I have a 97 F350 P/u. For about two years(don't drive it much) the odometer would randomly go blank and it would start shifting hard and at odd times. The overdrive light on the shift lever would flash off on the shift lever. It seems to be getting worse also. Have had Rear sending unit(think thats what it is called) check, but no fix. Numerous mechanics have looked at it, but could not diagnose the problem. It only happens sometimes, and never happens when i bring it to them. any help would be appreciated! thanks

 

My money is on the PSOM (programmable speedometer/odometer module) that is in your instrument cluster. They can be repaired, but it's way cheaper to buy a used cluster at a wreckers. If you don't have tach in your factory cluster, try to find one with a tach (plugs right in and works fine). Just make sure to buy a cluster from another 97 as there were small differences in the cluster wiring from year to year.
Oh, and WELCOME to fte! If you scroll down the forums list, you will find a lot more forums with info more specific to your truck that will be very helpful to you.
Forgot to add- the only caveat to swapping the PSOM is your truck will now show however many miles the donor rig had as the mileage is stored in the PSOM. You can find clusters for around $40, I paid more for the one in my old 95 ($125) because the mileage was within 10 miles of what my truck had.

 

This is a common symptom of the VSS sensor going bad in the rear differential.

I'd just replace the sensor, since you said it was "checked" - which doesn't mean much. And it's not too expensive ($30? or so?)

 

Before you go ordering parts, try a few things first.
1. Pull the VSS out of the rear end (1 10mm bolt right on top of the diff). Look it over and make sure there are no large chunks of metal on it- fuzz is normal, large chunks aren't. Total cost = free.
2. If there are no large chunks on the VSS, reinstall it and start the truck. Now start jiggling the wire harness that runs to the back of the truck in as many places as you can reach it (have someone in the cab to tell you if the odo acts up). If it does you've got a bad spot in the wiring. Again, no cost.
3. If you did find large chunks of metal on the VSS, it's time open up the rear diff. There is a part in there called a tone ring or exciter ring- its behind the ring gear I believe and it's what the VSS picks a signal up off of. It should have evenly spaced teeth all the way around it. If all looks okay, seal up your diff cover and top off with fresh fluid (if you haven't changed it in a while you're probably due anyways).
4. If none of that solves the problem then you are back to the PSOM. krewat brings up a good question though- did they check or replace the VSS? There is really no way to check one without swapping in a new one. VSS is around $30 but I still put my $ on the PSOM because of the odo going out on you.

 

Yeah, very true - is this the ODOMETER or SPEEDOMETER?

 

I would check all the grounds and batt cabels/ everytime I do stuff that makes me unhook the batt it will reset the odo/cluster sweep sooo I am thinking complete curcits

 

Odo or speedo, doesn't much matter as both are part of the PSOM.

 

Yes it does matter, if it's the speedo that's going nuts, that points at the VSS as a possibility. If it's the odometer, that's the cluster.