747 VSS Question

[rr]

The optical buffers I've seen are lime-green in color. They have
a three wire cable to the optical head. The edge card conn has
two sets of outputs, one for the ecm, the other for cruise.

Recently I grabbed a '747 out of a van that had a small black
box attached to the ecm mount. At first I thought it was a drac.
However, no jumpers and not too much inside. Now I'm thinking
it was maybe a magnetic buffer. Next time I run into one at the
yard, I'll check more closely for the pickup. An inline mag unit
that goes to this buffer would be handy.

And yes, I've kinda' wondered about that magnet generator
shown on the prints.

BobR.

Bob Valentine wrote:

> No ABS on the van, front or rear.   If it makes a difference this was a
> factory TH400 van.
>
> I'm going to open up the VSS buffer tomorrow and see if there's something
> like a unused set of inputs for a mag sensor.
>
> -> Bob Valentine
> -> bob at tecmark.com
>
> At 07:19 PM 12/15/2000 -0500, you wrote:
> >
> >
> >Sounds like the G20 had maybe some version of ABS??.
> >For those they need a high resolution VSS, so yes there would be a DRAC of
> >some fashion.   This is all off the top, of my head seen I've never actually
> >seen what you have there.
> >bruce
> >
> >
> >
> >> 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?
> >> Is there a different VSS Buffer for magnetic and optical?  Is there such a
> >> thing as a '747 truck w/ a mag. VSS?
> >> 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.
> >> -> Bob Valentine
> >> -> bob at tecmark.com
> >

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