For the second time I took apart the 2 speed hub. The first time it worked again for half an hour then went wrong again. I think the 2 locknuts on the left are critcal and they came loose again. This time I sat down and had a good look at it to discover exactly how it works. It is very simple: The right hand side is the drive side and the turns the left side through a 1.38:1 planetary gear so the left side turns faster than the right at all times. But the left side also has a retractable freewheel clutch operated by a sequential cam when you back pedal. When the left side freewheel pawls are sticking out they engage the inside of the hub and drive it at the higher speed. When they are retracted there is a freewheel clutch on the right that engages the hub and drives it directly. When the high ratio is selected these freewheel pawls on the right make the familiar steady click as the hub passes over them due to its now faster rotation. Simple and brilliant - when it is set up right.