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Thread: shelled out tranny

  1. #1
    Registered User
    Join Date
    Mar 2004
    Location
    Kansas City, Mo
    Posts
    8

    shelled out tranny

    Recently purchased a '78 R100/7 and shelled out the tranny in the first 500 miles. Are gearboxes a weak link on these old bikes? Someone suggested that sitting around trashes out the bearings and failure is common. Someone else has informed me that synthetic lube doesn't transfer the heat off the gears well and they overheat. Good source of used parts? Will another used tranny do the same? Any good rebuilt boxes out there? Any help would be appreciated trying to understand this thing.

  2. #2
    Brrr YB in IN's Avatar
    Join Date
    Apr 2003
    Location
    Bloomington, Indiana
    Posts
    1,185
    You might want to check out the tech pages at airheads.org in addition to info you get here. Good Luck!
    Garth Eppley
    1990 K75s
    Yankee Beemers Midwest
    Rounder No. 7
    Midwest Clan

  3. #3
    Blocking the slow lane
    Join Date
    Mar 2003
    Location
    Elburn, IL
    Posts
    1,843
    Both of the old Airheads we refurbished needed tranny rebuilds, which started with ruined input splines from LACK OF SERVICING. The input spline shaft is $300+, and as long as you've got the gearbox apart, get new bearings and seals in the thing. A rebuild bill of $1000 is not uncommon, and anyone who tries to sell you a rebuilt one for less probably didn't go all the way.

    The transmissions do last a long time when minimally maintained. My K75 gearbox has 180,000 miles on it with just annual gear oil changes and spline lubes every 3-4 years.
    Jon Diaz
    BMW K75/K12GT
    BMWMOA Ambassador

  4. #4
    James.A
    Guest
    I recently saved a long neglected transmission on an R75/6. If you go with a used box, try this.

    1-drain all the old gear lube.
    2-install transmission
    3-re-fill with fresh gear lube. I use 80w90 hypoid.
    4-using the rear wheel to turn the transmission, engage all the gears upshifting and back. If you have a helper you can do this holding in the clutch, otherwise take out the spark plugs.
    5-Run the bike on the road enough to cycle all the gears a few times.
    6- drain and re-fill.

    The transmission I re-habbed in this manner had sat un-used for 6 or 7 years. When we started, it would only shift into first and second, and then sometimes not hold second. After the proceedure, the box works fine. A good dose of insurance for any used gearbox.

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