Oops I did it again... another '74 /6.

Discussion in 'Airheads' started by crazydrummerdude, Oct 31, 2011.

  1. TipsyMcStagger

    TipsyMcStagger Long timer

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    Thanks for the comprehensive explanation, Disston. So, it seems it's really just the tranny that gets the bad rap? And if I'm understanding correctly, just about any 1975 to early 1980 box can be swapped to the 1974 and alleviate the problems associated with the '74 gearbox?

    I'm not sure how difficult it is to source a '75-'80 box, or how expensive they tend to be, but if I'm understanding correctly, the '74 R60/R90 are decent bikes, the weak gearbox notwithstanding.

    Tipsy
    #41
  2. disston

    disston ShadeTreeExpert

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    You can get untold of miles out of a 1974 Airhead. When it breaks then you can say you have been there. Nobody can say when that will happen or for that matter that it absolutely has to happen. It's just a matter of it has happened to many of us. BMW changed a lot of stuff in many of the years of Airhead production. The first edition 5 speed trans lasted one year, 1974. I guess it's the one really really bad thing we like to harp about.

    When it comes to Airhead boxes there is one thing to know so you can swap them around. All boxes made from model years 1970 up till and including 1980 are long input shafts. This is the same shaft with the splines that we talk endlessly about lubing. Model years 1970 trough 1973 of course are 4 speeds but you should maybe know that you can use a four speed /5 trans on a bike that originally had a five speed. As long as it's a long input application. Long input boxes use the flywheel and then in 1981 we get the short input transmissions that use the clutch carrier.

    So you have a 1974 bike and are maybe worried about this box being a problem some day? If a 4 speed drops in your lap grab it but I recommend you try to get a 5 speed. The 4 speeds are good trannies but I think the 5 speeds are better that's all. I will get no end of gruff from riders that want me to tell you that a 4 speed is OK. Alright, it's OK. But a 5 speed is what you want.

    You are therefor looking for a 5 speed for models 1975 thru 1980. Any Airhead box will do including the early R65es or an R60.

    If you are feeling really adventurous and wanted a better clutch with faster acceleration then you could find the parts for a clutch carrier and use a short input shaft trans. But if you are thinking of going to all that trouble it might be better to just get a later model bike to start with. Don't worry it has been done numerous times. And since you are starting with a 1974 bike the swap to a clutch carrier is the most involved, it is easier after 1976.

    So you want a newer trans. that's all. If the one you have is working don't worry about it. A good deal can still be had on these boxes if you are patient.

    I advise you to follow any and all threads here about transmissions. There are some finer points we cover and the subject of riders rebuilding their boxes is never ending.

    I've rebuilt one box myself but I'm using a used box right now. I need to rebuild another.

    BTW, your assessment in the last post was right on. The 1974 box is a weak point. But there are certainly other things that can give you heck while you're worrying about the trans. :lol3

    BTW, if you can come with a suitable replacement and the '74 box still works it can bring decent money because so many riders think there's some advantage to owning a kick starter trans. Or it makes a good spare maybe.
    #42
  3. JonO

    JonO Been here awhile

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    Original gear box went out on my '74 R90/6 about 3 years ago. At the time, the bike had a little over 100K miles on it. Luckily I was only about 2 miles from home, and made it there in 1st gear.

    At first, I looked into repairing it myself. It sounded like it could possibly be a broken pawl spring, which is an inexpensive part. But after much thought, and knowledge gleaned from ADVRider, I decided not to. Mainly due to lack of mechanical skills/tools/experience in that area. I got quotes to ship it out to get fixed, and they were all $600+.

    Found a '75 Transmission with 60K miles on ebay. Got it for around $275 shipped to me. I installed it, and have had no problems since. Now it was not exactly an easy task to replace the transmission, but if you go slow, and stay patient, you can do it no problem.

    I still have the 74 Transmission sitting in my garage waiting for me to repair. Maybe...someday...
    #43
  4. crazydrummerdude

    crazydrummerdude Wacky Bongo Boy

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    Sorry for a potentially saucy response, but I find it funny when people on internet forums tell me how bad my bikes are. :lol3

    I have probably 50-60k miles on my 1974 transmissions with no problems. I did have two of them rebuilt just as a matter of refreshing them from a two-decade-slumber.

    You all forgot about the smaller front axle, solid rotor (for R75 and R90), flywheel bolts, oil-pump cover screws, under-tank master cylinder, etc of the 1974s! Surely each thing alone would kill anyone who dared to ride one!

    But guess what.. They're all fine bikes and there is no reason to avoid them. Yeah, someone who owned one three decades ago might have some horror story that's been endlessly perpetuated on the internet since then, but.. I currently own three almost-bone-stock 1974 BMW airheads and none of them have stranded me, let alone given me any 1974-year-based problems.

    I'll bet I could have one swapped out in 30 minutes.
    #44
  5. OD650

    OD650 Adventurer

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    In my 1974 after GASP! only 30k miles due to severe abuse on my part and most importantly excess use of the kickstarter by the former owner which got little metal bits into the bearings. Actually the bearings weren't to bad I figured since I was in there to replace all the leaking seals I might as well freshen it up. Well lets add that to the 74's bad rep,the transmission seals dry out and leak after only 38 years! But seriously nothing wrong with these bikes, maybe the trans has a higher re-build rate than other airheads but that doesn't make it unreliable by any means.
    #45
  6. bgoodsoil

    bgoodsoil Dare to be Stupid

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    You crack me up, man. You're gonna be like that kid that bought up every copy of a crappy baseball card so he could make them rare and worth something :D
    #46
  7. crazydrummerdude

    crazydrummerdude Wacky Bongo Boy

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    :lol3

    Uh oh, you bumped this thread.

    So, let's see:
    My 1974 BMW R60/6 (this thread),
    My 1974 BMW R75/6 (my first BMW),
    My 1974 BMW R75/6 (my latest BMW),
    My 1974 BMW R90/6 (my real learning experience).

    I was really hoping my 4th 1974 BMW would be an R90S so I could complete the collection, but another R75/6 is a fine addition.

    ..and lets not forget my /2s (which haven't yet got their individual threads).
    #47