Sleigher

Hi,
I replaced my aluminum tail housing on my NV 4500. Everything worked great for a couple hundred miles and then my speedo started bouncing around and mostly didn't work. my Gear Vendor splitter also was not working.
I figured it was due to a problem with the cable running from my Gear Vendor unit to my speed sensor and since the unit was due for service and it is a no charge service and I was in the area I would go to Unitrax and see what they said.
I had to make an appointment and once I got it in there we determined that the cable was in fact thrashed; the ends were rounded out and not spinning the signal generator which in turn spins the VSS (vehicle speed sensor).
Great, except that with the new cable installed my splitter was working but the speedo and odometer were barely working. Usually reading zero but sometimes picking up and reading close to speed when going fast. When going slow it would drop back to zero.
Today I replaced the VSS. Went in without a hiccup and when I started my test drive it seemed like it was going to work great..........for about a hundred yards and it went back to zero and stayed there. Didn't try getting on the freeway.
I went to my trusty Dodge service manual which usually covers everything. There were at least a couple references to testing the VSS all of them telling me to go to the "Powertrain Diagnostics Manual", which I have never heard of before? And I have had my truck since new and have had the book almost that long.
So, any ideas?

Thank you in advance.

Peter

infidel

The Powertrain Diagnostics Manual is a must have for the limited electronic parts of these trucks.
They were only about $10 but I don't think they are available any more. Might find one on ebay though.

I would start by checking grounds.

Sleigher

Thanks Bill,
I found some on Ebay. They wanted a lot more than $10.00 for most of them but I offered someone $15. and they took it plus $6.50 for shipping.
I've got a feeling the problem is between the signal generator and the VSS. Like the slot isn't holding onto the drive from the VSS.

Thanks again, for this and all the help in the past!

Peter

infidel

Don't let the first few pages of the PDM scare you off.
It makes it sound like you need an expensive diagnostic reader when in fact most tests can be done with a volt/ohm meter.

Stamey

Does it have a VSS on the rear axle? I ask this because of my trucks, 96 and up, which use the rear VSS for speedo functions. In my case, I have a VSS in the tail housing of the tranny and the rear axle. My understanding is both are required for the speedo to work. The one in the tail housing just tells the computer to pay attention to the VSS in the axle and the computer uses the axle VSS for speedo and ABS info.
If your truck works the same way, you might have an axle VSS problem.
Obviously you should verify what I have said applies to your truck before proceeding.

Chris

Sleigher

Hi and thanks for the reply.
Mine only has the one VSS.
The problem was with the coupling which is only used with the Gear Vendor unit due to the removal of the speedo gear from the transfer case output shaft.
I have another gear that is on the output shaft of the Gear Vendor unit. None on the rear end. Why do they have to complicate things with another on the rear end?
Anyhow, the signal generator was not completely snug in this coupling. The signal generator has a cable going in one end and a square hole for the VSS to couple with it.
The VSS housing was a hair too long so it was causing the signal generator to bind. Also, the VSS has a tiny "E" clip on it. When installing the VSS I must have mis-aligned the shaft and the shaft got forced forward which dislodged the "E" clip and allowed the shaft of the VSS to slip back out of the signal generator; which also might be a little rounded at the end but still slotted enough to work.
Anyhow, put it back together. Checked the voltage on the connector which i now know was supposed to be 8 volts (due to my new manual) and it was.
All is working fine.
Of course while I was under there I noticed that a tiny drop of what looks to be gear oil coming off of the PTO cover of my transfer case. And I know that there should not be gear oil in my transfer case.
And, a little dripping from my rear end pinion seal.
Does it ever end?

P

joem

when my dana 70 self destructed I lost my rear VSS and the abs light came on, but the speedo still worked perfect

infidel

The rear sensor is for the ABS but I thought it was only used for the speedometer below 30 mph on 1998 trucks.

vssman

Yup. The 12V 2nd gens used the rear axle sensor for ABS and the VSS off of the trans/transfer case was for the speedo. That was changed around 1998 with the "redesign" - I don't remember anymore when it exactly happened. I used to make these things back when they were still made "on shore". It's basically a hall switch and an 8 pole rotating magnet. It has a couple of capacitors to filter the signal. Just use care when installing the unit into the tranny/case as the o-ring cuts easily and you'll have a nice oil leak.

bo Rodgers

Dodge Ram 3500 5.9 cummins iv had this truck for a year. The speedometer and odometer have never worked. I have a freshly rebuilt transmission in my truck. I have changed sensor in the rear end. Changed cluster, abs controle module, checked all fuses and not sure we're the relay is if there is one. Teath in rear-end are fine as well. Is there a way to re wire it or get it to work any other way this is ridiculous don't know what to do can any one help?

AlpineRAM

Remove the speed sensor and twist the gear by hand really fast, have a helper observe the speedometer.

I've seen the sensors installed so that the teeth of the plastic gear spinning the sensor are not aligned correctly with the shaft. You may need to lift the rear axle and rotate the drive shaft while installing the sensor to get it to align properly.

HTH

Busboy

I'm pretty sure it's a monopole sensor in the rear end with a "twisted pair" wire harness, what year truck are we talking here. Just realized I'm in the 12v section so could be an older truck with the vss in the trans and perhaps it was missed when the transmission was replaced.