wonderful speedometer

[dieselhotrodder]

my speedometer never works.. i put a new speedometer and a new drive gear and sensor and all that in it.. it still never works.. once in a blue moon it will jump up aorund the right speed and fluxuate 10mph over or under.. its a pain. when it does work its olny for a brief second.. any ideas!!!?? id driving me MAD

[gear jammer 91"]

Mine was bad because of a short in the factory plug at the vss. Your issue sounds like it might be something else, but it could be worth checking.
I've also heard that the drive gear in the tail housing of the transfere case, or trans if it's a 2wd can come loose and cause erratic speedometer reading's. I did see that you replaced it.
The gear reduction unit that screws onto the tranny could also be bad, either internally, or the little square drive shaft that slides into the tranny and connects it to gear reduction unit could be rounded off.

[Ace]

Mine was bad because of a short in the factory plug at the vss.

This is why it's always a good idea to reinforce and stress-relieve connections to the driveline -electrical, hydraulic, fluid, pneumatic, whatever. Vibration will deteriorate and eventually ruin small connectors of all types, especially in this type of vehicle.