Airhead transmissions

Discussion in 'Airheads' started by Touchthewindrider, Nov 22, 2010.

  1. Touchthewindrider

    Touchthewindrider Touchthewindrider

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    I'm just now finishing up on a rebuild of 72' R75/5 SWB. Apparently,
    a PO swapped transmissions, from the original four speed to a five speed.
    In replacing the neutral switch the switches are listed as: "to 9/75" and
    "from 9/75."

    The question is: how do you determine what year "model" your tranny is?
    Serial number on the tranny?

    Thanks!
    Cliff
    #1
  2. wirewrkr

    wirewrkr the thread-killer

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    look on the front face of the trans and see what year stamp is on it.
    But if it worked properly just buy the same one that you have now.
    the two switches look and work different.
    #2
  3. Touchthewindrider

    Touchthewindrider Touchthewindrider

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    Oddometer:
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    I checked out the numbers on the transmission and all I could find
    were the following: Y12131

    I wrote BMW and received this:

    "The old generation Gear Box cover has the 1352153 and the new is 1243097 the material alu row is biger."

    They also sent the engineering drawings for the two switches, neither indicating which belongs to which production years.

    Just thought I'd pass this along.
    Thanks!
    Cliff
    #3
  4. crazydrummerdude

    crazydrummerdude Wacky Bongo Boy

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    Unless wirewrkr and my memory are both wrong, there is a date stamp on it. A circle with a 2-digit year.
    #4
  5. mark1305

    mark1305 Old Enough To Know Better

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    The key words in the discussion are "front face" which is where the date stamp should be found as per wirewrkr; and "gear box cover" which is the info BMW replied with.

    The date stamp on the front cover is the info to go by.

    Or, if the old switch will work intermittently, use an ohm meter to see if it is normally open or normally closed. For example the boxes that have been in my 83 R80 (one an 83 box and one and 84 box) use the switch that is normally closed and passes current through it to light the neutral light. When in gear, the profile of the shift pawl pushes in the button in and opens the switch turning the N light off. If I'm not mistaken, that is the style from at least the early 80s onward.
    #5
  6. batoutoflahonda

    batoutoflahonda Long timer

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    #6
  7. Xcuvator

    Xcuvator Justa Venturer

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    As far as I have ever been able to tell, the only difference between the switches is that one is normally open and the other is normally closed.
    So the switch needs to be compatible with the way your bike is wired. Since the change in wiring/switches occurred 9/75 and your bike is a 72, my money would be on the early switch as the one you need.

    The wiring on your bike could have been changed, so to be sure, I would try to find out which way the switch you have works. I just grabbed a switch marked "early" and it is normally closed, but I'm not 100% sure it is marked right. I can't remember which is which.
    #7
  8. Wirespokes

    Wirespokes Beemerholics Anonymous

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    Xcuvator - his trans was changed to the newer five speed (it came with a four speed) and we don't know which one it is.

    Hopefully it's the earlier one since those are much cheaper. :wink:
    #8
  9. Xcuvator

    Xcuvator Justa Venturer

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    What I was trying to say is the bikes wiring will determine which switch he needs. I have changed a transmission and had to use the original neutral switch in order to make it work.
    #9
  10. TimTowtdi

    TimTowtdi Been here awhile

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    Actually the shift mechanism inside the trans determines which switch is needed. The wiring is the same regardless.
    #10