Opened up my gearbox and found this. Heart sank. This is layshaft (intermediate shaft) second gear? that has dogs both sides and slides between 3rd and 4th. Based on some searching and reading, it looks like I have the early five-speed gear with thinner boss where the dogs attach. This is pretty surprising as my bike is a 1976 R75/6 built in 1975. So how the bike got this gear I don't know. I haven't had the bike for many miles but I guess it is possible that it could have had the gearbox replaced with a '74 box and the gear been like this for many miles. No evidence of the missing dogs when I changed gearbox oil or opened up the gearbox.
So my next question then is what to do about it. Is there anyone on this forum who can push these gears off for me and replace the offending gear? Does anyone have a complete layshaft in good condition lying around that they might be interested in selling? If not, can you recommend someone who can rebuild this shaft for me? It looks like a part may be available but could be very expensive. If I replace the gear with a later one with the thicker boss does this mean a change in shifter fork as well or can the fork I have be machined thinner?
Thanks,
Tobin
Holy cow dudes! Forty six views and ZERO replies!! A lot of lurking on this forum!!
Went through the extensive service records I inherited with the bike and low and behold a replacement gearbox was fitted in 1994 at around 50K miles. Bike now has 76K miles. I checked gearbox case and it is stamped "74". So this is why I have what looks like an early five-speed gear in my gearbox. Because I HAVE a 1974 gearbox! Still trying to figure out what to do!
Sorry to hear about your g/b issues.
Very nice photos. Didn't want to speak up in case there was another more qualified contributor. Not a BMW gearbox expert by a long shot, but I do a LOT of gearbox work on motorcycles I've never ever seen before. In lieu of no other volunteers, I feel qualified to do the press work for you.
You'd need to supply ALL the parts, etc, etc. I can only send back what you send me. You can email me from within my profile.
Having said all that, if you could buy a complete gearbox of the correct year or later, you might be ahead of the game.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thanks Wobbly! I am talking to an Airhead gearbox expert right now and he may have the parts I need. Trick is that the appropriate gear with the broken dogs may be available new but is horrendously expensive. So if he has a serviceable layshaft around, I might be OK. Otherwise, your suggestion of a later used gearbox is a good one!
Trick is that the appropriate gear with the broken dogs may be available new but is horrendously expensive.
I know what you're talking about. I've seen the price of replacement gears go from ~$12 to over $100. So you don't need too much work done before buying a complete gearbox becomes a much cheaper alternative.
The number of these bikes that were scraped over the last decade and the number of "breakers" selling Airhead parts and whole units really works in your favor.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Update: Found a replacement intermediate shaft so should be able to put 'er back together soon!!
Hi Everyone,
Found a replacement intermediate shaft. Guy who sold the shaft to me thought it was from a 1974 bike so I wasn't sure this was the best option given the problems that have been reported with '74 gearboxes (ie. early 5 speeds) and that is what I already had with 2 missing dogs! I got several different opinions from experienced Airhead gearbox people from "look for a '75 to '83 intermediate shaft or entire gearbox" to "I wouldn't hesitate to run another '74 intermediate shaft at all". I didn't want to go to all the trouble of putting my gearbox back together only to have dogs breaking off again.
Decided to buy the used '74 shaft and run it. Got the shaft this week and low and behold it has thicker metal on the boss where the dogs are attached! Yippeee!! See attached. New shaft is on the right in each photo. Not sure if this shaft really is out of a later bike or BMW changed them mid '74 run or what. But the boss on this shaft does look a lot beefier and makes me feel a lot better about running this shaft.
Tobin
Glad that worked out for you.
Good luck!
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