canklecat

Last time my can't-deliver brakes squealed was after I degreased the rims. Drove me and everyone else nuts during a group ride. So during a break I blasted down a nearby steep hill, slamming on the brakes until the squealing stopped.

In that case, dirtying stuff up helped.

Also, Kool Stop Eagle 2 brakes are the easiest I've found to adjust for can't deliver brakes. The design automagically puts 'em in the optimal toe-in position. Just mash 'em flat against the rims, align visually, crank down the bolts, done. Good pads, nothing magical about the salmon vs black pads that I've found. But a good design for easy adjustment on cantis.

Mike120a

I have done this along with sanding the brake pads. It helps

Jonathan Hanson 

Thanks for those ideas. I'll look for the Eagle 2 pads.

Jonathan Hanson 

Update: I swapped my front brake to the rear and rear brake to the front, installed new pads on the front. Squealing is 95 percent gone. So I suspect the old front brake had some sort of wear in the pivot that caused the squealing. Oddly it's not squealing in the rear position, so it's still a bit of a mystery.

2manybikes

It's typical that the back brake does not squeal. The force from the back wheel is shoving the brake arms onto the mounting posts. It takes up a little slack and makes the joint held down better. Harder for them to squeal when they are pushed together tightly.
The front does the opposite, it tries to pull the brake arm off the posts and increases the ability of the arms and pads to move and vibrate a little to make the squealing sound. New brake arms added to the existing posts can have a slightly tighter fit onto the posts. This is why new brakes can often stop the squeal.
Not always, it depends on the fit of the new arms and how worn the posts are. There are other causes of squeal, but this is often why the back does not squeal and the front does. Rim condition , age of pads (they dry out over the years) and toe in of the pads are often the reason. Sometimes by sanding of the surface of the old pads can expose better softer pad material.

Jonathan Hanson 

Thanks for that; it makes sense.

SJM205

My rear brake began squealing so badly it actually hurt my ears. However, it would scare small animals out of the way, and even whales.

Rode it to my LBS and they sanded the pads for me in minutes, no charge. I did manage to fall in love with a new pair of shoes, so it will cost me later...

MarcoBianchi

V brake booster, AKA "gorillas", woeked for my Focus Mares.
Something like this, there are tons in the market.
Brand-X Thermoplastic V-Brake Booster | Chain Reaction Cycles