Intermitten speedometer and trip odometer.

[cat0020]

Now that it's getting cold again, the speedometer and trip odometer on the 1987 K75 Standard seems to be working intermittenly. Within the first 6-8 miles from my house to work, the speedometer sometimes stays below 20 mph even though I am traveling much faster and teh trip odometer does not keep acurate milerage... I think/hope the odometer keeps accurate milerage.

My question is:

 

Are the speedometer and trip odometer connected to one another and seperated from the occumulative odometer?

 

[kioolt]

The trip meter,odometer, and speed meter are all hooked up to the same sensor on the rear drive. I would suspect that since you have two of the three that you know are not working right than the third one is probably not working right either. Anytime the speedometer on my 91 K100LT would act up all I had to do was to reseat the connector coming off of the speed sensor. That has fixed it everytime that it has happened to my bike. Not that there have been that many in the last 14 years. I don't remember having any trouble for several years now.

[Dennis Andress]

They all did that....

 

The speedo housing isn't vented on early K's. Sometime along about 89 they added a couple of Goretex covered holes in the housing to let moisture out. About all you can do is disassemble the speedo and clean every little electrical contacts. Eventually this will stop working when the contacts are worn.

[RFW]

Now that it's getting cold again, the speedometer and trip odometer on the 1987 K75 Standard seems to be working intermittenly. Within the first 6-8 miles from my house to work, the speedometer sometimes stays below 20 mph even though I am traveling much faster and teh trip odometer does not keep acurate milerage... I think/hope the odometer keeps accurate milerage.

My question is:

 

Are the speedometer and trip odometer connected to one another and seperated from the occumulative odometer?

 

 

OK, Here's how it works. The sensor at the rear sends "pulses" (OK, it sends a speed-dependent pulse train) to the instrument cluster. There, the electronics drives a stepper motor at a speed proportional to your bike's speed. The little motor then drives a conventional speedometer/odometer/trip odomoter (just like a normal speedometer cable would do, if you had one).

 

So basically, to answer your question, the speedo and odometers are mechanically related. If 2 (probably 3) are not working, then look for a common cause.

 

The "common cause" is probably that you need to remove the sensor at the rear (just one screw), and thoroughly clean it of any metallic debris. It has a small magnet in it, as I recall, and that may attract steel shavings that may cause it to malfunction. I believe the sensor is a Hall Effect chip that has a small magnet near it, and the rotating of a toothed ring in the rear end causes the magnetic field sensed by the sensor, to fluctuate, resulting is the transission of the pulse train I mentioned.

 

In fact, this happened to me some time ago (I have an '86 K100RT). All I had to do was wipe the thing clean.

 

The only other thing that could happen is that the electronics that controls the speed of the little motor in the instrument cluster, is hooped. As someone mentioned, this could be related to moisture accumulation causing corrosion.

 

In the late '80s BMW replaced a lot of these clusters with new ones that had a pair of Goretex-covered breathers. Check yours. The breathers are 2 round plastic bits about a half inch in diameter on the bottom surface.

 

If cleaning the rear sensor doesn't help, then disassemble the cluster and check for corrosion. The cluster is full of FPCs (flexible Printed Circuit Boards) that are reasonably robust, but you should be careful not to tear them. The disassembly and reassembly of the instrument cluster is very straightforward (if somewhat complex), so you shouldn't run into any serious problems if you have at least a modicum of mechanical skill.

 

Bob.

[RFW]

One more thing I forgot.

 

Check the connections between the rear sensor, and the instrument cluster. In particular, unplug and re-plug the small 2-pin connector under the right-side side panel a few times, and also the connectors that plug in under the cluster.

 

If you have some silicone grease available (Dow Corning #4, or #111 silicone grease), then squirt a blob into each connector. NEVER use ordinary grease since it is moisture sensitive. Vaseline can be used in a pinch.

 

Bob.

[cjack]

The trip meter,odometer, and speed meter are all hooked up to the same sensor on the rear drive. I would suspect that since you have two of the three that you know are not working right than the third one is probably not working right either. Anytime the speedometer on my 91 K100LT would act up all I had to do was to reseat the connector coming off of the speed sensor. That has fixed it everytime that it has happened to my bike. Not that there have been that many in the last 14 years. I don't remember having any trouble for several years now.

 

As some have noted, the speedo, odo, and trip are all related to the pulse input from the rear drive. There are very few problems from the inductive pickup at the rear drive. Cleaning the inside surface of it probably won't help, but do it. Then there is the two pin connector at mid bike right side. Make sure that is clean and a good connection. The problem is, however, most likely inside the pod. The most common issue there are the three pins which convey power to the speedo itself. I have cleaned, coated, etc. these pins, and the only sure fix is to wire around them from the speedo to the circuit board. The next issue is the pulse amplifier four pins. Again the permanent fix is to wire around these four pins. You can tell if it is the amplifier or the speedo by using your turnsignals. If the cancel distance is much longer than normal or non cancel, then the problem is in the amplifier. If the cancel is normal, then the problem is in the speedo pins. This is because the cancel signal comes from the amplifier output, which also goes to the speedo.

On the subject of moisture, I sealed the clear face plate of the pod from the inside on our '86 K100RSes fairly early on, carefully with super glue, and had no more moisture problems. This is where the moisture was getting in.

[bmwmick]

Go here: http://ibmwr.org/ktech.shtml and page down to Instrument Cluster. Begin reading. My vote is for an intermittent connection/corrosion inside the pod.

 

Mick

[cat0020]

Thanks for all the replies..

I checked out the IBMWR sire and FAQs.. excellent

[RFW]

Jack,

 

Good description of the possible problem scenarios. By the way, you're right: the sensor is an inductive sensor, not a Hall Effect one as I had suggested.

 

Do you have an actual detailed schematic of the instrument cluster electronics? I was thinking of reverse engineering it myself (for lack of anything better to do), but I'd be interested if one already exists; it'd save me the trouble!

 

Bob.

[Bruce C]

One more thing I forgot.

 

Check the connections between the rear sensor, and the instrument cluster. In particular, unplug and re-plug the small 2-pin connector under the right-side side panel a few times, and also the connectors that plug in under the cluster.

 

If you have some silicone grease available (Dow Corning #4, or #111 silicone grease), then squirt a blob into each connector. NEVER use ordinary grease since it is moisture sensitive. Vaseline can be used in a pinch.

 

Bob.

 

This is the spot where my '85 K100RT speedo screwed up. The point of connection is on the forward leaning frame member just above the rear brake reservoir.

Bruce C