Lost Clutch Issue

My 74 commando gradual restoration has gotten to the point where it has been running pretty much problem free last summer and this summer. Im really enjoying it and and getting some wings as a new rider in my early 60s. Last weekend I got it out on a chilly 50 degree morning and rode it around the neighborhood to warm it up a bit. 1/2 mile into the ride my clutch cable went completely slack. Like the cable broke. I limped it home and shut it down. Later that day I dug into it and discovered
-the cable was not broken. Its only 1-2 years old.
-the cable end was properly seated in the operating lever fork in the gearbox.
-the operating lever was in a proper position.
-the lever roller looked in tact.
-the clutch adjustment stud was not loose. Jam nut was secure.
-the circlip seemed to be in place. the clutch basket had no inboard outboard movement.
-nothing looked out of place on the handlebar end other than the clutch lever had no cable tension.
-when I moved the clutch lever at the handle bar it actuated the fork lever in the gearbox up and down freely. No resistance.

So then I loosened the jam nut on the clutch adjusting stud and went through the full clutch adjustment process (one turn out) and everything seemed back to normal.

I did not ride it. I left it as is then started thinking maybe the operating lever roller sleve failed in some way. So last night I took the outer cover off and pulled the roller. Its a little loose / worn but nothing that would explain why my clutch went slack all at once. The ball looked ok.

So I'm confused as to what caused it. Id rather not pull the clutch basket for further investigating if I dont have to. Any ideas?

The last time the gearbox and clutch were touched was the rebuild 1.5 years and 2,500 miles ago.

I would check that the clutch centre nut is tight.

I've had clutch cables fail like that, before completely breaking.

As mentioned above, go lookkng some more.

Mainshaft nut behind the clutch pivot is also suspect.

cliffa said:

I would check that the clutch centre nut is tight.

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Same as above ....

Thanks Gents. Time to pull the clutch apart.

Would a clutch center nut (fixing nut) issue cause the clutch to go from good to fully slack in a few seconds? Seems like that would show symptoms in the clutch feel as it loosens.

Saber said:

Would a clutch center nut (fixing nut) issue cause the clutch to go from good to fully slack in a few seconds? Seems like that would show symptoms in the clutch feel as it loosens.

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Yes.

I had this exact issue on a 1973 850. The clutch center nut had walked out, unbending the bent keeper as it went.

Replace the keeper and use some loctite

Saber said:

Would a clutch center nut (fixing nut) issue cause the clutch to go from good to fully slack in a few seconds? Seems like that would show symptoms in the clutch feel as it loosens.

Click to expand...

Yes, I've also had the same problem, clutch centre nut came loose, the clutch was free to move in and out so all sorts of wacky characteristics turned up.

MichaelD said:

Yes, I've also had the same problem, clutch centre nut came loose, the clutch was free to move in and out so all sorts of wacky characteristics turned up.

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Did you have a tab washer fitted ? It's usually the soft metal that's made of that causes the problem

I'll check when I go into the primary side.

The old loose nut on the clutch trick, but then I've had loose nuts for a long time lol, in my brain and down below lol.

ashman said:

The old loose nut on the clutch trick, but then I've had loose nuts for a long time lol, in my brain and down below lol.

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Is that you, agent 86?

Had similar problem by over tightening clutch nut and unknowingly broke the spacer clutch locator leaving clutch basket to float

Center nut and tab washer look intact.

That looks like it could be the last plate in the stack next to the pressure plate which would normally be a friction plate or have you removed a friction plate or added an extra plain plate to the stack?

The one that bedeviled me had unscrewed without completely flattening the tab washer- it still looked as though it should have been preventing rotation. As you are there make sure the nut hasn’t moved.

In my case it was obvious as the entire clutch moved when the lever was pulled.

Given the suddenness of the original issue, could it be the nipple wasn't correctly seated in the gearbox end lever, and decided to drop in to place during the ride?

The great thing about this hypothesis is nobody can prove it

It's not 100% clear from the description, but did you have to wind the adjuster screw in substantially to get the clutch back to normal?

I'm also alongside Phippsy's theory that the circlip behind the clutch could have jumped out/failed if the above is a load of b******s

The nipple not seated theory could explain it. But 2,500 miles of running well before the seating event?

Regarding plates, i took the photo when i was pulling plates. Some were out and some were still in the basket.

Saber said:

The nipple not seated theory could explain it. But 2,500 miles of running well before the seating event?

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I don't see why not, and in the absence of any evidence of the clutch/mainshaft working loose - your due diligence here seems to have provided the answer to that question.
If readjusting the cable slack got your clutch operating as before, then I'd say it's likely the most rational explanation.