Can't shift when moving

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steelcap

steelcap

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First tech post here, so some background:
1975 850 Mk3 purchased by me last month as a 90% complete project. PO bought he bike 4 years ago from the original owner and I was told mileage was under 400. PO never had the bike running.
There was no wiring and some missing electrical components, but mechanically it was all there with many upgraded/aftermarket pieces - 3 phase alternator, podtronics, tri-spark, Mikuni, cNw hydraulic clutch etc. etc.
I have rewired the bike and everything is working as expected. The bike starts first kick or on the starter button.

The problem.
With the bike not running, I can shift by hand into all 4 gears easily. When the bike is running at a stop I can pull in the clutch and shift into first without a problem. The bike doesn't try to move forward with the clutch pulled. As I release the clutch the bike sets off as expected.
It will sometimes jump out of first gear. Once moving I can't shift up into second when I pull the clutch in. If I slow the bike and partially pull the clucth I can shift up into second.

I have removed the gearbox outer cover and made sure the ratchet spring is correctly set up as per the Old Britts article. I have double checked the hyraulic clutch setup per the cNw instruction sheet. I don't have the original cable operated parts to test with them.

I have ordered a clutch tool and will be checking the plates this week, but given that I can shift into first and roll the bike back and forth with the clutch lever pulled in, it doesn't seem like stuck plates to me.

I'd appreciate your thoughts and suggestions

Mark
 
I suspect that cleaning your clutch plates will solve your problem. Jim



steelcap said:
First tech post here, so some background:
1975 850 Mk3 purchased by me last month as a 90% complete project. PO bought he bike 4 years ago from the original owner and I was told mileage was under 400. PO never had the bike running.
There was no wiring and some missing electrical components, but mechanically it was all there with many upgraded/aftermarket pieces - 3 phase alternator, podtronics, tri-spark, Mikuni, cNw hydraulic clutch etc. etc.
I have rewired the bike and everything is working as expected. The bike starts first kick or on the starter button.

The problem.
With the bike not running, I can shift by hand into all 4 gears easily. When the bike is running at a stop I can pull in the clutch and shift into first without a problem. The bike doesn't try to move forward with the clutch pulled. As I release the clutch the bike sets off as expected.
It will sometimes jump out of first gear. Once moving I can't shift up into second when I pull the clutch in. If I slow the bike and partially pull the clucth I can shift up into second.

I have removed the gearbox outer cover and made sure the ratchet spring is correctly set up as per the Old Britts article. I have double checked the hyraulic clutch setup per the cNw instruction sheet. I don't have the original cable operated parts to test with them.

I have ordered a clutch tool and will be checking the plates this week, but given that I can shift into first and roll the bike back and forth with the clutch lever pulled in, it doesn't seem like stuck plates to me.

I'd appreciate your thoughts and suggestions

Mark
Click to expand...
 
I think too tight a primary chain will make the bike not want to change great as well.
 
Until the "jump out of gear" is solved, you should cease operation. It can get expensive... $$$$!!!
 
ewgoforth said:
I think too tight a primary chain will make the bike not want to change great as well.
Click to expand...

As it's an 850 Mk3 with auto-tensioner an over-tight primary chain is unlikely to be the cause.
 
If you don't know the layshaft bearing has been replaced, you're going to want to do that anyway. While you're in there, you may find worn dogs on the gears or other reasons for your problem?
 
Thanks for the replies. Given the condition of the inside of the primary, outer gearbox and general condition of the bike I do believe the low mileage is correct. Worn gb parts seem unlikely, but not impossible. I'll check the clutch when the tool arrives and if that doesn't sort it, dig into the gb.

Mark
 
I've seen "low mileage" bikes with worn out gearboxes. I'd take a look at least.
 
Just to follow up on this. I pulled the clutch plates today and they were pretty sticky. I cleaned them up and now the bike shifts beautifully. Just took it for an inaugural ride around San Diego bay.
Can't shift when moving

Can't shift when moving

Can't shift when moving
 
steelcap said:
Just to follow up on this. I pulled the clutch plates today and they were pretty sticky. I cleaned them up and now the bike shifts beautifully. Just took it for an inaugural ride around San Diego bay.


Glad to hear it worked.

Do not dismiss the layshaft bearing replacement. On a MK3 it will fail somewhere between 10 and 15000 miles and it can do serious damage both to the bike and the body when it does.
There may be no warning before it happens. Jim
Click to expand...
 
Good call on the sticky clutch plates, Jim.

I recently rebuilt my gearbox and replaced both my drive side bearings. I was pretty scared that it was going to be very complicated and I would screw it up. My gearbox has 20,000 miles on it and the bushings were good, so it wasn't as hard a job as I thought. (actually both the bearings I removed looked good too... but I'm glad I got it out of the way. I don't need my gear box self destructing at 70 mph... It's not that hard to do if you have the time and a little patience..
 
Your tab washer is doing nothing to stop the nut coming undone, as its there it needs installing so it works as designed.
 
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