I LOVE My Squealing Front Brake!
 

Actually, I don't. I have an LHT, and thus cantilever style brakes. Only the front brake was squealing. I took my bike to a bicycle shop. He pointed out my brake pads were low. I have since:

1) Changed both front and rear brake pads
2) Lightly sanded down both my front and rear rims. (120 grit)
3) Toed-in the pads.

Now, I still have the same situation, i.e., ONLY the front brake squeals. I now have much better stopping power, but now my front brake squeals in all weather conditions, whereas before the front brake only squealed when it was raining, or when my bike was left out in the cold (cold rims and such).

I toed in the front brake pads. It squealed. I re-adjusted so the pads were NOT toed-in. It squealed. My tire is true. Before installing the new pads, and before lightly sanding the rim I made sure to wash the crud off my rim as best I could.

Any ideas?

As Sheldon Brown writes, it is a fairly complicated issue and I have not really resolved it fully myself. I personally believe that it stems from a very slight mismatch of rotating parts' diameters, and it cannot be merely done using a tighter fit because the materials used as fillers would normally be much more flimsier than the base metal.

I have an ad-hoc solution that silences the front brake: Use a very fine sandpaper and glue it on the toed-in portion of the brake shoe. Every time you brake, it sands down and modifies the surface somewhat. But when the sand runs out (which is, btw, very soon after installation), you will have paper and glue rubbing against the modified surface. There is still a 'hiss' sound, but it is relatively silent and I am quite happy with that.

you washed your rims squeaky clean?

puns aside, which cantis did your bike come with?
some are more prone than others.

I have a couple suggestions, but as you're probably aware this problem can have a lot of causes, so YMMV.

Try tightening the brake pads to the arms with as much torque as you can reasonably put on the nut. Lightly oil the threads and really crank them down. In order to get the alignment right, you might have to initially tighten the pads so they're rotated slightly CCW, so that when you give it the final quarter turn, they rotate into place. Again, oiling the threads helps mitigate this. This made my Tektro Oryx brakes on my Trek 520 go from always squealing to only squealing in the rain. No toe-in needed, and they've been fine for hundreds of miles.

The other thing that helped a little was to remove the brakes from the bosses, slather on the most viscous grease you have on the bosses, and reinstall the brakes. Wipe up any grease that oozes out. This did not work as well as the previous suggestion though.

If you haven't tried them already, Kool-Stop salmon pads may help.

I am using Kool Stop salmon pads; those are the pads I replaced them with, haha.

And yes, I do have the Tektro Oryx brakes; I'll try that method tonight.

If your cable stop is mounted on your stem, you may want to get a different stop that mounts on the crown.
I've been told that it changes the pull angle and will sometimes take care of the problem.

sometimes the koolstop salmons contribute to the problem rather than solve.

i have just finished:

1) re-cleaning my rims
2) lightly sanding my rims (this time perpendicular to the direction the rim goes; i noticed i did it parallel to rim direction during initial installation and suspect doing that didn't create quite enough friction)
3) lightly sanded my brake pads (which had since acquired a tiny bit of gunk from the past 10ish miles of use)
4) tried the oil threading method that stedalus suggested (i noticed that when i went back to remove my front brakes the nuts were not as torqued as i thought they were); brakes are no longer toed in

i was about to go outside to test them, but it's raining here in san francisco and i didn't want to ruin what has become my little experiment. it should stop by the time i begin my morning commute tomorrow. i'll post my results.

i will note, however, that from manually moving my wheel then applying the brake i hear a nice "tttthhhhhpppt" sound, instead of a light squeal as before. i know that practically means nothing compared to testing it in real world conditions, but i'll take what i can get right now. :)

If all else fails, try the black Kool Stops. I run the dual-compound (salmon and black) Thinline pads on my hybrid. They squealed at first, but after a few miles they quieted down.

Good luck!

(1) Brakes can squeal if the rims are contaminated. My usual first step is to clean the rims first with soap and water, rinse thoroughly, then clean again with alcohol so as to leave no residue. I think if you've been sanding your rims after cleaning (?) you might be leaving a layer of metal dust on them.

(2) get yourself on a steep downhill and break in your pads with some hard downhill braking. Preferably when raining. I squeal sometimes when I have been riding too much flat and not braking hard enough.

Sometimes if all else fails the culprit may be an overly flexy fork that lets the canti bosses spread on braking -- booster arches help with this. But I've got an LHT fork and it's a stiff beast of a boat anchor, so probably that's not the problem. But you can search for an old brake booster arch on the ebay if you want to try one -- they really work, reduce squeal and increase power.

Honestly though, nothing I've done eliminated as much squeal as changing my Avid Shorty 4's in front for Tektro CR720's. Kept the same kool-stop pads before and after the change, too. I was surprised but there you go. The metal around the slot where the pad bolts on is thicker/stiffer which might have something todo with it.

Pre-Results:

I was giving my rims a quick wipedown after the light sanding.

Results:

Squeal is still there. It's not there on a soft brake, and definitely there on a hard brake. It sort of got better during the end of my commute (I'm assuming as my pads slightly wore down to match the rim). A few factors counsel hesitation though:

1) The roads here in the city were still wet. It wasn't raining, but it definitely was giving me some moisture on my wheels, rims, and after an examination at the end of my ride, the brake hardware.

2) The pads are no longer toed-in.

3) I don't have machine-precision skill, so the pads may not be perfectly hitting the rim until they wear down a bit more. That's not to say I half-assed it, however.

Conclusion:

F it. It's better than it was before. Who knows, the squeal might be non-existent when the roads dry up and the pads wear down to match the rim more. I'm going to leave it as is indefinitely.

Any more ideas are much appreciated, though! Thanks all.

Edit: I'll keep in mind buying the black koolstops next time, and maybe even new brake hardware in the future.

Just make sure the brakes work well before trying this! :)

You are correct.

Downgrading to the cheap bulk $5 black pads usually kept in the back of the shop(jagwire?) got rid of my squealing. (Had kool stops before)

Kool stops the v-brake/canti compatible variety have a history of squealing. Get yourself some noname $5 pads and see if that makes a difference.

I get some squeal even on foggy days, so I bet you'll see more improvement on a dry sunny day. Good luck finding that in San Francisco, of course.

When my bike is loaded with a front rack and panniers there is never any squeal, so if you can get a brake booster for cheap it might be worth trying.

My experience with brake squeal is documented here: http://www.bikeforums.net/showthread.php?t=436386. Like you I had squeal on just the front brake. Nothing worked long term until I installed a cheap brake booster from nashbar.

My brake squeal issues have always been pad alignment with the rim. Usually what happens is that as the pad wears, it begins to hang off the lower edge of the rim. This causes what I'd consider a medium volume squeal. With the pads mounted too high (usually after an adjustment or pad replacement) I get a high volume squeal. The squeal is there regardless of weather and usually gets progressively worse as I apply pressure. Realigning the pads so that they fully contact the rim has always cured the squeal and also greatly increases the braking power, even if the misalignment was only slight.

last option would be to use a different set of cantis like tektro CR720 or a beefier fork if the brake booster doesn't help.

Dump the Loud Stop pads and get Avid Pro's, aka Quiet Stops. REI has them. bk

One idea I encountered from chatting at the dudes from box dog bikes in san francisco that I did not encounter in this thread (or the reference thread the kind poster linked to earlier): metal-backed brake pads.

Pads (like my particular kool stops at issue here) are one piece of brake material. The force of placing the pad up against the rim could cause the brake material to flex and thus squeal.

Solution: Metal backed brake pads might provide that bit of rigidity needed to get that squeal out of a canti brake (similar to adding rigidity via a brake booster to dissipate vibration, but earlier in the braking sequence).

You can see examples of both here: http://www.sheldonbrown.com/harris/brakeshoes.html

The Avids have a little softer compound, and are very forgiving when it comes to toe settings. I suppose you get a little more black smear on your rims, but that's easy to clean off. Like I said, they are Quiet Stops. bk

I'm just thinking out loud, here, but I wonder if Kool Stops for V-brakes would be easier to quiet down if the short side of the pad was installed facing the rear of the bike. That way, the short side would be the leading edge as the rim rotates towards it. Toe it in towards the rear, and then the long side is the trailing edge. Might work. bk

Kool Stop Thinline dual-compounds come with the black material up front on the pads, so they impact first on the rim. With initial toe-in, I've had no sonic disturbances. But I have kept the Avid pads that came with my set of Avid SD 7's. They look like nice pads. Softer though.