Airhead Transmission inspection

Discussion in 'Airheads' started by sigpe57, May 14, 2012.

  1. sigpe57

    sigpe57 Been here awhile

    Joined:
    Oct 11, 2005
    Oddometer:
    349
    Hi,

    Can you inspect the condition of a airhead 5-speed transmission when it's out of the bike? or it needs to be in running condition?

    What are the symptoms of a transmission when it needs a rebuild?

    Are the parts and gears available from BMW?

    Thank you for the reply,

    TT
    #1
  2. benthic

    benthic glutton 4 punishment

    Joined:
    Dec 24, 2011
    Oddometer:
    397
    Location:
    sunny san diego
    you can't really inspect anything without opening up the gear box, and that has to happen with it out of the bike.

    I just had mine rebuilt and it was $550 labor, and i needed $450 worth of parts. If I had only had it "inspected" - stopping after the case was opened to see how bad it was, I still would have had to pay a couple hundred $'s. I believe all the parts are available new. or at the very least, used.

    some symptoms would be lots of metal on the magnetic plug, lots of bearing noise, difficulty shifting...

    Hopefully some actual knowledgeable people will chime in:)
    #2
  3. sigpe57

    sigpe57 Been here awhile

    Joined:
    Oct 11, 2005
    Oddometer:
    349
    Bob's bmw- $385 labor- Parts $220-$360. Total $740. Has anyone done the rebuild with good result and cheaper price?
    #3
  4. benthic

    benthic glutton 4 punishment

    Joined:
    Dec 24, 2011
    Oddometer:
    397
    Location:
    sunny san diego
    just be warned - I was initially quoted the same estimate for parts. It doesn't always work out that way;)
    #4
  5. disston

    disston ShadeTreeExpert

    Joined:
    Mar 22, 2011
    Oddometer:
    12,311
    Location:
    Silver Spring, Md
    That sounds like a good price for a rebuild at a dealer but I'm not surprised by which dealer that is, Bob's. Look's like the bare minimum parts tho, nothing wrong with that, probably all it needed. Bob's is one of the few dealers recommended regularly for Airhead repair and that includes transmissions.

    There are maybe a dozen known mechanics around the country for Airhead 5 speed repair. It's recommended to use somebody with experience and a proven tract record. This does mean that sometimes you will have to ship the trans to somebody who can do the work.

    In the bike the best indicator of problems is metal in the oil, on the magnetic plug, when the oil is changed. There will be a bit of soft black substance on the magnetic plug of a healthy transmission. This is soft when squished in the fingers. The danger signal is gritty, starts small like sand grains, particles. This harder metallic swarf is disintegrating bearing metal. If you find hard gritty metal on the magnetic plug the trans is ready for a rebuild. It can be postponed for a couple hundred or a couple thousand miles but it gets worse and the longer you wait the more expensive it is likely to get.

    High mileage 5 speeds get several problems that indicate repair needed. False neutrals, whinning bearings, missed shifts. Some of these are expensive to fix and some of them you can learn to live with.

    That's all for now. You don't mention what year 5 speed. Like most other parts on the Airheads the transmissions went thru a lot of changes. Repair options will depend on the vintage.
    #5
  6. DiabloADV

    DiabloADV Semi-Occasional

    Joined:
    Oct 17, 2010
    Oddometer:
    2,410
    Location:
    Nor Cal, USA
    I'll find out in two weeks. Gearbox tech day in NorCal!

    I have a box full of ~$300 of parts. Some from Hucky; some from dealer. I have all six bearings; all seals and gasket; all the springs and miscellaneous little bits like felts and rubber ring on clutch push piston. If anything is bad besides what I have, I might be returning the parts and binning the gearbox.

    Labor? FREE! Expert guidance and all tools will be on site. :clap
    #6
  7. hzbloke

    hzbloke n00b

    Joined:
    Nov 23, 2010
    Oddometer:
    9
    Location:
    Bottom right corner of Oz
    If your gearbox is from the period when BMW thought a circlip (actually a snap ring) was not necessary on the front bearing on the output shaft then I strongly suggest that you have a groove turned in the shaft and fit one.

    I rebuilt my gearbox without installing one and so had to rebuild it again in about 15,000km. BMW seem to have relied on the bearing being a tight enough fit on the shaft for it not to move. Mine moved. The bike has now done about 30,000 with the re-rebuilt gearbox and it's excellent.
    #7
  8. robsmoto

    robsmoto Motorcycleton

    Joined:
    Jul 15, 2001
    Oddometer:
    338
    Location:
    Columbus, Ohio
    I rebuilt my 77RS transmission for slightly less (although I spent more when including the tools purchased.) I needed a replacement intermediate shaft ($200 for used one from Re-Psycle BMW), around $400 (guessing a bit) for bearings, seals, gasket, shim kit, shift upgrade "kit" (included new pawl spring) from Re-Psycle, local bearing distributor, and Cycle Works.

    About $40 for Cycle Works Transmission Re-Build video. About $35 for Chinese depth micrometer (worked surprisingly well). Borrowed tool from local BMW dealership for holding shafts/bearings for shim measurements (subsequently purchased my own from Cycle Works). Got some free advice from Re-Psycle BMW's transmission guy.

    I had already purchased a Harbor Freight 12-ton press (way less than $100 on sale).

    I took my time and made multiple measurements to determine the shim sizes needed. I used Olympic scoring - after about a dozen measurements for each bearing I threw out the high and low values and averaged the remaining measurement values.

    The experienced guys at Re-Psycle indicated that a dancing spit bubble on the transmission would be the indicator that it was hot enough to disassemble / assemble (upon heating with one or more torches). I decided to use several Tempil-Stiks (175, 200, 225, and 250 degF) to help me determine when the proper heat was obtained. Now I have an infrared temperature measuring device (from HF for around $30) that works quite well - the red laser dot shows where the temperature is being taken.

    Bike shifts easily, no odd noises, and transmission is pretty much free of metal "fuzz" and other bits after a few oil changes. I run a dollop of Dow Gear-Guard M (also called MolyKote) with Valvolene 80W-90 transmission oil. The Gear-Guard M seems to help the shifting be a bit smoother (although maybe the shift kit helps somewhat also - the shift kit was from Re-Psycle BMW).
    #8