I’ve tried everything. Anyone KNOW of a sure fire way to remove the thick, aged undercoating?
Why would you want to do this?
If you’re alluding to rubberized undercoating, you’d need a petroleum based solvent and a really, really strong constitution.
If you’re alluding to rustproofing, I’m unsure what if anything would cut it.
Either way, I wouldn’t want to subject all the hoses, brake lines, bushings, sealing beads, bonding agents, paint, etc. etc. to powerful solvents.
You could bead blast it, but you’d have to remove the drive train and suspension to make sure that the sensitive parts mountainbike alluded to are safe.