V-brake Boss / Bolt query

Joe_Rides

Senior Retro Guru
I'm currently building up an Explosif which came with v-brake bosses as well as a disk tab (full disclosure, the bike is newer than 97).

It's been ran with disks forever, and the original plastic covers were still on the v-brake boss. Having removed the covers and cleaned the bosses up, it's apparent that one side is pretty badly rusted up internally.

A standard brake bolt won't wind in fully, this is after a lot of cleaning, soaking, winding bolts in and out to remove swarf etc. It just gets VERY tight then comes to a stop.

Question: Any issues in just using a shorter bolt?

Photo shows the bolt wound in as far as I can get it without getting serious tools out. It's probably 2/3rds in (ish).

Looks wet because plus-gas.

20211214_215213.jpg
 

ishaw

Gold Trader
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You could run a shorter bolt, depends on the brakes. I'd try the following before that though:

1. Small wire brush to try and get any rust off.

2. Have the thread chased with a proper tool (lbs should be able to help).

3. Carry on trying to chase the thread with a good steel bolt. Tighten, loosen, tighten loosen etc, try and clean out any loose stuff between goes, and preferably use a bolt without threadlock on it.

4. Can you thread a bolt in from the rear?

5. Can you remove the boss? If so, replace with a shiny new one.

Good luck, I hope you get it sorted.
 

W7Ford

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I'd run a tap through it as suggested. Any local engineers would do it if you don't have a tap and die set to hand. They are M6 x 1 from memory but double check.
 

novocaine

Retro Guru
if you haven't got a tap, cut a clearance groove in the bolt with a file (unless you have a dremal, in which case use that). it just needs to be a a groove running length wise up the bolt.

bolt dia x 1.5 is the rule of thumb. it's an M6 so you need 9mm of thread engagement (there are other rules of thumb like 3 full threads etc.).
 

Joe_Rides

Senior Retro Guru
Thanks all.

Can't thread a bolt in from the back unfortunately, and it's difficult to find anything narrow (but abrasive) enough to clean the threads that way. I don't have a tap / die set either (something i've been meaning to get for years).

I will keep going with it using some of the tips above, and hopefully make some progress.
 

Woz

Old School Grand Master
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I'm currently building up an Explosif which came with v-brake bosses as well as a disk tab (full disclosure, the bike is newer than 97).

It's been ran with disks forever, and the original plastic covers were still on the v-brake boss. Having removed the covers and cleaned the bosses up, it's apparent that one side is pretty badly rusted up internally.

A standard brake bolt won't wind in fully, this is after a lot of cleaning, soaking, winding bolts in and out to remove swarf etc. It just gets VERY tight then comes to a stop.

Question: Any issues in just using a shorter bolt?

Photo shows the bolt wound in as far as I can get it without getting serious tools out. It's probably 2/3rds in (ish).

Looks wet because plus-gas.

Advice above is to do a proper job, but still ...... to come back to your question.

Just what exactly do you mean by a standard brake bolt? The lengths are all over the place, and often the rear is delibrately shorter than the front. For the rear, I would say at least 15mm of insertion, more better, but there is no need to go the full depth either.
 

Joe_Rides

Senior Retro Guru
That's a good point, and the XT V-brakes i'm fitting didn't come with bolts, so i'm having to raid the spares box.

I found an original shimano canti bolt which was quite long. This was my barometer, but no idea whether it was a 'front' or a 'rear' bolt. The bolt i've photographed is just an m6 bolt taken from a set of disk brakes (I went through a few bolts to make sure it was indeed the boss threads which were defective)

I might be able to work with c15mm insertion, will check again later.
 

Woz

Old School Grand Master
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I've just measured a Tektro and XT rear v-brake with specific rear bolts; looks like anything from 10mm to 15mm insertion will be fine.
 
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