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Topic-icon R75/6 gearbox bad news

  • tpeever
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6 months 4 weeks ago #3348 by tpeever
R75/6 gearbox bad news was created by tpeever
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

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6 months 3 weeks ago #3352 by tpeever
Replied by tpeever on topic R75/6 gearbox bad news
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!

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6 months 3 weeks ago - 6 months 3 weeks ago #3354 by Wobbly
Replied by Wobbly on topic R75/6 gearbox bad news
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.

Don't hide 'em, Ride 'em !!
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Last edit: 6 months 3 weeks ago by Wobbly.

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6 months 3 weeks ago #3356 by tpeever
Replied by tpeever on topic R75/6 gearbox bad news
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!

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6 months 2 weeks ago #3357 by Wobbly
Replied by Wobbly on topic R75/6 gearbox bad news

tpeever wrote: 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.

Don't hide 'em, Ride 'em !!
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6 months 1 week ago #3418 by tpeever
Replied by tpeever on topic R75/6 gearbox bad news
Update: Found a replacement intermediate shaft so should be able to put 'er back together soon!!

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