1993 Cummins TD Speedometer Erratic

[travwm]

The speedometer on my 1993 Cummins TD 4wd stopped working other than an occasional erratic small jumping up and down of the needle, generally short lived and at lower speeds.



1. The hall effect sensor (VSS or Vehicle Speed Sensor) checks good for pulsing with a test light circuit. Turning the shaft at various speeds produces pulsing light at various speeds to match the speed the shaft is turning.



2. Manually Pulsing the 2 wire VSS Circuit from the VSS sensor location using a switch produces no result at the speedometer head.



3. Wiring and connections appear to be clean and free of corrosion. This includes the wiring at the Cruise Control Unit.





I'm beginning to suspect the speedometer head. Has anyone else had this problem?



Does anyone have a wiring diagram for this?



Thank you in advance!



Travwm

 

[Bob Beauchaine]

If you could fill out your sig it might help us to help you. The reason I say this is because in this instance there is a problem that manual trannys have that autos do not that might help.



Getrag - G360 or 518 auto?



Bob

 

[travwm]

If you could fill out your sig it might help us to help you. The reason I say this is because in this instance there is a problem that manual trannys have that autos do not that might help.



Getrag - G360 or 518 auto?



Bob

G360 Transmission

 

[travwm]

I'd be happy to fill out a sig but I don't know what t is. My Truck has a G360 Trans

 

[Bob Beauchaine]

For your sig just go to your user CP and you will see to the left I think a menu click on "edit Signature" then let us know about your truck.



As far as your speedo goes here is what you can try. The problem was first found on G360 equiped 4X4s. At the rear of the trans. you will need to drop the drive line - just at the trans. You will see a nut holding the rear yoke to the output shaft (I can't remember the size) - that nut needs to be torqued to 290 lb ft. The drive gear is held i place by a jamb spacer on either side of it. Those are the only things that keep that speedo drive gear from slipping - thus causing the VSS to send eratic signals to the speedo. I've seen cases where a movement of that nut by only 1/8" or less has cured a bouncing speedo. Put everything back together and give it a try.



It solved my bouncing speedo and mine is a 2 by - the NV4500HD came later.



Bob

 

[travwm]

I torqued the nut and still no good sooooo I used a 9 volt battery and light bulb as a test fixture for the hall effect switch. The light bulb pulsed (turned on and off) very rapidly even at just a crawl for speed. At any higher amount of speed the light just stays on as the pulses are so rapid and constant. Makes me suspect the VSS (vehicle speed sensor) although while I had the VSS disconnected the Speedometer jumped several times.

A real head scratcher!