gsa103

So I've noticed that the dual pivot brake calipers sometimes get knocked out of alignment to the point where a simple brake lever squeeze doesn't re-center them. What's the best technique to fix this?

Option A: Grab caliper and twist slightly.

Option B: Adjustment screw.

Option C: ??

FBinNY 

First of all, properly mounted brakes don't move that easily. If this is a problem, try to resolve it at the source by making sure you can tighten it well. Some factors may include, a bolt or nut bottoming on the last thread preventing tightening properly or a badly matched face on the contact area. You can also add a serrated washer behind the brake, to bite into both the fork (or frame) and brake, locking them together. I use course lapping compound for the same purpose. (One can of lapping compound replaces thousands of washers, and there's never a question of fit).

Now for small centering adjustments (find tuning), use the balancing screw. For larger adjustments, or when newly installing, set the brake to a balanced position (both arms one in front of the other, and reach equal on both sides), center over the wheel and tighten while holding there. Finish by fine tuning if needed.

What you don't want to do is force it home while tight. If you have a serrated washer, that simply makes a circular score, and ensures that you'll have the problem forever.

HillRider

I've never needed to use the balance bolt to center any double pivot caliper as just grabbing the arms and twisting by hand does it fine. I keep the mounting bolt tight enough that the brake is hard to pivot but not impossible and I've never used serrated washers because of the problems FBinNY noted.

gsa103

It doesn't move very easily, but I tend to run my brakes with <2mm clearance on each side, so any motion is enough to put it into the wheel.

On my previous bike, I would consistently use the centering screw. But since it was 105 it was crappy Phillips that eventually rounded out. The new bike doesn't have a serrated washer and its a carbon frame, so I'm not sure its possible to really get it tight enough to prevent some motion.

FBinNY 

Go to your favorite oato mechanic and beg a teaspoon of coarse lapping compound. Smear a dab between the brake and fork, center, tighten and forget it for the next century (unless you crash).

BTW- there's some play in the linkage between the arms, so if the brake isn't kept lubed, it may move from side to side slightly, making you think the caliper moved. If you find it moving often, it's either loose, or you aren't keeping it lubed.

blamester

I loosen the nut on the brake bolt.
Pull and hold the brake lever and tighten the nut back up.
Brakes centered perfectly
Make sure the wheel is properly centered first.
I am gonna go with some lapping paste from now on too.

FBinNY 

One thing I should add here. Many times people have trouble keeping brakes centered, and go crazy moving them back and forth. But it's often not the brake that's moving at all, but instead the front wheel.

Be sure not to reverse the wheel if you remove the skewer, and always mount the wheel with the bike flat on the ground. This lets gravity ensure that the axle is always fully and consistently pocketed into the dropout.

The the other thing that can drive you crazy is a slightly bent on off center axle. This has no effect when riding since the axle is stationary, but can change the position of the wheel depending on orientation. When someone reports brake movement problems that don't diagnose quickly, I set the bike on the floor, with the QR open, and use a cone wrench to rotate the axle while watching the rim between the brake shoes. This us usually more of a problem on rears than fronts, but can affect either.

BTW- I still use single pivot brakes which I prefer for better modulation. Despite their reputation for drifting off center, I've never had to move brakes after initial installation ---- ever.

Short version, make sure you identify the real problem before you waste time fixing what ain't broke.

Jed19

Same here. I rotate about seven wheelsets, and have been grabbing brake arms to center the brakes forever. I once saw Alberto Contador do the same thing to both his front and rear brakes before a stage at the Tour.

FBinNY 

Question for both you and Hillrider. Not wanting to be argumentative. but curious about the logic. If your brakes are loose enough that you can move them back, might that not be why they move in the first place? Why not set them so they stay put in the first place?

Jed19

Yeah, probably. I have always thought about tightening it down, but was of the view that I'll probably need a serrated washer/lapping compound, and I never got around to that. Then I saw Alberto Contador do the same thing I do, then never bothered.

FBinNY 

So, am I right in gathering that carbon frames are slipperier? Or are folks are nervous about tightening as much, so brake slippage is more of an issue on carbon than with metal?

gsa103

Probably a combination of both. High gloss paint + not as much torque. There doesn't seem to be a torque spec anywhere on the fork for that bolt.

FBinNY 

Thanks. I've always used lapping compound there, so never had issues. Now I know not to stop. From the sound of things, if someone is concerned about the lapping compound, they might cut a washer from a pair of latex gloves or balloon, and use that to improve traction.

At least I understand the problem better now, and don't have to wonder about all those moving brakes we hear about from time to time.

lopek77

Toothpaste which contains hydrate silica will work as a lapping compound

Kimmo 

It's possible to have the mounting bolt too tight to be readily straightened by hand, yet loose enough to occasionally be whacked off-centre in a car or something...

So IMO it's best to have it just tight enough to be almost difficult to centre by hand.

As for serrated washers, when I consider the leverage exerted upon them, I can't imagine what they're good for beyond making a mess. Hate em. They go in the bin next to valve caps and collars, spoke protectors, etc.

HillRider

Well, "loose" is an overstatement, they are very snug and require a bit of force to center them. They never move spontaneously and I can remove and install the wheels at will with no need for recentering. The only time they move is if they take a good whack when the wheel is out and then they can be recentered by hand. I do have the mounting nuts good and snug, just not crushing tight.

rpenmanparker 

Do I understand correctly that "lapping compound" is another name for polishing compound, perhaps the coarser grit? Would carbon paste work instead?