JoeRomo

Ok so this morning I looked at my speedometer and the needle was constantly bouncing around and the truck was shifting weird as if it was bouncing back and forth from gear to gear. I was thinking it might be a fuse. Any ideas anyone?

dr_bowtie

VSS sensor.... check the connector and wiring

JoeRomo

Where is it located? And what does it look like? And honestly, what is it?

dr_bowtie

Vehicle Speed Sensor....

Google has tons of info on it

JoeRomo

Would that have caused the transmission to shift funny?

dr_bowtie

the VSS

RoadKingRocket

I just bought a 94 F150 XLT...has 118,000 miles on it. So far a great truck for its age/miles. But I am also having the speedo issues that the OP is having. Does fine until about 35-40 mph, then the needle goes all crazy after that. Also noticed the Overdrive acts a bit funny, as well. Could this also be the VSS? Thought maybe the cable was just slipping. Just looking for a place to start...

f150cam

yes the VSS could cause that also.

94 flared out

Start on the back axel there's a sensor on top of the middle of the back axel. Follow thoes two wires that's sounds the same as mine

RoadKingRocket

Bought a new ABS Speed Sensor today ($17). Installed it and it corrected my problems with the speedometer...mostly. The needle is definitely more stable...but still wants to bounce a little at higher speeds (50+ mph). Overdrive shifting is definitely better. The fluctuations in the needle is around 5 mph or less (for example: dances between 45mph to 50mph when I am doing approx. 50mph). Much better than a 15-20+ mph spread. I did notice when I removed the old sensor that there was some black sludge-like residue on the portion of the sensor that was housed within the housing. Could this residue cause bad readings by the sensor? I just bought the truck, so there is no telling when (or if) the case oil has changed. I am sure it could use a good fluid change.