I think brake squeal is caused by oil & grease residue. My shade tree method: Flip bike upside down on seat & handlebars. Get cotton balls & rubbing alcohol. Soak cotton ball, apply to rim, rotate rim, continue until no more dark residue appears on cotton ball. Soak a corner of shop rag with alcohol. Squeeze rag between rim & brake pad. Pull rag back & forth across brake pad. Wait till everything dries up. Get some 200 grit sandpaper. Apply to rim, rotate rim, continue until rim has shiny new appearance. Sandpaper the brake pads. Good to go - no more squeal until the rim gets oil on it again.