Unusual Transmission Problem

[cyclegary]

I have a 79 R65 with 18,000 miles on it that I bought last January. Its been running fine until two weeks ago when I felt the clutch slipping a little in 4th gear. A couple of days after that, the clutch wouldn't work at all, and I had to get help getting the bike home.

When I got it to a safe place and started my diagnosis, I could feel the tranny shift into 1st, neutral, 2nd, 3rd, etc. but the bike would not move. When it's in gear with the clutch out, the bike will roll as if it were in neutral.

The engine runs fine and makes no odd noises. The neutral lights works as normal. When I put the bike into 5th gear, the clutch engages, and the bike operates like it should.

The cable and clutch operating lever appear to be operating correctly.  Squeezing the clutch lever feels normal, with no rough operation.

That makes me think the clutch is OK, but something is wrong inside the transmission.

I own 3 airheads and an ST1300, and have over 200,000 miles in the saddle, so I'm not a noob, but have only recently gotten serious about doing my own repairs.

Any ideas on what's wrong?

[nhmaf]

It is possible that you may have fallen victim to the dreaded pawl spring breakage problem - it doesn't happen often, but it does happen.   When it occurs, you are basically left with the gear that it was in when it happened - though if memory serves, generally one cannot get the transmission OUT of that gear unless one can turn the bike upside down and work the gearshift lever - but maybe it can also fail in a way to give you a bunch of false neutrals, except for the one-still engaged gear.

If you are positive about the 5th gear being engaged/connected thing, then I agree it probably isn't a clutch issue.   There are several very good guys for repairing/rebuilding these transmissions.   While it isn't rocket science, it is a very finicky job, and requires a number of special tools and shims to do the job properly.  These aren't as basic to work on as most Japanese bike gearboxes, so if you haven't done BMW bike gearboxes before, I'd recommend you to send it out to be fixed.  

you can keep your eyes open on the internet for a rebuilt gearbox (typically around $500 or so) which will be roughly about the same cost to repair yours.   You can then swap out the gearbox on your own and get the broken one fixed at your convenience, and have a spare for the future.

[tvrla]

It's very difficult to come up with a cause for that one! It's WEIRD!

It really sounds to me like a throw-out mechanism issue - but I can't even start to come up with a reason why it'd work in fifth and not the rest!

It could be a shifter mechanism problem and that seems to make some sense.

At any rate, it won't do any good speculating on the issue - the answer may come while pulling the throw-out mechanism. If not, the fault is inside the box and should be obvious enough once it's opened up.

[Barry]

If the fault happened all at once the pawl spring breakage would seem plausible. Being preceded by clutch slip is weird unless it's just a coincidence of  both pawl spring breakage and throw out mechanism faults at the same time.

The gearbox ought to be in good shape at only 18,000 so if  it was me unless I was planning to keep the bike for a very long time I might be inclined to resist at least some of the "while you are in there replace everything"  philosophy. That might change when you see what state it's in but a gearbox ought to last more than 18,000.

[Bob_Roller]

I had a shifter shaft seal issue, the seal was binding up the shift mechanism .

When the problem started, I could up shift to 5th gear, but then couldn't downshift to the next lower gear, kinda got a 'false' neutral .

With the bike on the center stand, get the transmission in any gear other than neutral and 5th, slowly rotate the rear wheel , move the shifter and see if the transmission will go into another gear .

Just a wild guess !!!

[cyclegary]

I got it dissambled today and the clutch disk is dry, with the
usual amount of clutch-dust grit on it.  The rear main appears
to be good too.

But as you can see, the inside of the front of the trans and
the "bell housing"  area are covered with oil, so it looks
like the input shaft seal is leaking.

Now that its out I'm going to have Nathan at Boxerworks in GA
rebuild it.  When I bring it down to him I'll also ask him and
Dean Graham to inspect the entire clutch assembly to see if
any of those parts need replacing.

I'll know what's wrong with it (and will let ya'll know) after
they break open the trans.

[montmil]

You've definitely got a rear seal in the engine that's gone gerfunken. Clutch assembly will ha e to be removed to fix that issue.

The transmission input splines look to be OK so that's a good thing.

And please learn how to scale your photos to fit the forum requirements.

[tvrla]

I'm not so positive about the engine rear main being bad, considering the amount of oil on the trans - maybe it came from there?

I've heard that a leaky rear main won't cause a slipping clutch, it's the trans input seal that does it.

A good clutch is 6mm thick, worn out is 4.5mm.

Also check to see the pressure plates aren't cone shaped.

[cyclegary]

Once I took the flywheel off and saw the amount of fresh, clean, engine oil running down the back of the engine casing there was no doubt whatsoever about the rear main being bad.  The bike must have sat without running for much too long for it to have that kind of leak with 18,000 miles on it.

I also believe the front trans sealing leaks too.  But that's really moot since I'm having the trans completely rebuilt, and all the seals and gaskets will get replaced.

And I apologize for the massive photos, but figuring out how to right- size photos for the forum is a bigger pain that trying to figure out which of the technical specs in the Haynes manual are correct!

[montmil]

Gary,

You may wish to utilize a free, web-based photo storage service such as Photobucket. You upload your images into albums that you create.

When you wish to post a photo to the forum, or an email or whatever, Simply scroll the cursor over your selected photo and a menu appears. For the forum, select IMG Code and it will be copied and ready for you to post with your message. The image will be correctly sized... by magic.

I get dizzy trying to scroll around these billboard-sized pics and usually just move on to the next posting.

[cyclegary]

I took the tranny down to Nathan's (Boxerworks, in Watkinsville, GA) today, and before I even got home he called to let me know what he's found.  Turns out there was a tiny little screw holder pressed into the upper part of the casing that fell out.  It got lodged in the mechanism that controls changing into 1st thru 4th gears, which is why it would only travel in 5th gear.  Nathan said that's the first time he'd ever seen that. He expects to get it completely rebuilt in the next couple of days.


Since it was quite obvious that the rear main seal in the R65 was leaking badly, it had to be R&R'd.  Boxerworks had a new seal in stock, and I stopped at Clanten Austell's shop (Machine Works, Lexington, SC) on the way home from Nathan's to borrow his seal installing tool.  I got the seal and flywheel installed this afternoon after devising a front-of-the-crankshaft block using a wood shim and the original front cover.


Tomorrow I'll clean and install the clutch, after I procure a few of the 6mm bolts I need to put the danged thing back together. Hopefully the whole shebang will be reassembled and ready to ride by this weekend, so I can ride it to the MSF class I'm scheduled to teach.

[Bob_Roller]

Was it the Phillips head screw that's visible on the top surface of the transmission ?

If it is, that screw holds an oil 'raceway' that directs oil onto a bearing, if you take the screw off, the part falls into the transmission .

Good news, is that it's not an expensive repair, compared to what it could be .