Speedometer cable trouble!

Can't figure out where to post this, so I'll try here. Last week I pulled the instrument cluster out of my 1973 Dart 4-door to fix all the dead bulbs. That worked well, but for the life of me I can't seem to get the speedo cable to set back in so it works. The needle 'bounces' all over the place, often showing 100mph when I'm doing about 25! I've pulled and reset it many times (and it sets fully into the back of the speedometer). Also makes a slight dinging (bell) sound. Worked fine before I pulled the dash.
Any ideas?
Thanks!