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I am having an issue with my speedometer. The needle bounces around and doesn't show me my driving speed. It starts bouncing all over the speed range from the moment I start moving and doesn't ever really settle down.
I have already tried replacing the speedo gear. Tried different teeth gears as well. I also installed a new cable. Still the same issue. Anyone else experience this. Is it that the speedometer is just bad?
There is an outside chance that the speedo cable is binding up and then releasing. If so, some cable lubricant might help. Otherwise, it will likely be the speedometer head is faulty.
Here's one test. My drill didn't really have enough torque to hold the speedometer steady, but it's a decent way to test for certain things.
Ian, if you determine that your speedo head is bad, and you are wanting to rebuild the one you have, Palo Alto Speedometer in . . . . Palo Alto Ca. does excellent work, though it may cost you your left nut. I say that because I noticed you too are in Cali. There are equally good places out of state for less money, someone will chime in shortly.
Didn't consider a rebuild of it. Not a bad idea. Palo Alto is 7 hour drive from here but I can always ship it in.
Gonna take out the speedometer today at lunch time see what I can figure out.
So I pulled the dash down and lubed up the gearing area of the speedometer. I connected the old cable to it and attached the drill to the other end and the speedometer seems to moving up correctly and hold if I keep the speed even. I put everything back but no change when i drive the needle bounces all over the place.
Pull the cable out of the jacket, apply a thin layer of grease. Re-insert. Greasing speedometer cables has been something I have done for over 40 years. Fairly common cause of needle bounce in the older vehicles.
Things being what they are today - are you convinced you’ve got the correct speedo cable? Or, that it is not defective ( made in China)?
I always accept paying a premium for Genuine Ford, over cheap questionable re-pops, if they can be found. Even if it does have the formerly reputable Dennis Carpenter name attached.
Not your year truck 81 F100.
Little back story when I got the truck on the road back in Nov 2019 the speedo did not work, found the drive gear on the out put shaft stripped.
When I replaced it I also replaced the driven gear and it worked and was on the money based on my GPS and mile markers and good for 4000+ miles.
Forward to last weekend when I swapped out the BW T18 for a NP435 and added an Advance Adaptor over drive unit.
Because the trans is moved back 7.5 inches the speedo cable was stretched to fit in the trans.
On a test drive the needle bounced where it did not before being stretched and of unknown drive gear. I found this drive gear was worn a little more than I liked.
I was able to get a longer cable, reusing the driven gear on it and I swapped the drive gears on the trans.
The speedo now works as it did before the trans swap & OD unit.
So I would say make sure the cable is not making any sharp bends, I lubed the new cable with Redline MT-90 gear oil I poured down the cable before I installed it and that the drive gear on the trans is in good shape.
I don't know if it was the cable or the drive gear that fixed it but it is working like the factory had it.
Good luck
Dave ----
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