For now it was stuck open diaphragm the reason to disasseble the lens.
Well, the ring that holds aperture group was just unable to move either way. Aluminium ring just smashing around the helicoid border. And the helicoid seems to be damaged now. I can't assemble it as it was. Aperture blades unstucked by the way, may be becouse of WD40 I droped in the blades pins holes? So there's some oil on blades now ((( Now my DA40 unrepairable, I think.