I've changed the place of two ring gears and problem solved:). Before changing the diff gears diff was not only nothcy it stucks on some positions when I turn it by hand.Now it's still nothcy but don't stuck. Thanks for your interest and help. I'll try mugen gears maybe on next rebuild and let you know mike. I'm now tired of fasten and loosen the screws and don't want to open it again:)