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Speedometer Fixes

Flaky Speedo Fix

From: Rob Lentini
Date: Wed, 8 Mar 95 10:10:54 MST
Subject: BMW: Motometer Fix

Dan Eggert asked what can be done to fix Motometer speedometers on Ks:

Dan, I had numerous (I think 4 or 5) speedometer failures soon after I purchased my K75S new in ’87. Nothing really fixed the problem until Iron Horse in Tucson replaced the entire instrument module under warranty. New modules are identifiable by two small Gore-Tex vents on their undersides.

Assuming you’ve got the older type and can’t get it replaced for free, try the following:

Intermittent speedos are usually caused by a fault in the internal connector to the speedo subassembly. Remove the entire module from the bike and lay it on a towel, face down on your work bench. Remove all the perimeter phillips screws. Remove the module back cover being very careful to not damage the gasket. With the speedo to your right, you will notice a plastic arm with a printed circuit run that plugs into the speedo input connector. The speedo female-side contacts are usually the culprit. Corrosion can form between the male pin and female contacts, or the female contacts lose spring pressure on the male pin. What you’ve got to do is separate the connector, carefully bend the female contacts tight again, and reassemble with perhaps just a SLIGHT amount of copper anti-seize compound on the male pins to assure long- term continuity.

At this point it will be easy or hard on you. Early speedo connector arms had a service bulletin performed that actually called for sawing the arm in two, then cementing the connector to the speedo with RTV. If yours has had this done, you should be able to carefully pull the connector back and off the speedo to service the contacts. If the arm is unmodified, you will need further disassembly including removal of the instrument assembly from the bezel cover, and them removal of the speedo module itself–all this to get to the contacts! It can be done, requires patience and dexterity, but if you’re intimidated by all this have your dealer do the procedure. Hell, he may get you a new cluster courtesy BMWNA just to avoid the hassle of working on yours!

The new Gore-Tex Motometer modules supposedly have improved contacts, and the speedo connection is screwed onto the rear of the speedo, eliminating (or at least greatly reducing) vibration-induced loosening the the connector. My new module has been very reliable. I’ve only been into it to replace a burned out bulb.

Good luck!

Date: Wed, 8 Mar 1995 15:15:41 -0500 (EST)
From: Charles Goodspeed IV <CGOODSPE@CAIS.CAIS.COM>
Subject: BMW: Re: BMW K75 Intermittent Speedometers

I have experienced all of the intermittent problems previously mentioned regarding the speedo on my K75. I have taken it apart, cleaned everything, to no avail. I finally found that the little connector that is located under the right side cover, a 2 pin connector, was crudded up, thus the intermittent problem. I cleaned it and voila it worked, for a while. The next time it went intermittent, about 1 year later, I took apart the speedo unit, and noticed black corrosion between the 24 pins on the back of the unit, and the flexible copper circuit tape. The solution to this it to scrape away the corrosion, very carefully, and buy some rear window defrost fix-it paint from your local auto parts store, and paint each pin carefully. Let the paint dry, and then make sure the paint between adjacent pins is scraped away, or you may get a short. It this doesn’t fix your problem, I would be very surprised.

Early K Instruments – keepin’ em dry and working

By: Don Eilenberger

Keepin’ em Dry:

My ’85 K100RT would fog the instruments if there was a cloud within about 100 miles when I got it. Since these instruments are known to have moisture related problems, I decided there must be a cure.

Hint Numba 1 – vent it. It isn’t necessary to go the gore-tex route (although this would be nice). A single hole drilled in the back cover of the instrument cluster between the rows of pins will work fine, and be in a spot that doesn’t get wet. Disassembly of the instrument is recommended so you don’t drill into the guts.

Hint Numba 2 – seal it. This hint came to me from England – and if they don’t have moisture I dunno who does. After you add the vent above, and reassemble the cluster – carefully replace the useless “O” ring in the groove between the halves (it isn’t REALLY an “O” ring – it’s a foam ring..). Then using HIGH QUALITY (3M can’t be beat!) electrical tape – run a single layer of tape over the joint between the 2 halves. This will provide a very effective seal, and when mounted on the bike (especially on an RS or RT) is virtually impossible to find (and if you do it neatly – it looks like it belongs there).

Having done the above – my K has survived downpours, cold weather, hot weather, rides in the rain – and has never fogged up again.

Not a bit – really!

Cost – about $0.10 worth of electrical tape.

Making ’em work again:

As other people have noted – the big problem with the early K instruments was moisture induced corrosion of the pins and sockets connecting the various electrical goobers (tech-term) inside the instrument pod. Problems can be fixed, or avoided.. it can easily be done while the instrument is apart for the hole drilling to let the moisture out…

The instruments plug into each other and the main circuit board mostly using square pin connectors into square sockets.. your job it to make these connections good electrically, and prevent future corrosion.

Remove each component of the cluster with care – they unscrew and unplug. Haynes manual shows the process of disassembly.

Clean the connections as other people have described. On badly corroded connections – a bit of scraping with the edge of a tiny screwdriver until some bright metal is seen will help.

Then – the trick stuff:

Trick numba 1 – VERY carefully – take a good quality small pair of pliers (I would use ones with a tip about 1/4″ wide, and narrow ends), twist each square pin about 5 degrees (direction isn’t important). Be very careful not to damage the plastic they are mounted in (using two pairs of pliers is even better, hold the bottom of the pin near it’s mount and carefully twist the top just a tiny bit.

What you’re doing here is adding pressure to the connection, and exposing 4 sharp edges of the pin to the inside wall of the sockets, improving the electrical conductivity of the connections.

Trick numba 2 – (and thanks to Brian Curry for this one!) find your metallic based antiseeze and a toothpick. Goosh (tech term again) some antiseeze out on a clean surface (not much – you’re only gonna use a tiny amount, and it is messy stuff). Take the toothpick and pick up a tiny amount of the antiseeze. Push it into one of the square sockets. Do each one, with only a tiny bit of antiseeze.

What you’re doing here is two things:

1. Filling the voids so oxygen can’t get at the nice new connections you’ve made by doing hint numba 1. Some people have advocated using greases such as silicone – these are non-conductive, which isn’t good…

2. You’re increasing the conductivity – yep! The metallic based antiseeze is conductive. It’s the metal in it. (Usually either copper or aluminum).

Reassemble as per Haynes, reinstall and enjoy working instruments… unless you have a ’85 – in which case I’d suggest removing the fuel warning lamps (they don’t work worth a damn when they are working) and installing a FuelPlus+ – which is when I did all of the above!

The bending of the pins may have been an official BMW repair technique.. my pod had been repaired when the bike was about a year old.. and it continued working even with the severe fogging I experienced with it. The antiseeze is the icing on the cake.. too bad motometer didn’t do it at the factory and use something besides a swiss-cheese rubber ring to seal the things with!

More K-Bike Speedo Failure Diagnostics

By: Robert Bini
April 2003

It was my turn lately to have the speedo on my 1990 K75 pack up at 67000 miles. I followed the advice given previously on this site by scraping the connecting pins, twisting them slightly and reassembling with petroleum jelly, but to no avail.

However, the thought of the vast sums of money necessary to have BMW sort it out induced me to persevere and a bit of patience and the use of a resistance meter solved the problem.

Here is the procedure.

1) Check the sensor in the rear transmission and the continuity of the wiring between sensor and instrument panel:

  1. Disconnect the plug that connects to the back of the instrument panel.
  2. As you look at the two rows of female pins on the plug, connect a resistance meter between pins 2 and 3 starting from the bottom of the row on the left.
  3. A reading of approximately 280 ohms will confirm that all is well.

Should there be no continuity, note that the wiring has also a connector situated next to the rear brake fluid reservoir.

2) Check continuity within the instrument panel

  1. Open the instrument panel by undoing the 9 screws.
  2. Lay the panel glass face down. The male connections to the above plug nearest to you.
  3. The matching pins are now 2 and 3 from the bottom of the row of pins on the right. They are connected by the ribbon to the small oblong printed circuit board immediately to their right. This board is the speedo signal amplifier.
  4. Note the connecting plug between the ribbon and this board, it has 4 contacts.
  5. The first two contacts on the left of this plug are directly connected by the ribbon to pins 2 and 3.
  6. Check for continuity by connecting the meter to the FEMALE contacts of the socket, just visible on the underside, which, feed the sensor signal to the amplifier chip on this board.

In my case there was no continuity between male and female contacts of the first terminal on the left. I was surprised at how much scraping, reconnecting and retesting was necessary before continuity was re-established, even though there was little evidence of oxidation.

A further connection can be traced from the fourth pin of this plug to pin 3 of the 3 pins plug right on top of the speedo itself. I take this to be the amplified output signal fed to the meter.

Clearly, the above procedure only checks the path of the un-amplified signal, but as this consists of a very small current, it is the most likely occurrence of a break in continuity.

More Comments on Speedo Problems/Fixes

Date: 9 Aug 1995 09:24:48 UTC
Subject: BMW: K75 Speedo Problems

Jim Colburn enters the world ‘o K:

>The speedometer on the 1986 K75C that I just got has stopped working. The
>previous owner says “just tap it/honk the horn/wait a while” and it’ll start
>working again. Is there a cheapish way to fix it? I see from Capital Cycle’s
>catalog that they only stock the whole instrument cluster at $625….. is
>the speedo available separately? I tried calling speedo-fixer Irv Simon and
>he says he can’t repair it.

Something I recently learned about the speedo is that it may be the pickup cable from the final drive to the head unit. When it craps out, try wiggling the wire down on the swingarm and see if anything comes of it. My speedo has shut itself off for about 40 miles on two different occasions this summer (both stinky hot days, FWIW), but since the last hiccup it has been fine for about 1200 miles. Weird.

If the turn signal stays on forever, then it is likely this cable. If it turns off, then the unit is still reading distance and you have the pin problem inside the speedo assy.

Just another thing to check……and this wire goes for $52 (dealer invoice $35 or so :)). I checked.

jon diaz

From: (Chuck Hawley)
Subject: Re: BMW: K75 Speedo Problems
Date: Wed, 9 Aug 1995 13:27:43 -0500 (CDT)

I found the intermittent contacts to be where the speedo plugs into the printed circuit board inside the housing. Just moving the unit around seems to clean the contacts for awhile. I installed a small 3 pin plug and socket on both of our ’86 K100’s, and they seem to be cured. I introduced a problem on one of them in that when I soldered to the signal input on the circuit board on the speedo, the trace connected to it became unconnected. This caused the symptom where the speed needle goes full scale and wanders around in general. So I found that eventually and fixed it. Incidentally, the input to the speedo pins are signal, gnd, and +12 looking at the back of the speedo unit. The signal comes from the small circuit board strip attached to the back of the speedo (on the later units it’s attached to the main circuit board, but is still in the same location). The signal that this board puts out is a 0 to 6 volt square wave, and is sent to the speedo unit signal input pin (it also goes to the turn signal unit via the main housing connector). The input to the amplifier strip is the pickup unit on the bevel gear housing. I found that a 90 Hertz square wave gives about 80 MPH. You could figure this out by counting pickup pulses for a wheel rotation…etc.

Does anyone know what the chip on the speedo PC board is? It is a stepping motor driver for the odometer, and puts out a current proportional to freq. for the meter (speedometer). I have never known one to go out, but it would be good to have a spare chip. The amplifier chip is an LM2904. This one sounds available.

I wish I had a few of the jillions of K instrument units that were thrown out. I feel that we could make all of them work. Oh. Also I fixed the trip odometer. Two of the wheels would not reset. They needed to have a couple of nibs glued back in place inside the wheels. It’s tiny but able to be done.

Charles Jack Hawley Jr.
Amateur Radio KE9UW (A.K.A. ‘Chuck’ in Ham Radio)
BMW K100RS BMWMOA #224 (A.K.A. ‘Jack’ in Motorcycles)
Sr. Research Engineer Emeritus
Univ of Ill, Urbana-Champaign

Date: Wed, 9 Aug 1995 15:22:45 -0400
From: Rob Lentini

Ah, the Motometer shuffle, again.

You probably don’t have the updated instrument pod, identifiable by two Gore-Tex vents on the back cover (and internal electrical improvements).

Do the easy stuff first:

  1. Remove, clean, and reinstall the speedo inductive transmitter located on the top of the final drive. Be careful not to let dirt enter into the open hole.
  2. Remove the right battery cover and black plastic alternator cover. Separate, clean, lubricate, and reconnect the two-wire connector coming forward from the inductive transmitter. Use silicon grease to lube.
  3. Separate, clean, lubricate (again with silicone) the two strip connectors on the back of the instrument pod.

If you’re lucky, the speedo will work. If not, options:

  1. Take the bike to a dealer. They may update the old-style pod with the “new/improved” version (and it really is, BTW).
  2. Let them attempt to fix what must then be a failed speedo module inside or, more likely, an internal connection problem at a strip connector on the back of the speedo module.
  3. Or, YOU open up the back of the pod and repair the (probable) bad connection on the back of the speedo. Delicate work, my friend, so be REAL careful. The haynes manual shows the basics of back panel disassembly and bulb replacement–that’s all. If you’re careful, patient, and not a klutz, you have little to lose at this point.

Don’t give the bike back! This problem is fixable and not expensive. Good luck.

Rob Lentini
’87 K75S
Tucson, AZ
K Whiner MC#11

Date: Wed, 30 Aug 95 10:47:43 EDT
Subject: K-Bike Speedo Problems

I have an ’88 K75S. The speedo has failed 3 times. First two replacements were done under warranty at dealers stateside. The third Lone Star BMW sent me a unit to replace myself. Did so, same problem. Turned out that the sensor ring in the final drive had come loose. Fix is to take the final drive apart, epoxy the ring back in place, put back together.

Tom Yeager, AKA Rainman

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