Does it need to be calibrated with a W123 also? When I replaced my speedo needle, I just set it roughly in place, then hooked up the cable and went for a drive and noted the speed reading when I was going 45 mph via GPS (speedo said I was going 55). When I got home I pulled the speedo back out and spun it with a drill up to 55 mph. Then I had someone pull the needle off and set it at 45 while I kept the drill at a constant speed.

Always wondered if it's accurate through.

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Milan Brown 1979 240D, rebuilt OM617.952 turbo diesel, rebuilt 722.315 transmission - engine spun a rod bearing, sold to pick your part

1979 300SD, ~90k original miles, all stock