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Old 06-13-2010, 06:20 AM   #1
Ze Red Baron OP
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/6 Clutch / Gearbox issue

I finally had a chance to go out for a Sunday morning ride with a friend today, and about 15 minutes into the ride, as I come around a corner out of an intersection, the bike shifts into second, and then stops shifting altogether. Can't downshift to get it into neutral, can't upshift into third. When I pull in the clutch lever, it disengages the gear.

I was able to jump start by coasting and popping the clutch, and limp home in second. Anyone have any ideas of what the issue might be, and how involved diving into it might be?

Thanks,

Gero
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Old 06-13-2010, 06:25 AM   #2
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Quote:
Originally Posted by Ze Red Baron
I finally had a chance to go out for a Sunday morning ride with a friend today, and about 15 minutes into the ride, as I come around a corner out of an intersection, the bike shifts into second, and then stops shifting altogether. Can't downshift to get it into neutral, can't upshift into third. When I pull in the clutch lever, it disengages the gear.

I was able to jump start by coasting and popping the clutch, and limp home in second. Anyone have any ideas of what the issue might be, and how involved diving into it might be?

Thanks,

Gero
The issue is that you broke your clutch shifter pawl spring. Happened to me and left me in 2nd gear as well. "C" in the photo is the clutch shifter pawl, and there is a torsion spring that keeps it in contact with the big wheel with teeth on it.



Going to have to pull the transmission, and yank it apart to fix. Might as well install new bearings, seals, and maybe a shift kit while you're in there.

EDIT: And I see you have a '74 gearbox. The '74s are known for having some bad gear dogs on 3rd(?) gear that can break off and get chewed up in the system.

Here's what broken dogs looks like.



The two chunks missing from the top are the broken ones, the two intact ones are... well.. intact. So take a look while you're in there. That gear is from my box. The damage was noticed while we were in there for the pawl spring. I hadn't noticed any oddities about the box, but I went back and upended the oil catch container I'd been using for years and one of the dogs fell out. Don't know where or when the other broke off. Replaced the gear with one from another box.


You might want to look into a newer style gear box, either from a later/6 or a /7. The problem with the dogs was a one year only issue. I have a later model /6 gear box sitting in a corner waiting for the day when my gear finally grenades...
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Old 06-13-2010, 06:37 AM   #3
Ze Red Baron OP
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Quote:
Originally Posted by Boon Booni
The issue is that you broke your clutch pawl spring. Happened to me and left me in 2nd gear as well.

Going to have to pull the transmission, and yank it apart to fix. Might as well install new bearings, seals, and maybe a shift kit while you're in there.

EDIT: And I see you have a '74 gearbox. The '74s are known for having some bad gear dogs on 3rd(?) gear that can break off and get chewed up in the system.

Here's what broken dogs looks like.



The two chunks missing from the top are the broken ones, the two intact ones are... well.. intact. So take a look while you're in there. That gear is from my box. The damage was noticed while we were in there for the pawl spring. I hadn't noticed any oddities about the box, but I went back and upended the oil catch container I'd been using for years and one of the dogs fell out. Don't know where or when the other broke off. Replaced the gear with one from another box.


You might want to look into a newer style gear box, either from a later/6 or a /7. The problem with the dogs was a one year only issue. I have a later model /6 gear box sitting in a corner waiting for the day when my gear finally grenades...
Thanks Boon - this is very helpful. If the dogs from 3rd gear broke off, I should still be able to get into 1st though, shouldn't I?

Not what I was hoping to have to do, but might as well get down and dirty...
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Old 06-13-2010, 06:44 AM   #4
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Quote:
Originally Posted by Ze Red Baron
Thanks Boon - this is very helpful. If the dogs from 3rd gear broke off, I should still be able to get into 1st though, shouldn't I?

Not what I was hoping to have to do, but might as well get down and dirty...
Yes if the dogs break you only lose one gear as long as the dogs don't lock the transmission up on their way to the bottom of the sump.

Your issue is, without a doubt, the clutch shifter pawl spring.

I was just giving you too much info on something to look for while you're in the box fixing the spring.
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Old 06-13-2010, 06:48 AM   #5
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...and why I keep calling it the "Clutch" pawl spring I couldn't tell you.

It's the shifter pawl spring.
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Old 06-13-2010, 07:00 AM   #6
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Shifter pawl spring makes more sense as I was able to get neutral by pulling in the clutch lever, or I'd still be by the side of the road

I'll figure out what parts I need and give Bob's a call.

thanks!
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Old 06-13-2010, 08:14 AM   #7
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Same thing happened to my '74 R90/6 a couple of years ago. I got the transmission off the bike, then got quotes to fix it. It was out of my price range at the time, and I didn't have the necessary equipment/patience/desire to rebuild the box myself. I got a '75 transmission off of ebay for $250, installed it, and has been running just fine since. My '74 box still sits in my garage waiting for the day I decide to tackle it. Here is an excellent site with details and pix on rebuilding a transmission: http://jhau.maliwi.de/mot/gearbox.html
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Old 06-13-2010, 08:21 AM   #8
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If you have a 74 box, don't bother with it. Plain and simple.
Scavenge the input and output shafts and the kickstart parts (if they're worth scavenging) and toss the rest into the metal recycling bin.
Buy a used 75-80 box and try it. The previous poster was on the mark with his.(except for the part of saving the 74 box for a later build)
There was a reason BMW redesigned the transmission for the 75 model year.
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Old 06-13-2010, 06:21 PM   #9
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Thanks Jon and Robert. I will look for a later gearbox and start getting to work. I'm sure you'll see me back here as I start tearing down and replacing the parts.

Gero
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Old 06-15-2010, 06:02 AM   #10
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So I called Bob's to see if they had new gear boxes and described the problem. The guy at the parts desk indicated that they had a "shift update set" with beefier parts, deeper teeth and a better pawl mechanism.

I know Jon and Robert suggested ditching the current gearbox in favor of a later one - would it be worth even considering this update set instead of just basic replacement parts (which I don't want to do based on your helpful feedback)?

Thanks,
Gero
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Old 06-15-2010, 06:06 AM   #11
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No. The shift kit does nothing to address the weaknesses of the '74 gearbox. Plus it's really expensive now; for that money you can find a used '75-'80 gearbox.
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Old 06-15-2010, 06:15 AM   #12
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Anton,
thanks for your input. They said the shift update kit was about $435, so I think I'll look around for a used 75-80 gear box as you suggested.

Gero
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Old 06-15-2010, 06:30 AM   #13
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I stand ready to be corrected, but I don't think the improvments appeared at the begining of 75. I have seen the 74 stuff in a 75 box, so unless someone put it there......?
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Old 06-15-2010, 07:26 AM   #14
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in reality

The only other train of thought as far as gearboxes . Let`s say you can get ahold of a 74 box,at a reasonable price. If you open it & replace a bearing or 2 ,how far do you think you`ll travel on this transmission? 75000 miles, 48000 miles?Are these older transmissions really unusable for the use they`re likely to get? Just a thought
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Old 06-15-2010, 07:34 AM   #15
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Quote:
Originally Posted by Ze Red Baron
...so I think I'll look around for a used 75-80 gear box as you suggested.
The later, the better. I think the final improvements in the pre-'81 gearbox came in 1977, although the fully ribbed case showed up later.

Quote:
If you open it & replace a bearing or 2 ,how far do you think you`ll travel on this transmission?
It's not a matter of bearings. If it keeps working, it keeps working. If a gear wears or breaks, you have to change a lot of other NLA parts as part of the repair. So if you have a '74 box that works, keep riding it. If it breaks, be ready to replace it rather than repair it.
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