If the odometer works, it's not the sensor.

 

Exactly

 

UPDATE. I know nobody probably cares anymore but I'm getting worse about not following through with my threads! Picked up a whole new cluster from the junkyard with cracked glass for $45 and a new cluster visor for $30. Took about an hour and a half to take the whole dash apart and swap in new parts because I'm kind of a slow worker. Just took the face from my old speedo and replaced the cracked face on the funtioning speedo and VOILA! Good as new.

 

I Recently had a similar scenario, where the po had replaced the TC with a gear driven unit out of who knows what that used a mechanical speed sensor. I ended up getting the marlin crawler mechanical> electric adapter and plugged it in. Cruise control started working, odo started working, Speedo was slow by 10-15 mph all the time. Long story short, ended up having to replace the cluster with one i found through CL locally, and now, everything but the trip odo works. I'll consider it mostly a victory though.

 

And somehow my speedo is spot on even with 33's! Plus every single gauge works except when I turn the key one notch a light comes on that says A/T Overdrive or something like that but im not complaining for $45!

 

I have a very similar problem, my speedo won't work for the first few minutes, but the odometer works. When hitting the left signal the speedo drops to zero then picks right back up. I'll look for a replacement speedo, thanks for the follow up.
Scott