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Ok so I'll try to make it short sweet and to the point as best I can.

I recently put my truck back on the road after many years of it waiting its turn to be finished. It's a 97 ram 2500 2wd nv4500 single cab , with 201 xxx on the clock. I installed a big input southbend dual disk, turbo, wheels tires blah blah blah.

Well after 111.6 miles of breaking it back in, I noticed my speed and odometer just quit. No ABS light no air bag light like I've a lot of people have pop up under this condition.

First thing first I pulled the transmission speedo drive sensor, cleaned it re installed.....nothing

Next I pulled the rear diff wheel speed sensor, cleaned it...nothing.

Okay.....next I replaced both sensors with new ones, still nada

Next I re clocked the speedo drive the tail shaft drive gear, I also thoroughly inspected both gears, no effects that I. Could see in either of them.

NOTE, the only thing I noticed, is when you look in the hole of the tailshaft housing where the sensor housing goes in, the tailshaft drive gear was about an 1/8 inch off enter to the left (toward the front bumper)

After that I traced some wiring back and fond driver side between the IC and the fender well a bundle of wires had been pinched. I crack the loom open and find BLACK/ LT BLUE tracer chaffed to the copper. I know that's the sAme color as the middle wire on the speed sensor. Patch it up , nothing


Ok, grab the snap on test light with built in volt meter , I get 3.9v and 7.1v...from what I've read I should have gotten 5v and 8v

Last ditch diag. Effort...I slap the scan gauge in....hers what I notice

-I have no MPH input which I would think rules out my cluster being bad
-water temp is glued at -40 thermostat cycles fine on the dash gauge
-from the dash tachometer vs. the scan gauge, the scan gauge is low by about 200-300 rpm when I'm rowing gears from a light until up to highway speed or back to idle.
- with my air on full blast, wipers on high, radio on high beams on, the scan gauge reads 13.2-13.3v MAX. With the loads off it reads 13.5 MAX

MY QUESTION IS...could my alternator be my problem? And outside of the aforementioned procedures....anyone's insight IS GREATLY APPRECIATED
Because I just want a speedo so I can get my truck inspected

Is there a check engine light and have you checked for trouble codes?

Ummm... First off the speed sensor is in the rear differential housing at the very top. Then the signal is fed to the ABS computer. After that the signal is set over the CCD Network to the PCM, ECM, and cluster modules. 

 

The sensor of the tail shaft of the transmission is for the speed sense for the PCM for transmission control and has nothing to do with the speedometer.

 

There was also another member here that had the carrier bearings in the rear diff fail and the whole carrier moved over pushing the tone out of the path of the sensor and speed signal was lost. 

9 hours ago, 215_12v said:

-I have no MPH input

 

This is because there is no signal from the ABs computer on to the CCD network.

9 hours ago, 215_12v said:

-water temp is glued at -40

This is because the ECT lead is shorted to ground. 

 

9 hours ago, 215_12v said:

- with my air on full blast, wipers on high, radio on high beams on, the scan gauge reads 13.2-13.3v MAX. With the loads off it reads 13.5 MAX

That's based off the battery temp sensor so if the battery are warm and you are in a warm climate the charge voltage will be lower. 

 

9 hours ago, 215_12v said:

-from the dash tachometer vs. the scan gauge, the scan gauge is low by about 200-300 rpm when I'm rowing gears from a light until up to highway speed or back to idle.

This is because of the update rate of the ScanGauge II and the dash. Being the dash is updated faster the ScanGauge II is always behind on information.

Edited September 20, 20177 yr by Mopar1973Man

Hawkez- no check engine light, I haven't scanned it with the scan gauge but when I get a few moments I will. Thanks!

 

Mr. Nelson- thank u for the explanation. as I Had understood the speedo on early NV4500 trucks was driven off of the tail shaft on 2x4s or tcase output shaft. I'll check the rear sensor again and see if I can get a good look through the sensor hole

Edited September 20, 20177 yr by 215_12v

20 minutes ago, 215_12v said:

I'll check the rear sensor again and see if I can get a good look through the sensor hole

 

You'll need a mirror to see in the hole for sure. 

 

20 minutes ago, 215_12v said:

I Had understood the speedo on early NV4500 trucks was driven off of the tail shaft on 2x4s or tcase output shaft.

 

Nope... That comes from the old school speedometer setup idea. Everything with RWAL or 4W ABS all get their speed signal from the ABS computer. Even my 1996 Dodge 1500 still the same thing speed sensor is in the rear diff housing top. 

 

Funny the weird things that break without speed signal. 

• Grid heaters don't shut off during road travel.
• Cruise Control doesn't function
• High idle will not cancel for movement. 
• Speedometer / odometer function
• VP44 idle function doesn't step down like typical at stops.
• Trip computer doesn't work.
• ABS failure (light tripped).