1980 Honda speedometer question

Can someone answer a speedometer question?

I have a CM400T and the speedometer is jumping all over place. I replaced the cable (that was broken) and that didn't help.

So the question is, can I get a generic speedometer off of eBay and will it read accurately? Or do I have to find a specific or OEM one? I see one for an older Honda 350 that looks pretty close.
-Mark

Since it isn't working, I would try lubricating the speedo with a light grease, putting a little into the cable receiver orifice.
Also, try doing an internet search for CM400 jumpy speedometer, in case there's a fix. or use CB350 or CB750 etc instead of CM400.

As for a replacement speedometer, I'm pretty sure all Japanese motorcycles use the same 2240 ratio (revs per mile), so just get that type. The CM400 speedo may have the ratio stamped in ink on the back. Keep in mind that a replacement may not be the same size, so it might not fit correctly. Aftermarket are usually listed as 2240@60mph or something like that.

2240 revs = 1 mile

2240 revs = 1 mile

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Thank you, great info.