You said it comes off the speedometer so just thread your cable out of the cabling between the front forks, make a diagram of how it's routed prior to taking it out so you'll know how it goes back. Remove the front wheel with the cable attached then take off the threaded spacer that goes between the forks and the drive unit. Now remove the drive/cable assembly and have a close look at it to determine what's holding it on. If it's working, don't break it trying to get the cable off, I'm assuming your just trying to get the front wheel off to fix a flat or put new tires on. You've accomplished that, now just put it back together and let sleeping dogs lay.