My 94 f 250 has a problem.The speedometer will go from 20 mph then up to 50 then down to zero then back up to 20 mph when im going 20mph.its been doing this for a few weeks.It does this everyday when im going the same speed the speedometer will jump all over the place like im speeding up and down but im staying at the same speed.what is it thats making it does this? would it be the speedometer cable or the speedometer itself?or something else?any info will help thanks.

 

Your speedometer is not cable driven, it is electronic. Does the transmission shift abnormally or "hunt" for a gear when this happens? The most typical cause of your issue is the VSS sensor on top of the rear axle.

It is always advisable to check for any stored codes before swapping in parts.