Bicycle Mechanics - Cant figure out how to center brakes

Hi I have sidepull caliper brakes, and i cant figure out how to center them. The tutorials i saw all said to loosen the back bolt, center it and tighten the back bolt... but whenever i do that the brakes just slide back to their original positions.

I have attached pictures.

http://img521.imageshack.us/img521/2497/dsc00473z.th.jpg (http://img521.imageshack.us/my.php?image=dsc00473z.jpg)

http://img254.imageshack.us/img254/3470/dsc00474hgs.th.jpg (http://img254.imageshack.us/my.php?image=dsc00474hgs.jpg)

Should be flats on the mounting stud just behind the arms. Hold that with a thin wrench as you tighten the mounting bolt on the back side of the fork.

if all else fails, there is always this approach
http://davesbikeblog.squarespace.com/blog/2006/11/8/centering-side-pull-brakes.html
it is fairly radical though, so don't use unless absolutely necessary.

I always use a punch and a hammer to centre brakes... it's an old mechanic's trick that amazes the newbs every time I do it.

I just loosen the nut on the back, clamp the brake down and then tighten the nut. Seems to work just fine as long as you tighten it enough.

You MUST hold the front of the centre-bolt in place while you tighten the back. You need to use a 13mm cone-wrench on the front to prevent it rotating while you tighten the nut in back. It's that very last 10-degrees of tightening in the back that spins the front.

http://www.parktool.com/images_inc/repair_help/obw01.jpg

Park Tool makes a couple of "Offset Brake-Wrenches" to do this job as shown above in DannoXYZ's posting. That shows one of them. What works just as well is a cone-wrench. They are cheap - if you get the silver double-ended ones with 13mm on one end, and 14mm on the other. Your local bike-shop may have these.

Is it wrong to just do it by hand?

Without that special wrench, they can be VERY annoying.... And on a lot of older bikes, they tend to stick those ratty reflectors somewhere in the stack of bolts and washers....You have to take the whole thing down to toss 'em.

Is it wrong to just do it by hand?

Do you have flat fingers that are made out of metal? If so - knock yourself out! :D

Is it wrong to just do it by hand?It's not "wrong", but extremely VERY difficult to get the brakes tightened in a centered position. Holding the caliper arms by hand WILL NOT keep the centrebolt from rotating as you tighten the nut in the rear. The ONLY way to keep the centrebolt steady is to use that thin 13mm cone-wrench.

In the amount of time you've spent fighting these brakes and the amount of frustration you've faced, you could've just gotten the correct tools to do the job and be done with it. If you don't have the $4.95 to spend on the cone-wrench, call around to local bike-shops and colleges. They often have DIY stations where you can service your bikes with their tools. Typically, once you've used the correct tool just one time and experienced how easy it is, you'll most certainly buy the tool yourself. Just your wasted time alone is worth it. if you earn more than $10/hr, and you've spent 30-minutes wrestling with these brakes, you could've just spent the time working your job and would've had enough to pay for the tool already. :)

Actually Park Tool makes 3 of these wrenches.

OBW-1 10mm and 13mm.

OBW-2 12mm and 11mm.

OBW-3 14mm and spring-spanner.

If you know of any others, please post same? Thanks!

I find the double-double ended cone-wrenches are simplest if you want to get just one tool. There are various brands that make a 13/14+15/16mm wrench.

You MUST hold the front of the centre-bolt in place while you tighten the back. You need to use a 13mm cone-wrench on the front to prevent it rotating while you tighten the nut in back. It's that very last 10-degrees of tightening in the back that spins the front.

http://www.parktool.com/images_inc/repair_help/obw01.jpg

The basic concept is right - you have to hold the brake in position while tightening the nut, or put the brake in position with a tightened nut.

Some brakes have flats on the front, like an older Campy, and some don't. Some of the ones that don't, like the Shimano 6207 (600 or Ultegra grade single pivots from the early '80s) are designed for an Allen key, and the old Weinmann sidepulls have an acorn nut and lockwasher on the front of the brake pivot stud. If these two are jammed together well without destroying either one, they can by used to hold the caliper in place, but with not as much torque as you can get if the brake was designed with a pivot bolt rather than a pivot stud.

With all these techniques the last bit of tightening does the most damage to the alignment.

Moral of the story: after you get them adjusted right, don't let anyone do you the favor of snugging down your bolts for you.

Thanks guys!
one of my big problems now is that after I align the brakes, then i squeeze the brakes they dont stay properly aligned. One of the arms goes in and just doesnt come out as much as the other. Does that make sense? Its like squeezing it somewhat misaligns it. Its the arms that attaches to the cable the highest if that makes a difference.

My bike is ridable now though, so that makes me happy.

Your brake-cable may be too short. Make sure it's not fully stretched and straight when you squeeze the lever. You can test this by unwrapping the bar tape and seeing if the cable gets pulled away from the bars when you squeeze the lever.

Also, DO NOT centre the brakes with the cable removed. Have your cables installed and barrel-adjuster set to operating width between the pads.

Another cause is that your brakes have previously been centered using the "punch" method. This bends the spring and changes its preload, but on one side only. This causes an identical force on each arm to move one arm more than the other. What you must do in this case is to squeeze the lever FIRST to equalize the spring-tension as much as possible. Then using the cone-wrench on the centrebolt, hold it so that the side that moves more is further away from the rim. So if you've got one side that moves 7mm per squeeze and one 5mm, set up your brakes that way with uneven centering so that both pads will hit the rim simultaneously.