Speedos gone whacky

OK uys my speedo has gone crazy, it flips back and forth from high to low whilst driving. Can anyone tell me what's wrong?

91 cherokee 5speed 4.0

Is the speedo needle "wiggling"? Or does it jump widely? If you have the cable speedo and I think you do, than the cable could kincked (one of the many problems with my old S10), unlubricated or the connection on the speedo loose. It could also be the gear connection with the cable itself. I guess it could also be stripped/sticking gears internal to the speedo.

I had this problem on my '94 Chev P/U - ended up being a short in the steering column (more specifically the blinker switch) that was somehow grounding back to the speedo. Toward the end before I fixed it, when I would suse the signal, the ignition would cut out and bounce the speedo needle!

if its one of the newer jeep, i had a similar prob and it turned out to be one of the harnesses on the back were loose.

pete

I know it's electronic, I have one of those speed sensors. So it can't be a cable binding problem.

As for the motion I'd say that that it's kind of a gentle lowereing of the needle. It never goes higher than the speed at which I'm going, but goes 10-20 mph lower then comes back up. this normally only happens around highway speeds.

ALSO, if I'm driving with my cruise control on it will sometimes slightly dip andn kick the cruise off, so do you think it could be a vacuum issue?

any input is usefull thanks

I had the exact symptoms a month ago.

I removed the speedo sensor/gear assembly to find the o-ring had disintegrated leaving pieces littering the sealing surface. It was not allowing the speedo pinion gear to fully engage the mating gear on the t-case output shaft.

Bought a new o-ring from the dealer (~$5) and all is well.

HTH