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Thread: Speedo gremlins - '85 K100

  1. #1
    Carguz
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    Speedo gremlins - '85 K100

    I recently replaced all the gears and LCD display and all was well until a couple of weeks ago. The speedo from one ride to the next started registering erratically. It either doesn't work at all or sometimes maxes out at 40 mph.

    It's actually gone back to working a couple of times but mostly is between not working or maxing out at 40 mph.

    I removed the sensor tube and all looked clean. I cleaned it with a rag anyway and some choke solvent, to no avail.

    Any thoughts? Obviously no speedo is a real pain as it registers no miles and doesn't turn off the turn signals.

    Thanks.

  2. #2
    Registered User godzilla's Avatar
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    Did it happen to rain shortly before it went wonky on you? If so, maybe your glass needs resealed.

    Also clean the connector cable on the back. That can cause problems.

    These speedos are a known problem on the early K's. Mine got wet and was so bad I had to replaced it. I went from 113K down to 31K! I HATED that!
    Godzilla!
    '85 K100 "ZoomZoomZoom"
    '71 R75/5 "Zippy"

  3. #3
    A bozo on the bus deilenberger's Avatar
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    Two thoughts:

    1 - Simple one. There is a connector - black, squarish, on the right side frame tube that goes up toward the front of the bike (there are actually two one with round pins, one with flat pins.) Disconnect and clean these connectors. (One is the brake light switch - the other is the speedo sensor wire from the rear wheel.)

    2 - Less simple. Visit www.ibmwr.org - look under K-tech, there are quite a few articles there on repairing early K bike instrument clusters.
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  4. #4
    Carguz
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    I have already cleaned the wheel side. Where does it lead and does that need cleaning too?

  5. #5
    A bozo on the bus deilenberger's Avatar
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    Quote Originally Posted by Carguz View Post
    I have already cleaned the wheel side. Where does it lead and does that need cleaning too?
    It's not clear to me what you mean by that...

    I'm not talking about the sensor itself - I'm talking about the connector where it connects to the main harness (and that's where it goes.)
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  6. #6
    Mars needs women! 35634's Avatar
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    another possibility, mine used to max out around 4o, then started sticking there when
    stopped. The needle was binding on a warped faceplate. I was able to shim the face-
    plate down a little and pull the needle up on the shaft enough to fix it.
    1987 K75S
    Original litter
    Original owner
    2012 Ural Gear Up

  7. #7
    chuck_donahue
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    I have an 85 k100 too. Mine has 2 speedometer's. When one stops working due to riding in in the rain ( I do that alot) I swap them , open it up and let the wet one dry, clean the contacts, and put it on the shelf untill the next long rain ride.

    My advice would be open it up again, clean all the contacts, bend all the male pins just alittle at the top ends so when they go into the female conncctor they scratch a fresh line in the metal connector, to make better contact.

    And if the gasket is original ......... get a new one.

    Just my .02
    I know with inflation I owe you another dime

  8. #8
    Registered User 41107's Avatar
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    if it is the original 85 speedo then it does not have vent holes in the back of the housing.Mine used to steam up on the inside until i drilled about 3-4 little holes,1/8 in dia. into the back (top centered).The newer ones had ,i believe ,2 larger holes covered with kevlar for venting.Moisture on the numerous pin connectors inside the speedo causes all sorts of weird problems.
    If handy take the thing apart and really go over it good.I had a problem like yours and it turned out to be a intermittent contact from a pin to the circuit strip (bad solder joint).
    If you have a Ohmmeter check the pick-up in the differential.As you spin the wheel there should be a reading( if i remember correctly something like 1280) and a drop to zero. This you do at the little square (black & yellow wires) connector that should be next to the coolant overflow tank on the frame.If that works and you checked the things D. Eilenberger mentioned you are now up in the speedo it selfs.Almost forgot.Inside the speedo there is to the lower right a little board held in place with 2 screws.This is the the part that takes the signal from the pick up in the differential and converts it to voltage to drive the needle and odometer.Mine was fried at one time.That was an other fix.The dealer actually could get me the little board for a lousy $38. Happy wrenching and good luck
    Karlheinz
    1998 r1100 rt/p
    1985 k 100 rs
    2001 k 1200 rs
    99 740 il

  9. #9
    K Bikes Complex by Choice cjack's Avatar
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    Quote Originally Posted by deilenberger View Post
    It's not clear to me what you mean by that...

    I'm not talking about the sensor itself - I'm talking about the connector where it connects to the main harness (and that's where it goes.)
    Ditto. If it doesn't cancel the ts, then it is probably not getting into the pod. So the end of the lead on the sensor stretches to just about the right rear of the gas tank on the left side. It plugs into the main harness there. It has been known to be an issue. Clean it and try to pinch the female pin sockets slightly tighter if you can.

    Otherwise, it's at the back of the pod on the big connector...or just inside where the pins are staked into the ckt board...or at the four pin strip where the trace goes after it comes off the staked pin. Not likely though...usually the connector at the right rear of the tank.
    BMWMotorcycles, fun when they're running...
    My other bike is a BMW.
    Jack Hawley MOA and RA #224, KE9UW ("Chuck")

  10. #10
    Layton layton's Avatar
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    I cleaned my contacts on the cluster with a pencil eraser..... works but it aint accurate... got an older r80 and the speedo on it aint accurate......come to think of it my 325 is and my 525 wagon speedos arent that accurate either.....could be a bmw thang!

  11. #11
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    Pull the sensor in the final drive and look inside with a flashlight to see if your speedometer drive ring is loose. These frequently get loose, you can probably use a pencil to see if it spins independently of the wheel turning. If it is loose, you'll have to take the drive apart to fix it, plan on a new bearing, and a new ring. Will also take some heat to loosen the drive bolts up.

    Had the same thing happen to me, exactly as you described it and wasted a bunch of time thinking it was the cluster.
    Dave Stockslager
    2002 R1150GSA "Fat Bastard", 85 K100RS SOLD
    South Coast BMW Riders web page: http://www.scbmwrc.com/
    Hermosa Beach, CA

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