1984 F250 Speedometer issues

[84FS460]

My 84 F250 4x4 speedometer wasn't working when I got it, so I checked the speedometer and its fine. Then I checked the cable and appears fine along with the gear. I hooked the cable to the speedometer while its out of the pickup spun the cable and it shows to be working fine, then I installed the cable back into the pickup and the speedometer doesn't work. OK I then disconnect the speedometer and left the cable connected to the pickup and the cable spins so I know the gear is fine and working the back of the transfer case. I am baffled on why the speedometer and its related parts are fine but are not working when put together.  

[Gary Lewis]

I wonder if the drive gear, the one on the transmission or transfer case (you don't have a signature so I don't know if your truck is 2wd or 4wd) is stripped.  If so it might spin the cable when there's no speedo attached, but the drag of the speedo might cause it to slip.

Pull the cable from the transmission or t-case and check the driven gear.  And peer into the transmission/t-case and check the condition of the drive gear.

[ArdWrknTrk]

His first sentence says "'84 F250 4X4"
So it's pretty obvious the drive gear is in the transfer case, on the output shaft.

If the cable was out, in order to be spun by a drill, one would expect the driven gear got a look.

Maybe the TC has been apart and someone forgot to stick the locating ball in there with grease when replacing the drive gear?
There might be enough drag to turn the cable, but not enough to turn the speedo?

[Gary Lewis]

I missed that, Jim.  Glad you caught it.

On the BW1345 there wasn't a locating ball I could find.  The output yoke captured the drive gear between itself and the bearing's inner race, forcing it to turn.  So perhaps the nut on the output yoke is loose?

[85lebaront2]

Possible stripped gear, again enough to spin the cable, but not the speedometer, internal hole in the plastic driven gear worn, again to the point it will spin the cable but not the speedometer. Can also, if the cable has been replaced, the plastic tip on the universal cable rounded so it won't drive the speedometer, or it is cut too short and not engaging.

Cable housing not fully snapped in place on the speedometer (don't ask).