1992 ford f350 351 windsor, zf 5speed. Reg cab, long bed, 4x4. Speedometer doesn't work and cuts out at 3500rpm.
Speedometer
For a while the speedometer in the truck had bounced when driving over bumps, railroad tracks ect. The truck was an auto and when the speed would jump, the trans would see 0mph and downshift. The truck was swapped to 5 speed for more fun to drive (worth it). The speedo only bounced downward. And during smooth driving was fine and cruise control worked. The speedo worked the same after the swap as before, until recently the speedo has quit working all together except for at random times it would work 100%, then the next time the truck is driven, nothing. Abs light is on. Sensor is new, wiring has been visually inspected and looks fine. Gauages have been removed and visually inspected and look fine. Odometer does not work when speedometer isn't working.
Sputter at 3500
Under hard driving conditions the truck has a tendency to "sputter" at about 3400-3600rpms where (at wot) the truck will accelerate hard until the rpm range is hit and will miss and not tach any higher. Sounds like a backfire. Is there a built in rev limiter if the speedo is at 0 to keep from blowing them up? The sputter started a few weeks ago along with the speedo completely cutting out.
Any help would be greatly appreciated. Thanks, Noah

 

Does the odometer go blank when you say "Odometer does not work when speedometer isn't working"?

If no then you have either bad wiring to the rear end or a bad rear end.

If yes then you have a power or ground problem at the dash.

 

Yes, it displays the current mileage of the truck. But does not increase due to truck only seeing 0mph. Where is the ground/gounds located within the dash? I looked through it the other day and could not find one from the top
Also if it was a "bad" rear end, how could I tell. From peeking in the home from the top of he diff the speed ring looks fine, teeth are a little round but all there with no metal shavings in fluid. What is the path of the wires? I've traced them to the computer but that's as far as I've gotten. Do they run from DSS to computer to rabs module then the dash or what? Thanks for the reply BTW

 

The path of the speed sensor wires, sometimes called the VSS in later trucks:


1995 wiring diagram below, your in 1992 is close to the same.


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Awesome! Tracked down the break with a voltage meter, fixed it, and she works 100% thank you much sir! And have a happy holidays