Hey everyone, new member and Cummins owner. The truck is a 1997 3500 with the 12V P-Pump 2WD and NV4500 5 Speed. I bought the truck with the trans stuck in 5th and the shut off tied with wire. A relay and a little hot wiring got the truck cranking and shutting off with the key. The syncronizer strut was the cause of the 5th gear problem. While working on that I found out the pinion bearing is gone, (almost a 1/4" of play up and down) but luckily the gears are okay. Don't know how but just need the bearings swapped out so no biggie. The reason I joined and the title is the speedometer is not working. Hasn't worked since I bought the truck. I checked the worm on the main shaft while the tail housing was off and everything looked okay (no flats, worn, boogered, or other damage that I saw) nor was it loose on the shaft. Put everything back together, drove to make sure trans. shifted through the gears and parked. Started researching and found several causes for this. Voltage to sensor is 5.+ volts. Pulled sensor off and spun by hand with the key on and the speedometer moves smoothly, no jerky movements. Check the flats on the sensor and looked to be in good shape. So that eliminated 90% of the problems with the abs and rear sensor because I don't have any lights staying on after the key is turned on. So I pulled the pinion assembly out and checked it. The gear looks good like the worm. No visual damage that I could see. I visually inspected the square drive of the pinion and looked good. Had a saw file with a square shaft and inserted to double check and there's a nice fit and no slip. Put the sensor and pinion together and as before, the speedo worked like it should. I know the pinion assembly is made with an eccentric shoulder for adjusting to different pinion tooth counts so thought maybe the previous owner ( poor guy pulled the tail housing off 2 times to fix the 5th gear problem) might have pulled the pinion out and didn't get it "clocked" back in the right position. And without thinking I did the same thing when I pulled it to check the pinion and didn't mark it so we all make mistakes. So with the saw file, I put the pinion assembly back on while spinning by hand. I could feel the gears ratchet when it got close and used the retainer to fine adjust it. Thought I was done so took it for a ride and nothing. Came back repeated the process and nothing. Came back repeated and this time, instead of lining the tangs of the retainer with the grooves in the pinion assembly, I went past to "tighten" the mesh. The result was the tangs not sitting in the groove and instead, holding the pinion by the flange. Drove it again and this time the speedo starting working to 20mph and then just quit like you unplugged it. The next day I had to go about 4 miles from the house so took the Cummins. On the way back, the speedometer started working when I got above 35 mph, under 35 and it quit working altogether. I can't wrap my head around the fact that everytime I try it by hand, it worked like it was supposed to and everything seems to be as the Germans say "goodentight" but when I put it back together it does everything but work. Am I overlooking something or what? The only thing I had come to mind is the worm on the main shaft when looking through the pinion hole looks to sit farther forward than I would think. If you look in the hole, the back edge of the worm looks like it is about 3/8 to 1/2" past the left edge of the hole if that makes sense. I took a flat bladed screwdriver and carefully tried to slide the worm back but it felt tight so didn't try to force it. Also checked the tip of the pinion that rides on the right side of the case but didn't look worn. I got nothing, any suggestions?

 

I think I got my speedometer problem figured out. Looks like the worm on the main shaft was slid too far forward. I saw a video of a guy doing the 5th gear nut fix and noticed the worm was resting against a clip. Went out and looked at my shaft and saw the worm was about 1 1/2" from the clip. I took a pry bar and caught the worm on the very front and it slid back to the clip. Can't try it right now because the batteries are dead but I'm pretty sure that was my problem so I'm going to jump it off tomorrow and try it. Hopefully that will get the speedometer working.

 

I got to drive the truck today and the speedometer is fixed.