A Woodworker’s Guide to Gearbox Rebuilding

[ME 109]

ME, "I could give you an output shaft failure that I doubt you will find answers for on the net."

What is the failure?

Damage consistent with the out put shaft being pushed/pulled backwards.
Failed rear bearing, first gear bush ends, washers either side of first gear.
First gear wheel was trying to climb over the washer in front of it.

1, overshimed. I don't think so. Very close shim stack went back in when I repaired the tranny.
2, taller 5th gear fitted. Did it push the shaft backwards?
3, failed overheated rear bearing caused the calamity?
4, Out put shaft pulled back by driveshaft.

Never could work out what the cause was. I did look very closely at all the damaged parts and worked out what happened, I couldn't work out why.

[Duane Ausherman]

I don't know that one either. Thanks.

You experienced what happened to me. After a dozen or so rebuilds, I was confident. I was wrong, as by then I started running into the rare failures.

However, now with the Internet we can collect experience from many people and add it together to get a far better picture.

Back then I only had Roy Reynolds to consult. We did at least 10 transmissions for his one, so we were seeing things that he hadn't. Roy was a very good mechanic and helped us often, but on this issue, we were way ahead of our source of help.

[ME 109]

You can see a fair bit of heat developed as a result. The rear bearing id got to the point of galling the shaft.
This result was three years after rebuild with new bearings and taller 5th added.
What alerted me to a problem was the final drive clunking when rolling the bike in neutral. The clunking was caused by the tranny rear bearing 'loading up' and releasing as the shaft rotated. The 'clunk' was from the fd/wheel splines slop.
I was 100% sure the problem was the fd, until I took it off. It was fine. After I took the swing arm off and turned the output shaft flange, I knew where the problem was.
So the damaged components revealed the shaft was either pushed/pulled backwards, or the rear bearing was pushed forward as over shimming would do. Too much damage to be caused by over shimming.

[Ross]

The problem that I now see is that we don't bother to use what is readily available. I see many questions asked that are answered on my website, but few bother to look. It is hard to have a BMW motorcycle question that isn't answered on one of several websites.

Google is your friend.

Er, that's exactly what Ross has done, Duane. He's telling us about it, not asking questions. Yet.
I could give you an output shaft failure that I doubt you will find answers for on the net.

I am gathering information at present to help me make an informed decision. That being pay someone $1K to $1.5K to fix my box or have a mate help me do it ourselves.

I am reading websites and watching videos taking it all in.

One question I have is hey Charlie want to rebuild my gearbox?

[Duane Ausherman]

Ross, I would suggest that a good appraisal of the symptoms will likely show the job to be done. That will give you a good idea of what it needs and you can make an informed decision from there.

[Airbear]

...

One question I have is hey Charlie want to rebuild my gearbox?

G'day Ross. It appears from your description that your gearbox may need more than just bearing and seal replacement. The likelihood of output shaft trouble complicates matters. You would have to start by opening the box to see what is wrong in there. Do you have it out of the bike yet? It's worth running through Duane's bench testing procedure, here ...

http://www.webring.org/l/rd?ring=bmwbik ... e%2Fbmw%2F

Scroll down and select 'Chassis and Drive Train' etc

After checking the state of the magnetic plug I would be listening to the noises while rotating the input shaft (with a clutch plate attached if available) and output flange in different gears. You should be able to get an idea of what might be wrong.

There must be somebody in Sydney who has the necessary tools to borrow to get the box opened up. Jeff made these ones ...





... and there are plans for much fancier ones out there on the net. If you can't make them a local engineering shop will be able to oblige. These and a heat gun are all you need to get the rear cover off and the shafts out for appraisal. Follow the Guide and report findings with good photos.

When reassembly time comes around you could drive down here and I'll assist with bearing replacement and shimming. It's about a full day's work.