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  • GPS Speedometer

    Ever since I installed the Supra 5-speed transmission I've been very happy with the way it shifts and how nicely it drives at higher speeds on the freeway, but I've been unhappy because the speedometer is so far off. The original speedometer has to stay but it needs to be accurate. What's the best way to make that happen? Thanks

  • #2
    Maybe contacting Westvalley at : https://www.westvalleyinstruments.com/
    Triumph TR6 - 1974 - Mimosa, O/D, black interior.

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    • #3
      Originally posted by TR6quebec View Post
      Maybe contacting Westvalley at : https://www.westvalleyinstruments.com/
      Morris Mintz at West Valley can change the gearing in the speedometer. He'll get you to run a test in which you remove the speedo, but leave the cable connected to the drive. You mark the cable with a piece of tape, then push the car a specified distance, counting the number of turns of the cable.

      Using that information, he can then figure out the gearing required to translate the rotation into an accurate reading on the speedometer. Think he quoted me $180, but that was a year or two ago.

      Anyway...contact Morris and he'll inform you what you need to do...
      Keith, Huntsville AL, 1971 CC66559U
      10.0:1 CR gasflowed head | Weber DCOEs | CP "150hp" Cam | Distibutor by Advanced | Lightened flywheel | Phoenix SS Exhaust System | HVDA 5-Speed | Good Parts suspension and anti-roll bars | Konig Rewinds | Boyd 15 gal tank | Miata Seats and Mr Mikes covers | Carl Visser dash | Mohair hood | Gas-strut bonnet and boot lift kits

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      • #4
        http://obswww.unige.ch/~wildif/cars/...edo_repair.pdf Good chance I'm wrong but the gearing is about the odometer and as for calibration of the speedometer, it is set so 60 mph indicates 60 mph. I believe there are a couple issues here. First, if the number of turns per mile are not the same as OEM, then both the odometer and speedometer will be off. Two, the speedometer needle can be biased up or down from a reference speed even when the turns per mile per time is correct. Third, the magnetic drag on the can may not indicate speed accurately either due to bad magnets, or bad spring. Assuming that the third issue isn't part of the problem, I could bias the the speedo to read 60 @ 60 even with the wrong turns per mile, but it will be off above and below that reference speed. From my perspective, I would first ensure that the magnet can/spring combo is accurate, then ensure the needle bias is correct when using the OEM turns per mile per time. That way it is an accurate instrument for both mileage and at all speeds above coming off the peg. That leaves the elephant in the room if the turns per mile coming out of the transmission are different than OEM, either because of the transmission or a change in differential gear ratio or both. To solve that problem, any decent speedometer shop will have ratio boxes that can correct for this and can make up the custom cables to/from the box. This is an elegant solution, especially if you change your tire size/profile, just change the gears in the ratio box. The box can be mounted below the passenger floor pan and then the cable routes can be optimized for bending and length.
        Last edited by HuhReally; 05-13-2019, 10:51 PM. Reason: spelling

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        • #5
          Here is a way to convert your TR6 Speedo to utilize GPS so that your speed reading is not dependent on input from your drivetrain.

          https://www.classicautoinnovations.com/classic
          1976 TR6
          Carbs by Poolboy !

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          • #6
            I've been very happy with the work Morris at Westvalley has done on my speedometer and other instruments. And yes, calibrating the speedo and odometer are separate exercises. However, the test, counting revolutions over 1/100th of a mile gives the data needed to calibrate both apparently,
            CF1634U+O Pimento/Chestnut
            2nd owner, since 1975
            Now in Fair Oaks, CA

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            • #7
              I was the guinea pig for Morris' first GPS speedo conversion..... it's dead on accurate to my Garmin GPS and is no longer dependent on Differential gearing, wheel/tire size.... not only did he convert it but he painted my gauges Magnolia to give it that old time classic look. You can't go wrong with West Valley. Click image for larger version

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              1975 Mimosa with a few upgrades/mods:
              Patton TBI
              HVDA Toyota 5 speed
              Goodparts Nissan Diff
              Goodparts CVJs
              AAW Wire Harness
              Miata Seats
              Boyd Welding Custom 15 gallon aluminum gas tank

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              • #8
                I purchased my conversion kit from HVDA a few years ago. there was an instruction sheet in there with the exacts steps. I will see if I can find it. Some of the above i recall. You had to lay a piece of tape on the ground of a certain diatnce, like 52 1/4 inches, line up the car at the beginning of the tape, disconnect the cable and hold your thumb over it, and while your friend pushes the car the exact distance of the tape, you count the revolutions. Send that number to the rebuild place and they will recalibrate it. Will look for the sheet tonight

                Francis

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                • #9
                  Here's the info on calibrating speedo ....2 options: The West Valley way and the DIY way http://tr6.danielsonfamily.org/Speed...alibration.htm
                  1975 Mimosa with a few upgrades/mods:
                  Patton TBI
                  HVDA Toyota 5 speed
                  Goodparts Nissan Diff
                  Goodparts CVJs
                  AAW Wire Harness
                  Miata Seats
                  Boyd Welding Custom 15 gallon aluminum gas tank

                  Comment


                  • #10
                    Originally posted by rgauthier View Post
                    Ever since I installed the Supra 5-speed transmission I've been very happy with the way it shifts and how nicely it drives at higher speeds on the freeway, but I've been unhappy because the speedometer is so far off. The original speedometer has to stay but it needs to be accurate. What's the best way to make that happen? Thanks
                    West Valley Instruments did the recalibration on mine, using the xx.x feet of travel method they require for this change. Don't remember the exact no. 52.8 maybe. The results of the new gear pack in the speedo came out perfect, according to road side radar speeds and the 5 mile mileage markers. Right to the 10th of a mile.

                    Dick

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                    • #11
                      I just use an iPhone app called Speedometer, of all things.
                      SR
                      73 TR6. HT/AC/OD
                      86 930
                      91 535i

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                      • #12
                        My speedo agrees with the really good Waze GPS app so I’m happy!
                        1974 TR-6 Logic Overdrive

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