Hello everyone. Is it possible to hook up the cable style speedometer, from the transfer case, and install a gas speedometer gauge? 1993 Cummins. I think that I can bypass the PCM and the electrical/Goldberg speedometer. Trucks from the 70's still have working speedometers and we have all sorts of problems with our speedos. These are the same trucks but with a diesel engine? Thanks, Rich

 

A 90-93 gas truck is electric too. You'd need the 89-older dash cluster (5 digit odo).

Have not tried the swap, but seems like it could be done. Not sure what the PCM will think of not having a signal.

 

It won't have cruise control nor will the od work if you have an auto trans

 

What problems are you having with the electric speedo? Most of the time they can be sorted out with a little diagnostic work and a couple new parts.

 

Speedometer and odometer stopped working completely in 08. Speedo would read around half the actual speed. I can spin the gears at the odometer by hand and they will turn the numbers. Something went wrong with the PCM in 08. I had to wire in a voltage regulator when that happened. I use a Garmin navigator for a speedometer. I was just thinking the cable style might work. Rich

 

The PCM rarely fails, there is a VSS on the transmission that commonly fails as well as the wiring connection can fail as well from oil/diesel and the movement of the wires back and forth during driving conditions. Replace the VSS and wiring connector/pig tail usually gets things up and running. Also checking to make sure your CPS is functioning properly and adjusted correctly will also help, since the PCM needs to know the motor is running to allow the signal to pass to the speedometer motor.

Sometime the speedo will read incorrectly due to axle gear swaps, or larger tires etc, but the purchase of the correct ratio adapter can have things reading correctly, so the system is fairly robust, and fairly easy trouble shot and repair.

 

Thanks for your replies Thrashingcows. I did replace the part on the transfer case, (VSS?). Didn't solve it. It just started reading way off. Started in 2004. Coming back from the beach, on I95, speedo read 55-57 but I was passing the mile markers every 37 seconds. I know people will call BS, but once up to speed these trucks can go! I only drive my truck a couple of miles on the weekends so it's not a pressing issue. Thanks, Rich

 

The vss is the top piece in this photo, the reducer is the second part which is what I'm going to assume you replaced as you stated that your speedo was way off after replacing it. if you still have the old one you can open it up and count the teeth on the gears to figure out which one you need. You can also check the square shaft that goes into the reducer from the vss as sometimes it gets rounded off and won't spin the vss