reach than brakes exist for. It doesn't look like it though.

I see what happened and would not hold the shop at fault for it breaking in the first place. The main way for it come off like that is poor brazing at the factory.

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  • Shortage where? There are many bikes around here. Even those from 2018 or 19 with a nice discount. – Vladimir F Jul 16 at 5:51
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    Is this seat stay bridge really intended for caliper brakes? – Michael Jul 16 at 5:53
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    @VladimirF at least in the US and UK, presumably. Keep in mind that we continental Europeans have benefitted from governments that didn't completely botch the pandemic response – but other countries, well... – leftaroundabout Jul 16 at 9:51
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    @VladimirF apparently there is a "worldwide shortage of bikes", but the sorts of bike that are in short supply (cheaper, non-premium bikes) probably aren't the sort of bikes someone frequenting this site are looking for. – MikeTheLiar Jul 16 at 14:01
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    @computercarguy Welding aluminium frames generally starts at difficult and gets harder from there. Steel is much more weldable - this bike could be either but looks like steel to me. – Criggie Jul 16 at 20:24
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So it looks like the cantilever brake stud was pressed/punched into the frame from the rear of the brake tab, like in this photo, about 25 years ago. Over time and with braking this connection failed, and also maybe the bolt holding the canti arm onto the stud came loose and was lost.

The non-invasive fix is to buy a replacement cantilever brake stud, example only linked and locate a suitabel lock washer and nut (better, two, if the replacement stud has enough thread) and lock that stud down tight.

This is well within the technical ability of any bike shop, but you may have more success if you find a shop that is more at the 'bike-freak' end of the spectrum or if you know a bike enthusiast who will invest the time in it for you. Some shops may reject this as they are opening themselves up to liability from making 'creative' changes to safety critical parts of a bike.

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    Great answer - welcome to the site. Some bike shops want to sell a new bike more than fix an old bike. – Criggie Jul 17 at 9:53
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You can get cantilever bosses with a threaded end that can be removed from frames if your using disc brakes. That's definitely savable but it will take someone with an ounce of common sense to fix.

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    Depends if there's enough meat left in that mounting stud to take a thread. I've not seen a canti boss that has a threaded part and a nut on the far side, probably not secure enough to mount a bolt. Good first answer - thank you. Do please take a moment to browse the tour too. – Criggie Jul 16 at 20:26

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