Electronic Speedometer Question

[78SilveradoSWB]

If one were to convert to Autometer gauges and choose to use the electronic version speedometer vs. the mechanical one, does this eliminate the speedo cable to the tranny? If so, where and how does the speedometer read the speed? A sensor goes somewheres?

[RockHQ]

It does eliminate the speedo cable. You would replace your tramsmission's speedometer drive gear with a magnetic pickup unit, or a VSS sensor and run the wires to your speedometer.

[swervin ervin]

I don't think so. I think the cable is still used but the speedo has a built in vehicle speed sensor. I asked Autometer about this when I was installing my Pro Comp gauges. At the time they didn't have an electric speedo in Pro Comp's and was told I would need to use the electric Sport Comp if I wanted to use my cruise control. Hooks up the same way as a mechanical gauge.

[cliffsta]

yeah swerve man is correct. the cable still exists, but instead of the colored gear in the tranny its got a little dillio thingie, its on the 87 models i think. but don't take that as in stone.

[1972C10]

Nah get a full electric gauge .. On that Th-400 you should * be abel to use a vss off an 89 C1500 W/T With 305 And A Th375 Try that it

VEHICLE SPEED SENSOR for a
1989 CHEVROLET TRUCK C1500 1/2TON P/U 2WD
WITH AUTOMATIC TRANSMISSION (Change)
Normal Stock
Special Order
Not Available



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It didnt give me an option to put in Th375 So either the W/T Had it special and vatozone dont have the option in the computer Doubtfull..

Or the 700R-4 And Th-400./375 use the same Vss as the 700 So maybe any 700R4 VSS will work Just make sure to use the proper drive gear to retain correct reading.

Althou i think most automter electric speedos have a recalbration mode.

[1972C10]

After market makes Vss senders that just hook onto the speedo cable Hookup on the trans. as well as some that still retain cable operation but have wires for Electric VSS as well.

[SanitysBane]

on all of the factory eletric speedometers that i have seen it was a meatle gear on the output shaft with a magnent sensor and wires running out, no calbe, i've got one sitting around out of a 700R4

[RockHQ]

To put it shortly:

Factory electronic speedometers use a transmission mounted vehicle speed sensors or VSS's. No cables, never. No optical devices either.

Factory mechanical speedometers use a cable. If there's an electronic cruise control it uses a speedometer mounted VSS.

Aftermarket electronic speedometers may use:

1. A factory magnetic induction VSS on the transmission.

2. A conversion kit magnetic VSS that replaces the speedometer cable but is GEAR driven by the transmission output shaft

3. A conversion kit that retains the speedometer cable, the speedometer itself has a VSS output for cruise, abs etc.

When using a magnetic VSS and electronic speedo there are no optional drive "gears" on the transmission. The VSS signal is fed to a buffer, modulated for the proper gearing and tire size and then fed to the speedometer, cruise control and ABS if equipped. If you change rear end gearing or tire size and want the speedo to read correctly you'll need to change that buffer (DRAC or Digital Ratio Adapter Controller is GM lingo for it) or modify the existing one. This is how GM did it, anyway.

So the proper answer to the original question would be:

It depends on whether or not you get a semi-electronic or full electronic speedometer. If the former, see swerve's answer. If the latter, see mine.

[78SilveradoSWB]

Thank you all for your respective answers.