speedometer inoperative

[acoulter]

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

[jlevie]

Have you checked fuses?

[agent]

I am also chasing an intermittent speedometer issue. The odometer is mechanical, though what I am seeing is that the odometer's operation is dependent on the speedometer working. Correct me if I'm wrong Jim, but wouldn't a fuse either allow power to be supplied to the unit or prevent power from being supplied to it? Couldn't we safely rule out a fuse as the cause of an intermittently working unit?

[Gregs///M]

Fuse 12, 7.5 A

Or

Bad solder joint somewhere in the speedo/odometer.

[Gregs///M]

I am also chasing an intermittent speedometer issue. The odometer is mechanical, though what I am seeing is that the odometer's operation is dependent on the speedometer working. Correct me if I'm wrong Jim, but wouldn't a fuse either allow power to be supplied to the unit or prevent power from being supplied to it? Couldn't we safely rule out a fuse as the cause of an intermittently working unit?

Odometer operation is dependent of the speed sensor input from the sensor in the rear differential. This input drives the speedometer and odometer operation. If one of these gauges work, and the other does not, the problem is local to the non operative gauge.

For both to lose power, it would either be loss of power, ground, or speed signal. A micro crack on the fuse could cause intermittent operation. So can oxidized ground lug. Another culprit could be a bad/cranked solder joint from the many decades of road vibration.

[agent]

Yep, fuse 12 was blowing every time I jump-started my car until I replaced the battery. Fuse 12 also governs (OEM) radio power, so it was obvious when it was blown.

[agent]

Odometer operation is dependent of the speed sensor input from the sensor in the rear differential. This input drives the speedometer and odometer operation. If one of these gauges work, and the other does not, the problem is local to the non operative gauge.

For both to lose power, it would either be loss of power, ground, or speed signal. A micro crack on the fuse could cause intermittent operation. So can oxidized ground lug. Another culprit could be a bad/cranked solder joint from the many decades of road vibration.

I'm still of the opinion that my issue is localized to the speedometer itself. I recently sold a cluster to another forum member that worked perfectly in my car, aside from the known "late cluster in an early car gas gauge only going down to half way" caveat. I have not yet installed the refurbished SI board I purchased.

[bastianshaw]

you have a bad speedo the intermittent on/off of the odometer stressed the gears and they broke.

pull your speedo out and resoder w flux

[jeffnhiscars]

I have an intermittent speedo in one of my cars which responds well to a fist thump. Since it has new gears (which are driven by an electric motor) and the speedo and odo either both work or neither works, its clearly a bad ground or cracked solder and NOT bad gears.

[nando]

the speedo isn't run by any gears anyway.

[cabriodster87]

When i wiggle test the white C2 connector the speedometer/econometer responds.
(accessible from under dash, and drive wheels off ground)

[Gregs///M]

you have a bad speedo the intermittent on/off of the odometer stressed the gears and they broke.

pull your speedo out and resoder w flux

Ignore this. Bad odometer gears will not cause your speedometer to fail in any way.

[Ferdinand]

See this post for example of cracked solder joint in cluster.

http://www.r3vlimited.com/board/showpost.php?p=2417825&postcount=26

[bastianshaw]

Ignore this. Bad odometer gears will not cause your speedometer to fail in any way.

perhaps i wasnt clear the speedo failing intermittently placed extra "stop and go" stress on the gears causing them to fail.

[nando]

No, they don't run on the same motor or anything. The speedo motor has its own output from the odometer, they have nothing to do with each other.