The speedo in my 88 f250 quit working all together now.
Before it would bounce up and down but when I pushed in the clutch, brake or gas it would drop down to nothing. I changed the speedo gear out and it worked for a little bit but was still floating a 15mph range. Then it went straight back the what it was doing before and now it doesn't even flicker.

I've changed the gear out that goes in the transfer case.
The cable spins freely and when one end moves the other follows, it's good.
I know the cluster is good, but in my truck only the speedo doesn't work. Tach and everything else are fine. It's something down along the mechanical speedo system. The speedometer moves works properly when the input is spun.

What else is there to check and replace, I'm stumped. Is it possible the worm gear in my t-case is bad? Or whatever spins it? Should I try a new cable and see if that makes a difference? Any help or advice would be greatly appreciated.

 

if you spin the cable end that goes into the transfer case and the gauge moves, that leaves either the gear on the cable end or the gear in the case that is bad.

 

Ok i honestly didn't think of that. I'll try that, and if its in the transfer case would it be easier to buy a rebuild kit or something or just get a new one? It's a BW 13-56 i'm pretty sure. I imagine it's difficult to rebuilt something like that not to mention expensive. Maybe I'll head to my local junk man and see if he has a ford out there with one and i'll just do him a part for part swap.