700r4 question

[77c10]

I recently swapper a 700r4 in my 77 c10. My problemis that my speedometer does not work. I unhooked the cable at the trans and spun it with a drill and my buddy told me the speedo moved. Before I hooked the cable back up I grabbed the end of the driven gear that the cable goes into and I could spin it by hand. This leads me to believe that it is not "meshing" with the gear on the tail shaft of the trans. I spun it several times and tried to push in on it but it would not go in any further.

I am wondering if the driven gear is too large to mesh with the drive gear. Best I remember the drive gear was brown and the driven gear is red.