What I thought was a problem with my 3-speed hub turns out to be the 2 speed changer. The chattering I got before I believe now was coming from the derailleur and not the 3-speed. Funny, enough though changing the gears on the 3 speed hub did rectify it. Perhaps both need attention. Anyway, I can't get the chain to move from the larger sprocket (lower gear) to the smaller sprocket (higher gear). I watched the short video on the Brompton's web site and downloaded their PDF file and will try to adjust it this morning. Has anyone tried this on their own Brompton? Is it easy or is is a chore? At least I can't break anything trying -- I hope, at least, considering I am mechanically challenged . If I can't get it sorted, then I will bring it to the bike shop.