cyberdyne speed calibration box

[Shannen Durphey]

Here's the brunt of my investigation:

1) when calibrated correctly, speedo cable spins at 1000 RPM (that's
revolutions per mile).

2)early speed sensors were DC output, 2,000 ppm (pulses per mile)

3)early speed signals were cut in half for cruise control and  multiplied 2X
(i believe) for rear wheel ABS.  Buffer is available still from GM

4) modern speed signals, specifically 700R4, 4l60E, are AC, 40 pulses per
revolution of the driveline.

4.5) to find out how many ppm are sent to signal buffer, by 40 tooth sensor,
divide 5280 by tire circumference in feet, multiply by rear axle ratio, and
multiply by 40.  A car with 29" tires and 3.72:1 axle produces 103,483.3
pulses per mile.

5) 91 to present pickup truck has DRAC, (Digital Ratio Adapter Controller),
which can be programmed via jumpers to multiply and divide speed signals.
DRAC also has outputs for cruise, ABS, and speedo.  If interested, I can
furnish some info, especially on programming DRAC.  Speed sensor for this
type vehicle is 40 tooth.

6)United Speedometer and Instrument, (800) 877-4798, sells speed signal
generators.  They build them to generate square wave (DC) or sine wave (AC)
signals, in two, three, or four pulse per revolution configurations and
install between speedo cable and trans. If converting, get DC type with
appropriate # of output pulses.

7) It's been over three years since I installed C[rossfire]FI into my '57
pickup, so the above information is subject to correction as needed or
wanted.


Shannen

Joe Boucher wrote:

> Andris wrote:
> >
> > I'm planning on putting a T-56 tranny into my IROC as part of the twin
> > turbo project, and would need to calibrate the VSS signal for my
> > speedometer. As far as I know, it works on pulses per mile. I know the
> > cyberdyne box lets you adjust this, but costs $100. Is there a circuit
> > that I could build that will do this? Thanks everyone :)
> >
> > ********************Skulte Performance Designs********************
> > Andris Skulte askulte at tufts.edu http://www.eecs.tufts.edu/~askulte
> > (617)627-1601   89 IROC M5 305 TPI  320 hp / 470 ft-lbs
> >
> > Leave late, drive faster, still get there first. ;)
>
> If there is I'd like to know it also.
>
> I ran into the speedometer wall when I did my conversion on the
> Suburban.
>
> VSS signal into the ecu is either 2000 pulses per mile or 4000.  The
> trannies with the reluctor wheel and sensor coil are the 4000 and the
> trannies that output through a mechanical speedo cable are the basis for
> the 2000 pulse systems.
>
> The speedo system is a led bouncing light off a shiny arm in the back of
> the speedometer.
>
> The 4000 pulse system takes the reluctor and coil ac signal and converts
> it to a pulsed or on/off 12 volt DC signal.  One of the sparkies here
> said $20 at Rat Shack could buy enough parts to make a circuit to do
> that.  But he didn't offer to help.  With forty teeth, that would mean
> 40 peaks every turn of the tranny output shaft. Right?  Getting from
> there to an on/off signal is beyond me.
>
> Joe Boucher
> '70 RS/SS Camaro  '81 TBI Suburban