stingerssx

I read that there is supposed to be a buffer behind the guage cluster. I don't have one. I have a mechanical speedo. Am I supposed to have one?

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'82 Firebird, dead stock, 9 bolt disc rear, over 200,000 miles and still going strong, more to come...
http://www.spinfrenzy.com/stingerssx...easures.html#4

Jza

Yeah. There's a bar spinning on the end of the cable, and a pickup next to it. From there the wires go into the buffer.

[This message has been edited by Jza (edited January 16, 2001).]

stingerssx

Is it supposed to be behind the guage cluster, or is it somewhere else. My VSS is in the cruise control next to the charcoal canister. could it be there, or near the ECM?

Tim Burgess

Isn't the ECM in the center console in '82? I know that the speedo cable connects to (goes through) the cruise control assembly, under the hood, in '82. The VSS may have been located differently in '82, as well, but I don't know for sure.

On units where the VSS is on the back side of the cluster, the sensor device is optical, not magnetic. An LED shines on a luminus reflective / absorbtion wheel, which reflects a chopped luminus pattern to the photodiode receiver when the "chopper" disc rotates with the speedo cable. This chopped pattern is the 4000 pulse per mile signal that is buffered and sent to the ECM.

Tim

Jza

It might be optical, but take one apart and see if something metal sticks to it.

If you can't I got one right here; it's from an 89 full-sized van but it's exactly the same style. I could post a pic...

Also my Haynes says "Permenant Magnet Generator" 400 and 401 to "Vehicle Speed Sensor Buffer" 437 to ECM A10. Now I don't put a great deal of stock in Haynes, and it could be referring to the reluctor ring in the transmission for later models, but that was the reason for what I described.

[It came off kinda rude the first time I typed it, just know that's not my intention]


[This message has been edited by Jza (edited January 17, 2001).]

Tim Burgess

Yes, the "permanent magnet generator" would be referring to the VSS mounted to the transmission in the non-cable driven speedo systems.

Tim

Jza

The bar spinning behind the speedo is still magnetic. That's what actually raises the needle, isn't it?

Tim Burgess

The speedometer mechanism is probably a galvonometer (permanent magnet generator / voltmeter) setup, as you have indicated, however, the speedometer readout circuit, which drives the speedometer gauge, and the VSS pulse generation circuit, which drives the ECM and the cruise control modules, are isolated electrical conversion systems, which are driven by the same mechanical speedometer cable.

Tim

stingerssx

Check this out,

I was talking about the extra guage panel that I had hanging around. Today I took the one from the car out, and it has it.

Thanks for all of your help, and sorry.

84FTA

Just when I was thinking the mechanical engineers at GM were crazy I find out that the eletrical engineers at GM did everything in a more round-about way.

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1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 Trans Am T-tops
4-bolt main 350, performer intake, headers, Holley 650, T-5, hayes clutch, dual elec. fans and 3.23's.
Daily driver and restoration
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