I have a 1988 F250 4x4 and the spedometer doesnt work.
I have removed the sending unit on the transfer case tail piece and changed the gear several times with different gearing.
The speedometer will show erratic movement but not accurate. The cable seems to be intact and I can spin it with a drill and the speedo on the dash shows a normal reading.
I'm starting to think that the gear on the output shaft might be damaged or broken.
Anybody have any ideas?