Jumping out of first gear

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Stuffa

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72 850 commando. I’ve owned the bike for nearly a year. It’s been a bad year with cancer and back op. Between all the health issues every time I take the bike out something else goes haywire. I thought I had everything sorted and took it for a spin today. Everything was good then in first gear it went back to neutral, I thought it was the clutch slipping at first. It happened about three times on the ride.
Any ideas on what would cause this? Is it a case of having to strip everything? Or could it be something simple.
I was hoping to get a few weeks riding in before going in for a neck op next month. If I ride it as is could I cause further damage.
Cheers Chris
 
The holes in the first gear and/or the dogs in the sliding gear are worn. Also if the layshaft inner bearing has been changed to a roller (which is recommended as the ball bearings cage fails too often) then the endfloat on the layshaft may be too much and needs shimming.
 
I'd also check that it's actually going fully into first gear, I had a problem like this once that turned out to be the gear selector spring
 
Stuffa said:
I was hoping to get a few weeks riding in before going in for a neck op next month. If I ride it as is could I cause further damage.
Cheers Chris
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Just an opinion: As long as you don't over rev the engine when it slips out, I would say ride now - fix later.

If worried, consider changing the gearbox oil and see if there are any metal chunks in it - if not, you probably haven't and won't hurt anything.
 
N0rt0nelectr@ said:
I had that issue at one time. Replaced the 1st gear lay shaft bushing and the problem went away.

John in Texas
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If it happens under hard acceleration, yup. I've replaced mine twice in 43 years and it needs it again.
 
Often the kick-start stub needs to be shimmed against the inner cover to solidly locate the knuckle within the layshaft first gear--an Isolastic shim is just about perfect. Old Britts outlines the whole procedure on their web page, I believe--best of luck



Tim Kraakevik
kraakevik@voyager.net
630 940-2420
 
Before you dive into the box have a look at the detent plunger spring. I had exactly the same symptoms and someone on this forum told me to check this first as no one ever replaces it during a rebuild. My spring was broken but it could be weak as well. Easy job to do and cheap to try.
 
Jumping out of first gear



Jumping out of first gear



Exploded view courtesy of:
Jumping out of first gear
Replace part number 10 first. Also look at Old Britts page or on this forum for how to install it correctly. $4.55 for the spring and $6.65 for the gasket and seal kit. A buck or two worth of gearbox oil and your good to go or you've at least eliminated the easiest fix. If it still hops out of gear it's time to open up the box and check the shift dogs and gear teeth especially if there has there been any unusual chunks of metal crap in your gearbox fluid.
 
 
If you hold it in bottom on the clutch when stationary it should be ok .. I would leave it for later
 
If you fit a new ratchet return spring remember it's possible to fit it the wrong way up.
If it were me I'd live with it and sort it later.
It's going to be one of the above suggestions, i can't imagine it being anything else. None of the above is going to cause any damage in the short term. In my opinion.
 
Hello!

I´m in with Kraakevik´s shimming of the kickstart stub.
Grab the kickstart and feel for excess axialplay. That should be shimmed away.
Been there,... and first gear was solid from then on.

Benton
 
I am also in with Kraakevik's recommendation to shim the kickstart stub.
[or the layshaft -however you want to look at it]

A new gear will also solve the problem but if you don't shim the layshaft with the new gear the problem will come back eventually.
 
My 750 does that after a rebuild to replace the lower shaft bearing. It only does it when I put it into first from neutral when pulling away quickly. If I put it into 2nd and then into first it seems to locate properly and not slip out even under hard acceleration.
It seems to have bedded in over the last year or so and not done it recently.
 
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