I did some searching on this one and didn't really come up with any threads that matched up to the issue I've been having. Long story short my speedometer/odometer doesn't work.

Longer story: When I bought the truck a little over a year ago the brakes were non existent and the typical abs light/brake light/no speedo deal was going on, but I got all of that fixed finally. Well the truck sat for a few months while I was supposed to be fixing/rebuilding the rear drums & emergency brake. In that time I had replaced the transfer case sensor once and the rear end speed sensor twice trying to fix the speedometer and it was working great once I did the transfer case sensor. I got in it to get it inspected one day and the speedometer just didn't work (it also failed inspection for the parking brake but that's not the point). On the way home it just started working again when I pulled away from a stop light, so I thought all was well. Next time I took it out, it was still working great for about 20 minutes, I slowed to make a turn off of the highway and the speedometer needle never rose back up. The odometer naturally mimics whatever condition the speedometer is in. The brake & abs lights are off. The cruise works just fine and it isn't jumping or kicking or doing anything else weird. I even bought a second transfer case sensor just on the chance I didn't splice the harness right the first time, but it still isn't working. On a whim I had my brother check the gauges as I spun the little arm on the new sensor and he said he saw the tach move a little. Obviously I wasn't spinning it fast enough to do much, but it makes me think that at least maybe it's registering and it's wired correctly.

All of the other gauges work save the temp gauge, which I haven't even begun to look into yet (any help on that would be appreciated too).

I was thinking maybe I hit the rear end speed sensor when I was replacing the parking brake cable, but I don't think so and I don't want to drop more money on a guess without hearing from some people that may have a totally different idea.

Truck is a 1994 Ram 1500 4x4 with the 5.2 and automatic and a little over 275k when it stopped tracking








...and it did finally pass state inspection.

 

Speedo is driven off the sensor on the tailshaft of the t-case. It's essentially a gear driven signal generator. Since you have already replaced the sensor once, did you also replace the gear? Inspect its condition? Condition of the drive gear on the shaft? Could also be wiring issue..... I think that is on the eight volt bus, Looks like the orange wire is sensor feed, black with light blue trace is ground, white with orange trace is signal return to both the PCM, and the cluster. (pin 47 on the PCM connector.)

 

That sensor is offset. If it's not turned (clocked) correctly, the teeth won't engage the gear in the transfer case.

 

Thank you guys, I went to look at it Friday night but it was raining so I didn't get to roll up under it. I'll let you know what I come up with. I know I tried to get the sensor out once before but it didn't want to budge so I didn't force it and started working on something else.

 

Ok, so update. I went by where I have it parked and I tried working on it some. I checked out the PCM, and while I didn't trace the wiring fully, the connections there look good as does the wiring into the cab and the wiring from the sensor up past the transfer case.

I tried out both of the sensors again and still had no luck with it. How do you go about clocking it? Maybe that's what I'm doing wrong, I tried rotating it all the way hoping to feel something click or catch but no dice. It just rotates on around and I end up just sticking the bolt through it and hooking the connector back up. Like you both said, perhaps it is the gear that feeds into the case itself. The bolt attached to it was stuck on there and I didn't have any sort of pipe or breaker with me to get it loose so I could check it out and it got dark on me so I just gave up for the night.

 

I think there are numbers on the VSS body, that correspond to the number of teeth on the driven gear, line that up with the mark on the t-case housing, and that should be it. How does the gear inside look? Not apple-cored is it?

 

So another update on this. I was driving it night before last and out of nowhere it just started working again. Now keep in mind that despite the great advice here I had yet to crawl up under since the last post to look at it. I had driven it like 20 some miles that morning and was like 16 miles into the evening drive, which was all highway at that point, and I happened to look down because something caught my eye.

It’s very weird how it just comes and goes like that, it makes me wonder if it’s the sensor underneath or maybe something in the dash itself. I know it’s too much to hope it just keeps working but it is very curious how it just comes and goes without being touched.