Squealing sidepull brake
 

I recently installed a new pair of these Kool stop pads and they make a loud honking squeal every time I squeeze the brake.
What is the magic trick to get them properly adjusted? Any advice appreciated, thanks!
https://cimg7.ibsrv.net/gimg/bikefor...73417d24c.jpeg
https://cimg9.ibsrv.net/gimg/bikefor...8d938a08b.jpeg
https://cimg0.ibsrv.net/gimg/bikefor...2c4528479.jpeg
https://cimg1.ibsrv.net/gimg/bikefor...e0dd0d320.jpeg
1981 Redline cruiser, custom built wheels w/ Phil Wood hubs

Squeal is due to a part vibrating.
With brakes this is common; the pad sticks, the arm twists[1], the pad slips, the arm untwists, repeat three thousand times a second.
When the frequency is a good match for the arms' resonant frequency you get squeal.

Change either the stick-slip nature ("new pads"[2]) or the resonant frequency (adjust pivot clearances) and the squeal may change enough to disappear[3].

[1] or moves on the pivot, or some other small motion happens
[2] what you just did
[3] or appear

Absolutely! And proper toe-in, meaning the forward end of each pad touches the rim first, is more often than not the cause of squeal.

You can use an adjustable wrench to twist the arm a few degrees to toe in the pads.

https://www.sheldonbrown.com/rim-brakes.html

Not all calipers will tolerate a twist. Universals are one, cant speak to the OP's caliper.

Also, if the caliper is not stiff, all the toe in in the world won't help much. Again, can't speak to the OP's caliper, but flimsy is flimsy.

I've twisted calipers like that. I know about the Universal ones. I also would not try a Campagnolo arm.

When I first installed a set of Kool Stop Continentals, they squealed. But after a little riding the pads seemed to settle in and the squealing was gone. All the advise above is correct and good. I would add two things. 1. BMX brakes have a long reach and that doesn't help when you have grippy pads, 2. You could also try sanding your pads to get that molded outer surface scuffed up. I don't know for sure if scuffing the pad is the key, but it is worth a try.

Oh, one more thing. A free number 3. This is just my opinion. BMX bikes like your Redline above were more inclined toward racing and BMX racers used the the brakes carefully when maneuvering on the track, that was only for slowing slightly, So, the brakes on these bikes were never that great. Or said another way, great BMX track brakes would have been geared more toward modulation rather than stopping power. Again, just my opinion. So those long arm brake calipers coupled with less grippy pads would be ideal for the track.

Number 4. Get the pivot adjustment so that if the tension nut is as tight as it can be with the arms still being able to return to their ready position. If this nut allows any play, because of the long arm, you may get squeal. And be sure that the jam nut and mounting nuts are "German Torque". Good-n-tite.

I'm sure that the rim, since it is custom build, is aluminum. But it looks shiny, is there a bright plating on the rim? Or is it just new and shiny aluminum?

I am hoping just braking them in and some of the other tips will get the squeal out. Unless you are racing it is preferable to have a bike that stops rather than slows.

Nice bike @biketiger . I always liked Redlines.

I'd try switching to Kool Stop's black pads. The salmon ones are best for wet weather

Interesting to know! I noticed that when the pads were moist from rain, they were silent.

Just be careful bending caliper arms as some manufacturers us very brittle aluminum alloys that were stiff but would crack suddenly, instead of bending....

Another cause for the noise is the rims which look to be polished or chromed slick none faced rim's can tend to be noisy with nearly any caliper pads. One thing you can do is wash the rims real good with hot water to make sure there is no cleaning stuff or wax on the rims which can add to the noise.

Water is not a bad lubricant sometimes - poor film strength and temperature range, but if flooded good enough to cut the peaks of the stick-slip cycle - less stress on the arms, less chance of hitting the resonance hard enough.

Toe in the shoes as suggested by noglider in post 5. Don't worry about breaking the arm.

I've had much better luck with the Sunlite branded pads that say "for steel or alloy" on the pad holder. Once your adjustment is set up, if it still squeals, I'd go to a different pad. I could never quiet down the regular Kool Stops I've tried with chromed steel rims.

Edit - The one Kool Stop pad I've had that worked was the black "John Bull" replacement pad. The rubber on that seemed better suited to steel.

Got it! That's the ticket post #5 - thanks Noglider! I never would have thought you have to take wrench to the caliper arm and bend inward. I removed the pads, got the mouth of a big crescent wrench in position where the pads would go and squeezed. Hard. The caliper tab seemed to just barely move in.
I re-installed the pads and took it for a test ride.
Silent. Absolutely silent.

Glad to hear it worked. I wonder why there aren't videos on the technique. My way is to use a 6" wrench and twist the arm with the pads still on. That way, I can see my progress as soon as I let go.

Actually, I do know why. New style calipers are not made for twisting, and it's not necessary because of the spherical washers that come with brake pads. But your style brake is old, hence the advice I gave (and worked).

Another interesting observation. I did watch a couple of videos and neither said anything about bending the calipers. The Park tool video (which are normally great) did not even mention how to make any adjustment for noise/chatter.
I did attempt a stop from a faster speed and got some squeal but still a huge improvement over the howl it used to make. Also, for reasons I don't know why, it would make noise every forth or fifth brake pull. This happened over and over again like it would squeal on multiples of five or so! Maddening.

After some experimentation I've got them adjusted so it is mostly silent stopping at various speeds while pulling the brake successive times.
Just as advised, the front half of the pad must engage the rim first while there is a 1-2 mm gap between the rear half of the pad and the rim.
Any more taper, the noise comes back. Full pad even with the rim as originally set up, horrendous noise.
So, thanks to your guys' help, this went from frustration to one of the most satisfying repairs I've done. Now I brake with a grin.

Do you remember Click and Clack, the tappet brothers, also known as Tom and Ray Magliozzi? They had a radio show called Car Talk. Very funny guys, and they cracked each other up. One of their mottos was, "Europeans don't care if their brakes squeal as long as they stop. Americans don't care if their brakes don't stop as long as they don't squeal."

It's deceptively tricky to set up old side-pull calipers on chrome steel rims - dealing with flex, binding calipers, noise, pad types, etc. Often you're making a series of compromises in set up until it is just acceptable. If your brakes work reasonably well and are quiet or mostly quiet, then you're doing well. You fix the "little problems" one at a time until finally, usually, you've fixed the "big problem" by fixing all those little ones.

Car Talk was a great program!
Ray is part of the group recycling some of the old broadcasts into "best of" podcasts, which can be downloaded here.
..or it's probably available via your favorite podcast app.

Steve in Peoria
(RIP Tom Magliozzi)

Biketiger ,
Take it from an old ABA and NBA rider, If you really want to stop the squeal, slip on a pair of these NOS ACS Z-rims! (Pay no attention to the current price for these) They will definitely keep the squeal away. And they will upgrade the bike considerably. Smiles, MH
https://cimg7.ibsrv.net/gimg/bikefor...623bd19d88.jpg
I hoarded these for all the years thinking I might find the right BMX bike for them.
https://cimg9.ibsrv.net/gimg/bikefor...c8ddf507fe.jpg
Original factory paint markings on them.