97 E Superduty Cutaway 7.3L PSD with E40D.
Speedometer started the fluctuatring and wild swings including droping to Zero while traveling 65 mph.

The transmission would hold as long as I was traveling at speed. off the freeway and in stop and go traffic it felt like the transmission was slipping or would outright have no pull. The transmission problems seemed to go hand-in-hand with the speedometer behavior.

I read the posts about the VSS and replaced it promptly. No change. Also changed the gear driven sensor in the aft end of the transmission. No change.

When i first start driving it shifts a bit erratically but after a few miles of street driving it will loose all forward pull and I get nothing as the engine revs up.

Is it the transmission causing the speedo problem or is the speedo problem causing trouble with the transmission?

 

I think the speedo problem is causing the transmission problem.

Since you have replaced the sensor it is either the tone wheel that the sensor is reading, or even more likely a bad wire between the speed sensor and the PCM.

 

Thanks for the reply. Is the Tone wheel in the differential? That would explain the metal bits I found on the end of the sensor when i pulled the old one out.

 

Yes, the tone wheel is in the differentail. The VSS points at it and reads each tooth as it passes by. If it is damaged it affects the speedometer reading.

 

It was the wire. I bought a new VSS yesterday morning. When I experienced the problems again in the afternoon I pulled over and changed the VSS. I went about 6 miles with no problems at all. Then it went so wacko on the speedo and the transmission that I thought for sure it was the transmission saying goodbye. So I rode it in gently to the barn, about 15 miles.

I double checked everything and it all seemed fine. Then today after reading your reply and discussing the situation with the Ford service and parts department at Kearny mesa Ford in San Diego, I bout replacement pigtail connectors for the VSS and the speedo sensor on the side of the transmission.

Sure enough, one conductor in the connector was open. I spliced in the new one, pulled up the code for the VSS and cleared it then drove it around. That problem was gone but the shifting problem remained. Later I'll post what I learned. Its is running just fine, in fact better than ever.

Thanks for the help.