Speedo/Odo aren't working on a 1998 12v project truck. What are the most common reasons behind this so I can go through and check them out. Any help is greatly appreciated. Thank you!

 

Check the vss on the rear diff, and the wires to it

 

The 98 peedo connects to the rear diff?

 

Yep, the vehicle speed sensor is mounted on the top of the diff, one little bolt to take it out, common for the wires to get eaten by rocks and things, there is a resistance reading for the sensor can't think of it off the top of my head though. Maybe someone else will help out with that

 

If I'm not mistaken the '98 uses two VSS.
One on the differential is is for under 30 mph, the one on the t-case or tranny is for higher speed.

 

Mine only has the one in the diff, replaced it once because of the same issue, very well could be variances through the year though

 

Well it doesn't work at any speed, and if there's something on the bell housing they guys who replaced the stock tranny with the built one could have gotten something wrong. They said they reused the old sending unit cause it was working. Just moved, soon as I clear some crap out of my garage I'll crawl under it and look both places. It worked fine for 300 miles after tranny swap.