Speedometer not working

[jlevie]

What model/year is this car?

[Grackle]

Mine is an 86 325es.

[Grackle]

If the odometer gears are broken, the speedometer can still function normally, correct?

[TSI]

If the odometer gears are broken, the speedometer can still function normally, correct?

Yes.

[Grackle]

OK thanks, that's what I thought.

[jlevie]

The speedometer/odometer system is really pretty simple. The signal originates from the sensor mounted in the differential and then goes straight to the speedometer in the cluster. Given the pinouts of the cluster connectors (see http://wedophones.com/BMWManualsLead.htm) it isn't hard to check for continuity or shorts in the wiring. To check the signal you really need an oscilloscope with the rear wheels off the ground and turning.

[Grackle]

I found one that was a better match on Ebay. Hopefully this one works.

[Gregs///M]

All speedometers are interchangeable among all years of e30. VDO brand speedometers commonly have circuit board failure and require reflow, we do this almost weekly at Bavarian Restoration.

Before anything, replce (DONT check, just replace) all fuses associated with cluster, 10, 12, and 21. Also check rear differential speed sending unit. Make sure wires are not hard, brittle and connector copper is not oxidized.

[Grackle]

Thanks Greg. I had checked all that already. I got my "new" speedometer off of ebay, unfortunately the car is stuck on jackstands right now since I am redoing the suspension on the car. But I ran it up to 20mph in 2nd gear on the stands and this speedo works (at least to 20mph). So it is some sort of failure inside my original speedo, as all the solder joints "appear" to be OK. Though I haven't taken it into work yet and stuck it under a scope to be sure.