View Full Version : 86 - 735i - speedo, odo problem - any ideas?

11-17-2011, 03:38 AM
Both the speedo and odometer don't work. The tach, fuel consumption guage and all else on the cluster work just fine. I'm thinking that if it was the sensor at the differential I wouldn't get the tach reading. I took the cluster apart - there are 2 NiCads on the speedo side. Could this be it? Or capacitors maybe.

The old beast is pristine in and out - runs perfectly. It did sit in a barn for 2 years before it was given to me.

Thanks for helping.


11-17-2011, 04:39 AM
as you talk about battery in the cluster, that must be an E23. 1986 models is an E23 model, probably the last year of production, in Europe the E32 came into the market from autumn 1986 and in USA in 1987.
For E23 the best info is here
The 7 Series E23 Forum (http://www.bimmerboard.com/forums/e23/)

BMW E23 7-series information and links (http://www.e38.org/e23/)

Removal and Service of VDO Instrument Cluster
Old Sevens (http://www.e38.org/e23/oldsevens/articles_vdo_cluster.php)

Replacing Service Indicator Board Batteries on the E30 BMW 3 Series
Did your tach suddenly stop working? Have all your gauges suddenly gone dead for no reason? Are the service indicator lights dead? Chances are that the batteries on the service indicator board have gone dead. This is pretty common problem on the E30 BMW models. In this tech article we will discuss replacing the batteries and get that service indicator working again.

The E30 3 Series as well as other BMW models have a neat little feature that illuminates a row of lights over a certain amount of miles and informs you of when routine service needs to be performed on these cars. Normally, simply running the car re-charges the batteries and keeps the service indicator lights operating. Sometimes, however, the batteries can fail, causing the lights to go dead. It can also cause the tachometer and other gauges to stop working as well. In the case of my car, the lights stopped working as well as my coolant temperature gauge. The tachometer also started jumping erratically and then finally stopped moving.

As the batteries are located in the instrument cluster, it is necessary to remove the cluster. The first step is to remove the steering wheel. Use a flat-head screwdriver to pry out the steering wheel emblem, underneath; you will see a 19mm nut holding the wheel to the steering column. Make a scribe mark or paint mark to align the steering wheel in the right position when you re-install it. Now, remove this nut. Next, rotate the key to the on position, but do not start the car. Turning the key will disengage the steering wheel lock and allow you to remove the wheel. Now pull the steering wheel off.

The next step is to remove the lower panel under the dash, remove the three plastic screws in the front of the panel and the other three screws holding the panel on at the bottom. Now remove the panel. Next, we will need to remove the lower dashboard fascia panel in order to provide clearance to remove the instrument cluster. Reach up under the dash on either side of the fascia piece and feel for a knurled round nut on either end. Loosen and remove these nuts. You can now remove the fascia piece.

Next, look at the bottom of the instrument cluster; you will see four screws holding the mounting frame to the cluster. Remove these. Next look at the top of the cluster. You will see two screws holding the frame into the dash. Remove these as well, and pull the mounting frame free of the car. Use caution as you do this. The frame is very fragile and can break off the upper mounting flanges very easily.

Now, with the frame off, you can now remove the instrument cluster. This may take a little time, as you will have to rotate the cluster around so you can disconnect the various electrical connections in the rear. Take a look at the back and mark each connection. Now disconnect them all. You should be able to remove the cluster from the dash now.

With the cluster out, take a look at the backside. I should take this time to point out that not all gauge clusters look the same, BMW had a few different manufacturers for the clusters, but for the most part they look the same. You should see some Phillips head screws around the perimeter of the cluster. Remove all these, and you should be able to lift the backside of the cluster off.

Look at the center of the cluster. You will see a single Phillips head screw holding this plate on. You must remove this screw to access the S.I. board. Now remove the plate, and grabbing the board by each side, pull it directly out, using care not to break or damage the board.

Now, with the board out, look for the two Ni-Cad batteries, they wont be hard to miss. This is what we are replacing. Be sure to get a hold of two NiCad “AA” batteries that are 3-volts (not the regular ones you find in the store, they might have to be found at a specialty retailer like Radio Shack). You should be able to pick these up at Radio Shack or Frey’s Electronics. Note the service indicator LEDs on top. Simply pull up on the light board and it will pull off.

Next, get your soldering iron out and let it warm up. You will want to use a low-wattage soldering iron to remove the batteries; otherwise you risk frying the board. 10-15 watts should be the max. Also, familiarize yourself with the battery polarity and make sure you understand which way to solder these batteries into the board. Once the soldering iron is ready, unsolder the old batteries. They should pop right out of the connectors when the solder is removed. Before you install the new batteries, make sure they have had time to charge. Now, making sure that the polarity is correct, place the batteries in the connector, and then solder the connections. Keep in mind that we re working around sensitive electrical components, so it’s a good idea to use an anti-static wrist strap.

With the new batteries in place, now is a good time to test the various light bulbs in the cluster and replace any burned out bulbs as needed. I found a couple that needed replacement. Place the LED board back onto the S.I. board. Now, place the board back into the cluster and slowly push it into place, making sure that the pins line up correctly at the bottom. Re-install the access cover and the single Phillips head screw holding it in place.

Next, re-install the rear cover of the cluster and tighten the Phillips head screws. This done, we are now ready to re-install the cluster back into the dash. Reconnect the electrical connections on the back of the cluster, and rotate the cluster so it is oriented facing towards you.

Now, re-install the plastic frame around the instrument cluster and screw it down in place. Once tight, install the two screws through the mounting flanges and up into the dash. Take care when doing this that the cluster is properly aligned. If not, loosen the screws, re-align, and re-tighten.

Now, reinstall the lower dash fascia plate and reaching from under the dash, install the two knurled round knobs. This will pull the fascia plate tight against the cluster.

Now re-install the lower dash panel and tighten the three plastic screws in the front and the three screws in the bottom. With the lower dash panel on, use the scribe or paint mark from earlier and re-install the steering wheel. Once in place and when it is correctly oriented, put the 19mm nut back on and torque it to 50 ft/lbs. Place the steering wheel emblem back in place making sure it is lined up correctly.

BMW Speedometer & Tachometer Intermittent Operation – E23, E24, E28, E30, E32, E34 | Bavarian Autosport Blog (http://blog.bavauto.com/3891/bmw-speedometer-tachometer-intermittent-operation-e23-e24-e28-e30-e32-e34/)

BMW Speedometer & Tachometer Intermittent Operation – E23, E24, E28, E30, E32, E34
This answer is applicable for many BMWs in addition to the one listed below.

1987 325es (E30 chassis)
The tach and speedo work most of the time, but sometimes work sporadically.

Here is a write-up on the initial steps in tracking down a speedometer and/or tachometer problem.
Applies to: E23, E24, E28, E30, E32, E34 with speed sensor units mounted in the differential housing cover.

1) Speedometer – The speed sensor may be faulty. The sensor is mounted in the differential cover. Remove the harness plug and remove the sensor. Clean the sensor and measure the resistance (should be 0.0 Ohms). If there is any resistance higher than 0.0 (zero Ohms), replace the sensor. If the resistance reads correct, reinstall the sensor.

2) The wiring at the connector plug for the speed sensor (in the differential housing) may be faulty and corroded …. pull the boot back from the plug housing and inspect the wires and the pins.

3) The actual speedometer and/or tachometer head may be faulty. It may have a loose connection within it or a cracked circuit board.

4) The speedometer or tachometer head may be loose on the main instrument circuit board (do the gauges change or move if you smack the top of the dash, above the gauges?). Remove the instrument cluster and check the mounting of the speedometer/tachometer to the circuit board. See the attached issues of our Fast Times newsletter for assistance in removing the instrument cluster, on E30 3-series models (see the articles on replacing the PC board and replacing the odometer gears for info on the removal of the instrument cluster).

11-17-2011, 04:51 AM
Thanks Shogun. I'm thinking sensor since the tach is operating perfectly. I'll pull it and check the harness, clean and spray the connections etc. Will post the results of that.