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Thread: Speedo conversion questions

  1. #1
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    Speedo conversion questions

    I am converting to the 180 MPH speedometer. The speedo overlay and adapting crystal are in the kit at http://www.jbrianriley.com/ My car was an 85 MPH car so I had to find a 120 mph speedo, as directed on the Riley website. My engine is the 4.9 Cadillac and there is also a conversion that needs to be done at the ECM to feed the speedo the right info. All this I understand.
    However, I am thinking I may have another problem. My car originally had an 85 MPH speedo. Is the wiring going to be different in my car or is the 120 mph a "plug and play" I asked Riley this but didn't get an answer.
    And the joke is,<br />when he awoke his,<br />body was covered in Coke fizz !

  2. #2
    Senior Member FerrariFan's Avatar
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    Re: Speedo conversion questions

    It shouldn't be any different. The speedo uses the purple and yellow wires from one of the connectors that goes to the instrument pod. The speedo uses pulses generated by the transaxle. Do a search on Pennocks for 4.9 install. Rockcrawl made a custom PROM for me when I had a 4.9. Removed the rev limiter, the p/n switch and the passkey among other things.
    Here's a couple threads that may help.

    http://www.fiero.nl/forum/Forum2/HTML/076338.html

    http://www.fiero.nl/forum/Forum2/HTML/061613.html
    Even the longest journey begins with the first step.

  3. #3
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    Re: Speedo conversion questions

    Thanks for the links.
    I was concerned because I do notice a slight difference in the wires. When I plucked the 120 mph speedo from a U-pick salvage car, I left the 3 wire connectors in it and just cut the wires. This gives me wires to compare to my own car. I do see a couple differences there but they may have to do with something else like a different placement of idiot lights or gauges.
    And the joke is,<br />when he awoke his,<br />body was covered in Coke fizz !

  4. #4
    Senior Member FerrariFan's Avatar
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    Re: Speedo conversion questions

    the difference is that the 120 speedos come from a GT or Formula. These cars have the aux gauge panel in the center of the dash. The 85mph cars have the volts and oil pressure idiot lights in the main guage pod. do you have a schematic? Very helpful.
    Even the longest journey begins with the first step.

  5. #5
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    Re: Speedo conversion questions

    Yes, I have an 86 service manual and a sharp mechanic.
    And the joke is,<br />when he awoke his,<br />body was covered in Coke fizz !

  6. #6
    Moderator FunnyWheels's Avatar
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    Re: Speedo conversion questions

    How are you going to get up to 180 MPH anyway?

    Do you change the sending unit on the transaxle?

    I am just interested in what need to be done.

    Dave
    If you're not confused, you're not paying attention.

  7. #7
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    Re: Speedo conversion questions

    Dave The signal must come from the transaxel through the ECM, and then on to the speedo. However, you need the proper adapting device between the ECM and the speedo to create the 180 MPH reading.
    Look here: http://members.shaw.ca/efog/Pen/4.9/4.9%20speedo.jpg
    And the joke is,<br />when he awoke his,<br />body was covered in Coke fizz !

  8. #8
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    Re: Speedo conversion questions

    I guess that should read....... to create the proper readings for the 180 mph speedo. I don't intend on bringing this creation up to 180!
    And the joke is,<br />when he awoke his,<br />body was covered in Coke fizz !

  9. #9
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    Re: Speedo conversion questions

    what about using the harnesses some sell for this like fiero north america?

  10. #10
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    Re: Speedo conversion questions

    I might consider. I couldn't find FNA with a search. Do you have a website address?
    And the joke is,<br />when he awoke his,<br />body was covered in Coke fizz !

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