Speedometer questions

I would pull the speedometer pinion gear out of the transmission and make sure the teeth on it are good before doing anything. If they are not clocked correctly for the tooth count it will either chew them up or not make contact with the drive gear in the transmission. While you are under there you may as well look for a tag on the rear end as to the gear ratio so if you need a new pinion for the trans you'll have a start point for the tooth count needed. If no tag you can spin a tire while counting number of turns on the driveshaft. It will get you close.