Rafael

I was driving 60mph on hwy. and suddenly the speed dial started to behave erraticaly and next the rpm increased like when the overdrive is turned off, then speed dial went down to 20-30mph while driving about at 40 or 50mph.

I reduced speed and got home ok. Everything works except speed dial and seems to be without overdrive.

The truck is all stock, no modifications and never before had a problem.

BC847

Hey Rafael. Welcome to our forums.

The signs and symptoms you describe point to the Vehicle Speed Sensor (VSS) as being whacked. It's a common issue with our older trucks. When it fails, the overdrive goes to acting a fool.


If I'm not mistaken, on your truck, it's located on the driver's side of the transmission's tailshaft housing. It'll be mounted on a small gear-set assembly. It's attached by way of a single threaded sleeve-nut (you'll see).

- Before you go run out a buy a replacement, just check to see that the attached plug and associated wiring is in good shape.

wannadiesel

Also be sure the drive gear is not rounded out.

Rafael

I appreciate your advice.

Rafael