I have a 2011 Surly LHT with Tektro Oryx #992 Cantilever brakes. Bike has around 800 miles on it. Brakes have been fine until today. After I gave it a bath and washed the rims, the front brake developed a really bad squeal. I know you need some toe-in to keep them from squealing, but I didn't change anything and never had a problem until today when I washed the bike. Any idea what I have changed that has caused this problem and how I might correct it?
too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
The mistake you made is to clean residue off the rim and pad surface. Now there's more friction, which means higher forward/twisting force on the shoes compared to the squeezing force applied by the brake. The change in the ratio causes the squeal. On the bright side you're enjoying better braking, but don't worry, the squeal will go away soon as the residue builds back up and the braking degrades back to what you're used to.
Release the brakes and scrub the brake pads clean, then rinse the rims thoroughly, then wipe them down with alcohol.
If they still squeal, wet the rims and dust them with Comet or Bon Ami or similar mild cleanser. Go for a short ride, applying the brakes lightly while pedaling or coasting down a hill. Clean everything again and see if that helps.