I have an odd one. While riding this weekend, my speedometer slowly began to read progressively lower. It took about 2-3 hours of riding to get to the point where it now barely registers. Anyone had this happen? Is it fixable or should I just look for a replacement?

If you are talking about mc18/21 with an analogue speedo then my money is on the plastic drive that goes over the gearbox output shaft. The Speedo cable plugs into an angled drive on the sprocket cover that plugs into the white plastic drive that goes over the output shaft.

The angled drive eventually rounds out the slot in the white plastic bit, usually the Speedo works intermitently before it finally gives out.

Yes, it's an MC18R5K. I know the piece to refer to--I'll check it out. Thanks.

the other possibility is it could be the part that attaches to the back of the speedometer. It screws onto the speedometer, it could have backed off over the ride.

I had this problem when the cable gradually stiffened up and it chewed out teh plastic drive gear. After repalcing both bits and nicely lubed all is good. So when you are replacing the drive check your cable is OK as well.

The suggested plastic piece was split. Replaced it and works perfectly again. Thanks.