Are there different size frame mounting bosses for different make V brakes?



surfbaba

New Member
Oct 6, 2011
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Hi! Just received a lovely new set of shimano deore V brakes in the post in order to give my trusty old Claude Butler Hybrid the care it deserves.

I had to change the Calipers because on my old Vuelta ones (also V brakes) I had sheared off the Cable fixing bolts because the bolt threads had seized due to corrosion.

I had originally purely wanted to just change my brake Cables!

To my surprise, when I offered the new caliper on to the frame stud (Frame mounting Boss) I noticed that not only was the frame boss not long enough to come all the way to the end of the "face" of the caliper,where it should by about 5mm (where the back of the bolt head comes to rest once tightened) but also the fit seemed sloppy. On comparison there did seem to be differences between the Vuelta and Shimano brake arms.

Please could somebody help? Do I need to change the frame bosses for ones that accept shimano?
I remain perplexed........Off now to make a cup of tea.....
 

tafi

Active Member
Jul 31, 2003
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Originally Posted by surfbaba .
I noticed that not only was the frame boss not long enough to come all the way to the end of the "face" of the caliper,where it should by about 5mm (where the back of the bolt head comes to rest once tightened) but also the fit seemed sloppy.
Do you mean to say that the boss is 5mm too short? That seems very odd. Perhaps the back fo the arm is fouling on the base of the boss (preventing it from going on all the way)? If it doesn't go on all the way then you can guarrantee it will also be a sloppy fit. All measurements aside, once the pivot bolt is done up the arm should turn freely and not be "too" sloppy.

You can get bosses with different lengths, but I don't know how may differnent lengths there are or how different they are. I've only had to switch the bosses once, becasue the boss was fractionally too short (but not 5mm short).

Also check that the bushing is where it should be and hasn't fallen out of the arm.

Note also that there are different types but this usually relates to the arm geometry (some types are designed to mount to cantilever bosses).
 

dabac

Well-Known Member
Sep 16, 2003
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The absolute majority of v-brakes don't turn directly on the boss, but on a bushing permanently mounted in the brake arm. Deore are definitely in that category. Bushing goes over boss, and gets pinched in place by the screw. Brake arm flop isn't governed by mounting screw torque, but by precision at manufacture.
While having a boss ending 5 mm below the face of the brake arm is a tad more than I'd expect, it's not functionally important - just make sure you have enough turns of engagement on the screws, and that the brake arm indeed has made it all the way down.