Gearbox with busted dogs

Discussion in 'Airheads' started by SamH, Dec 26, 2012.

  1. SamH

    SamH 90S on the bench

    Joined:
    Aug 14, 2005
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    436
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    It's the 90s again! I'll cram all these questions into my main thread eventually.

    Here's a pic of my intermediate shaft. I've installed the new gear, haven't pressed the final cog back on yet, and you can see the original gear sitting beside the shaft.

    [​IMG]

    So now I need to either modify the shift fork or get a new one. I understand that they were all like this post 74'.

    Can I modify the shift fork I already have? Do I just need a new one?
    Can I just replace the damaged gear and get a replacement for or do the new dimensions mean I have to change other stuff?

    I've had a read on largaider.com and he mentions changing to 17.5 degree gears and totally ruined gearboxes but I'm not sure if he's talking about what's happened to my box or damage to the lay shaft.
    #1
  2. disston

    disston ShadeTreeExpert

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    I believe the change in shift fork size for the narrow groove gears was specifically to fix this problem. The other thing you mention, 17.5* gears, comes later, in April 1982.

    To use the narrow groove gear you need the narrow shift fork. Don't know if you can grind the wide fork but I would think not.

    The angle of the gears change is that gear on the left of your lay shaft. It's one of three angle cut gears. If any of them go bad you have to change all three. That one you show looks good.

    How does the wear look on the input and the out put gears?

    [​IMG]

    Look for wear between the coupling of parts 4 & 5. I think Anton covers this also.
    #2
  3. disston

    disston ShadeTreeExpert

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    From your last sentence it seems maybe you don't understand the basic facts about these boxes.

    The five speed gear box was brand new in 1974 for the /6 Airheads. You have a first year five speed Getrag gear box. This transmission was destined to go through numerous changes over the years. The first year five speed is the Red Haired Step Child if there ever was one. It had several problems the most serious of which were changed for 1975.

    There were many other changes in later editions but it is often advised that what you want to do with a 1974 box is get rid of it. I think this is good advice myself and another trans is not out of the question in today's market.

    You will most likely have to give up the kick starter by getting a later box but this is not a big deal, if the kick starter you have works now it is rare, they almost all develop problems and are pretty useless.

    Any five speed with a long input shaft will bolt directly up to your bike. You can also use a four speed from a /5 bike if you like. I personally would want to stay with a five speed at least. The short input shaft boxes start for the 1981 model year and these bikes enter production in September, 1980. So any box made before this will fit your bike.

    So it looks like you are well along the way of fixing the box you have. Please do. You've almost got it. But keep an eye out for a box that doesn't have as many problems. Check the market. This 1974 box will probably have more problems later on.
    #3
  4. SamH

    SamH 90S on the bench

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    Yeah, I'd already figured out that the 74' box isn't really the pick of the bunch.
    You're certainly right about my ignorance about these gearboxes, this is my first time inside.

    I was digging through the boxes of bits just now and found the rest of the gearbox rebuild kit with the case gasket, springs and new bearings. I figure I'll keep on with rebuilding this gearbox and I'll keep my ear to the ground for a newer one.

    While I'm here, does anyone know if there's a preference for leaving seals on the replacement bearings or removing them? The new ones have seals, the old ones didn't and I've read that there's been rebuild kits that have both.

    P.S. To the comments that I've read about the place saying that these bearings and gears will come off with a three arm puller... HAH! This gearbox will be the death of my press.
    #4
  5. Rob Farmer

    Rob Farmer Long timer

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    I've seen a few of those on heavy flywheel machines. Usually on bikes where there's a problem with the clutch and the riders crunching the gearbox. all the problem boxes I've seen have been 79/79 machines but thats probably because they get abused more and are far more common than the /6 machines.

    heres the last one I sorted out. The biggest pain with this issue is that the intermediate shaft gear are not available on their own, you need to buy the whole intermediate shaft which comes with a 17 1/2° taperred helical gear meaning you have to upgrade the input shaft and fifth gear. We all know airhead owners never want to pay more than $5 for anything so it usually means hunting down another gearbox.

    [​IMG]
    #5
  6. SamH

    SamH 90S on the bench

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    Yeah, looks like I was lucky getting the replacement gear with the bike.
    #6
  7. disston

    disston ShadeTreeExpert

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    I was wondering how come you had a separate gear.

    Any luck yet on finding a spare shifting fork? I have some but they are not near here. May be not till after the Winter that I can check my stash.

    I've been thinking about the idea of grinding the fork to fit. Maybe that's not such a bad idea. Do you know if he can do this, Rob?
    #7
  8. pkboxer

    pkboxer Adventurer

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    Replaced my 74 intermediate shaft a few years ago. Had the fork ground to fit the "new" gear.

    Removed the material from the side where the boss was increased in thickness to keep the fork in the same place in relationship to the gear.

    Worked fine and still is. YMMV
    #8
  9. SamH

    SamH 90S on the bench

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    I'll give the grind option a go. As mentioned, I'll just take it off the side that corresponds with the increased gear lip thickness.

    Just got to figure out how to hold everything parallel.
    #9