75 r75/6 transmission advice

Discussion in 'Airheads' started by dilandau, Sep 25, 2013.

  1. dilandau

    dilandau Been here awhile

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    Hi all:

    I just made a deal on an r75/6 in pretty decent shape- except it has a blown transmission. I have no confirmed info on how bad the insides are, but from the riders description of grinding noises and power loss I expect its pretty bad.

    What say you gurus of cyberspace? Do transmissions from other years/models mount up easily? are there specific years with better ones- should I rebuild this one or get a more robust one and build it up?

    Frankly im tempted to just buy a used one on ebay, slap it on, and hope. this is because i have a 2 year old and a very busy work schedule.. so the avenue of least time is good.
    #1
  2. Plaka

    Plaka Brevis illi vita est

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    Looks like you have plenty of bikes to ride. You just bought somone elses problems. Figure they know somethjing. They sold the bike. Big hint there.

    Buy one on ebay and you do it again. The sellers most often are breakers working with wrecks. They never heard the bike run. might see if the tranny will go through the gears on the bench. Says something but not a lot. if they won't give a 5 yr. warrenty, forget them.

    Folks here know even less about that box. But they can tell you what they'd do if they were spending your money.

    Call some of the well know rebuilders and find out what it would cost to get an estimate. Go from there. They also might have a line on a decent used box. Maybe a hopeless case they bought cheap and rebuilt in time to make some cash on.

    I don't mean to be too harsh on you, but you bought a wreck knowing how little time you have to put into it. I'm guessing the price was irresistible. Ain't no free lunches. if you like to gamble or are just planning on flipping it, anything will work. if you want to travel on it ('cept you don't have time) you want a box a pro has gone through and evaluated, even if no repairs are needed.

    Any tranny will work. There were some problem years but any of those boxes may or may not have been corrected. Have to open it up to know. The 4 spd. is more durable than the 5 sp. Means nothing looking at an unknown box. Any can be more or less worn or broken.
    #2
  3. disston

    disston ShadeTreeExpert

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    I will try to cover the pertinent data. You have a choice, to rebuild the currant trans or obtain a used trans. I'm a fan of getting another trans. But it may be more complicated. "loosing power" may be the clutch? This will have to be checked anyway while the trans is out or being swapped.

    How long before you have the bike in your hands? Are you driven to rebuild this yourself or ship it out?

    It is recommended that if you want a good rebuilt trans you have one of the few known transmission experts handle it.

    So begin looking for a trans that is expected to be serviceable. A direct swap. There are a number of suitable years.

    Any Airhead transmission built from the first /5 four speeds in 1970 through the 1980 model year will work.

    I recommend you not go with a 4 speed, eventually these two transmissions will be used maybe to build one working trans. If you get a four speed now you don't have any parts later to fix a 5 speed. So stick with only 5 speeds.

    The 5 speeds were introduced in the /6 bikes and the first year is 1974. Aside from the issues some 1974 transmissions have many of the parts are different in the 1974 model year. For the same reason you don't want a 4 speed trans you also don't want a 1974 5 speed. Don't sweat the issue of the 1974 trans having a kick starter. The kick starter has issues and you don't need it.

    That leaves 6 model years for you to consider. 1975 though, and including, 1980. The Airheads of course continue through 1995 but these transmissions do not fit your bike. In 1981 the clutch was redesigned and the flywheel was eliminated. The transmission got some changes and one small change makes these two vintages not compatible. In 1981 the input shaft was shortened. The earlier transmissions, such as your bike, are called the long input shaft. The later transmissions, starting in 1981 are called short input shafts.

    You need a long input shaft Airhead transmission.

    There are almost always several for sale on Ebay. Don't buy a broken one just yet. The one with a broken cover is too expensive for needing a rear cover. Don't buy one with a kick starter, they are a waste of energy. A good one with no guarantee will go from $200 to $400 on Ebay. Wrecking yards may go for about the same unless they have a really nice one, then they want more.

    At this point you just want to check out the market.
    #3
  4. dilandau

    dilandau Been here awhile

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    thanks for the replies.

    1. It was cheap yes. so if i have to spend even 2k on the transmission id probably still be ok on resale.

    2. I do not plan to sell.

    3. I have heard they need rebuilds every 60k or so (on average) so I figured why not start fresh than deal with one that might go in 10k.

    4. thanks for the rundown on transmission that will work. exactly what I was looking for- appreciate it. I have some time- so i'll be keeping an eye on ebay and making some calls.

    5. I might have it tomorrow depending upon his schedule- otherwise next week. but i'm impatient and want to get a jump on the issue.

    6. I can do most the heavy lifting mechanics myself- but might send the unit out for a rebuild depending upon how hard it is- and how much it is for someone else to do it.
    #4
  5. Wirespokes

    Wirespokes Beemerholics Anonymous

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    It only takes 45 minutes to get the trans out (when you've done it a few times before) so it's will worth running the 'new' one to see if it's gonna work out.

    Transmissions don't necessarily go out at 60K, some last twice that or longer.

    I'd recommend watching for a late 70s transmission. I think LamontSanford has one for sale right now. He's an airhead owner and you can trust his evaluations. He'll say right up front whether it's good or not, or that he doesn't know.
    #5
  6. dilandau

    dilandau Been here awhile

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    on CL is a local 74 r90/6 transmission- but you are thinking that is a pass right? if i could get it for like ~100 is it worth it or just forget it and get a later model.
    #6
  7. disston

    disston ShadeTreeExpert

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    1974 is the first year of the 5 speed transmission. It was extensively redesigned for the second year, 1975. Many of the internal parts, gears and shifting forks, from a 1974 do not fit any of the other years.

    [​IMG]

    1974 is called the one off transmission year.

    PASS

    Is my advice. There are people that want that transmission. They are trying to fix another 1974 transmission and used parts are their only hope.

    http://www.ebay.com/itm/BMW-Motorcy...Parts_Accessories&hash=item3cd65a3a9f&vxp=mtr
    #7
  8. chasbmw

    chasbmw Long timer

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    My June 75 transmission also has the NLA 74/75 shifting forks. I'm not sure when BMW made the change but likely that 1976 model years, ie built from September 75 will have the later parts.
    #8
  9. Pokie

    Pokie Just plain Pokie.

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    I would wait until the bike is home then determine for yourself what the problem is. Too often I've seen people start buying things they think the bike needs before thay actually get the bike, only to have most of those things spend years on the shelf.
    #9
  10. r60man

    r60man Been here awhile

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    You may be amazed at what a fluid change will do. Give it a shot, it is only a few dollars and you may be sitting pretty.
    #10
  11. trc.rhubarb

    trc.rhubarb ZoomSplat!

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    I agree here. I don't know tons about airheads but am learning every day.
    I bought my bike with a host of 'big issues' that got me a good price, but not as good as yours it seems.
    Took less than an hour to take a barely running bike with all sorts of strange issues into a solid machine.

    Could be anything at this point that is causing your issues.
    #11
  12. dilandau

    dilandau Been here awhile

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    have the bike in hand now- actually I have the transmission in hand now as well.

    Does not turn well, makes grinding noise. opened up- and i do not see where its binding yet, but yes, its fubared somehow.

    pics later.
    #12
  13. disston

    disston ShadeTreeExpert

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    I hope you have a good tech article on taking this transmission apart. Heat is needed in several steps. failure to do this right could cause damage. There are a few special tools needed.

    You will need access to a shop press. Usually the ones labeled 20 tons are big enough. A smaller press will work if of a good quality. The cheapo Chinese presses are a waste of time, IMHO, I had one.

    The taper joint on the output shaft and the flange attached must be clean when you put it together.

    The shafts will fall out when the case is heated after taking the shifting parts out.
    #13
  14. isdt BMW

    isdt BMW willserv@aol.com

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    I just fixed one for a friend, he said it was making awful noises and he was afraid to ride another mile. Total parts outlay one bearing, 4 seals, one gasket. The bearing retainer came apart. no other damage, sometimes you get lucky. No one can estimate repairs until you open it up and check the internals.
    #14
  15. dilandau

    dilandau Been here awhile

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    it was delivered already open actually. Not sure if it was taken apart by the book, but it looks fine- surfaces clean - no pry marks or anything weird.

    all the parts look clean, no missing teeth or anything- feels like a bearing is out and its not holding perfectly straight- and its grinding.

    only had a few minutes to look. thanks for the advice. Ill probably bring it to an experienced local hand and pay for an opinion.
    #15
  16. disston

    disston ShadeTreeExpert

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    Had an idea this might be the case.

    Not sure how close this is to you but it would be advisable to take that transmission to somebody that does Airhead transmissions. There are several operations that should be done by Airhead experts. This is one of them.

    http://www.beemershop.com/

    Ted Porter is not only one of the Airhead Gurus he is one of the transmission rebuilders recommended most often. There are only half a dozen mechanics that will get regularly recommended for this work.

    While the transmission is being done has the clutch been measured and the rear main oil seal replaced yet? This work is usually done while the transmission is out.

    If the flywheel is on the engine it has to be removed to get at the rear main oil seal. Make sure the crank is blocked up front under the engine cover so the crank can't be moved while the flywheel is off.
    #16
  17. Pokie

    Pokie Just plain Pokie.

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    Personally, the transmissions on these bikes are pretty easy to get in and out. I'd just rebuild the transmission and plop it back in, assemble the bike and see how it does. I wouldn't pull the clutch and I wouldn't pull the flywheel without good reason. If there's black oil everywhere and dripping on the floor, that's good reason. Just idle curiosity, that's not a good reason.

    If you go looking for trouble, you're going to find it.
    #17
  18. Plaka

    Plaka Brevis illi vita est

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    lets say your transmission was having problems and you had your choice between two mechanics:

    One is a seasoned pro with a well earned reputation for solid work. he has all the needed tools, does lots of them, tons of experience and excellent judgement. He finds a problem here and he knows what else is going to be weak and ought to be fixed there to avoid future failures.


    The other is a complete beginner. He's never done one before but he's eager to learn and make all the beginners errors---on your box. He has no supervision or anybody checking as he goes along, no one to show him the olds pro's tricks or supply the judgement that only comes with having made the errors already. He doesn't have the measuring gear to set it up but figures, hey, how complicated can it be? BUT, he's willing to work for free if you just buy the parts. Your transmission is his little learning project.



    You just recommended he take it to the second guy.

    If you're flipping it, what the hell. Throw some sawdust in it to shut it up, shine it up and get it on craigslist. You'll be long gone. That's as old as used car lots. But if you plan on depending on it...


    I don't work on BMW transmissions because I know I will never be as good as the guy I want working on my transmission. I'm not a professional and I don't have the opportunity to get the kind of experience that I want in my transmission guy. And, having worked on different kinds of transmissions, I have a whole lot of respect for what these particular boxes need. I can set up a Rover 4 speed with a transfer case and rear PTO with a set of feeler gauges. You don't play that with a clamshell gearbox. I've also made the mistakes. The sound of a layshft thicker than your wrist snapping in half under your butt is ...mmm...memorable. Didn't seat a bearing right. Expensive bit of tuition. I don't care to have that experience on the other side of the country on a trip. I don't want to lay out a lot of cash for tooling I'll use extremely rarely (If I do things right)...it's cheaper to take it to any of a number of highly qualified individuals and know it'll be thorough and right and I can count on it 98.7%..
    #18
  19. Plaka

    Plaka Brevis illi vita est

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    Where did you get 60k from?

    I get 110-120k on a 4 speed then you turn the shift forks around and throw in fresh bearings just because and do it again.

    I have heard 5 speeds are not quite so durable. I have about 100k on one now with no issues. But I also have a backup in a crate so I'm not down while it's being worked on.
    #19
  20. Pokie

    Pokie Just plain Pokie.

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    ?????

    Who said anything about having a noob work on a transmission?

    How the heck do you turn shifting forks around to wear on the other side?

    Are we all talking about BMW motorcycles here?

    Am I missing something?
    #20