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  • Speedometer Adjustment Calibration: How To

    [ Moved back from the defunct Supra Wiki, Sept. 7, 2011 ]

    Speedometer calibration can be a bit tricky, so pay attention! First of all, read everything here, you may not need to adjust anything, you may have other, larger issues. Start with the following:

    - Check your tire size and make sure it is the correct diameter to read correctly. (Stock is 225/50R16, which is 24.9 inches)
    - Check your odometer, make sure it is accurate before anything else.

    If your odometer IS NOT correct

    - You've got gearing issues, are your tires incorrectly sized? If not, you've got a problem related to the speedometer gearing in the transmission, usually due to one of 2 things: either the transmission or differential was changed out at some point.
    - You're going to need to figure out what was changed, if you have the correct differential, you'll need to change the speedometer gears in the transmission. If you have the incorrect differential, you can either change the differential gears or the speedometer gears in the transmission to match your new differential.
    - After you have your gearing corrected, and you've now confirmed that your odometer is reading correctly, check your speedometer for accuracy. If it is not correct, continue with the following instructions.


    If your odometer IS correct

    - Your speedometer cable is spinning at the correct speed, which is a good start. Typically speaking all Toyota speedometer/odometers are calibrated to the same specification, which is 637 revs = 1 km, or 1026 revs = 1 mile. What that means is, all A70 speedometers are interchangeable, so don't worry that you've got the wrong speedometer in there and that is what's causing the problem, it's not.
    - Check how much out your speedometer is, if it is a consistent speed out all the time (it reads 25mph when you're actually going 15mph and it reads 85mph when you're actually going 75mph), chances are the needle is in the wrong spot and just needs to be moved. Carefully remove the gauge cluster and pop off the speedometer needle. Reinstall it to offset the amount you are reading incorrectly. When it is at rest it really should sit perfectly at or just below 0 on the gauge.
    - If your speedometer is out by a percentage (it reads 25mph when you are actually doing 22mph and it reads 85mph when you're actually going 76mph), chances are it needs to be adjusted, if it is reading too high, you'll need to tighten the tension spring on the back of the speedometer. If it is reading too low, you'll need to reduce the tension on the spring. If you need to adjust the speedometer tension spring, continue to the following instructions.


    Adjusting the speedometer tension spring:

    - You need to get the speedometer right out of the gauge cluster, I'm not going to get into that here, but you need access to the back side of the speedometer. Get cracking.
    - Once you have it out, you'll need to adjust the tension, now I've found that you have approximately +/- 15% adjustment on the speedometer, so if it's beyond that, I'd suggest replacing the speedometer.

    This is what the speedometer looks like once the gauge face and needle are removed. You can go to this level, but it is not required. You can to the adjustment from the back side through the adjuster hole.



    To tighten the spring, move the adjuster downward (this will decrease the speed shown on the speedometer). To loosen the spring, move the adjuster upward (this will increase the speed shown on the speedometer). This image illustrates how moving the lever will change the speed shown on your speedometer:



    - You're going to have to do some trial and error with this before you get it just right. I hope you have some time on your hands, this can take quite a while.

    Jeff
    This article was originally published in forum thread: Speedometer Adjustment Calibration: How To started by Jeff Lange View original post
    Comments 8 Comments
    1. Devin LeBlanc's Avatar
      Devin LeBlanc -
      Thanks Jeff, My Speedo is GPS verified and also driving next to a car 5mph off. When im doing 45 my speedo shows 50. Ill go in and do some adjusting!

      Thanks,
      Devin
    1. MikesFixedRoof's Avatar
      MikesFixedRoof -
      My speedo is fine, but my trip counter has never worked since I've had my mk3. Looking at your great pics I'm suspecting that little pinkish gear there on the right of the trip counter is busted on mine . Is there any hope of fixing that? I remember back when I had my old E30 Bimmer that you could buy an actual replacement gear because people would always go to reset the trip while moving, which was a big no no and stripped the teeth off the thing.
    1. toyotanos's Avatar
      toyotanos -
      Mine had the same issue, and after tearing the speedometer mechanism apart; I found that the plastic housing that holds the gears had broken apart (not repairable). Replaced with a similar year speedo head assembly (not the entire cluster) and I have a tripometer again
    1. MikesFixedRoof's Avatar
      MikesFixedRoof -
      Quote Originally Posted by toyotanos View Post
      Mine had the same issue, and after tearing the speedometer mechanism apart; I found that the plastic housing that holds the gears had broken apart (not repairable). Replaced with a similar year speedo head assembly (not the entire cluster) and I have a tripometer again
      Wow the actual housing was broken and all that wasn't working was the trip counter? Crazy. I'd hate to pull mine apart to discover something like that
    1. toyotanos's Avatar
      toyotanos -
      Its not that hard to take apart- I could tell the housing boss was broken with it still installed in the cluster- just press the trip reset button while watching the backside to see if the mechanism is broken.
    1. Nick M's Avatar
      Nick M -
      That spring is a primary culprit of your bouncing speedo needle. If you didn't know. If it bounces all the time, cable. If it bounces when you start off and smoothes out, it is the wound spring.
    1. hockysa's Avatar
      hockysa -
      - You're going to need to figure out what was changed, if you have the correct differential, you'll need to change the speedometer gears in the transmission. If you have the incorrect differential, you can either change the differential gears or the speedometer gears in the transmission to match your new differential.
      I've got a an R154 from a JZA70 and a 3.737:1 diff from a 7MGTE

      How does one go about changing the speedometer gears in the transmission?
      Where do I purchase the correct gears?
    1. Roger UK's Avatar
      Roger UK -
      I am slightly confused by this, having played about trying to re-calibrate my Speedometer after changing to a lower ratio Differential. I notice there is a similar adjustment lever to the one that adjusts the sensitivity - although you don't refer to it. This one adjusts where the needle sits at rest. So - Supposing you have found that your Speedo is always reading 10 mph too high (at any speed), are you saying you should: 1. Take the needle off 2. Replace it so it is pointing to the equivalent of 10 mph BELOW the zero mark 3. Adjust the lever that sets the rest position so the needle comes back up to the zero mark. OR - should this all be done the other way round?! 1. Move the needle down below zero, using the adjusting lever 2. Take the needle off 3. Put it back on opposite zero. Obviously the second method will have completely the opposite effect - so which is correct?!
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