I have an 89 250 4wd with a 5 speed manual. The speedometer doesn't work. I found that the speed sensor gear housing was broken, so I bought a new one. The speedo jumped a time of two and that was it. So now I have a few questions.




The first picture is a few speed sensors and gears.
The left is a sensor and 18 tooth gear from an AOD. This sensor had a little yellow plug where the cable would normally go. Why was it there?
The middle is just a regular cable end with a 18 tooth gear from an AOD.
The right is my replacement sensor with the original 19 tooth gear that was in my truck.
The bottom picture is a comparison between the unworn teeth of a gear and the worn teeth from my truck.
Would this wear cause my speedo to not work?
Why can't the gears between an automatic and a manual be interchanged...other than the number of teeth. The sensor with the 18 tooth AOD gear will physically fit in my truck, but I didn't drive with it in there.
My cable turns freely and so does the gear/sensor assembly. However, when the cable is pushed into the gear and it clicks in there, everything is tight and there is some stiff resistance. What's going on there?

 

Bump to the top to try and get some help.

 

the worn teeth on the bottom gear will most likely not spin the speedo, or make it skip. the top gear is different. the alignment dowel is way to long.
i have extra 17,18, and 19 tooth short pin gears. if you want one, let me know the gear count, and i will send it to you for postage price.

 

Thanks for the offer. I just got back from the parts dealer and I may have one here in the morning. I'll report back on my progress.
The gear with the long alignment dowel will physically fit into my transfer case. I haven't tried to drive it that way, but I may give it a shot for the sake of experimentation.



I did get some info from the Ford service tech today.
Earlier I asked/described the sensor on the left side. It had a factory installed plug over the cable hole. I took it out and everything looked ready for a cable. So how did the speedo work with the hole plugged? This is the scenario...
The middle gear/cable was how speedometers worked. the gear turned the cable that turned the speedo.
Later came the assembly to the right. The gear turned the cable that turned the speedo, while an electrical connector told the computer at what speed the vehicle traveled.
Then a rear differential sensor was added to control ABS.
Then there was a time when the cable was no longer needed sensor/gear assembly got a plug to cover the cable port. The speed sensor alone told the computer the speed traveled AND provided the signal to an electrically operated speedometer.
Finally, the speed sensor/speedo cable assembly was done away with and the rear differential sensor provided all the signal to the computer, speedometer, and ABS system.

 

i think you got it rite. once upon a time, we had cable only.
then we got cable and VSS in the tailshaft, then cable in tailshaft and VSS in rear diff, then VSS in place of the cable still in the tailshaft.
finally they went to VSS in rear diff only.

it is SLIGHTLY confusing.

 

Well, the wrong gear came in today. Not tan with 19 teeth. Red with 21 teeth. Probably packaged wrong. Hopefully the right one will be in soon.

 

The two speedometer cables with the 2 pin electrical plug are
used for vehicles with cruise control.

 

Hmmm. My truck has cruise control? I'll have to check that out. I've never really paid attention.

 

Reviving an old thread to update and possibly help someone else.

I finally got my speedo working in my 89. It turns out that over the years the cable "grew" in length and made for a tight fit when all assembled and installed. My speedo gear/speen sensor assembly would turn freely on the bench as would the speedo cable/speedometer. Stick it together and the gear would turn, but there was a lot of resistance. Drive it down the road and the speedo needle would jump and sometimes stop working entirely. I ended up taking a 4.5" angle grinder and grinding away a little from the end of the cable. I kept testing/checking until everything turned smoothly and freely. In all, I guess i removed about .250" from the cable end. My speedometer is smooth and stable now.