I recently had the transmission ( E4OD ) rebuilt on my '92. The truck was a recent purchase, I understood it needed work. The tranny guy said the torque converter was shot and he rebuilt it to current specs for that unit.

Before I took it for a rebuild I noticed wild speedometer gyrations above 60 MPH or so. The needle will wobble, and plunge as low as 0 sometimes. Othertimes it's OK. Now that the tranny's rebuilt, I've noticed that the worst gyrations match up with surging at high speeds. It's like it's shifting out of OD when the speedo guage plunges. It also happens if I turn OD off with the button. Before I take it back to the tranny shop I need to suss out the speedo as a possible cause.

So far, I've found out that the speed sensor sends a signal to the Programmable Speedometer/Odometer Module ( PSOM ), which then signals the PCM. The PCM may then signal the transmission to downshift, but I can't verify that. Anybody have any info/experience with this type of problem ?

Thanks in advance......

 

Both the speedo and tranny are controlled by the main computer that gets it's signal from the VSS on the rear diff. It can be unbolted easily and cleaned or replaced.

Adrianspeeder

 

I had a problem with my speedo jumping around and was told that the VSS has a square metal shaft with a plastic gear on it. Sometimes the metal shaft grinds out the square plastic hole in the gear and you get erratic readings on the speedo and sent to the pcm which makes the tranny shift incorrectly. Check the plastic gear.