does anybody know how many pulses per mile or minute the speedometer needs to read in order to run?

 

anyone? the unit i'm looking at to drive my speedo is a 4K pulse pickup. i need to know if that's enough or not enough.

 

I believe the speedometers VSS sends either a Square Wave or a Sine Wave signal to the speedometer and not a Pulse.

I do believe but I could be wrong, I think Dave would know.

What are you trying to do?
Jim

 

Nope, I don't know. My guess is that it puts out low voltage DC pulses but I do not know that for certain, nor do I know the frequency/speed ratio.

 

Your asking for the truck in your signature?

 

i'm trying to drive my speedo with 4k pulse magnetic setup from dakota digital. magnets attach to the drive shaft and the pick up using the bracket sits about an 1/8 inch away from the magnets reading the pulses and the pick up wires up to the signal interface box in the second picture.



the interface box is adjustable in order to calibrate the speedometer which i'll do with a gps by my side.

so i'm trying to figure out if this is the only way to make the speedo work or not. i may just go by the local speedo shop and just have the guys look over the truck and my situation and see what they have to say.

 

yes i am. the tranny does not have a vss in it. i've looked already. the tranny is out of the '02 model truck and in those, the vss is in the rear end. the only plug on tranny is for the reverse lights.

 

If it's the truck in your signature I don't think there's anything but a mechanical cable that drives the speedo... From the transmission to the back of the speedometer. The newer 1st Gens had elect./pcm speedo.

Ok, newer trans. Gotcha...

 

my speedo is electronic. i don't believe any of the 1st gens, pcm or not, had a cable driven speedo.

 

The earliest non intercooled trucks have mechanical cable drive speedo, there is no PCM. When they went to internal voltage regulator some functions were thru PCM, not sure what functions and not sure of the year, non i/c or i/c. And when the automatic overdrives came into play I believe there was more PCM controlled stuff to include the speedo.

 

hmmm well i know my speedo isn't mechanical. i've had that dash apart numerous times.

 

If it's a 1990 Cummins truck it is/was a cable drive unit. Unless someone put a newer instrument cluster in.

 

the truck's all original. it's an electronic speedo. i've looked at the back of the instrument cluster. there is no place for a cable in the back of the speedo. it had a getrag before the nv5600 and the getrags have a vss in them. since the swap there has been a plug, that is unplugged, zipped tied to the tranny. i'm 100% sure it's not mechanical.

 

dave, if you say it probably uses a low voltage, this pick up obviously will be generating voltage. i'm wondering if the adjustment on the signal interface box is adjusting the voltage so that it puts out the right amount until it's calibrated. sound possible to you?

 

There you go, if was a Getrag and they had a VSS, I won't argue with you anymore . The 90' automatic did have the cable drive...

I have a 90' Factory Service Manual, I'll go look see if I can find something on the pulse count for you.