Speedometer calibration - Mercedes-Benz Forum
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post #1 of 14 (permalink) Old 02-04-2019, 06:46 AM Thread Starter
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Speedometer calibration

Hello R107 fans.

I am in the process of calibrating my electronic speedometer.

I would need the relationship between frequency and speed to calibrate the speedometer.

Does anyone has this information ?

The speedometer is that of a 500 SL of 1984.
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post #2 of 14 (permalink) Old 02-04-2019, 11:06 AM
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Maybe a speedo shop might have the set frequency? If you have a frequency generator, you can figure this out by placing two reference marks on the odometer wheel, one on the far right 1/10th mile wheel and one across from it on the speedo face using tape to mark it with. Keep adjusting your frequency until you can time 60 seconds for the far right wheel to make one exact turn. This will be 60mph. Set your needle at 60mph at this frequency.

This will calibrate the speedometer to match its designed frequency. It will not make up for tire, rear axle, or other potential changes or if you have a speedo designed for a different combination or car.

Rick

Last edited by rick; 02-04-2019 at 11:09 AM.
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post #3 of 14 (permalink) Old 02-04-2019, 06:17 PM
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Do you want to adjust it or just check it? It's real easy to check by using the App Waze on your iPhone.

Waze will tell you how fast you're going... best checked at constant highway speed.

Nobody gets out of this life alive.
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post #4 of 14 (permalink) Old 02-05-2019, 05:38 AM
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Drive shaft Revs per mile = gear ratio x 63360/(Tire diameter x Pi)

Drive shaft Rev per kilometer = gear ratio x 39380/(Tire diameter x Pi)

To get pulses per mile/kilometer or multiply one or the above by number of teeth on tone wheel.

I believe the number of teeth on the tone wheel is 4 but not 100% sure. You can count the teeth by pulling the sensor out of the transmission and counting teeth while rotating the drive shaft one complete revolution. Might require a mirror. Or perhaps someone has a transmission out on the bench and they can count them for us. Anyone?

To get frequency in Hz. Multiply pulse per mile/kilo by speed and divide by 3600.

Last edited by roncallo; 02-05-2019 at 05:43 AM.
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post #5 of 14 (permalink) Old 02-05-2019, 01:12 PM
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"if" you need to adjust it and there no way to adjust it look to "dakota digital" they make cheep conversion/adjustment boxes that you install between the pickup and the speedo, ive had one on my alfa gtv6 for 10 years now
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post #6 of 14 (permalink) Old 02-07-2019, 10:03 AM Thread Starter
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Thanks for your interesting answers. I found the following information but I don't know whether they are reliable:

Hz MPH KMH

59. 25-29 40 - 47 km/h
118. 50-56 80 - 90 km/h
176. 75-81 121 - 130 km/h

so I'm still interested in accurate datas
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post #7 of 14 (permalink) Old 02-07-2019, 05:14 PM
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Quote:
Originally Posted by Stretoo View Post
Thanks for your interesting answers. I found the following information but I don't know whether they are reliable:

Hz MPH KMH

59. 25-29 40 - 47 km/h
118. 50-56 80 - 90 km/h
176. 75-81 121 - 130 km/h

so I'm still interested in accurate datas
Using a tire with a rating of 817 revs/mile calculated to a 24.69" rolling tire diameter.

Assuming 2.47 gear ratio your calibration comes out to Hz = KPH*1.3925

Using the manufactures revs per mile/kilometer over advertised tire diameter is far more accurate that calculating rev's per mile/kilo form the advertised tire diameter. The tire I used for this calculation had an advertised tire diameter of 25.4"
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post #8 of 14 (permalink) Old 02-26-2019, 03:54 PM Thread Starter
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Quote:
Originally Posted by roncallo View Post
Using a tire with a rating of 817 revs/mile calculated to a 24.69" rolling tire diameter.

Assuming 2.47 gear ratio your calibration comes out to Hz = KPH*1.3925

Using the manufactures revs per mile/kilometer over advertised tire diameter is far more accurate that calculating rev's per mile/kilo form the advertised tire diameter. The tire I used for this calculation had an advertised tire diameter of 25.4"
Many thanks for your help.

In my case:

with tires 205/65/15, diameter is 64,75 cm: 491,62 revs/km

my gear ratio is 2.24 so the calibration is Hz=1.2236

Conclusion: I had two problems with my speedo 1) speedo face was wrong (260 km/h instead of 240 km/h) 2) calibration was wrong and was corrected usind the above ratio and a Hz generator free program downloaded from the net. The result was checked using my GPS speedo.
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post #9 of 14 (permalink) Old 02-26-2019, 10:17 PM
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Stretoo, can you explain the process you did to calibrate thie speedometer? Genuinely curious .
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post #10 of 14 (permalink) Old 02-27-2019, 12:43 AM
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Yes I also would like to know which pot to turn on the speedo since I will be doing one shortly.
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