Motorcycle Repair: Yamaha 1981 400 special speedometer, speedometer cable, worm drive

Question
Chris,
I just had my front and rear tire replaced and the speedometer/odometer will not work. Is there any troubleshooting suggestions?  It had worked prior to tire replacement. It is a Yamaha 400 special, 1981

Thank You
Kelly

Answer
Hi Kelly.
 The proceedure to check the speedo is fairly simple.  Most likely, it is not the speedo since they do not tend to fail like that.

1)  With the bike on the centerstand, jack up the front end of the bike so that the front wheel is off the ground.

2)  Disconnect the speedometer cable from the speedometer.

3)  While looking at the cable, spin the wheel.  If the cable moves, the problem is in the speedometer.  If it doesn't, then you either have a broken cable or a broken worm drive.

3a)  If the cable hasn't moved, remove the front wheel and worm drive mechanism.  Check the mechanism for misalignment to the wheel or excessive wear (preventing it from engaging).

Make sure that you have the repair manual as it will have illustrations and pics of all of the parts as well as wear specs for you to compare the parts against.

Good luck.
FALCON