Ok there is a rubber bump stop in the dust tube, it’s just like a thick rubber tube. It’s possible it’s dislodged or deformed. Sorry but the fix is to strip it down again and try the dust tube on its own without the spring over the top of the kingpin and make sure that the top of the pin will go all the way up to the top of the dust tube if it doesn’t you need to push out the rubber bump stop turn it over and re-insert so you have a fresh side where the pin engaged and put a ring of grease around the top of the kingpin to lubricate its passage through the bump stop. That should sort it.
BR
Colin
