Dead Tach - K75C

[offroadcruiser]

I have an '86 K75C and the tach as decided to stop working. About the same time the speedo quit as well. With the vast amount of information available on the web I was able to get my speedo going again. The tach is still dead.

I have taken the instrument cluster apart and cleaned it and the contacts. I have disconnected and re-connected the computer under the seat. I have cleaned all the coil connections. I have checked all the fuses. No luck. The tack just lays there.

Any ideas?

Thanks.

[dlearl476]

Originally posted by OffRoadCruiser
Any ideas?

Thanks.

Ebay.
Sounds like you've done everything to confirms it's NOT the well know intermittant connection problem. You could also try Palo Alto Speedo, but I think you'll find a better deal on Ebay.

[breyfogle]

As common as a failed Tach is on K-bikes, I have to still suspect contact corrosion. Are you SURE you cleaned the Tach connector ? With the Speedo/Tach unit sitting face down and the back off, the problem connector is a three prong thingy that sits near the top center of the right hand side.

[deilenberger]

Originally posted by OffRoadCruiser
I have an '86 K75C and the tach as decided to stop working. About the same time the speedo quit as well. With the vast amount of information available on the web I was able to get my speedo going again. The tach is still dead.

I have taken the instrument cluster apart and cleaned it and the contacts. I have disconnected and re-connected the computer under the seat. I have cleaned all the coil connections. I have checked all the fuses. No luck. The tack just lays there.

Any ideas?

Thanks.

Can we assume you followed all the instructions given on the IBMWR K-tech pages? Including using something to enhance conductivity of the internal connectors on the instrument pod?

The coils and fuses won't do much for you (but it doesn't hurt anything to clean them and check fuses) since the tach receives it's signal off the ignition module which is located under the fuel tank (right behind the steering head). It's worth looking at that connector since the rubber boot on your connector has undoubtably gone to rubber boot heaven by now. Remove it and use some electronic contact cleaner.

If this doesn't work - you're to the point where more advanced diagnostics are needed (such as looking for the signal at the pod connector with an oscillosope), or looking for a replacement tach. As someone mentioned - it's likely to be least expensive to keep your eye open on the IBMWR Marketplace or on EBay under Euro bike parts. There are also some bike-wrecking yards that might be able to help you out.

A few tricks besides the ones mentioned on the IBMWR tech pages to help assure conductivity in the instrument pod are:

1. Put some foam-rubber on the back of each of the long arms (with contacts) inside the pod. Something about 1/8" thick is ideal.. The rubber will push the arms into better contact with the circuit boards when the pod is reassembled. BMW did this on the late model pods and it did help.

2. Find Stablant#22 - a very expensive and very good contact conductivity enhancer. It's available at NAPA auto parts stores - something like $60 for 10cc's. 10cc's doesn't sound like a lot - but you need very little of it on every contact. If forms a molecular layer that helps electricity flow from one metal to another, and resists flow on insulators such as plastic. Good stuff, just a bit expensive. The NAPA part number is CE1 (for Contact Enhancer 1).

BMW specifies this for use on their cars in low voltage/low current signal paths, which is exactly what the tachometer circuit is.

Use just a tiny drop on each contact before assembling them. They just have to be damp - not dripping.

HTH - electrical problems can be a real PITA..

Best,