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I have some dia compa ac 500 brakes on an old road bike. While the calipers are installed on the bike, with everything tightened, I can move (rotate) the calipers side to side with my hand. I've already searched online and there seems to be a lot of different suggestions and opinions ranging from using loctite to the idea that the hole in the frame/fork is "compromised".

Here's a picture for reference (mine are not exactly identical): http://4.bp.blogspot.com/_rFnXZUx3BwQ/TFH3HR5jIhI/AAAAAAAABpI/_VXBnW0Yhdw/s1600/DSCF0446.jpg

The calipers are held to the frame/fork with a metal rod with threads, a (capped) nut that gets screwed in in the "front", and a piece of metal that screws on to rod in the “rear”. Tightening that front nut only seems to add friction between the callipers. So, for example, when I release the brakes, the callipers do not return to their original position. Tightening that piece of metal in the rear seems to make it more difficult for the callipers to move (rotate). I’ve tightened these rear pieces as much as I could.

I have no idea if these brakes have been assembled correctly. One had 2 washers between that front nut and the calipers, the other one didn’t. Are washers even necessary? Regardless, both calipers rotate can be rotated like I described before.

How is this problem normally solved?

UPDATE:

I meant to describe some negative symptoms. Why is it a problem?

It's a problem because they get off center as you brake. You get one brake pad rubbing against the rim as you release the brakes. So in other words, they don't retract evenly. Ideally, I would want the brake calipers to be an even, fixed, distance from the rim (not loose).

I thought maybe it was an issue of friction. I disassembled one and greased it. I also put lube on the inside of the cable housing. This didn't help.

What might also be a problem is the length of the cable housing. In the front, the housing definitely causes the calipers to tend to one side.

It might also be an issue of unequal tension in the spring. I'm reluctant on bending it though.

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That style of caliper brake is problematical. It's critical that the pivots be as frictionless as possible, and also that the cable housing not constrain the brake, so that it will return to center when released. In addition, getting the brake to center in the first place is an art, and may require bending the springs. –  Daniel R Hicks Aug 5 '13 at 4:14

1 Answer 1

As Daniel R Hicks pointed out; that style of brake caliper can be a pain to work with, however there are a few things that you can do:

Make sure that the calipers can rotate side to side, they're supposed to be able to do this.

  • This is intended to work as a self centering system.
  • Imagine the brake being set up off center(where one pad is much closer to the rim than the other). When you hit the brake one pad is going to the hit the rim first. In the case of the brake pivoting around the mounting bolt the other pad will be forced toward the rim. If the brake is fixed at the mounting bolt, then the frame will resist the force coming from the pad/rim interface, and you will essentially be braking with only one pad.
  • The mounting pivot usually consists of an acorn nut and locknut system. The locknut sets the appropriate pressure on the brake arms to eliminate play while allowing the system to loose enough to pivot smoothly.

Make sure all of the pivot points are smooth

  • Clean out the pivot points as best as you can and apply a little oil(chain lube works fine)
  • I wouldn't take the calipers apart, even if you know what you're doing, it's a pain and usually not worth it.

Finally, you can re-bend the springs to center the brake

  • This is best done with the Park Tool OBW-3 Park Tool OBW-3
  • Bend the spring when the brake is mounted. Make small adjustments, and keep re-checking to see if the brake is centered. You want fatigue the spring as little as possible.
  • Be careful doing this! Old springs are usually oxidized and you can snap them when you re bend them. It is also possible to snap the washer that clamps down on the spring.
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