I am troubleshooting an inoperable speedometer on a 1994 Ram 1500 4x4, 360 Magnum, 46RH. I have been restoring this truck for just over a year and have rebuilt the transmission, transfer case, and engine. I was very diligent in ensuring that everything was double checked prior to completing each project, but on the first test drive, I saw that my speedometer was inoperable. I do not know if it operated prior to restoration as it had a bad transmission. I ensured to clock the senor in the transfer case properly and I have check the connections to make sure everything is plugged in. I have referenced the service manual and it tells me to refer to the "Powertrain Diagnostics Test Procedures Manual" for appropriate tests. If anyone can provide a link to that manual it would be greatly appreciated. I searched this site prior to posting and was unsuccessful. Thank you in advance.

 

Service manuals are available here. Diags are generally in the section for the system you are working on.

You have an electronic speedometer, the VSS is gear driven off the tailshaft of the t-case. Signal is split and goes to the PCM, and cluster. If the PCM doesn't get a signal, it should set a code....

 

I ended up pulling the VSS out of the mount and running it on a drill. The speedometer functioned, but did not show as many MPH as I would have thought at the rpm the drill was spinning (none of this is scientifically measured, just assumptions based on the way things are believed to work). I then removed the VSS mount and counted the teeth on the gear. 30 teeth. I clocked the mount with the 26-31 marking pointing in the 6 o'clock position per the service manual. I had to turn it to about 5:45 in order for the locking tabs to line up in the mount (I assume that needs to be done, although my assumptions have been incorrect in the past). I then reinstalled the VSS and took it for a short drive. The speedometer does not start registering MPH until around 20 MPH (estimated), and at around 45 MPH (estimated) it reads 15 MPH. When I had the transfer case apart during the rebuild of the truck I saw that the gear on the main shaft of the transfer case was in excellent condition. I am thrilled that I have some type of speedometer, but would like to be pointed in the right direction before I load up the parts cannon and fire a new VSS at it. Is my assumption that the locking tab for the VSS mount has to line up with the grooves in the mount? Is there a way to test the VSS for proper operation. I appreciate any help given and will hopefully be able to provide advice to others in the future once this thing is completed.

 

Sounds like a bad VSS...... Get one from a junkyard to test.

 

Ended up getting a new VSS and comparing old vs new on a drill. Both register the same on the speedometer at max drill rpm 25 mph. I did notice that my odometer is working leading me to think that I may have a bad speedo. I also pulled the VSS mount to inspect the drive gear and everything looks great. I feel like the next step is to pull the speedo out of the dash and see if something is obvious. Is there anything else that controls the speedometer reading? Thanks again for the help.

 

Its all electronic..... No user serviceable parts inside. If the speedo is bad, have to replace the cluster.

 

I pulled the speedo out of the cluster to look at the PCB and it looked fine except for a slightly discolored spot on one of the traces, but it still had continuity between the two lands. Going to trace the grounds and make sure there isn't too much resistance somewhere. Going to recruit some assistance from my brother who taught helicopter electronics in the military and figure this thing out. Thanks again for the help.

 

There is a diagnostic self test for the cluster. Hold odometer button down with key off. Turn key on, but don't start. Release the button, the cluster will cycle gauges and lights to verify operation. Not sure if that is much help at this point.
Power Train Diagnostic Manual is not the same as a Service Manual. Step by step diagnosis of codes/problems/systems. Relies heavily on the DRB tool, but has a lot of good information. I have a '95 and '03. Very useful.

 

Thanks for the info. Does the self test work for my non-digital cluster? I am not near the truck or I would try it.