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Series 1 speedo error

Discussion in '"Stock" Alpine' started by beamdream, Jul 26, 2020.

  1. beamdream

    beamdream Gold Level Sponsor

    Interesting reading, I have almost given up on getting an accurate Speedo in my S1.

    With the PO having carried out a restoration using a mixture of Alpine bits, trying to find the right combination of components has done my head in.

    Currently I have a non 1st syncro box with od, 4.2 diff and goodness knows what speedo, at 50kmh gps the speedo (yes down under km not mph) reads approx 35kmh.

    I believe there were/are different speedo output pinions around, anyone have any ideas on this ?
     
  2. hartmandm

    hartmandm Moderator Platinum Level Sponsor

    beamdream,

    You are 30% off. Look at the speedo faceplate right below the needle center to find the model number and the number of turns per mile. E.g.

    upload_2020-7-26_22-35-14.png

    Hopefully it wasn't a faceplate swap onto some other speedo model guts.

    Have you ever checked the odometer against a measured distance? The speed reading could be off even though the odometer advances at the correct rate, or at some other rate that is different than the speed reading error. The odometer is directly counting the cable turns and actually reflects the true number of turns per mile the speedometer is calibrated for. The speed reading involves magnetism and can have separate errors.

    Mike
     
  3. beamdream

    beamdream Gold Level Sponsor

    Thanks Mike, no I haven't actually done a measured distance check, will go and do that.

    I'm suspecting the ratios are wrong as I've unscientifically swapped speedo(s) over the years and the inaccuracies have changed by different amounts with each change.

    I know there's a lot of archival info on this site re correct speedo fits, but was wondering if thats the correct speedo face for S1 with od in your answer above ?
     
  4. hartmandm

    hartmandm Moderator Platinum Level Sponsor

    That faceplate is from a series 3. I used it because it is easy to see where the model number and revs per mile are located.

    The MPH series 1 speedo faceplate looks like:

    upload_2020-7-27_0-1-29.png

    I haven't seen a KPH speedo faceplate, but assume it would reverse the position of the MPH and KPH numbers on the face.

    Mike
     
  5. beamdream

    beamdream Gold Level Sponsor

    Thanks again, perhaps I should explain that we have the same speedos except we refer to the kmh scale rather than mph as we went metric back in the 70s.
     
  6. Tim R

    Tim R Silver Level Sponsor

    Beamdream,
    It is possible to get your speedo to be very accurate pretty much all across the rev range. There is an MG video on YouTube showing how to calculate the turns per mile and fit the appropriate cog into the speedo taking into account differential, tyre size etc by just rolling the car for an exact 100' on flat ground. You can fit different face plates to the speedo but must get the internal gear rotations correct. In this video on raising the gearing on our Alpine you can see just how accurate our speedo is. We are comparing it to the Sat Nav reading. (about 2minutes 40 seconds in to the video). We got this more by luck than judgement but it is lovely to have a speedo that is so accurate.

    Tim R
     
  7. hartmandm

    hartmandm Moderator Platinum Level Sponsor

    Which speedo model do you have?

    Mike
     
  8. Mike O'D

    Mike O'D Gold Level Sponsor

    The needle return springs seem to weaken over time, which causes the speedo to read high even if it's the correct one for the set-up. At least based on the 2 different ones that I have checked.
     
  9. beamdream

    beamdream Gold Level Sponsor

    61117/02 with 980 turns, so correct configuration for S1 with od and 4.2 diff
     
  10. beamdream

    beamdream Gold Level Sponsor

    Yes that's certainly a probability, but the 30% error seems a rather exacting number.

    I suspect a spring induced fault would show a varying degree of error as the speed changed.
     
  11. beamdream

    beamdream Gold Level Sponsor

    So perhaps my next step is to do the measured mile and see if the odometer reading is correct.

    The other thought I had was to verify whether the od unit is actually an original Alpine unit, if not it could be that the speedo drive pinion is incorrect? Any thoughts on this from from the collective gene pool ?
     
  12. hartmandm

    hartmandm Moderator Platinum Level Sponsor

    Please do the test of driving a measured distance and comparing it to the odometer (I really mean the "trip odometer", which has the 1/10ths digit). Then we'll use that info to consider next options.

    Mike
     
  13. beamdream

    beamdream Gold Level Sponsor

    Thanks, it's now on my "to do" list. Will report back, maybe a day or two.
     
  14. Tim R

    Tim R Silver Level Sponsor

    Why not measure out 100', take the speedo head off and count the wire turns then do the calculations as shown on the MG calibration video on YouTube? This is much easier and more accurate than covering a measured mile.

    Tim R
     
  15. beamdream

    beamdream Gold Level Sponsor

    Ok, lots of driving today (realising my GPS can be set to miles) the upshot being that both speed and distance are under reading by 30% .

    So given that the correct S1 od speedo and diff are fitted then I'm guessing the od unit is probably not Alpine, and I suspect that the output pinion gear is wrong.

    Which means a fix will be based on trying to find the proper pinion, or that's how I see it, anyone have better ideas ??
     
  16. alpine_64

    alpine_64 Donation Time

    There were several laycock d type overdrive units worh a few different ratios.. Iirc the reduction ratio is on the data plate on the unit.
     
  17. beamdream

    beamdream Gold Level Sponsor

    Yep, as I recall this one was 27%, bit hard to read the plate now it's installed.

    But that doesn't solve the pinion gear sourcing, if I have to go down that road.
     
  18. Alpine 1789

    Alpine 1789 SAOCA President Platinum Level Sponsor

    I realize this doesn't solve your problem, but given the scarcity and cost of the proper OD transmissions, it would be interesting to learn what your car has, assuming it isn't stock. Once you figure out how to get the speedo to read correctly, your car could serve as a model for others. Of course, there is no guarantee that whatever transmission you have is available in other countries, but it would still be worth knowing the details.
     
  19. alpine_64

    alpine_64 Donation Time

    Jim id assume its just a different ratio d-type OD bolted on..it would use the standard alpien OD adaptor and mainshaft etc... It was likely a box from another rootes car with the other ratio.. Or an OD unit swapped off to replace a failed OD unit
     
  20. hartmandm

    hartmandm Moderator Platinum Level Sponsor

    Beamdream,

    Unless I am missing something, you should have 3 options to sync up the gearbox cable spin rate with the speedo:
    1. Change the gearing inside the gearbox that spins the cable.
    2. Add a gear increaser to either end of the speedo cable. A gear increaser would be the reverse of a gear reducer, such as those at:
    http://www.speedograph-richfield.com/html/minature_gearbox.html
    3. Change the gearing inside the speedometer.

    I have no personal experience with any of these, and have no idea how easy / hard it might be to source any of the parts necessary for any of these options. On the plus side, there are outfits that will custom fabricate parts once you provide the part's spec.

    Mike
     

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