My Jeep came without the speedometer working properly. I crawled under to find that the connector was not only unplugged, but had been sheared off when they'd recently replaced the transfer case. So, I found a new connector at Auto Zone, wired it up in the parking lot, and headed home finally knowing how fast I was going. As I suspected, they'd never re-geared the speed sensing gear for the 33" tires. This makes the speed indicated read low by 15% or so. I checked my differential ratio, measured the actual tire diameter, and found a chart to tell me the right number of teeth to get. Then I installed it and got no reading at all… It turns out, you have to rotate the speed sensor housing into one of four different orientations depending on the number of teeth. I did that and now it is spot on and works great! It's nice to have an older and very common vehicle where I can look up just about anything about it on the internet!
So, I calculated that it has 120K miles instead of the 101K it reads. So, add 19K ;)
As an extra bonus, I found another sensor on the transfer case that was unplugged. I fixed that and now my check engine light is off too! I am really happy with my new little hobby truck. It is pretty "clean" with enough little things to do to enjoy tinkering in the garage. It all works and runs and has minimal rust in the body and frame (especially considering its age).
