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Another non working odometer thread(it’s not the gears) 83 380SL

1677 Views 10 Replies 5 Participants Last post by  plinker17722
I have an 83 380sl that ive been trying to figure out why I can’t get the odometer to read. This car was purchased brand new by my sisters late father in law. When he passed away approx 30+ years ago, my brother in law gained ownership. Unfortunately, my brother in law passed away a few years ago and my sister didn’t want to see it sit... So I gave it a home, the car was well maintained it’s entire life, only going to Mercedes dealerships for all its service, including quite some extensive maintenance work. It now has 88k miles on it and all of a sudden the odometer stopped working on a ride to get coffee last weekend. After hours up hours of research, it led me to pulling the cluster out and taking a look. I immediately seen broken gears, so went ahead and ordered a set. Did the repair smoothly as per a thread on here actually, but did not resolve the issue. Everything else on the cluster works, aside from the clock (which I know from reading, that’s also prone to need repair). My main concern is the odometer though. I have a multimeter to troubleshoot, but don’t know where to begin. I’d love to be able to verify it’s getting proper signal to the stepper motor or whatever magnetic system it uses to drive the odometer gears. I can spin the shaft and see that the gears are working correctly and odometer moves. Once installed back in the car, nothing. Looking to see what my options are. Any advice is greatly appreciated.
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It looks like there are a couple small motors that drive the gearset based on the speed signal that also drives the speedometer. Perhaps resoldering the joints on the board may correct an age related issue. I have done this to both my cruise control and climate control boxes and restored function to both.
The only way I can think of testing it is to find out what type of signal is sent from the sensor in the tail of the transmission, then duplicate it with a signal generator while applying power & ground to the appropriate terminals. I can't find the sensor on any of the diagrams I have, and I don't know if the signal goes to the speedometer first and then to the cruise control amplifier or the other way around. In any case if the speedo reads accurate the signal must be good. There is only one speed sensor. I suppose with a scope one could read the signal while running on jacks.
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