I just did this procedure on my 06 iron as I just installed a new chain...What I found is to be sure you check that the bronze spacers (aka: distance collars) are put on correctly..One side is larger than the other (just a large looking washer)...The other thing was that the 30 mm Thin nut that goes on first tightens the hub assembly and the outer castle nut with split pin pulls/tightens the rear long spindle (essentially securing the rear chain/hub/brake to the rear frame assembly..For what its worth, it seems to be that one nut in unison with the rear hub spindle that secures the tire and associated hardware to the rear frame..The split pin prevents the castle nut from backing off and falling off (not a good thing to happen)...As a matter of fact I have to readjust the chain as it's a bit too tight. One notch down should do the trick as sitting on the bike only makes it tighter (u might want someone close to your weight to sit on the bike as you verify your chain adjustment)...GM