BMW 318i Speedometer Problems, Inoperative – E30, E23, E24, E28, E31, E32, E34, E36
I have an 84 318i and the speedometer works only sometimes. I recall something about a plastic gear that needs to be replaced.
The gear replacement that you have eluded to would be for the odometer, not the speedometer. An intermittent speedometer can be due to a number of potential issues. An inoperative speedometer would typically fall into one of three scenarios. These points apply to; later E23 (7-series 83-87), later E24 (6-series 83-89), E28 (5-series 82-88), E30 (3-series 84-91), E31 (8-series), E32 (7-series 88-94), E34 (5-series 89-96) and E36 (3-series 92-98).
1) Speed sensor – The speedometer speed sensor is located in the rear cover of the differential. The sensor may need to be removed and cleaned, the wiring connector could be corroded or damaged, or the sensor itself may be bad. Inspect the harness plug and the actual wiring connections to the contact pins, under the rubber boot. You can perform a rudimentary test of the sensor by checking for AC-voltage from the sensor (between the two contacts), with the wheels turning.
2) Instrument cluster harness plugs – The harness connector plugs on the back of the instrument cluster may be a bit loose. Can you wiggle the connectors, while driving (or with the rear up on jack-stands) and get the speedometer to operate or not-operate?
3) Speedometer unit – There may be a problem with the actual speedometer head assembly. In this case, the speedometer head would have to be replaced. These can be special ordered at Bavarian Autosport 800-535-2002.
If it is the odometer that you are having trouble with (and the speedometer works fine), check out the link below, for more info (E23, E24, E28 & E30 only).