tightening caliper brake without moving it
 

I'm well aware this is probably a laughable question to most of you, but googling is yielding me nothing but details of what screws go where, which I know. My rear brake is slightly loose -- I noticed it when I opened the brake to get the wheel out to clean some grime off. I put the wheel back on, pulled out the right hex key, and tried to tighten it -- I can't do it with only two hands, the brake won't stay put. As I tighten it, it twists.

Is there a trick? Rubber-banding the brake lever to tighten it on the wheel or something? I'd like to be able to do this myself, rather than having to shamefacedly take it into the shop and admit I was defeated by a loose brake.

What model and type of brake do you have? If it is the newer double pivot type, it can be centered by hand after the bolt is tight. If it is the older single pivot type, there should be wrench flats on the caliper side of the center bolt that will let you center it with a thin open end wrench after you tighten the bolt or you can grab the spring arms and use them to center the caliper.

also consider tightening with the brakes fully engaged by cinching the handlebar levers closed ...

That doesn't always work with single pivot calipers. If it did no one would buy centering tools. :)

New double pivots -- they're 2012 Shimano 105s. The bike I grew up with (and the only one I've done much of my own work on) has cantis, so I've never worked with calipers before. How would I center it when the bolt is tight? Or is it supposed to be able to move and I didn't need to do anything to begin with? I assumed it should be tight to the frame and immobile.

Yeah, that's what I meant by rubber-banding the brake lever -- I need two hands to tighten the bolt, because my hand-eye coordination sucks, but I could put something on it to hold it shut.

Try an old soft toe clip strap. Of a piece of rubber bar tape. Either will do.

Make sure the small set screw under the caliper (part 2 in the exploded view here) is tight. Then according to Shimano just compress the caliper by hand or other means and tighten the 5mm nut.

I actually have to give credit to Hillrider (as well as Google) I just Googled install 105 caliper and found a Bikeforum post of his referring to that hidden set screw (which is supposed to be tight). Then on to Shimano's site for their exploded view and service instructions - always one of the best places to go when dealing with new installation or "by the book" adjustment of Shimano products. (105 page) http://techdocs.shimano.com/techdocs/blevel.jsp

Yeah, I just wasn't sure if that was an OK thing to do, which was why I asked. (Out on the road, if I have to do it, a reflective ankle strap would probably do the trick. At home, since I am home now, I'll probably just be lazy and get my husband to hold the brake down while I turn the bolt, but I wanted to know that I could do it solo of I had to.)

I was just frustrated that all of the maintenance tutorials I found online were just like "and now tighten the bolt" and didn't give any indication that this was hard to do. So I wasn't sure if I was doing something completely wrong or if it'd be a bad idea to tighten it up with the brakes closed.

You really don't have to cinch the bolt so tight the calipers are impossible to move. Get it good and snug and you can still center the caliper arms by pivoting them by hand.

Yeah, I had found that already too (the shimano doc, not Hillrider's other post), and the rest of the caliper is fine -- it's just tightening the bolt that holds it on. But it sounds like from what Hillrider said in his last post that I actually got it tight enough before even making this post -- I figured if I could move it by hand into centered it was WAY too loose, because that's my usual assumption since I have weak hands. I've had (quill) handlebars and saddles slip because I couldn't crank them down enough, etc.

Thanks, y'all.

I've got a different theory.
If you're having trouble getting it tight, maybe the recessed nut is bottoming out on the main bolt. You could test this by removing the brake and seeing how far the bolt and nut thread together. If they don't go closer than you see them when assembled on the frame, that could be the problem.
New 105 rear brakes are packaged with an 3mm or so thick washer to take up space between the frame and brake body. Finding a similar washer, a shorter nut, or combination shouldn't be hard. Then it's just an matter of holding the brake body with one hand, and tightening with the other.

There's a screw in one of the arms to centre Shimano DPs, but I don't use it; I just adjust that so the brake looks good.

It's not necessary to have the mounting bolt super-tight; I do it up enough so the brake isn't going to move by itself but it's pretty easy to rotate the brake by putting a thumb on each arm at the pad and pulling apart while rotating in the desired direction.

If you just pull on one arm, they can move without affecting the mounting, but if you assist the return spring against the cable the whole brake can be moved as a unit. Unfortunately this approach is useless with SPs.

Some brakes have flats on the pivot bolt which allow you to hold it with a cone wrench. So those are easy.

For brakes without any obvious means of holding the pivot bolt, you have to be a bit more creative. The key is balancing friction, so start by making sure the mounting bolt has a clean, smooth thread which the nut spin on well, then grease the thread. Now you want to increase friction between the pivot bolt and frame. You can use a serrated washer, or do as I do and use coarse lapping compound. Either of these will provide bite between the bolt and frame and keep it from spinning.

Tighten the brake to where it's not quite firm, center it, then tighten and it won't move. Some times you need to give it a bit more help, and putting a wrench on the nuts on the end of the bolt will do that.

Single-pivot calipers are a lot more interesting.

It's one of the things that really lets a customer know that their mechanic has it.
I can't even guess the number of times a customer has timidly requested help with this "simple" task, or the number of tricks thay I've had to employ in each of the so many cases to get it done fast, but this job is one of those things that so often has the customer making self-deprecating remarks amid compliments to the chef, so to speak.
And so often, these single-pivots get pushed off-center by a cable housing's movement, often from a handlebar/stem adjustment or from a rear cable housing sliding to a different position within the top tube housing tunnel "loops".

With dual-pivots, I always use hand force, which also tells me right away if the mounting bolt is tight enough.
I use two hands, with one palm or the other pushing down on one side of the arch while the other hand's fingers pull up on the brake pad.
I always follow up with a glance at the pad's alignment with the rim and a lever pull to confirm the cabling is in order.

Oh, and one last thing: Before starting to do anything with front caliper centering or pad adjustments, always release the quick-release and then secure it while pushing down on the handlebar stem. This assures the axle is fully settled into the dropouts.
On the rear wheel, the same applies (but with downforce now applied to the saddle to fully settle the axle against chain tension).
And, on older bikes, the axle should also be confirmed as straight (and unbroken) by turning it before making any caliper centering or pad adjustments on an unfamiliar bike.