phlebas

Hi there,

I am a complete novice at bike repairs, so please be patient. I am trying to replace some rear v-brakes whose spring has gone on one side. I bought a new, cheap set of calipers from Halfords and managed to remove the caliper from one side with an allen key. The problem I am having is that I can't see how I'm supposed to attach the new caliper because the supplied bolt is too short. I have posted some pictures below to illustrate my problem.

This is where the old brake caliper was attached:


These are the old (left) and new (right) calipers:


The bolt below the new caliper came supplied with it. I don't seem able to remove the threaded red part from the old caliper.

Can anyone please explain to me what I need to do to solve this problem? Are there more than one type of caliper and have I bought the wrong type?

Thanks in advance,
Phil

rjacob

The mounting bracket on your frame is different than what I normally see. There is usually a tube that extends up, that the brake slides down over. The tube is threaded inside so the shorter screw would thread into that. I haven't seen mounts like the one you have in the picture.

Check this picture for what I am talking about:
https://www.parktool.com/images_inc/r...help/cant6.jpg

Maybe the tube/stud on your bike screws in, and is stuck in the old brake?

phlebas

Thanks for your reply.

I see what you mean. It did occur to me that the red threaded bit should not have come off with the brake, and this may be the tube you refer to. But I don't seem to be able to remove it, and there is nothing to get a grip hold of.

rjacob

Drown it with wd-40. The brake slides on the stud, so you should be able to push it out of the old brake. You probably have a bunch of rust/corrosion in there.

TallRider

yeah, it looks like the brake boss (which is supposed to stay in the frame) came off with the brake. I don't know if you've just got a non-standard frame that takes atypical brakes. what sort of bolt did you turn in order to remove your old brakes?

also, "calipers" typically refer to a single brake unit (centerpull or sidepull brakes), not to brakes made up of separate arms that attach to the bike's frame.

phlebas

OK, I'll give it a blast with WD-40 and see if I can shift it.

phlebas

The 'bolt' I undid was a sunken hexagon type (I used an allen key). Thanks for the tips on the nomenclature - I am finding it difficult to know what to call the various parts.

rjacob

Hey, I don't know the proper names for most of the parts either. But I have taken bikes almost entirely apart, and put them back together again.

Wordbiker

Try clamping the threads of the brake boss in a vise. To prevent damage to the threads, apply a strip of copper, aluminum or wood on the jaws of the vise. If you do not have a vise you can use a strip of material to protect the threads and use a pair of vise grips or pliers to hold the boss while you turn the mounting bolt with your hex wrench.

If you can get it free, inspect it for any damage or wear. If it's suspect at all, you should be able to pick a new one up cheap at your LBS. I'd suggest this anyway as the LBS should have a drawer full of them they'd be glad to get rid of (they come as spare parts with many new bikes) and considering that the brake boss acts as a bushing with the brass sleeve inside the brakearm...why not start out with a fresh one?

When installing it again (it should have wrench flats on it for this), use threadlocker on the part that goes into the frame, and grease on the internal threads and the shaft. You'll have less trouble removing it next time and your brakes should pivot freely.

rjacob

Is the hex bolts still screwed into the post that is stuck in the brake? If so, then yeah, like wordbiker said, you will need to get the screw out of the boss (tube). To do so you will need to hold the threaded part static while you turn the screw. Try not to damage the threads on the boss.

phlebas

Right, I think you guys are correct in your diagnosis. It just occurred to me to try undoing the arm on the other side, and this came off very easily, leaving the boss behind and looking just like the picture in the link rjacob posted. I've drowned the problem boss (and the hex bolt which is stuck in it) in WD40 and still can't get it loose. I don't have a vice so I think I'll have to buy a new boss. Hopefully my local bike store will have one. By the way, what is threadlocker?

rjacob

I am guessing Threadlocker is like Locktite. The opposite of oil, it works more like glue, to keep the part from unscrewing.
Well, if you are likely to be replacing the boss, then why not try carefully gripping the threaded part with a pair of pliers to hold it, and turning the hex bolt? It sounds like you don't have anything to lose in trying.

Wordbiker

Yes, threadlocker is a general term, Loctite is a brand name. If you do use Loctite brand, use 242 (blue). It allows removal again with hand tools. Do NOT use the red stuff...it requires a torch for removal. The blue material already seen on the mounting bolt is threadlocker, just a different type made for manufacturers formulated to be applied at the factory.

Please read my edited response above, I clarified a bit more.

phlebas

Just had a go at this and it worked! The boss looks fine so I think I'll go ahead and assemble the new brakes. Let's hope I don't encounter any more problems.

Thank you all so much for your help! You guys are great - I'm so glad I found this forum.

Phil

rjacob

Way cool! And I learned that tube/stud thingy is called a boss! LOL! Many of the guys on here are professional mechanics. Me, I have fun overhauling my own bikes, and mixing and matching parts. I am sort of a shadetree bike mechanic.

Michel Gagnon

I know I'm a bit late for this time, but when a v-brake or cantilever brake only opens on one side, there is a solution:

– Remove both brake arms from the bosses.

– Disassemble, clean with WD-40 and put fresh grease on the spring and cavity.

– Reassemble.

Wordbiker

I'd add to that: Then balance the springs. It is not only friction on the boss that causes brakes to be imbalanced.

phlebas

Thanks for your reply Michel. So you are suggesting that instead of just replacing the brake arm I might have been able to fix the old one? That would have saved me a bit of cash - shame I didn't post here before spending the money! Maybe I'll have a play with the old one later and see if I can loosen it up.

Thanks again everyone for your help.

Phil

rjacob

What di you mean "spring has gone on one side". Is it gone, as not there anymore, or did it break? Or were the brakes just off center? If they were just off center, they could have probably been adjusted.

phlebas

When I said 'gone' I meant that one arm was permanently jammed onto the wheel rim and it did not spring out when I unhooked the cable pipe, whereas the other one did. I haven't really inspected the offending arm (at the time I was only interested in replacing it because I'd already bought new arms), but I guess it's possible that it has just seized up or the spring is broken.

Before removing the old brakes I did have a play with the adjustments and I'm pretty sure they weren't just badly adjusted. I am even more sure of this having adjusted the new brakes I fitted yesterday.