I am trying to replace an axle on one of the rear wheels on my Sport. The new axle has a small pin which sticks up from the main axle and looks as though it is meant to lock onto something. I can't see anything obvious though. P&T didn't send me any instructions. Any ideas on how I fit it? I've had a look at the video P&T have put online on changing an axle and am still none the wiser.