either the speedo is damaged or the plastic stem inside the cable is broken inside.Pull off both end and turn it by hand or with a drill and see if the other end turns.
I have the same problem, Did you get yours fixed p0prcksandc0ke?
I have a new cable, new gear. When I am driving with spedo end of cable hanging out it clearly spins fine.
Is it common for the speedometer innards to get stripped out or something?
Also when in reverse and on it alittle the speedo will fluctuate up to about 40 mph then right back down, I think I got it narrowed down to being the speedometer cluster but I was just curious if this was a common problem.