The speedometer in my '93 F-250 starts jumping around erratically starting at about 40 mph. Anything less than 40 and it’s stable, but beyond that it starts flickering back and forth about 15 mph in either direction of “actual” speed. I’ve swapped out the VSS on the 10.25 but it still jumps. I checked all the chassis wiring, cleaned the plug at the VSS, but to no avail. I haven’t pulled the gauge cluster yet because everything works on it, even the speedo less than 40 mph, so I’m miffed. Anyone have this issue? Any solutions? It really sucks not to be able to use cruise control on long trips…

Also, I haven't pulled the cover on the rear recently, but when I swapped on the finned aluminum cover about a year or so ago, the tone ring looked perfect. The rear is a limited slip though, so could the additive or possibly clutch shavings be throwing it off at higher speed?

Any help would be greatly appreciated!

 

PSOM is bad, mine is the same way at anything above 70... They can be rebuilt BUT must be sent in to an authorized shop to do so.