the mileage is moving and display correctly.

 

The display would show up but the mileage stopped. It shifted like a Lenco too.

 

One thing to try is to unplug the ABS module located behind the glove box.

what happened with my truck (95 F150, 4x4, 5.8L, auto) was that my speedo started jumping, it started shifting funny, odometer quit moving and after a few days of that, the speedo died completely.

Unplugged the ABS module and everything works perfectly.

This was after I replaced the ABS sensor in the rear diff, checked all the wiring. I found out through hours of research, that the computer reads the signal from the ABS sensor in the rear, but it passes through the ABS module, if that module goes out, the computer gets a corrupted or no signal, and things don't work.

Try it out, it doesnt cost a dime and might fix it.

 

I Unplugged the ABS module but speedo is still jumping. ABS light now is off.

initially I replaced ABS sensor. I think next step is PSOM to correct speedo.

ABS module unplugged may affect the truck seriously??

 

at the very least, take apart the instrument cluster to get to the PSOM. It is not terribly difficult but just take your time. I can help you through it if needed.

When you get the PSOM out, check for capacitors that have fallen out or ones that are loose on the circuit board.

 

where are the main screws of the instrument panel? ( I don´t want to damage it)

Luis

 

You should have some trim pieces that run horizontal, just below the level of the shifter. Those should pop out and you will see some screws under there. You need to remove those first. If you are unsure of what I am talking about, post a pic and I can point them out to you

 

Won't have rear ABS, not that the rear ABS does a whole lot to begin with.

 

Im sorry to bring up an old thread- but I just bought a 93 f150 and am having issues with my spedo flicking at anything above 45 mph- did we ever nail down a real concrete answer as to a cause?

I cannot be unplugging ABS- Just to risky where I live and this time of year

 

My speedo starts jumping after 60 mph. I attribute it to maybe a defect on the tone ring in my rear end. Hopefully I will be able to check into that after the snow is gone. I don't drive must past 60 anyway.....in my truck that is. There is a lot of information on this forum about this issue.

 

These trucks have rear ABS only, it's not that effective when it does work.

There are multiple causes of your issue, a defective RABS module is common.

 

I had figured I would try replacing the speed sensor first, and your right, there is a LOT of information, different ideas and opinions, which is why its confusing and I have to ask where to start, but like I said I think speed sensor is first.

 

Replacing the VSS rarely fixes the problem on these trucks. It's worth pulling it and inspecting for signs of metal chunks/shavings, but I would not replace it just yet.