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Series V speedo disguised as a Series I

Discussion in '"Stock" Alpine' started by woodybap, Jul 25, 2020.

  1. woodybap

    woodybap Silver Level Sponsor

    While most of the body parts on my Alpine are Series I it now appears the transmission is a later Series IV or a Series V. I tried replacing my broken “Series I” speedo but the needle on the ‘new’ Series I ran wild. Further inspection revealed that what looked like a Series I speedo was really just a Series I body and faceplate into which a PO placed Series V mechanics. I am thinking of replacing the current faceplate [and broken O ring] with a Series 5 and re-using the Series I body so that the existing wiring will still mate up. Does this reasoning make sense? If so, does anyone have a lead on a Series I faceplate and O ring?
  2. hartmandm

    hartmandm Moderator Platinum Level Sponsor

    The speedo and the gearbox need to be in sync regarding how many turns of the speedo cable occur per mile.

    Do you have an all synchro Overdrive transmission?

    When you say the needle on the new speedo ran "wild", was the needle bouncing around a lot or was it consistently reading much higher than it should?

  3. woodybap

    woodybap Silver Level Sponsor

    The transmission is not Overdrive.
    With the SI speedo the needle bounced around wildly with no apparent purpose.
    The SV speedo [inside the SI body] worked OK but gave readings that were about 10% below actual when checked against GPS and radar.
  4. hartmandm

    hartmandm Moderator Platinum Level Sponsor

    The speedo needle fluctuating is probably an indicator the speedo internals need to be cleaned and re-lubricated. Some articles on that are in the Gauges section at: http://wp.mhartman.net/home/cars/sunbeam/alpine/info

    The "standard" speedos for series 1 were 1000 & 1020 turns per mile. Series 5 standard speedos were 1020 turns per mile. You can tell the series 4 vs 5 speedo because the odometer numbers are larger on the series 5. Check out pictures at: http://wp.mhartman.net/home/cars/sunbeam/alpine/gauges

    But even though the speedos may have the same turns per mile, maybe you still have a 3.89 differential whereas the series 5 would have had a 4.22 differential. Using a 3.89 rear with a series 5 gearbox will lower the speedo cable turn rate by 8.4%. Then throw in a possible different tire diameter from stock and it is easy to be at a 10% difference.

    Even if your series 1 speedo worked correctly, it would read low the same as the series 5 speedo.

    woodybap likes this.
  5. woodybap

    woodybap Silver Level Sponsor

    Wow! Thanks for all the resource material.
  6. Tim R

    Tim R Silver Level Sponsor

    There is a very good YouTube video featuring an MG where it shows how to calibrate your Smiths/Jaegar speedo exactly to your individual car. Tyre size, differential gearing etc can make differences from standard. There are apparently a large number of cog specifications that you can choose between to get the speedo 100% correct once you calculate the exact turns per mile for your specific car.
    Tim R
    woodybap likes this.

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