Speedometer suddenly inaccurate

I had the same problem with my '94 Explorer. It turned out to be a bad speedometer, and I replaced it with one from a junk yard. (I wasted a lot of time lubing the speedo cable etc before deciding it had to be the speedo itself. The key is the HIGHER than normal speedo reading.)

I took the bad one apart and figured out what caused it. The '94 and earlier speedos are driven mechanically by a cable. The cable spins a magnet in the speedo. The needle is attached to a metal cup that fits over the magnet. To keep the cup centered over the magnet there is a bushing in the center of the magnet assy, and a mating pin on the speedo needle assy.

When the bushing wears, the metal cup attached to the speedo needle can flop around. If the magnet rubs against the cup, it causes the speedo to indicate a HIGHER speed than actual. In my case, the needle tended to swing wildly too as it randomly touched the magnet more or less. Like yours, it only happened at higher speeds, 55 mph and up in my case.

If you get a replacement from a junk yard as I did ($17 at pick and pull) check the side play on the needle and compare it with yours. The new one should have very little side play compared with the bad one. This is a common problem, so you might see it on other vehicles with high mileage.

I got a speedo from an old Bronco, a 94 or earlier Ranger should also work if you can't find a donor Explorer.

If you have a 95 or later Explorer, none of this applies. Those have electronic speedos that work like tachometers- they use the pulses from the VSS (vehicle speed sensor) to calculate the speed instead of a mechanical cable.

-Paul

Thanks for the great info. I'll look into a replacement speedometer.

It's also possible it is just the cable needing grease. You might want to try that first before you take the whole dash apart to replace the head.

Thanks a lot Paul, what you describe is exactly how my speedo is acting. I'm shopping for a replacement on the internet, best price I've gotten so far is $50. It looks like a real job to get to the speedometer, any tips or tricks in removing and replacing it? Thanks again, I'll post results after I replace it.

You're right, I'll try lubing the cable first. Disconnect it at the transmission and shoot some grease into it?

I don't think you can do it that way. If you are really lucky and nimble you might be able to get your hand back up there and unclip the housing from behind the cluster and pull it down so you can pull the cable out to clean and relube it. It's been a long time since I had to play with mine but it seems like I had to pop the front off the dash (take out the two screws at the ashtray) and unbolt the cluster but not completely remove it in order to see and get to the speedo cable. It's been a long time.....