Speedo problems

[Ziggy81scott]

Hi I recently fitted a 250 superdream speedo to my cd125 and since doing this the speedo isn't operating properly.
It's fine up to about 40mph but over 40 it waves around randomly making it difficult to tell how fast I'm going.

I wonder if this is due to the speedo being geared to a 18 inch front wheel but being used with a 17 inch wheel?
Or could it be the a faulty speedo?

Thanks

[Ziggy81scott]

Just checked up on the superdream wheel sizes and found that the wheel size is 19 inch and the superdream has it speedo drive off the back wheel, my cd125 has 17 inch wheels and the drive is on the front wheel. Not sure if that makes any difference so maybe someone will know.

[Taught2BCauti...]

You can measure the drive ratio by attaching a piece of sticky tape to the inner cable, like a pointer, then count how many revolutions of the wheel it takes to do one complete 360° turn of the inner cable, but not much use unless you can compare it to the donor bike.

Whether the ratio is right or wrong, the speedo needle should be stable across the range - so my guess is the speedo head is potatoe.
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[bikenut]

a superdream250 has a 19inch front wheel and drives the speedo, from the front wheel not the back wheel.

are u the dude that had a seized speedo drive?
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[Ziggy81scott]

That's a negative old mate.
I think I've found the problem now anyway, it's the square drive in the back off the speedo head that has worn meaning the cable doesn't drive it as it should. ie. The cable is spinning round in the back off the speedo without gripping it, if you get what I'm saying

[bikenut]

unusual that one, flatten the cable square somewhat and re try, else a new speedo head.

if the speedo head gets too stiff or seizes, the cable usually breaks
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