I have a 1984 318i with 71,000 miles. Recently, the speedometer and odometer started quitting intermittently. Then they quit most of the time and would only start working intermittently. Now they are both dead all the time. I replaced the speed sensor in the differential (with OEM) and the SI board in the instrument cluster (with a Programa unit with capacitors instead of batteries), but the speedo and odo are still dead. The odo gears looked OK (though they are kind of hard to see). In any event, I think bad odo gears would affect only the odo and not the speedo. Does anyone know what would cause both the speedo and the odo to fail simultaneously? acoulter@wyoming.com
Wiring. Most likely a broken wire near the differential, especially if it shows evidence of getting 'baked' by an exhaust leak in the past. Otherwise, just check continuity from there to the dash connector - but it's probably broken where it got the most abuse.
I disagree. In my experience, the sending unit in the differential is rarely the cause of this problem. MUCH more likely is the speedometer head in the instrument cluster. Easiest solution is to replace the speedometer unit in the instrument cluster. Or repair can be attempted by reflowing solder on speedometer printed circuit board. There have been many discussions about this on r3v Limited forums (http://www.r3vlimited.com) and e30 Tech forum (http://www.e30tech.com). You can search either site without membership. I've seen links to tutorials on reflowing the speedometer circuit board.
My own experience has been a failed sender unit. That tells you what experience is worth. OK; here's the way to check for dodgy connections in your cluster. Smack the top of the dash with your hand while driving. This will likely jar the connections enough to close the circuit for a brief second. Don't be shy about it. 'Whip it good.' If that works, it's a cluster connection problem. If not, check your wires. Just remember that it's a lot easier to splice a wire than to pull the cluster and reflow all the joints ...
