Speedometer accuracy

[OldSwartout]

Does anyone else (or everyone) have a problem with the accuracy of their speedometer?  My original was waaaayyyy off, plus looking a little beat up, to say the least.  I bought a new one a few years ago from Richard. It looks much better, but the accuracy is bad; reads 85 MPH at 60 MPH actual (GPS reference).  Any ideas, or is this normal? I don't remember that much error from years ago. They were always a little optimistic, but this is silly.

[slawsonb]

I expect all to these (new and old) are from the same supplier, so I would expect minor variation from unit to unit, but not 42%. I have never disassembled a BS speedo. Do they work on a direct drive (gear ratio) or are they magnetically coupled like some automotive speedos?
...bert

[OldSwartout]

There is a worm gear drive in the front hub to drive the cable. The internal works uses the same magnetic coupling/spring setup that older mechanical automotive speedos use.  I  just was wondering what others experiences are. Both my old one and the NOS one are off about the same.

[Colin]

Sounds like a front wheel drive to me too, however I remember a long time back getting a little over indulgent with the grease on a speedo cable and the grease got up into the speedo itself and caused a similar problem, that's when I started reading manuals and service sheets and discovered I should not have greased the top part of the cable, something I seem not to have put into practice with the clutch rebuild on the GTR, you would think at 55 years old and having rebuilt a few bikes in the past that maybe I should remember the important things, hmm now when that anniversary 
Colin.

[OldSwartout]

Hmmm. That could have been the problem with the original speedo. It got kind of jumpy like most old speedos do when the input bushing is wearing out, so I probably greased the cable and the speedo bushing well at some time toward the end.  However, it's unlikely that there was excessive grease on the current cable nor on the NOS speedo.  However,  I should go pull the cable and see.

[old smokey]

Back when my GTR was in one piece, I think the speedo was no more than 2-3% off actual values. Either that or the tach also lied to match book values and local traffic didn't follow speed limits.