I think you should always do a couple of things before replacing the gear. One; make sure the cable is not broken and two; make sure the cable connector has not come loose from the back of the speedometer housing. Once you have eliminated these possible reasons for the speedometer not working it is time to replace the gear.
I posted how to do this somewhere last summer, but I didn’t save the info and can’t remember where I posted. Here is what I remember.
Put the bike on the center stand.
Place a short piece of 2x4 or 2x6 under the front of the engine case.
Place a floor jack under the wood block and raise the jack just enough to hold the block in place.
Remove the lower end of the speedo cable from the speedo drive gear.
Remove the pinch bolt on the left side of the front wheel.
Loosen the axle nut on the left side of the front wheel several turns and using the heel of your hand or rubber mallet tap the axle nut to begin moving the axle out of the forks and the wheel. Continue to loosen the nut more turns and continue to tap the axle out.
Remove the axle.
The jack under the engine will hold the bike. Gently lift the bike with the jack just a small amount until you can move the wheel down and a little forward of the axle hole without sliding the discs out of the calipers.
The speedo gear on the left side of the wheel should now drop out of the space between the wheel and the right side fork.
Insert the new gear, making sure you align the tab at the top of the gear with the slot on the fork so the gear is correctly seated in position.
Roll the wheel back toward the axle holes holding the gear in place.
Very, very slowly lower the jack as you guide the wheel and speedo gear back into alignment with the axle holes in the forks.
Insert the axle bolt, tighten the axle nut, tighten the pinch bolt, lower the jack completely, reattach the speedo cable and you’re done.
Quick & easy speedo gear replacement (Thanks to Rocket R
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