Speedometer problems--electrical????

[Woodturner Nate]

My '96 powerstroke is having ISSUES. First off, the E4OD transmission was just rebuilt after deciding it didn't want to go forward. Apparently some gear cylinder had a hairline crack. The garage I was dealing with removed the transmission, then it went to a specialty rebuild center, then the garage put it back in. They didn't do the tranny work, in other words.

Anyway, as I'm picking up the car, I drive it down the road and immediately notice that the speedometer is freaking out--it is jiggling back and forth, in about a 20mph range, with the bottom-middle range being about where the actual speed probably is. I promptly turned around and went back to the garage. I figured the speedometer cable was loose, and found out that it isn't a cable, but a sensor on the rear differential. They said they didn't have a sensor in stock, but that it should solve the problem, and wasn't related to the transmission work. I bought that, sounded plausible to me.

I headed home from the shop, as I didn't have the option of leaving it there-I needed the truck! I just was careful with my speed and went pretty slow. I realized that the tranny was having issues keeping itself in 3rd/4th/overdrive in between 35-45mph. The VSS (variable speed sensor) problem really made sense to me, and sounded like it was the issue, as it seems that it controls the OD function of the tranny??? (I've read that somewhere here on this site). At some point the next day, as I have to get a load of firewood or risk being cold this winter, I realized that when I pushed the trip odometer button, the problem seemed to instantly vanish. The transmission shifted fine, stayed in the right gear, speedometer was smooth. Then, a couple days later, same deal. Dancing speedometer. Same fix, except that the next time it happened, the third or fourth time, the odometer button didn't seem to fix it.


I bought a new VSS and installed it; no change in the problem. I also dismantled the dash and checked that the connections were all tight as best as I am able to check-nothing is loose or obviously disconnected. I had changed some light bulbs a while back and thought that I might have loosened something, but everything appears normal. The guy at the shop where I got the part said their shop truck, a GMC, does the same thing, and it has a motorized speedometer, not unlike the Powerstroke Ford. It is clear to see when you have the dash apart and look at the circuit board.

So now I'm confused about what I do now?? Will replacing the whole gauge cluster reset my odometer ?? Not doing anything isn't an option, due to the tranny shifting funny when the speedometer is between 35-45mph. What kind of electrical problem am I missing???

[JSchuricht]

The VSS sends a pulse as the teeth of the tone ring in the rear diff pass it. The signal goes to the PSOM and the RABS unit. It sounds like your PSOM has gone bad which is not uncommon. The PSOM or programable speedometer odometer is the center section of your cluster and the mileage is stored in it so when you replace it you will see the mileage of the new unit. On the plus side you can get one from just about any similar vehicle gass or diesel 150-350 and bronco. Your transmission relies on the output of the PSOM to operate properly, try not to drive it much, your transmission will go into limp mode and shift harsh or possibly break something.

[Woodturner Nate]

Yeah, its been shifting hard for certain. So, basically, if I disassemble the cluster itself I can replace just the speedometer odometer? I'll have to look at it again; I couldn't figure out how to remove the front and back plate from the dash cluster when I had it completely out of the truck.

[JSchuricht]

It's been a while but from what I remember you pull the cluster, remove the clear plastic on the front then just pull the gauge forward. It had around 4 tabs and a cable.

[Ford_Iowa_Boy_7.3]

I've been havin a similar problem as you described and was wondering what ended up fixin it. I also recently had a rebuilt transmission installed. Thanks!

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[Woodturner Nate]

I ended up having to replace the cluster with a used part. It has a different mileage than my truck did. I just lose the honor of looking like I have nearly 400K on it. The used cluster had about 80K less miles.

[Ford_Iowa_Boy_7.3]

How tricky is that and what year and model truck dashes can I use to replace it?

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[JSchuricht]

The PSOM is really easy to swap. You can use one from a 150-350 or Bronco. I don't know the year that that style started but 94-97 would be a safe bet for a donor, the older stuff was mechanical and looked vary different.

[Ford_Iowa_Boy_7.3]

Thank you sir

sent from my s3 while listenin to the sound of my turbo whistle

[madpogue]

'92-'96, or '97 F250-F350.