Gearbox whine?

[Nick R]

It's about time to put the bike up for the winter, but in the meantime, question for the Honda experts. It's the bike in my sig, an 85' Honda Shadow VT500C with 33,450 miles on it. In the first couple gears on acceleration, or crusing in those gears, there is what sounds like gear whine. It's pretty loud, and audible from down the street when someone else is riding it. I'm no expert on these bikes, but does the transmission use straight-cut gears, not helical? It's also shaft driven, and I have even less idea if the final drive has straight cut or not. Current fill is Castrol PowerRS 10W-40 FWIW.

Also same bike, in relation to first gear. First gear always grinds when you downshift into it. Yes, we are clutching properly. I can clutch, let off the gas, downshift into first, still holding the clutch, and it will grind. I call it a grind, there is definitely a grinding sounding component to it, along with a clunk. No idea if this is normal for these. It is a 6 speed transmission, and we only bought it this past summer with about 32k on it.

 

[tom slick]

They do have straight cut gears and they don't use syncros like a car transmission; they slide the actual gears back and forth with "dogs" engaging the combinations of gears. Which is an older design from the "constant" mesh newer bikes have.

http://www.gadgetjq.com/transmission.htm explains some

 

[billythekid]

May be a bearing in the transmission.

 

[Trav]

First make sure its not normal operating noise by listening to another one if you can find it.
There are a few straight cut gears outside the transmission unit, the clutch drum to crankshaft, starter, oil pump drive gear and idler gear (if used in your model, i don't know) all are straight cut and make some whining noise.

Honda transmissions this vintage don't like to be babied being put into first, engage it with some authority.
Check the clutch cable free play, to much free play can cause the clutch plates not to disengage properly.
Some of the older Honda clutches had more parasitic drag from the oil between the plates than usual, a very light blip of the throttle when the clutch is disengaged may help with the first gear engagement.

Slightly warped steels or weak springs can also cause an increase in clutch plate drag. Warped steels are usually from overheating, the steels(s) will have blue hot spots or scoring.