I’ll try to keep this brief, I recently installed a Teraflex 4:1 and 2 low in my NP231. While doing the install and talking to Teraflex they said I needed a 29-tooth speedo gear since I was running 35" tires and had 3:73 gears. When I first upsized to 35’s from 33's several years ago I was told I needed a 31 tooth speedo gear, that being said I figured I would order a 29 tooth speedo gear and be done with it, here lies the problem. After installing the gear and clocking the sensor to the correct position I dove the jeep about 1/8 of a mile before the speedometer died.

When I removed the sensor and gear I noticed that the gears teeth had been badly chewed up, I checked the worm gear on the output shaft and it appeared fine, so I bought another 29 tooth gear reinstalled it and had the same problem dead speedometer after about an 1/8 of a mile. This time I removed the tail housing and decided to replace the worm gear on the output shaft and a new 29-tooth speedo gear. I noticed that when I install the 29-tooth gear and rotate the yoke it feels like the gear binds and does not mesh correctly with the worm gear, so I removed the 29-tooth gear and reinstalled the original 31-tooth gear and it works perfectly. Does anyone have a clue as to why I would be having a problem with the 29-tooth gear meshing properly and not with the 31-tooth? At this point I just as soon leave the 31-tooth gear, the only issue is I’m not sure how much this will through off my speedometer reading, I thought I had read a while back that it was something like 3% for each tooth???? Any help would be greatly appreciated.

Thanks,
Bill