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Only One Pad Moves
#1
I chronically struggle with brake adjustment. I vaguely understand that I may have to readjust brakes several times before they function correctly, but I don't know how the caliper functions so I waste a lot of time. I spent 20-30 minutes during my last work shift on a single set of rear brakes. No matter how many times I adjusted the cable one pad barely moved, if at all. (I think it actually moved less as time went by.) I eventually gave up and told the owner to take his bicycle to a repair shop. That was a shameful thing for me to have to say; he had just taken it from the store's bicycle rack that day. It should already have been in working order.

Many hand brakes on Wal-Mart bicycles resemble the set in the "V-Brake" video. The only other type I've seen is horseshoe-like.
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#2
Which type of brakes?
For v-brakes there is some "gotchas" (well for me). Make sure the pads are adjusted so that they hit the rim squarely and the "holder" protrudes from the brake arm same on both arms, though the amount of adjustment possible depends on the type of brakes / holder you have. Then, make sure the cable is seated properly and nothing tugs on it, moving the whole brake setup to the side (this is my favourite gotcha, I had a cable lock hanging on the saddle that was constantly interfering with the brake, duh!). Finally, adjust the little screws (3mm hex key or phillips head screw) so that both pads have same distance from rim and hit at the same time when brake is engaged.

Look at http://www.sheldonbrown.com for a lot of information on bike parts and maintenance (and of course watch Alex's videos!). Sheldon put up quite a lot of information on how to route cables and stuff like that (so do his "heirs" who maintain and update his site).

Horseshoe-like brakes could be caliper brakes (e.g. on road bikes) or maybe U-brakes or maybe MAFAC-style centre-pulls (though those are really not used anymore ...)
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#3
Vbrakes usually have a small adjusting bolt on each side to help center them. "Horseshoe" (caliper brakes) you have to rotate the whole brake assembly to center. Loosen the bolt that mounts it to the frame, turn and retighten. Cable adjustment won't fix this on any bike.
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#4
(Some sidepull caliper brakes also have small screws for adjustment in the brake body.)

Reading through you post again: Yes, most likely it was the adjustment screw on the brake arms that would have fixed it, assuming that
- the springs spreading the brake arms were sitting both in the correct holes
- the pivots / axles were clean and slightly greased
- there were no washers missing from the brake arm mount
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#5
Quote:Originally posted by Joe_W
Make sure the pads are adjusted so that they hit the rim squarely...
I've been able to position the pads correctly. My problem is with the calipers.

Quote:Originally posted by Joe_W
...and the "holder" protrudes from the brake arm same on both arms...
I'm not sure what you mean by "holder." Do you mean the prongs for the brake pads?

Quote:Originally posted by Joe_W
Then, make sure the cable is seated properly and nothing tugs on it, moving the whole brake setup to the side
I haven't had problems with brake cables getting stuck on anything.

Quote:Originally posted by Joe_W
Finally, adjust the little screws (3mm hex key or phillips head screw) so that both pads have same distance from rim and hit at the same time when brake is engaged.
The screws on v-brake calipers don't seem to make any difference no matter how much I turn them in either direction.

Quote:Originally posted by Joe_W
Look at http://www.sheldonbrown.com for a lot of information on bike parts and maintenance (and of course watch Alex's videos!). Sheldon put up quite a lot of information on how to route cables and stuff like that (so do his "heirs" who maintain and update his site).
The videos here simply say to adjust the brakes "until they feel good." That doesn't explain how I can continually readjust a set of brakes for over 20 minutes and not get a correct alignment. As for the advice on Sheldon Brown's website, the caliper slides back to its original position the next time I pull the brake lever. The only thing I've managed to do with the center bolt is affect resistance against the brake cable. Tightening the center bolt enough to hold the caliper in an adjusted position stops the lever after about a quarter-pull and the brake pads barely move.

I've only tried to adjust a caliper spring once, so I'll have to try that some more. But Brown's site doesn't tell me how to manipulate it for the desired effect.

Quote:Originally posted by DaveM
Vbrakes usually have a small adjusting bolt on each side to help center them. "Horseshoe" (caliper brakes) you have to rotate the whole brake assembly to center. Loosen the bolt that mounts it to the frame, turn and retighten.
See my answers to Joe.
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#6
V-brake mounts have (usually) different holes where the spring can be installed. The hole determines the tension on the spring by rotating the neutral position of the spring. When the two springs are in different holes the whole setup cannot work. The remark that the adjustment screws did not change anything makes me believe that it could be something like this (as all other options I thought of are exhausted).
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#7
Today I spent an hour working on a set of rear v-brakes. I didn't see more than one hole for each caliper screw, but found the screws can affect an unresponsive caliper if adjusted in tandem rather than individually. I previously tried to adjust them independently of each other and wrongly concluded that they didn't work as described.

I also tried to manually deform the springs but succeeded only in smacking my fingers a few times. My attempts to overextend the springs as Sheldon Brown's site suggests made no noticeable difference.

I ultimately had to designate the bike as damaged to get rid of it. Fortunately for me a bent rear wheel which previously escaped my notice served to cover up a colossal waste of time.
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#8
Sorry to hear you had an unproductive day. Let me give you a few notes which might help for next time.

- Be precise in your terminology. Caliper brakes and V-brakes are different. Vbrakes have "cantilever arms". This matters because the two types are adjusted differently and you may be getting some of the above advice mixed up if you aren't sure which is which.

- On a caliper, there is a long bolt that the two arms pivot on and is used to bolt the caliper to the frame. The two nuts on the outside (facing rear on the back brake, facing forward on the front brake) as used to adjust how tightly the two arms are held together. I think this is what you were tightening when you found it would just stop the brakes from moving at all. On the other end of the bolt, there will be a single nut that tightens the whole assembly to the frame. This is the one that you loosen in order to rotate the caliper which should allow you to get it centered properly. It can be stubborn because as you tighten the nut, the whole things tends to twist back out of center. But this is the nut that controls it.

- On vbrakes (and cantilevers) there's two basic ways to center them. On a lot of these, there will be three different holes on the frame that the end of the spring can go in to. Sometimes moving it to a different hole will help, but the jumps are pretty big. Most newer/better brakes have the little screws that go into the side of each cantilever arms that give you a much finer/easier adjustment. All of this can be complicated by a cable that hangs up or a rough spot on the post that the brake pivots on.

- Trying to bend the springs on cantilevers is pretty hard. On calipers it can be done easier, but I'd consider this a last resort. If nothing else is bent, you shouldn't have to mess up the spring itself.

- Working on older/cheaper/rustier bikes can be frustrating because they don't always respond to adjustments the way they "should". Sometimes you have to take things apart, clean up, grease everything, and start over.

- While you didn't achieve much today. I'll bet you will be much more effective next time. It takes a while tinkering with bikes to get the hang of how things work. Once you "get" a lot of these adjustments, it will seem weird that it was so confusing at first.

- There are a number of good books out there which aren't too expensive and go through the basics very well. It's nice to have something like that you can have on the bench next to you instead of posting stuff online and waiting for a reply. Though these forums are great for the weird stuff or things that just stump you.

- People who don't consider themselves mechanically inclined are often surprised how easy working on bikes is because they assume it would take a lot of training. People who ARE mechanically inclined tend to be surprised how HARD working on bikes are because they expect to just grab a screwdriver and "fix it". Bikes are mechanically simple, but there is a lot of small complex mechanisms that have many tricks to get them working right, there's a lot of different types of brakes, shifters, etc. so knowing one type doesn't mean you know them all, a lot of things have to be done in a certain order or you get no where fast. Until you know these things, you can "waste" a lot of time.

good luck - keep trying!
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