747 VSS Question

[Shannen Durphey]

Bob Valentine wrote:
> 
> On a '88 G20 van I just ripped apart the VSS is optical and goes to the VSS
> buffer, which is what I expected.  Saved cluster and buffer just in case
> needed.
> 
> >From the '747 diagrams posted on /incoming (specifcally 747ecm5.jpg) it
> shows a "permanant magnet generator"  hooked to the VSS buffer and then to
> the ECM.   I thought '747 trucks used optical VSS?
87 pickups, and 88+R and V series truck used the optical sensor.  88+
c/k used p/m generator.  Schematic on .incoming is from 90 pickup with
auto trans.  Manual trans and 4WD used same sensor, though.
> 
> Is there a different VSS Buffer for magnetic and optical?  Is there such a
> thing as a '747 truck w/ a mag. VSS?
Yup, and yup.  Green vss buffer (and yellow, and maybe white) have
outputs for cruise module and ecm.  Cruise module output _may_ be 2x ecm
output.  Green buffer expects roughly digital input signal.
> 
> I looked in the archives and there's a ton of info about the later DRAC's,
> and about eliminating the pass. car VSS buffers for TBI -> '730 convert.
> I'm putting a '747 TBI on a '84 GMC pickup.     Might be able to put the
> 88' G20 van speedo guts in the '84 GMC pickup cluster if I need to, last
> resort.
Need 2000 ppm input to ecm.  I've heard of guys fabbing together
speedometers using optical sensors.  You could also buy an aftermarket
speedo sensor to install inline.
Shannen
> 
> -> Bob Valentine
> -> bob at tecmark.com
>
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