Gentlemen:

I am new here, and I am awkward in using this medium, but I am hoping you can make suggestions as to "what is wrong" with my speedometer, and "how to correct the problem."

Background:
1. Speedometer quit in 2005 = rebuilt by speedometer shop and worked fine
2. Speedometer started acting up again (i.e. - jumping, working off/on, then it quit completely)
3. Speedometer and VSS taken back to speedometer shop and bench tested in the spring of 2015 = both units functioned correctly/worked perfectly
4. Both speedometer and VSS replaced on truck and wires along transmission cleaned/new wire loom conduit added for additional protection against chafing = speedometer began working again.

Present Issue:
1. Speedometer quit again (August, 2015) - based upon previous experience (see above), "bad connection" suspected.
2. Continuity Tests Run On Wires/Connectors:
a. Ground Pin at Speedometer = continuity to chassis bolt and to ground at VSS connector (good grounds/OK)
b. Battery Positive Pin at Speedometer = O.K. when ignition switch engaged (current present)
c. Signal Pin at Speedometer = 1.75-2.2 volts when rear axle raised and first gear engaged

The long/short of this is that there seems to be a "signal from VSS" and there seems to be continuity through positive and grounding terminals at the speedometer connections.

I have also done the following:
1. Checked for rotation of mechanical drive from transmission (placed small metal scrap in drive pin socket and rotated rear wheels) = O.K./mechanical drive seems to work.
2. VSS - checked continuity between terminals = test light flashes as drive pin is rotated by hand (battery powered continuity tester)
3. Checked for VSS plug continuity - small jumper cables made from plug terminals to socket pins to ensure good connections = still no speedometer when gearbox engaged/rear axle spun (Dodge has a service bulletin about poor connections between VSS plug/socket)

I am mystified.
1. Speedometer/VSS checked in spring of year = both worked
2. Continuity of cables/connections = all seem to be correct
3. VSS seems to be generating a signal (if I interpret my findings correctly)

WHAT HAVE I MISSED, OR WHAT HAVE I DONE INCORRECTLY? I am about ready to go to Ebay and start looking for an old '80's vintage mechanical speedometer with a trip tick; however, so far, the only ones I can find are Canadian, and they register in kilometers.

I welcome your suggestions and/or advice.

Walt Banta

 

I gotta' say that I can't really help with your problem, but that this is absolutely the best first post that I have ever seen. Well thought out, you did your due diligence, just wow! Anyway, maybe someone that knows at least as much as you do about it will chime in. ...Mark P.S. Fill out your signature with your truck info so that the guys can give good answers...

 

A volt reading means nothing. A meter can not move fast enough to give a good reading. You need to take reading on an O scope. You need to know what the signal is doing. I have not had a VSS on a O scope. My guess is a square wave signal. That means on and off. The VSS might be sending something back.

Is it the correct signal??

What was the OHM readings from the dash grounds to the negative battery terminal?

We need to know what the truck is.