Most of my road bikes have older single pivot side pull brake calipers. I sometimes have trouble getting them to center properly.

On the troublesome ones, one arm moves when the brakes are applied, while the other one does not move or moves only a little. I know how to check that the cable housing isn't pushing or pulling the caliper. I also know to tap one side of the return spring to center the brake. But often the brake will not stay centered. This is not a problem, unless you are OCD. I am, a little, so it bothers me.

What is the trick here?

Remove the wheel and operate the brake. If the problem remains that one arm moves less try these two things:

1. Disassemble the brake and make sure that there is no roughness or corrosion on the mating surfaces for the problem arm. Use 000 steel wool to smooth if necessary, 400 grade sandpaper 1st if really bad. Reassemble, adjust the pivot for as you would a bearing (zero play) and lubricate the pivot.

2. Remove the spring on the problem side from it's stop on the caliper and bend outward, reinstall.

Recheck to see if the two arms operate equally, ignoring for the moment whether centered overall. Another trick to centering is this:

1. You will need wrenches to simultaneously fit the binder bolt on back and either of the locking nuts on the front of the caliper.

2. Make sure the nut and locknut used to adjust the pivot are locked well together, and the binder bolt in the rear is tight but not overly so.

3. Put one wrench on the rear binder bolt. Looking from the front, if you need to move the caliper clockwise put a wrench on the locknut. For CC, put the wrench on the inside adjustment nut.

4. Turn the front and rear wrenches in unison to center. Once done you should be able to tighten the binder bolt further if desired without affecting the centering.

Hope this works for you.

--Don

Maybe this video will help.

https://youtu.be/EZNrNys1UQ4

(1) Sometimes the problem is that the spring is weak or something is preventing one of the arms from moving freely. Post no. 2 provides a really nice check list for this kind of problem. (2) Sometimes, esp. with the less well made ones, the brake walks a bit away from center. Usually there is some kind of flat nut you can use to center with a thin wrench. I'd start with (2) before trying the ideas in (1). Sometimes a centering problem is just that, a centering problem.

Be sure the spring anchors and spring ends where they touch are clean and free of rust and dirt so they slide smoothly and evenly.

Park, and others, sold small thin "cone wrenches" with the opening (mine are 10 mm and 13 mm) at 90 degrees to the handle so they could slip over the thin wrench flats on the nut behind the brake arms. You used it to hold the caliper centered while you tightened the mounting nut.

My big complaint with centering cheap single pivot side pulls is the slop between the spring and the slot it sits in. The centerbolt has a part along it's length which doubles as the spring holder and the pressure point for both frame mounting (on one side) and arm mounting (on the other side). (What this part of the center bolt is called is beyond me other then "spring holder"). If the slot in this spring holder allows the spring to move about then keeping the brake centered will be difficult. You see it's the center section of the spring, the portion held in the spring holder's slot, that determines which side of the spring (and the associated arm) move how far from the rim. So any free slop/movement of this portion of the spring will mean that the arms/pads will also not maintain their location consistently.

On well made calipers the spring fits snuggly into the slot and by rotating the center bolt then locking this rotational Aspect in place one can control how far from the rim the two sides are. many better calipers have a pair of flats cut into the center bolt spring holder (Campy's NR as example) or the end of the center bolt has a wrench fitting on it (some Shimano and Weinnman examples) to help hold or fine tune the center bolt's rotational aspect.

But cheaply/crudely made calipers don't usually have these centering aids and the sloppy spring holding nature make these brakes a pain to center consistently. I have further tightened the spring slot up by careful bending the slot's end parts in. But I also have broken the end parts of the slot before, as many times it's made of brittle cast AL.

Running more rim/pad clearance is a common technique to eliminate pad rub in these cases. In the end as long as there's no rub during non braking it really doesn't matter if one pad is closer to the rim then the other. Expect for those of us who suffer from symmetrical system OCD. Andy. (Who goes through life looking at the vertical surfaces and edges about the world to see if they all line up. )

Thanks. I will revisit the current troublesome brake with these tips, and see what happens.

What I've been doing is adjusting the brakes so tight to the rim (minimal pad gap) that neither arm moves very much. This requires fussy truing but appeases my OCD. The bike I'm working on today is my son's high school bike, it leads a rather hard life and running such tight pad gaps isn't practical. The front rim takes a beating as he often lets the tire go too soft. It is a 36H MA40 rim, Mavic 410 (Modolo Speedy) calipers.

+1,000

This is key and usually the one and only issue with a brake that won't stay centered after being centered properly and tightened. Nothing moves, so recentering isn't the issue. But, the spring's leg slides against the caliper arm as it opens and closes. it's not a big distance, but any friction there can cause one arm to stick a bit and the other to make up the slack.

The cure is to make sure the point of contact is smooth and the spring can slide freely, then to make sure it does by applying a drop of oil there (and wiping off excess). You can also improve the action on certain brakes by sliding a piece of plastic tubing up the spring to act as a bearing where the spring and arm touch.

Once you have smooth consistent sliding of spring and arm, center the brake accordingly and it's stay put for eons.