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fitting new v brake arms, frame mounting pegs are too short?

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fitting new v brake arms, frame mounting pegs are too short?

Old 07-19-13, 06:16 PM
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cjard
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fitting new v brake arms, frame mounting pegs are too short?

The factory fit unbranded v brakes on my marin san Rafael fell to bits so i purchased a shimano deore box v brake. Upon removing the old brake arms and fitting the new, i note that the frame mounting peg that carries the arm is too short to reach all the way through the new thicker deore arm. The shop said that the pegs are a standard length and even disassembled several different bikes to check, but I'm still not sure that its a great idea to fit a brake arm that's 20mm thick onto a loose fitting peg that's 15mm long and wind the bolt up to hold it in place. Are longer pegs available?
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Old 07-19-13, 06:38 PM
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V-brake bosses (studs) are available but be aware that they come in at least 2 different threadings; M10X1.25 and M10X1.5 as I recall, so you'll need to match the threads on your frame.
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Old 07-19-13, 06:51 PM
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Originally Posted by cjard View Post
The factory fit unbranded v brakes on my marin san Rafael fell to bits so i purchased a shimano deore box v brake. Upon removing the old brake arms and fitting the new, i note that the frame mounting peg that carries the arm is too short to reach all the way through the new thicker deore arm. The shop said that the pegs are a standard length and even disassembled several different bikes to check, but I'm still not sure that its a great idea to fit a brake arm that's 20mm thick onto a loose fitting peg that's 15mm long and wind the bolt up to hold it in place. Are longer pegs available?
It shouldn't make a difference. The bearing surface on the Deore brake isn't between the post and the the brake, it's inside the brake itself. On many (most?) modern V-brakes, the bolt simply retains a pivot bushing/spring retainer assembly. It won't hurt things if the frame post is too short.
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Old 07-19-13, 07:56 PM
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As far as I know, canti boss length has been standardized for eons. So if it appears that your brake needs a longer boss, you're probably missing something.

Many (most) brakes are designed to fit exactly within the length of the boss so the bolt tightens to the boss leaving exactly the clearance needed for the brake to work right. But some brakes have a part which rides against the face of the stud, so while they seem to need more room, the reality is that they don't.

I don't know the particulars of every brake, but take a moment to look at the various parts of your brake, and see if the forwardmost parts have a 6mm hole instead of the 8mm(?) OD of the stud.
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Old 07-19-13, 11:45 PM
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As Jeff Will said. All you need to do is to pinch the bushing sitting inside the arm against the fork and you're good.
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Old 07-20-13, 01:18 AM
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I'm still not sure that its a great idea to fit a brake arm that's 20mm thick onto a loose fitting peg that's 15mm long

and wind the bolt up to hold it in place. Are longer pegs available?
Too much blind guessing [can't see] have a shop look at it.

steel frame? No..
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Old 08-24-13, 03:58 AM
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Ahh.. Its just the engineer in me thinking it cant be a brilliant idea to have a bolt that formerly wound into the boss a full 15mm (and wasn't responsible for resisting the twisting forces of the brake arm assembly) that now winds in only 10mm and is responsible for holding the brake arm too. Its much more likely that weedy bolt will break than the boss.. Not good for a front brake..
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Old 08-24-13, 05:01 AM
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Originally Posted by cjard View Post
Ahh.. Its just the engineer in me thinking it cant be a brilliant idea to have a bolt that formerly wound into the boss a full 15mm (and wasn't responsible for resisting the twisting forces of the brake arm assembly) that now winds in only 10mm and is responsible for holding the brake arm too. Its much more likely that weedy bolt will break than the boss.. Not good for a front brake..
Converted my TREK 820 to Shimano Altus V-brakes about 15 years ago and had the same situation you are seeing. LBS told me that was fairly common and not an issue. LBS was correct. Just switched to Shimano Acera V-brakes (for aesthetic reasons only) and moved the Altus with new pads to the wife's 820. The Altus still looked new after 15 years and I am 6' 1-1/2" and until a few months ago was just shy of 250 Lbs. Down to about 220 now.
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Old 08-24-13, 09:06 AM
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Originally Posted by cjard View Post
Ahh.. Its just the engineer in me thinking it cant be a brilliant idea to have a bolt that formerly wound into the boss a full 15mm (and wasn't responsible for resisting the twisting forces of the brake arm assembly) that now winds in only 10mm and is responsible for holding the brake arm too. Its much more likely that weedy bolt will break than the boss.. Not good for a front brake..
Once a bolt is threaded in its own diameter or more, the strength is as good as it's going to get. Since these are M6 bolts, 10 mm of thread engagement is plenty. Also,I don't think these bolts are cantilevered out of the studs enough and subject to any bending forces that will be a problem.
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Old 08-24-13, 12:24 PM
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Did you get the spring end into one of the holes in the boss?
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