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Speedometer Advice Needed


Fiddler's Gold

The car (1986 C4 heavily modified SCCA Solo-II Champion) does not have a working speedo for some unknown reason. PO used a GPS for the speedo but is not including it with the deal. All of the other electronic dash gauges were disconnected except for the fuel gauge which works fine. He suggests that I go buy a $100 GPS for speedo needs or have the speedo recalibrated and installed manually which he adds would be "much more expensive" --- :eek:

Any ideas on what direction I should go here? Are there any speedo-only type GPS with large LCDs? any optical speedos?
Or should I just get a small GPS and try to squint at the numbers as this speed demon flies around the street. (doesn't sound too safe) :L

How much are we talking for adding a speedo or recalibrating and adding a manual assembly? L98 roller cam block, Lucati cams, Camfield aluminum heads, headers, etc, etc, etc, with new BW 6-speed with Ripper Shifter to I believe a Dana 44 carrier.

Thanks for any and all info!
-=The Fiddler=-
Jun 20, 2002
Tallahassee, FL
none right now :(
You are getting into the marine industry here.... Gaffrig makes a GPS speedometer with a large readout (made for race boats really) you are looking at a boat speedo with a max speed of around 120, and single digit numbers for easy reading (so a 2 means 20 MPH) Gaffrig isn't cheap though, you are looking to spend a good 200 on the gauge, and another 100 or so on the GPS system as a rough guess.


Well-known member
Feb 2, 2001
Bartlett, IL. (Chicago Suburb)
1990 ZR-1
Speedo is not working at all? is the car still using the Stock ECM? if so I am wondering if the VSS on the Trans is bad.

the way the 1986 Speedo works is the Speedo feed a 4k PPM signal to the Cluster. the Cluster then sends a 2K PPM signal to the ECM. I would think that the wiring for the Speedo is bad or cut. or the VSS is bad.

Fiddler's Gold

Well he didn't mention that is was broken! :)

Another case of Caveat Emptor --- :eek

I will have to check it out and see the reasoning behind it. I think it is just a case of disconnecting the dash and not wanting to spend $ on a new speedo. I am probably wrong. How much to fix the speedo wiring and/or VSS?




Well-known member
May 9, 2002
1984 White Z-51/ZF6-40/Shinoda body
If you're using a GM ECM, which I'd guess is NOT the case, the speed signal from the ECM is not connected to the dash.

I am running a 'chipped' '90 Camaro ECM and had no speedo output, initially.

My pal's '84 uses two computers; one for the dash, the other for the engine.

Ask the PO how your car is set up. You'll want to know this, in any case. You might think about switching to a non-electronic dash. The fuel sending unit ranges from 0-90 ohms.

Failing the above, check on e-bay for a GPS like the one I'll probably sell (boat's gone).

:w Mike

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