[Second Series]

How do I keep the mechanical speedometer if I replace the old transmission with a modern unit with reluctor ring?
Use an electric motor to drive the speedometer.
I have been working on this for a couple months now. I found a 17 page discussion that spanned several years. Someone had a working prototype, but failed to share any relevent information, and then vanished.
Break down what needs to be done:
1. Identify a motor that will function at a slow speed and have a range of speed wide enough.
2. Analyze the signals in a vehicle.
3. Build a motor controller to drive the motor from the vehicle signal.
4. Assemble the parts including speedometer cable.
I’m using an ’88 GMC K2500 for a frame swap for a ’47 panel truck. I needed a truck for work around my house, so I got a ’90 K1500 basically the same setup as the GMC. I’m using the K1500 to look at signals, and eventually to test the ’47 speedometer. A fair amount of math is involved, and I try to double check the convoluted equations. Please let me know if something is off!

The reluctor ring creates 40 pulses per driveshaft revolution. The DRAC converts the 40 pulses to 128,000 pulses per mile for the RWAL Brakes, 4,000 pulses per mile for cruise control, and 2,000 pulses per mile for the ECM.
Use the 2,000 ppm for the speedometer motor control.
Look at the signal on that wire: