Try to find the service manual, it's really useful and full of pictures and explanations... (I can't remember where I found it, but there are some links somewhere on this forum)
By the way, sometimes the torquedriver will come loose when you put some grease inside the unit without disassembling it completely. There are some holes that allow grease to flow from the area where the drive shaft is sticking through the unit, to the area where the two halves of the pulley slide across each other.
For this you only have to remove the nut that holds the clutch bell and slide the unit off the drive shaft, the grease goes where the drive shaft came from.. Make sure to use plenty of grease, if all seals are intact it won't come out and won't do any harm but it will find its way through the holes to the torquedriver by centrifugal (centripetal ?) force.
If this doesn't work there is some damage or incompatibility (cheap replacement parts used) that causes friction and you'll have to disassemble and clean the unit entirely to find the culprit... (oh, and make sure all parts are in there, especially the three "guide roller pins", they are very important)
