Moisture in Tachometer

Discussion in 'Airheads' started by Vertical Pilgrim, Jan 18, 2013.

  1. Vertical Pilgrim

    Vertical Pilgrim Adventurer

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    Dec 21, 2012
    Oddometer:
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    Upstate SC
    The '75 75/6 and I got caught in the rain yesterday. I went for a ride today and noticed that there is now moisture in the tachometer (but not the speedo) and the center turn signal light failed to blink on at least one occasion. Any suggestions or lessons learned before I go figuring out how to disassemble my instrument panel and try to dry it out?

    Thanks for the help.
    #1
  2. craydds

    craydds Long timer

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    Here in Nuevo Mexico, it would dry out in a day or two. You likely have HUMIDITY. Take it apart, dry it out. See if you can find how the water got inside.
    #2
  3. riceless

    riceless Let's Ride!

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    My 83 R100RS does that too :ddog
    #3
  4. craydds

    craydds Long timer

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    Humidity; a phenomenon I have read about. What is it - exactly?
    #4
  5. disston

    disston ShadeTreeExpert

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    There are several bolts on the bottom holding the speedo/tach to the mounting bracket. Remove the speedo and tach cables. If the cables are not tight you can unscrew the large nuts with finger tips, often you will need some small pliers to get the large nuts loose. Careful not to scratch the large nuts with pliers. Remove small Phillips head screw holding big black plug for wiring harness on to back of speedo/tach.

    [​IMG]

    Once you have the piece off the bike and in your hands it's disassembly will be self evident. A number of small screws, be careful with them these parts are no longer available from BMW and the small screws are not a size you will find in the corner hardware store.

    Parts #11, 4 and 16 are the seals that keep moisture out. It should probably be considered moisture resistant and not moisture proof under the best circumstances. In addition the glass lenses on the front are often not sealed too well. After you dry it out and air it out it will be fine till the next time you ride in the rain maybe or if it gets very humid the moisture can accumulate on it's own. We used to replace these seals sometimes but they are not available anymore. You can't just glue the whole thing together because the unit does need to be able to be taken apart for repair.

    Look for cracks in the plastic case pieces especially part #2. These you might repair with some RTV or something.

    When you put it all back together do not over tighten the screws. This is how the covers often get ruined. No more than snug is tight enough.
    #5
  6. Wirespokes

    Wirespokes Beemerholics Anonymous

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    disston pretty well nailed it.

    I will add that the small slotted machine screws thread into brass inserts in the housing. They often corrode and seize in the brass. When removing those screws, if they don't unthread easily - stop! Continuing often breaks the insert loose in the boss, breaking the plastic.

    The best action when they're stuck, is applying some penetrating oil. Work the screw a fraction of a turn each way to help the lube penetrate down in there.

    On re-assembly put a dab of anti-seize on the threads to help prevent future problems.

    If the lenses get bumped it's possible for their mountings to come unglued. With the eyebrow removed, gently pull up on the lens. If movement is detected, it'll need resealing.
    #6
  7. Vertical Pilgrim

    Vertical Pilgrim Adventurer

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    These replies are fantastic. Thanks so much for the help.
    #7
  8. ME 109

    ME 109 Long timer

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    Real careful with the screws that hold part 9 to part 2. they will bust out of the plastic very easily.

    Check that rubber seal 16 is intact, and in place.
    Motobins have the seal 16 if needed.
    #8
  9. chasbmw

    chasbmw Long timer

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    The housing for your bike is NLA as is the plastic circuit board, so you need to be very careful.
    #9
  10. boxerboy81

    boxerboy81 Stay Horizontal

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    http://www.pbase.com/dwerbil/1978_r1007_odometer_repair

    When you take the rubber eyebrow off the instruments, you'll see the glass has a metal trim. Over time that trim can collect water and the trim can deteriorate. Be careful removing the rubber eyebrow, otherwise it may separate, if it is a wee bit loose.
    #10
  11. Paul_Rochdale

    Paul_Rochdale Been here awhile

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    When I had a K100RS, the instrument cluster would sometimes mist up and a tip then was to drill a series of tiny holes, 2mm would do it, along the lowest point as this would allow any moisture to drain away and allow the internals to 'breath'.
    #11