R80 Tach Needle doing the dance

The tach needle on my 86 R80 starts bouncing around at sustained high speeds. It looks just like the speedo needle does when the speedo cable is on it's way out. Only the tach on an 86 is electronic. The needle is fine a lower speeds. I tried damping the instrument pod with my hand but the pod wasn't really shaking much and it didn't appear to help much (I have to admit this was a quick experiment since I didn't get this old by riding one handed staring an the tach).

The R80 rarely sees sustained highway use, but since I have been slowly rehabbing it, I have been using it more than the other bikes.

Any thoughts? Do BMW electronic tachs get tired?

Likely something in the electronics is breaking down. My /7 has an electronic tach. It get its signal from the coils...the rate at which they collapse as the ignition works is converted to RPM. Snowbum has a page here:

http://bmwmotorcycletech.info/tach.htm

Contact Terry Vrla and get his opinion and estimate for the repair.

Thanks, I've sent Terry a note

I contacted Terry Vria who was both prompt and helpful in his responses. He suspected that it wasn't the tach itself so I did some more testing.

The bouncing tach needle appears to have been due to a poor electrical connection. I damped the instrument pod with a foam wedge and the tach needle oscillation was reduced and it also started to act like an ohm meter when someone makes and breaks the connection.

Since I have always been dissatisfied with the instrument lighting and the circuit boards have been known to be dodgy as they age, I ordered a Katdash and some Deoxit (terminal cleaner) from the Katdash folks. After removing the board it was clear that the tach wiring on the board was too robust to be damaged, but I installed the Katdash anyway. I used the Deoxit on all of the connections and also tightened the tach ground connector which seemed to be a bit too easy to unplug. The net result is that the tach is back to normal.

As a positive side effect, the Katdash lighting is so much better than stock I have done the upgrade just for that reason alone. It also adds a diode in the alternator circuit so you are no longer at the mercy of the charging light for your alternator function. I hadn't realized how crappy the stock lighting was until I was testing the bike after the install. I caught myself sitting at a stop light tilting the bike and angling my body to cast a shadow on the instruments so that I could see if the turn indicator was on. Definitely no longer necessary with the LED conversion.