Thanks gents. It's been fun trying to remember everything ...
To sum up …
Gearbox is back in the bike and full of fresh GL5 80/90 oil. I also added about 15ml of a moly additive on a friend’s recommendation. He presented me with a little jar of the stuff along with some good stories about its efficacy. As well as being a very experienced fitter/machinist he is a farmer who manages to keep a fleet of very crusty old work vehicles going forever.
The old dear is back on the front porch, ready to think about our next destination.
A few more kms and I’ll drop the oil to see what there might be on the magnet.
The gearbox feels good, much nicer than either of the donor boxes. It is still a proper clunky BMW gearbox but gear changes feel positive, it runs quietly at idle and in all gears. Finding neutral is really easy. And I have this new-found appreciation of what is happening in there. I really don’t want to hear those loud, embarrassing, dog-breaking clunks ever again. So how do you treat a gearbox gently enough to get long life?
The tricky gear changes for the boxes of this vintage are first to second and second to third, in my experience. Getting into first gear can also require care – I like the bike to be moving just a bit as I ease into first. Going to second is best done pretty quickly – that is, at fairly low revs. I will usually be in second before I reach the other side of an intersection when I’m taking off from the lights. If I wind it out in first I’ll usually get the big clunk. I also do the ‘pre-load’ thing, applying gentle upward pressure on the gear lever, then clutch, de-clutch and hold for a second or so. This works really well going from second to third. Fourth and fifth always seem to snick in nicely enough.
Costs: Bearings, seals, gaskets and shims were almost AU$400 delivered. I also bought a heat gun ($40), the ‘gear separator and puller kit’ ($50) and my own infra-red thermometer ‘gun’ ($50) (how the hell did I manage my life without one?).
Resources: There are other guides out there that I found very useful …
Jörg Hau’s gearbox page:
http://jhau.maliwi.de/mot/gearbox.html
Moto Phoenix made series of six YouTube videos about reconditioning a 1981> (ribbed) box, starting with this one:
https://www.youtube.com/watch?v=qqaXNmJ3Igg
Anton Lagiarder’s gearbox page with info on 4 and 5 speed boxes :
http://largiader.com/tech/airtrans/
And Snowbum and Duane Ausherman have written a lot, too. All worth digesting.
The gearboxes in our old airheads are something of a weak link. My view is that all airhead owners should have a backup box. And if you tour to far-flung places the backup should also be packaged up, ready to send by whatever means to wherever you are stuck.
While doing this refurb I bought another box, 1976 vintage, from a US dismantler. It was US$300, from a bike that had done a mere 38,000 miles apparently. By the time it arrived in Australia via USPS the cost in our little Aussie Dollars was $725. Still a bargain – these things are rare here. It feels like a new box on the bench – it shifts so nicely. I’ll be pulling the cover off to check everything out before it goes into the bike.
Importantly, I have the technology and I’m not afraid anymore.
Thanks to Jeff and Mal for their generosity. Also big thanks to Disston of ADV who sent me a 1974 sliding gear with all dogs, for the cost of postage. This will one day make it into another gearbox, I’m sure. We’ve gotta keep these old things going.
There are a lot more things to know than I have shown. Like how a gearbox actually works. The thing is that once you are in there and do a bit of poking around and experimenting it all becomes clear.
