1981 5 speed transmission rattling badly…

[Na Cl K9]

I was forced into a full emergency stop and couldn’t/didn’t de-clutch. As the engine died I heard a metallic “pink” that sounded much like a couple of wrenches tapped together once. Since then there’s a persistent rattle emanating from the area of the transmission. As the transmission warms up to operating temperature the rattle subsides to a point where it’s barely audible. While rattling away cold at idle, when the clutch is disengaged the rattle disappears and often when released the rattle subsides somewhat. I’m aware that a worn transmission can sound a bit loose and that carburetor imbalance can artificially induce a rattle at idle however this particular box has 30k on it, is original to the motorcycle and was quiet when installed and run for nearly 5000 miles. It’s not carburetor and it’s not clutch as the idle is spot on and the clutch is light, smooth and positive and the adjustment is fine. There’s no metal in the gear oil like shiny stuff on the magnet or gold sparkles suspended in the oil. I’ve switched to a higher quality gear lube but - no joy.

Thoughts and prayers?

 

[PAS]

My 81 (178,600 miles) rattles when in neutral also then subsides with clutch pulled in. Carb sync helps to some extent.

 

[20774]

You ticked off all the things I thought of to check! I include Anton's website about the circlip issue not because your box has this issue, but his pictures and descriptions:

http://largiader.com/articles/circlip/

He says that the input and intermediate shaft are always in use and the output shaft is under load in fifth gear. I'm wondering about what that means...so the output shaft is only in use in fifth gear? Doesn't make sense to me. But he mentions the input shaft/gear is held in place by the shock coupler. I wonder if maybe this coupler is broken in your case, creating some looseness? You might not see swarf on the plug indicating some kind of bearing failure as the coupler is a big piece and if broken would just be in place but in smaller pieced.

 

[Na Cl K9]

Thankfully I do have another box…

At first I thought it was carbs and attempted ’field setting’ them without using gages which reduced the rattle but left an imbalance in the throttle response. I took the carbs apart and made sure they were jetted, equipped and set the same - which they were. I reset the clutch arm position and fiddled with the hand lever adjustment. Nada.
Now, looking at the spring loaded thrust adapter I suddenly realized that the noise I described could have been the cam returning to its seated position after having been loaded by the addition of vehicle weight, or momentum. The moment the spring overcame the inertia caused by the panic stop it snapped the lobes back into place causing a metallic snap or ‘pink” sound. I wonder if the loading was sufficient to cause the cam lobes to completely index and would that matter?