Okay, so my speedometer and odometer didn't work. I have tinkered with the VSS and it appears to be correct, and just for the heck of it, I replaced my odometer gears. Now the odometer works, and the speedometer still doesn't. I didn't think that the speedometer would magically start working, but I also figured that the odometer couldn't work without the speedometer. Now the odometer does work and the speedometer still doesn't. Where do ya'll think I should start troubleshooting? Here in the middle of South Georgia, we are a ways from a speedo shop, so this is pretty much driveway tech...

 

Isn't there another gear for the speedo? My odometer worked for a bit and the speedo did not. A local guy told me there is a $25 tiny plastic gear that goes bad. I just use my GPS. Much easier!

 

As I understand it, there are two gears for the odometer, none for the speedometer. In the odometer, the bigger of the two drives the "numbers" part of the odometer, and the smaller gear rotates on a cutout in the actual housing to drive the larger gear. Basically, they both seem to strip out equally. I replaced both ( the originals were shot) and I have found out that while I was doing that, I should have tested the wiring prongs at the back of the gauge cluster (red is 12v, black is ground, and green is the input from the VSS at, I think, 5v - or some combination of those). Also, the VSS at the transmission tailshaft is oriented based on the gears in the VSS and the rearend ... in theory. If inventory wasn't looming in a few hours, I'd go crawl around under the truck and pull the VSS and the housing. So the next question for you guys that can help is, if the odometer is working, then logically, I have 12v and a good ground to the speedo head, so I should be checking continuity to the VSS? But if thats the case, how is the damn odometer working with no speedo? Is there a bench test for just the speedometer head? I just keep thinking that the odometer is somehow "downstream" of the speedometer function and it can't work without input from the VSS, which would mean that the speedometer should be functional, or, since its electric, it would result in an open short and the whole damn thing just wouldn't work. If it helps, the miles it read were reasonably correct. Frustrating, but at least I haven't thrown any money at it yet.

 

Try giving this place a call: Nationwide Speedometer and Instrument Cluster Repair

They also sell gears with a lifetime warranty here: Speedometer Gear-Odometer Repair-Odometer Gear

There is some info in the sticky for 1st gens here: Dodge Diesel - Diesel Truck Resource - Cummins - Home